class Hash

A Hash maps each of its unique keys to a specific value.

A Hash has certain similarities to an Array, but:

Hash Data Syntax

The older syntax for Hash data uses the “hash rocket,” =>:

h = {:foo => 0, :bar => 1, :baz => 2}
h # => {:foo=>0, :bar=>1, :baz=>2}

Alternatively, but only for a Hash key that's a Symbol, you can use a newer JSON-style syntax, where each bareword becomes a Symbol:

h = {foo: 0, bar: 1, baz: 2}
h # => {:foo=>0, :bar=>1, :baz=>2}

You can also use a String in place of a bareword:

h = {'foo': 0, 'bar': 1, 'baz': 2}
h # => {:foo=>0, :bar=>1, :baz=>2}

And you can mix the styles:

h = {foo: 0, :bar => 1, 'baz': 2}
h # => {:foo=>0, :bar=>1, :baz=>2}

But it's an error to try the JSON-style syntax for a key that's not a bareword or a String:

# Raises SyntaxError (syntax error, unexpected ':', expecting =>):
h = {0: 'zero'}

Common Uses

You can use a Hash to give names to objects:

person = {name: 'Matz', language: 'Ruby'}
person # => {:name=>"Matz", :language=>"Ruby"}

You can use a Hash to give names to method arguments:

def some_method(hash)
  p hash
end
some_method({foo: 0, bar: 1, baz: 2}) # => {:foo=>0, :bar=>1, :baz=>2}

Note: when the last argument in a method call is a Hash, the curly braces may be omitted:

some_method(foo: 0, bar: 1, baz: 2) # => {:foo=>0, :bar=>1, :baz=>2}

You can use a Hash to initialize an object:

class Dev
  attr_accessor :name, :language
  def initialize(hash)
    self.name = hash[:name]
    self.language = hash[:language]
  end
end
matz = Dev.new(name: 'Matz', language: 'Ruby')
matz # => #<Dev: @name="Matz", @language="Ruby">

Creating a Hash

Here are three ways to create a Hash:


You can create a Hash by calling method Hash.new.

Create an empty Hash:

h = Hash.new
h # => {}
h.class # => Hash

You can create a Hash by calling method Hash.[].

Create an empty Hash:

h = Hash[]
h # => {}

Create a Hash with initial entries:

h = Hash[foo: 0, bar: 1, baz: 2]
h # => {:foo=>0, :bar=>1, :baz=>2}

You can create a Hash by using its literal form (curly braces).

Create an empty Hash:

h = {}
h # => {}

Create a Hash with initial entries:

h = {foo: 0, bar: 1, baz: 2}
h # => {:foo=>0, :bar=>1, :baz=>2}

Hash Value Basics

The simplest way to retrieve a Hash value (instance method []):

h = {foo: 0, bar: 1, baz: 2}
h[:foo] # => 0

The simplest way to create or update a Hash value (instance method []=):

h = {foo: 0, bar: 1, baz: 2}
h[:bat] = 3 # => 3
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}
h[:foo] = 4 # => 4
h # => {:foo=>4, :bar=>1, :baz=>2, :bat=>3}

The simplest way to delete a Hash entry (instance method delete):

h = {foo: 0, bar: 1, baz: 2}
h.delete(:bar) # => 1
h # => {:foo=>0, :baz=>2}

Entry Order

A Hash object presents its entries in the order of their creation. This is seen in:

A new Hash has its initial ordering per the given entries:

h = Hash[foo: 0, bar: 1]
h # => {:foo=>0, :bar=>1}

New entries are added at the end:

h[:baz] = 2
h # => {:foo=>0, :bar=>1, :baz=>2}

Updating a value does not affect the order:

h[:baz] = 3
h # => {:foo=>0, :bar=>1, :baz=>3}

But re-creating a deleted entry can affect the order:

h.delete(:foo)
h[:foo] = 5
h # => {:bar=>1, :baz=>3, :foo=>5}

Hash Keys

Hash Key Equivalence

Two objects are treated as the same hash key when their hash value is identical and the two objects are eql? to each other.

Invalid Hash Keys

An object that lacks method hash cannot be a Hash key:

# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
{BasicObject.new => 0}

Modifying an Active Hash Key

Modifying a Hash key while it is in use damages the hash's index.

This Hash has keys that are Arrays:

a0 = [ :foo, :bar ]
a1 = [ :baz, :bat ]
h = {a0 => 0, a1 => 1}
h.include?(a0) # => true
h[a0] # => 0
a0.hash # => 110002110

Modifying array element a0[0] changes its hash value:

a0[0] = :bam
a0.hash # => 1069447059

And damages the Hash index:

h.include?(a0) # => false
h[a0] # => nil

You can repair the hash index using method rehash:

h.rehash # => {[:bam, :bar]=>0, [:baz, :bat]=>1}
h.include?(a0) # => true
h[a0] # => 0

A String key is always safe. That's because an unfrozen String passed as a key will be replaced by a duplicated and frozen String:

s = 'foo'
s.frozen? # => false
h = {s => 0}
first_key = h.keys.first
first_key.frozen? # => true
first_key.equal?(s) # => false

User-Defined Hash Keys

A user-defined class may be used as a Hash key if the hash and eql? methods are overridden to provide meaningful behavior. By default, separate instances refer to separate Hash keys.

A typical implementation of hash is based on the object's data while eql? is usually aliased to the overridden == method:

class Book
  attr_reader :author, :title

  def initialize(author, title)
    @author = author
    @title = title
  end

  def ==(other)
    self.class === other and
      other.author == @author and
      other.title == @title
  end

  alias eql? ==

  def hash
    @author.hash ^ @title.hash # XOR
  end
end

book1 = Book.new 'matz', 'Ruby in a Nutshell'
book2 = Book.new 'matz', 'Ruby in a Nutshell'

reviews = {}

reviews[book1] = 'Great reference!'
reviews[book2] = 'Nice and compact!'

reviews.length #=> 1

Default Values

For a key that is not found, method [] returns a default value determined by:

Default Value

A Hash object's default value is relevant only when its default proc is nil. (Initially, both are nil).

You can retrieve the default value with method default:

h = Hash.new
h.default # => nil

You can initialize the default value by passing an argument to method Hash.new:

h = Hash.new(false)
h.default # => false

You can update the default value with method default=:

h.default = false
h.default # => false

Incidentally, updating the default value (even to nil) also sets the default proc to nil:

h.default_proc = proc { }
h.default = nil
h.default_proc # => nil

When the default proc is nil, method [] returns the value of method default:

h = Hash.new
h.default_proc # => nil
h.default # => nil
h[:nosuch] # => nil
h.default = false
h[:nosuch] # => false

For certain kinds of default values, the default value can be modified thus:

h = Hash.new('Foo')
h[:nosuch] # => "Foo"
h[:nosuch].upcase! # => "FOO"
h[:nosuch] # => "FOO"
h.default = [0, 1]
h[:nosuch] # => [0, 1]
h[:nosuch].reverse! # => [1, 0]
h[:nosuch] # => [1, 0]

Default Proc

When the default proc for a Hash is set (i.e., not nil), the default value returned by method [] is determined by the default proc alone.

You can retrieve the default proc with method default_proc:

h = Hash.new
h.default_proc # => nil

You can initialize the default proc by calling Hash.new with a block:

h = Hash.new { |hash, key| "Default value for #{key}" }
h.default_proc.class # => Proc

You can update the default proc with method default_proc=:

h = Hash.new
h.default_proc = proc { |hash, key| "Default value for #{key}" }
h.default_proc.class # => Proc

Incidentally, updating the default proc (even to nil) also sets the default value to nil:

h.default = false
h.default_proc = nil
h.default # => nil

When the default proc is set (i.e., not nil) and method [] is called with with a non-existent key, [] calls the default proc with both the Hash object itself and the missing key, then returns the proc's return value:

h = Hash.new { |hash, key| "Default value for #{key}" }
h[:nosuch] # => "Default value for nosuch"

Note that in the example above no entry for key :nosuch is created:

h.include?(:nosuch) # => false

However, the proc itself can add a new entry:

h = Hash.new { |hash, key| hash[key] = "Subsequent value for #{key}"; "First value for #{key}" }
h.include?(:nosuch) # => false
h[:nosuch] # => "First value for nosuch"
h.include?(:nosuch) # => true
h[:nosuch] # => "Subsequent value for nosuch"
h[:nosuch] # => "Subsequent value for nosuch"

You can set the default proc to nil, which restores control to the default value:

h.delete(:nosuch)
h.default_proc = nil
h.default = false
h[:nosuch] # => false

Public Class Methods

Hash[] → new_empty_hash click to toggle source
Hash[ [*2_element_arrays] ] → new_hash
Hash[*objects] → new_hash
Hash[hash_convertible_object] → new_hash

Returns a new Hash object populated with the given objects, if any.

The initial default value and default proc are set to nil (see Default Values):

h = Hash[]
h # => {}
h.class # => Hash
h.default # => nil
h.default_proc # => nil

When argument [*2_element_arrays] is given, each element of the outer array must be a 2-element array; returns a new Hash object wherein each 2-element array forms a key-value entry:

Hash[ [ [:foo, 0], [:bar, 1] ] ] # => {:foo=>0, :bar=>1}

When arguments *objects are given, the argument count must be an even number; returns a new Hash object wherein each successive pair of arguments has become a key-value entry:

Hash[] # => {}
Hash[:foo, 0, :bar, 1] # => {:foo=>0, :bar=>1}

When argument hash_convertible_object is given, the argument must be a Hash-convertible object; converts the object and returns the resulting Hash object:

class Foo
  def to_hash
    {foo: 0, bar: 1}
  end
end
Hash[Foo.new] # => {:foo=>0, :bar=>1}

Raises an exception if the argument count is 1, but the argument is not an array of 2-element arrays or a Hash-convertible object:

# Raises ArgumentError (odd number of arguments for Hash):
Hash[:foo]
# Raises ArgumentError (invalid number of elements (3 for 1..2)):
Hash[ [ [:foo, 0, 1] ] ]

Raises an exception if the argument count is odd and greater than 1:

# Raises ArgumentError (odd number of arguments for Hash):
Hash[0, 1, 2]

Raises an exception if the argument is an array containing an element that is not a 2-element array:

# Raises ArgumentError (wrong element type Symbol at 0 (expected array)):
Hash[ [ :foo ] ]

Raises an exception if the argument is an array containing an element that is an array of size different from 2:

# Raises ArgumentError (invalid number of elements (3 for 1..2)):
Hash[ [ [0, 1, 2] ] ]

Raises an exception if any proposed key is not a valid key (see Invalid Hash Keys):

# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
Hash[:foo, 0, BasicObject.new, 1]
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
Hash[ [ [:foo, 0], [BasicObject.new, 1] ] ]
static VALUE
rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
{
    VALUE hash, tmp;

    if (argc == 1) {
        tmp = rb_hash_s_try_convert(Qnil, argv[0]);
        if (!NIL_P(tmp)) {
            hash = hash_alloc(klass);
            hash_copy(hash, tmp);
            return hash;
        }

        tmp = rb_check_array_type(argv[0]);
        if (!NIL_P(tmp)) {
            long i;

            hash = hash_alloc(klass);
            for (i = 0; i < RARRAY_LEN(tmp); ++i) {
                VALUE e = RARRAY_AREF(tmp, i);
                VALUE v = rb_check_array_type(e);
                VALUE key, val = Qnil;

                if (NIL_P(v)) {
                    rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
                             rb_builtin_class_name(e), i);
                }
                switch (RARRAY_LEN(v)) {
                  default:
                    rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
                             RARRAY_LEN(v));
                  case 2:
                    val = RARRAY_AREF(v, 1);
                  case 1:
                    key = RARRAY_AREF(v, 0);
                    rb_hash_aset(hash, key, val);
                }
            }
            return hash;
        }
    }
    if (argc % 2 != 0) {
        rb_raise(rb_eArgError, "odd number of arguments for Hash");
    }

    hash = hash_alloc(klass);
    rb_hash_bulk_insert(argc, argv, hash);
    hash_verify(hash);
    return hash;
}
new → new_hash click to toggle source
new(default_value) → new_hash
new{|hash, key| hash[key] = default_value} → new_hash

Returns a new empty Hash object.

The initial default value and initial default proc for the new hash depend on which form above was used. See Default Values.

If neither argument nor block given, initializes both the default value and the default proc to nil:

h = Hash.new
h # => {}
h.class # => Hash
h.default # => nil
h.default_proc # => nil
h[:nosuch] # => nil

If argument default_value given but no block given, initializes the default value to the given default_value and the default proc to nil:

h = Hash.new(false)
h # => {}
h.default # => false
h.default_proc # => nil
h[:nosuch] # => false

If block given but no argument given, stores the block as the default proc, and sets the default value to nil:

h = Hash.new { |hash, key| "Default value for #{key}" }
h # => {}
h.default # => nil
h.default_proc.class # => Proc
h[:nosuch] # => "Default value for nosuch"

Raises an exception if both argument default_value and a block are given:

# Raises ArgumentError (wrong number of arguments (given 1, expected 0)):
Hash.new(0) { }
static VALUE
rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;

    rb_hash_modify(hash);
    if (rb_block_given_p()) {
        rb_check_arity(argc, 0, 0);
        ifnone = rb_block_proc();
        SET_PROC_DEFAULT(hash, ifnone);
    }
    else {
        rb_check_arity(argc, 0, 1);
        ifnone = argc == 0 ? Qnil : argv[0];
        RHASH_SET_IFNONE(hash, ifnone);
    }

    return hash;
}
ruby2_keywords_hash(hash) → hash click to toggle source

Duplicates a given hash and adds a ruby2_keywords flag. This method is not for casual use; debugging, researching, and some truly necessary cases like deserialization of arguments.

h = {k: 1}
h = Hash.ruby2_keywords_hash(h)
def foo(k: 42)
  k
end
foo(*[h]) #=> 1 with neither a warning or an error
static VALUE
rb_hash_s_ruby2_keywords_hash(VALUE dummy, VALUE hash)
{
    Check_Type(hash, T_HASH);
    hash = rb_hash_dup(hash);
    RHASH(hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
    return hash;
}
ruby2_keywords_hash?(hash) → true or false click to toggle source

Checks if a given hash is flagged by Module#ruby2_keywords (or Proc#ruby2_keywords). This method is not for casual use; debugging, researching, and some truly necessary cases like serialization of arguments.

ruby2_keywords def foo(*args)
  Hash.ruby2_keywords_hash?(args.last)
end
foo(k: 1)   #=> true
foo({k: 1}) #=> false
static VALUE
rb_hash_s_ruby2_keywords_hash_p(VALUE dummy, VALUE hash)
{
    Check_Type(hash, T_HASH);
    return (RHASH(hash)->basic.flags & RHASH_PASS_AS_KEYWORDS) ? Qtrue : Qfalse;
}
try_convert(obj) → new_hash or nil click to toggle source

Returns the Hash object created by calling obj.to_hash:

require 'csv' # => true
row = CSV::Row.new(['Name', 'Age'], ['Bob', 45])
row.respond_to?(:to_hash)  # => true
Hash.try_convert(row) # => {"Name"=>"Bob", "Age"=>45}

Returns the given obj if it is a Hash:

h = {}
h1 = Hash.try_convert(h)
h1.equal?(h) # => true # Identity check

Returns nil unless obj.respond_to?(:to_hash):

s = 'foo'
s.respond_to?(:to_hash) # => false
Hash.try_convert(s) # => nil

Raises an exception unless obj.to_hash returns a Hash object:

class BadToHash
  def to_hash
    1
  end
end
bad = BadToHash.new
Hash.try_convert(bad) # Raises TypeError (can't convert BadToHash to Hash (BadToHash#to_hash gives Integer))
static VALUE
rb_hash_s_try_convert(VALUE dummy, VALUE hash)
{
    return rb_check_hash_type(hash);
}

Public Instance Methods

hash < other_hash → true or false click to toggle source

Returns true if hash is a proper subset of other_hash, false otherwise:

h1 = {foo: 0, bar: 1}
h2 = {foo: 0, bar: 1, baz: 2}
h1 < h2 # => true
h2 < h1 # => false
h1 < h1 # => false

Raises an exception if other_hash is not a Hash-convertible object:

h = {}
h < 1 # Raises TypeError (no implicit conversion of Integer into Hash)
static VALUE
rb_hash_lt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) >= RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}
hash <= other_hash → true or false click to toggle source

Returns true if hash is a subset of other_hash, false otherwise:

h1 = {foo: 0, bar: 1}
h2 = {foo: 0, bar: 1, baz: 2}
h1 <= h2 # => true
h2 <= h1 # => false
h1 <= h1 # => true

Raises an exception if other_hash is not a Hash-convertible object:

h = {}
h <= 1 # Raises TypeError (no implicit conversion of Integer into Hash)
static VALUE
rb_hash_le(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) > RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}
hash == object → true or false click to toggle source

Returns true if all of the following are true:

  • object is a Hash object.

  • hash and object have the same keys (regardless of order).

  • For each key key, hash[key] == object[key].

Otherwise, returns false.

Equal:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, baz: 2}
h1 == h2 # => true
h3 = {baz: 2, bar: 1, foo: 0}
h1 == h3 # => true

Not equal because of class:

h1 = {foo: 0, bar: 1, baz: 2}
h1 == 1 # false

Not equal because of different keys:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, zab: 2}
h1 == h2 # => false

Not equal because of different values:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, baz: 3}
h1 == h2 # => false
static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, FALSE);
}
hash > other_hash → true or false click to toggle source

Returns true if hash is a proper superset of other_hash, false otherwise:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1}
h1 > h2 # => true
h2 > h1 # => false
h1 > h1 # => false

Raises an exception if other_hash is not a Hash-convertible object:

h = {}
h > 1 # Raises TypeError (no implicit conversion of Integer into Hash)
static VALUE
rb_hash_gt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) <= RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}
hash >= other_hash → true or false click to toggle source

Returns true if hash is a superset of other_hash, false otherwise:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1}
h1 >= h2 # => true
h2 >= h1 # => false
h1 >= h1 # => true

Raises an exception if other_hash is not a Hash-convertible object:

h = {}
h >= 1 # Raises TypeError (no implicit conversion of Integer into Hash)
static VALUE
rb_hash_ge(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) < RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}
hash[key] → value click to toggle source

Returns the value associated with the given key, if found:

h = {foo: 0, bar: 1, baz: 2}
h[:foo] # => 0

If key is not found, returns a default value (see Default Values):

h = {foo: 0, bar: 1, baz: 2}
h[:nosuch] # => nil
VALUE
rb_hash_aref(VALUE hash, VALUE key)
{
    st_data_t val;

    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        return rb_hash_default_value(hash, key);
    }
}
hash[key] = value → value click to toggle source

Associates the given value with the given key, and returns value.

If the given key exists, replaces its value with the given value; the ordering is not affected (see Entry Order):

h = {foo: 0, bar: 1}
h[:foo] = 2 # => 2
h.store(:bar, 3) # => 3
h # => {:foo=>2, :bar=>3}

If key does not exist, adds the key and value; the new entry is last in the order (see Entry Order):

h = {foo: 0, bar: 1}
h[:baz] = 2 # => 2
h.store(:bat, 3) # => 3
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}

Raises an exception if key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h[BasicObject.new] = 2
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.store(BasicObject.new, 2)
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);

    rb_hash_modify(hash);

    if (RHASH_TABLE_NULL_P(hash)) {
        if (iter_lev > 0) no_new_key();
        ar_alloc_table(hash);
    }

    if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}
any? → true or false click to toggle source
any?(object) → true or false
any? {|key, value| ... } → true or false

Returns true if any element satisfies a given criterion; false otherwise.


With no argument and no block, returns true if self is non-empty; false if empty:

{}.any? # => false
{nil => false}.any? # => true

With argument object and no block, returns true if for any key key h.assoc(key) == object:

h = {foo: 0, bar: 1, baz: 2}
h.any?([:bar, 1]) # => true
h.any?([:bar, 0]) # => false
h.any?([:baz, 1]) # => false

With no argument and a block, calls the block with each key-value pair; returns true if the block returns any truthy value, false otherwise:

h = {foo: 0, bar: 1, baz: 2}
h.any? {|key, value| value < 3 } # => true
h.any? {|key, value| value > 3 } # => false

With argument object and a block, issues a warning ('given block not used') and ignores the block:

h = {foo: 0, bar: 1, baz: 2}
h.any?([:bar, 1]) # => true
h.any?([:bar, 0]) # => false
h.any?([:baz, 1]) # => false
static VALUE
rb_hash_any_p(int argc, VALUE *argv, VALUE hash)
{
    VALUE args[2];
    args[0] = Qfalse;

    rb_check_arity(argc, 0, 1);
    if (RHASH_EMPTY_P(hash)) return Qfalse;
    if (argc) {
        if (rb_block_given_p()) {
            rb_warn("given block not used");
        }
        args[1] = argv[0];

        rb_hash_foreach(hash, any_p_i_pattern, (VALUE)args);
    }
    else {
        if (!rb_block_given_p()) {
            /* yields pairs, never false */
            return Qtrue;
        }
        if (rb_block_pair_yield_optimizable())
            rb_hash_foreach(hash, any_p_i_fast, (VALUE)args);
        else
            rb_hash_foreach(hash, any_p_i, (VALUE)args);
    }
    return args[0];
}
assoc(key) → new_array or nil click to toggle source

If the given key is found, returns a 2-element Array containing that key and its value:

h = {foo: 0, bar: 1, baz: 2}
h.assoc(:bar) # => [:bar, 1]

Returns nil if key key is not found:

h = {foo: 0, bar: 1, baz: 2}
h.assoc(:nosuch)

Raises an exception if key is invalid (see Invalid Hash Keys) (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>)
h.assoc(BasicObject.new)
VALUE
rb_hash_assoc(VALUE hash, VALUE key)
{
    st_table *table;
    const struct st_hash_type *orighash;
    VALUE args[2];

    if (RHASH_EMPTY_P(hash)) return Qnil;

    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));
    table = RHASH_ST_TABLE(hash);
    orighash = table->type;

    if (orighash != &identhash) {
        VALUE value;
        struct reset_hash_type_arg ensure_arg;
        struct st_hash_type assochash;

        assochash.compare = assoc_cmp;
        assochash.hash = orighash->hash;
        table->type = &assochash;
        args[0] = hash;
        args[1] = key;
        ensure_arg.hash = hash;
        ensure_arg.orighash = orighash;
        value = rb_ensure(lookup2_call, (VALUE)&args, reset_hash_type, (VALUE)&ensure_arg);
        if (value != Qundef) return rb_assoc_new(key, value);
    }

    args[0] = key;
    args[1] = Qnil;
    rb_hash_foreach(hash, assoc_i, (VALUE)args);
    return args[1];
}
clear → self click to toggle source

Removes all hash entries; returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.clear # => {}
h1.equal?(h) # => true # Identity check
VALUE
rb_hash_clear(VALUE hash)
{
    rb_hash_modify_check(hash);

    if (RHASH_ITER_LEV(hash) > 0) {
        rb_hash_foreach(hash, clear_i, 0);
    }
    else if (RHASH_AR_TABLE_P(hash)) {
        ar_clear(hash);
    }
    else {
        st_clear(RHASH_ST_TABLE(hash));
    }

    return hash;
}
compact → new_hash click to toggle source

Returns a copy of self with all nil-valued entries removed:

h = {foo: 0, bar: nil, baz: 2, bat: nil}
h1 = h.compact
h1 # => {:foo=>0, :baz=>2}
static VALUE
rb_hash_compact(VALUE hash)
{
    VALUE result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, set_if_not_nil, result);
    }
    return result;
}
compact! → self or nil click to toggle source

Returns self with all its nil-valued entries removed (in place):

h = {foo: 0, bar: nil, baz: 2, bat: nil}
h1 = h.compact!
h1 # => {:foo=>0, :baz=>2}
h1.equal?(h) # => true

Returns nil if no entries were removed:

h = {foo: 0, bar: 1, baz: 2}
h.compact! # => nil
h # => {:foo=>0, :bar=>1, :baz=>2}
static VALUE
rb_hash_compact_bang(VALUE hash)
{
    st_index_t n;
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (n) {
        rb_hash_foreach(hash, delete_if_nil, hash);
        if (n != RHASH_SIZE(hash))
            return hash;
    }
    return Qnil;
}
compare_by_identity → self click to toggle source

Sets self to consider only identity in comparing keys; two keys are considered the same only if they are the same object; returns self.

By default, these two object are considered to be the same key, so s1 will overwrite s0:

s0 = 'x'
s1 = 'x'
s0.equal?(s0) # => false
h = {}
h.compare_by_identity? # => false
h[s0] = 0
h[s1] = 1
h # => {"x"=>1}

After calling #compare_by_identity, the keys are considered to be different, and therefore do not overwrite each other:

h = {}
h1 = h.compare_by_identity # => {}
h1.equal?(h) # => true
h.compare_by_identity? # => true
h[s0] = 0
h[s1] = 1
h # => {"x"=>0, "x"=>1}
static VALUE
rb_hash_compare_by_id(VALUE hash)
{
    VALUE tmp;
    st_table *identtable;

    if (rb_hash_compare_by_id_p(hash)) return hash;

    rb_hash_modify_check(hash);
    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));

    tmp = hash_alloc(0);
    identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
    RHASH_ST_TABLE_SET(tmp, identtable);
    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
    st_free_table(RHASH_ST_TABLE(hash));
    RHASH_ST_TABLE_SET(hash, identtable);
    RHASH_ST_CLEAR(tmp);
    rb_gc_force_recycle(tmp);

    return hash;
}
compare_by_identity? → true or false click to toggle source

Returns true if compare_by_identity has been called, false otherwise:

h = {}
h.compare_by_identity? # false
h.compare_by_identity
h.compare_by_identity? # true
MJIT_FUNC_EXPORTED VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
    if (RHASH_ST_TABLE_P(hash) && RHASH_ST_TABLE(hash)->type == &identhash) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
deconstruct_keys(p1) click to toggle source
static VALUE
rb_hash_deconstruct_keys(VALUE hash, VALUE keys)
{
    return hash;
}
default → value click to toggle source
default(key) → value

With no argument, returns the current default value:

h = {}
h.default # => nil
h.default = false
h.default # => false

With key given, returns the default value for key, regardless of whether that key exists:

h = {}
h.default(:nosuch) # => nil

The returned value will be determined either by the default proc or by the default value. See Default Values.

static VALUE
rb_hash_default(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;

    rb_check_arity(argc, 0, 1);
    ifnone = RHASH_IFNONE(hash);
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
        if (argc == 0) return Qnil;
        return call_default_proc(ifnone, hash, argv[0]);
    }
    return ifnone;
}
default = value → value click to toggle source

Sets the default value to value, returning value:

h = {}
h.default # => nil
h.default = false # => false
h.default # => false

See Default Values.

static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
    rb_hash_modify_check(hash);
    SET_DEFAULT(hash, ifnone);
    return ifnone;
}
default_proc → proc or nil click to toggle source

Returns the default proc:

h = {}
h.default_proc # => nil
h.default_proc = proc { |hash, key| "Default value for #{key}" }
h.default_proc.class # => Proc

See Default Values.

static VALUE
rb_hash_default_proc(VALUE hash)
{
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
        return RHASH_IFNONE(hash);
    }
    return Qnil;
}
default_proc = proc → proc click to toggle source

Sets the default proc to proc:

h = {}
h.default_proc # => nil
h.default_proc = proc { |hash, key| "Default value for #{key}" }
h.default_proc.class # => Proc
h.default_proc = nil
h.default_proc # => nil

See Default Values.


Raises an exception if proc is not a Proc:

# Raises TypeError (wrong default_proc type Integer (expected Proc)):
h.default_proc = 1
VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;

    rb_hash_modify_check(hash);
    if (NIL_P(proc)) {
        SET_DEFAULT(hash, proc);
        return proc;
    }
    b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
    if (NIL_P(b) || !rb_obj_is_proc(b)) {
        rb_raise(rb_eTypeError,
                 "wrong default_proc type %s (expected Proc)",
                 rb_obj_classname(proc));
    }
    proc = b;
    SET_PROC_DEFAULT(hash, proc);
    return proc;
}
delete(key) → value or nil click to toggle source
delete(key) { |key| ... } → value

Deletes the entry for the given key and returns its associated value.


If no block is given and key is found, deletes the entry and returns the associated value:

h = {foo: 0, bar: 1, baz: 2}
h.delete(:bar) # => 1
h # => {:foo=>0, :baz=>2}

If no block given and key is not found, returns nil:

h = {foo: 0, bar: 1, baz: 2}
h.delete(:nosuch) # => nil
h # => {:foo=>0, :bar=>1, :baz=>2}

If a block is given and key is found, ignores the block, deletes the entry, and returns the associated value:

h = {foo: 0, bar: 1, baz: 2}
h.delete(:baz) { |key| raise 'Will never happen'} # => 2
h # => {:foo=>0, :bar=>1}

If a block is given and key is not found, calls the block and returns the block's return value:

h = {foo: 0, bar: 1, baz: 2}
h.delete(:nosuch) { |key| "Key #{key} not found" } # => "Key nosuch not found"
h # => {:foo=>0, :bar=>1, :baz=>2}

Raises an exception if key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.delete(BasicObject.new)
static VALUE
rb_hash_delete_m(VALUE hash, VALUE key)
{
    VALUE val;

    rb_hash_modify_check(hash);
    val = rb_hash_delete_entry(hash, key);

    if (val != Qundef) {
        return val;
    }
    else {
        if (rb_block_given_p()) {
            return rb_yield(key);
        }
        else {
            return Qnil;
        }
    }
}
delete_if {|key, value| ... } → self click to toggle source
delete_if → new_enumerator

If a block given, calls the block with each key-value pair; deletes each entry for which the block returns a truthy value; returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.delete_if { |key, value| value > 0 }
h1 # => {:foo=>0}
h1.equal?(h) # => true #  Identity check

If no block given, returns a new Enumerator:

h = {foo: 0, bar: 1, baz: 2}
e = h.delete_if # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:delete_if>
h1 = e.each { |key, value| value > 0 }
h1 # => {:foo=>0}
h1.equal?(h) # => true #  Identity check

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.delete_if { |key, value| h[:new_key] = 3 }
VALUE
rb_hash_delete_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, delete_if_i, hash);
    }
    return hash;
}
dig(*keys) → value click to toggle source

Returns the value for a specified object in nested objects.

For nested objects:

  • For each key in keys, calls method #dig on a receiver.

  • The first receiver is self.

  • Each successive receiver is the value returned by the previous call to #dig.

  • The value finally returned is the value returned by the last call to #dig.

Examples:

h = {foo: 0}
h.dig(:foo) # => 0

h = {foo: {bar: 1}}
h.dig(:foo, :bar) # => 1

h = {foo: {bar: {baz: 2}}}
h.dig(:foo, :bar, :baz) # => 2

Returns nil if any key is not found:

h = { foo: {bar: {baz: 2}}}
h.dig(:foo, :nosuch) # => nil

The nested objects may include any that respond to #dig. See:

Example:

h = {foo: {bar: [:a, :b, :c]}}
h.dig(:foo, :bar, 2) # => :c

Raises an exception if any given key is invalid (see Invalid Hash Keys):

# Raises NoMethodError (undefined method `hash' for #<BasicObject>)
h.dig(BasicObject.new)

Raises an exception if any receiver does not respond to #dig:

h = { foo: 1 }
# Raises TypeError: Integer does not have #dig method
h.dig(:foo, 1)
static VALUE
rb_hash_dig(int argc, VALUE *argv, VALUE self)
{
    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
    self = rb_hash_aref(self, *argv);
    if (!--argc) return self;
    ++argv;
    return rb_obj_dig(argc, argv, self, Qnil);
}
each {|key, value| ... } → self click to toggle source
each_pair {|key, value| ... } → self
each → new_enumerator
each_pair → new_enumerator

Calls the given block with each key-value pair, returning self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.each_pair {|key, value| puts "#{key}: #{value}"}
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check

Output:

foo: 0
bar: 1
baz: 2

Returns an Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.each_pair # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_pair>
h1 = e.each {|key, value| puts "#{key}: #{value}"}
h1 # => {:foo=>0, :bar=>1, :baz=>2}

Output:

foo: 0
bar: 1
baz: 2

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration)
h.each_pair {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_pair_yield_optimizable())
        rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
        rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}
each_key {|key| ... } → self click to toggle source
each_key → new_enumerator

Calls the given block with each key; returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.each_key {|key| puts key }
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check

Output:

foo
bar
baz

Returns an Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.each_key # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_key>
h1 = e.each {|key| puts key }
h1 # => {:foo=>0, :bar=>1, :baz=>2}

Output:

foo
bar
baz

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.each_key {|key| h[:new_key] = 3 }
static VALUE
rb_hash_each_key(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}
each_pair {|key, value| ... } → self click to toggle source
each_pair → new_enumerator

Calls the given block with each key-value pair, returning self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.each_pair {|key, value| puts "#{key}: #{value}"}
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check

Output:

foo: 0
bar: 1
baz: 2

Returns an Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.each_pair # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_pair>
h1 = e.each {|key, value| puts "#{key}: #{value}"}
h1 # => {:foo=>0, :bar=>1, :baz=>2}

Output:

foo: 0
bar: 1
baz: 2

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration)
h.each_pair {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_pair_yield_optimizable())
        rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
        rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}
each_value {|value| ... } → self click to toggle source
each_value → new_enumerator

Calls the given block with each value; returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.each_value {|value| puts value }
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check

Output:

0
1
2

Returns an Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.each_value # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_value>
h1 = e.each {|value| puts value }
h1 # => {:foo=>0, :bar=>1, :baz=>2}

Output:

0
1
2

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.each_value {|value| h[:new_key] = 3 }
static VALUE
rb_hash_each_value(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}
empty? → true or false click to toggle source

Returns true if there are no hash entries, false otherwise:

{}.empty? # => true
{foo: 0, bar: 1, baz: 2}.empty? # => false
static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}
eql? object → true or false click to toggle source

Returns true if all of the following are true:

  • object is a Hash object.

  • hash and object have the same keys (regardless of order).

  • For each key key, h[key] eql? object[key].

Otherwise, returns false.

Equal:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, baz: 2}
h1.eql? h2 # => true
h3 = {baz: 2, bar: 1, foo: 0}
h1.eql? h3 # => true

Not equal because of class:

h1 = {foo: 0, bar: 1, baz: 2}
h1.eql? 1 # false

Not equal because of different keys:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, zab: 2}
h1.eql? h2 # => false

Not equal because of different values:

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, baz: 3}
h1.eql? h2 # => false
static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, TRUE);
}
except(*keys) → a_hash click to toggle source

Returns a hash excluding the given keys and their values.

h = { a: 100, b: 200, c: 300 }
h.except(:a)          #=> {:b=>200, :c=>300}
h.except(:b, :c, :d)  #=> {:a=>100}
static VALUE
rb_hash_except(int argc, VALUE *argv, VALUE hash)
{
    int i;
    VALUE key, result;

    result = rb_obj_dup(hash);

    for (i = 0; i < argc; i++) {
        key = argv[i];
        rb_hash_delete(result, key);
    }

    return result;
}
fetch(key) → value click to toggle source
fetch(key, default) → value
fetch(key) { |key| ... } → value

Returns the value for the given key.


When neither default nor a block given:

  • If key is found, returns its associated value.

  • Otherwise, raises an exception:

    h = {foo: 0, bar: 1, baz: 2}
    h.fetch(:bar) # => 1
    # Raises KeyError (key not found: :nosuch):
    h.fetch(:nosuch)
    

When default is given, but no block:

  • If key is found, returns its associated value.

  • Otherwise, returns the given default:

    h = {foo: 0, bar: 1, baz: 2}
    h.fetch(:bar, :default) # => 1
    h.fetch(:nosuch, :default) # => :default
    

When a block is given, but no default:

  • If key is found, returns its associated value.

  • Otherwise, calls the block with key, and returns the block's return value.

    h = {foo: 0, bar: 1, baz: 2}
    h.fetch(:bar) { |key| raise 'Ignored'} # => 1
    h.fetch(:nosuch) { |key| "Value for #{key}"} # => "Value for nosuch"
    

When both default and a block are given:

  • Ignores default and issues a warning: 'block supersedes default value argument'.

  • If key is found, returns its associated value.

  • Otherwise, calls the block with key, and returns the block's return value.

    h = {foo: 0, bar: 1, baz: 2}
    h.fetch(:bar, :default) { |key| raise 'Ignored'} # => 1
    h.fetch(:nosuch, :default) { |key| "Value for #{key}"} # => "Value for nosuch"
    

Raises an exception if key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):

h.fetch(BasicObject.new)
static VALUE
rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
{
    VALUE key;
    st_data_t val;
    long block_given;

    rb_check_arity(argc, 1, 2);
    key = argv[0];

    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
        rb_warn("block supersedes default value argument");
    }

    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        if (block_given) {
            return rb_yield(key);
        }
        else if (argc == 1) {
            VALUE desc = rb_protect(rb_inspect, key, 0);
            if (NIL_P(desc)) {
                desc = rb_any_to_s(key);
            }
            desc = rb_str_ellipsize(desc, 65);
            rb_key_err_raise(rb_sprintf("key not found: %"PRIsVALUE, desc), hash, key);
        }
        else {
            return argv[1];
        }
    }
}
fetch_values(*keys) → new_array click to toggle source
fetch_values(*keys) {|key| ... } → new_array

Returns a new Array containing the values associated with the given keys *keys:

h = {foo: 0, bar: 1, baz: 2}
h.fetch_values(:baz, :foo) # => [2, 0]

Returns a new empty Array if no arguments given:

h = {foo: 0, bar: 1, baz: 2}
h.fetch_values # => []

When a block given, calls the block with each missing key, treating the block's return value as the value for that key:

h = {foo: 0, bar: 1, baz: 2}
values = h.fetch_values(:bar, :foo, :bad, :bam) {|key| key.to_s}
values # => [1, 0, "bad", "bam"]

Raises an exception if any given key is not found:

h = {foo: 0, bar: 1, baz: 2}
h.fetch_values(:baz, :nosuch) # Raises KeyError (key not found: :nosuch)

Raises an exception if any given key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.fetch_values(:baz, BasicObject.new)
static VALUE
rb_hash_fetch_values(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
        rb_ary_push(result, rb_hash_fetch(hash, argv[i]));
    }
    return result;
}
filter {|key, value| ... } → new_hash click to toggle source
filter → new_enumerator

Hash#filter is an alias for Hash#select.

Returns a new Hash object whose entries are those for which the block returns a truthy value:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.select {|key, value| value < 2 }
h1 # => {:foo=>0, :bar=>1}
h1.equal?(h) # => false

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.select # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select>
h1 = e.each {|key, value| value < 2 }
h1 # => {:foo=>0, :bar=>1}
h1.equal?(h) # => false

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.select {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, select_i, result);
    }
    return result;
}
filter! {|key, value| ... } → self or nil click to toggle source
filter! → new_enumerator

Hash#filter! is an alias for Hash#select!.

Returns self, whose entries are those for which the block returns a truthy value:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.select! {|key, value| value < 2 }
h # => {:foo=>0, :bar=>1}
h1.equal?(h) # => true

Returns nil if no entries were removed:

h = {foo: 0, bar: 1, baz: 2}
h.select! {|key, value| value < 3} # => nil
h # => {:foo=>0, :bar=>1, :baz=>2}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.select!  # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select!>
h1 = e.each { |key, value| value < 2 }
h1 # => {:foo=>0, :bar=>1}
h1.equal?(h) # => true

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration)
h.select! {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}
flatten → new_array click to toggle source
flatten(level) → new_array

Argument level, if given, must be an Integer-convertible object.

Returns a new Array object that is a 1-dimensional flattening of self.


By default, nested Arrays are not flattened:

h = {foo: 0, bar: [:bat, 3], baz: 2}
h.flatten # => [:foo, 0, :bar, [:bat, 3], :baz, 2]

Takes the depth of recursive flattening from argument level:

h = {foo: 0, bar: [:bat, [:baz, [:bat, ]]]}
h.flatten(1) # => [:foo, 0, :bar, [:bat, [:baz, [:bat]]]]
h.flatten(2) # => [:foo, 0, :bar, :bat, [:baz, [:bat]]]
h.flatten(3) # => [:foo, 0, :bar, :bat, :baz, [:bat]]
h.flatten(4) # => [:foo, 0, :bar, :bat, :baz, :bat]

When level is negative, flattens all nested Arrays:

h = {foo: 0, bar: [:bat, [:baz, [:bat, ]]]}
h.flatten(-1) # => [:foo, 0, :bar, :bat, :baz, :bat]
h.flatten(-2) # => [:foo, 0, :bar, :bat, :baz, :bat]

When level is zero, returns the equivalent of to_a :

h = {foo: 0, bar: [:bat, 3], baz: 2}
h.flatten(0) # => [[:foo, 0], [:bar, [:bat, 3]], [:baz, 2]]
h.flatten(0) == h.to_a # => true

Raises an exception if level is not an Integer-convertible object:

h = {foo: 0, bar: [:bat, 3], baz: 2}
# Raises TypeError (no implicit conversion of Symbol into Integer):
h.flatten(:nosuch)
static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
    VALUE ary;

    rb_check_arity(argc, 0, 1);

    if (argc) {
        int level = NUM2INT(argv[0]);

        if (level == 0) return rb_hash_to_a(hash);

        ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
        rb_hash_foreach(hash, flatten_i, ary);
        level--;

        if (level > 0) {
            VALUE ary_flatten_level = INT2FIX(level);
            rb_funcallv(ary, id_flatten_bang, 1, &ary_flatten_level);
        }
        else if (level < 0) {
            /* flatten recursively */
            rb_funcallv(ary, id_flatten_bang, 0, 0);
        }
    }
    else {
        ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
        rb_hash_foreach(hash, flatten_i, ary);
    }

    return ary;
}
has_key?(key) → true or false click to toggle source

Methods has_key?, key?, and member? are aliases for #include?.

Returns true if key is a key in self, otherwise false:

h = {foo: 0, bar: 1, baz: 2}
h.include?(:bar) # => true
h.include?(:nosuch) # => false

Raises an exception if key is invalid (see Invalid Hash Keys):

# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.include?(BasicObject.new)
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
has_value?(value) → true or false click to toggle source

Returns true if value is a value in self, otherwise false:

h = {foo: 0, bar: 1, baz: 2}
h.has_value?(1) # => true
h.has_value?(123) # => false
static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}
hash → an_integer click to toggle source

Returns the Integer hash-code for the hash:

h1 = {foo: 0, bar: 1, baz: 2}
h1.hash.class # => Integer

Two Hash objects have the same hash-code if their content is the same (regardless or order):

h1 = {foo: 0, bar: 1, baz: 2}
h2 = {baz: 2, bar: 1, foo: 0}
h2.hash == h1.hash # => true
h2.eql? h1 # => true
static VALUE
rb_hash_hash(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    st_index_t hval = rb_hash_start(size);
    hval = rb_hash_uint(hval, (st_index_t)rb_hash_hash);
    if (size) {
        rb_hash_foreach(hash, hash_i, (VALUE)&hval);
    }
    hval = rb_hash_end(hval);
    return ST2FIX(hval);
}
include?(key) → true or false click to toggle source

Methods has_key?, key?, and member? are aliases for #include?.

Returns true if key is a key in self, otherwise false:

h = {foo: 0, bar: 1, baz: 2}
h.include?(:bar) # => true
h.include?(:nosuch) # => false

Raises an exception if key is invalid (see Invalid Hash Keys):

# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.include?(BasicObject.new)
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
replace(other_hash) → self click to toggle source

Replaces the entire contents of self with the contents of other_hash; returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.replace({bat: 3, bam: 4})
h1 # => {:bat=>3, :bam=>4}
h1.equal?(h) # => true # Identity check

Raises an exception if other_hash is not a Hash-convertible object:

h = {}
# Raises TypeError (no implicit conversion of Symbol into Hash):
h.replace(:not_a_hash)
static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);

    COPY_DEFAULT(hash, hash2);

    if (RHASH_AR_TABLE_P(hash)) {
        if (RHASH_AR_TABLE_P(hash2)) {
            ar_clear(hash);
        }
        else {
            ar_free_and_clear_table(hash);
            RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), RHASH_SIZE(hash2)));
        }
    }
    else {
        if (RHASH_AR_TABLE_P(hash2)) {
            st_free_table(RHASH_ST_TABLE(hash));
            RHASH_ST_CLEAR(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
        }
    }
    rb_hash_foreach(hash2, rb_hash_rehash_i, (VALUE)hash);

    rb_gc_writebarrier_remember(hash);

    return hash;
}
inspect → new_string click to toggle source

Returns a new String containing the hash entries:

h = {foo: 0, bar: 1, baz: 2}
h.inspect # => "{:foo=>0, :bar=>1, :baz=>2}"

Hash#to_s is an alias for Hash#inspect.

static VALUE
rb_hash_inspect(VALUE hash)
{
    if (RHASH_EMPTY_P(hash))
        return rb_usascii_str_new2("{}");
    return rb_exec_recursive(inspect_hash, hash, 0);
}
Also aliased as: to_s
invert → new_hash click to toggle source

Returns a new Hash object with the each key-value pair inverted:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.invert
h1 # => {0=>:foo, 1=>:bar, 2=>:baz}

Overwrites any repeated new keys: (see Entry Order):

h = {foo: 0, bar: 0, baz: 0}
h.invert # => {0=>:baz}

Raises an exception if any value cannot be a key (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: BasicObject.new}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.invert
static VALUE
rb_hash_invert(VALUE hash)
{
    VALUE h = rb_hash_new_with_size(RHASH_SIZE(hash));

    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}
keep_if {|key, value| ... } → self click to toggle source
keep_if → new_enumerator

Calls the block for each key-value pair; retains the entry if the block returns a truthy value; deletes the entry otherwise; returns self.

h = {foo: 0, bar: 1, baz: 2}
h1 = h.keep_if { |key, value| key.start_with?('b') }
h1 # => {:bar=>1, :baz=>2}
h1.object_id == h.object_id # => true

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.keep_if # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:keep_if>
h1 = e.each { |key, value| key.start_with?('b') }
h1 # => {:bar=>1, :baz=>2}
h1.object_id == h.object_id # => true

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.keep_if { |key, value| h[:new_key] = 3 }
static VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, keep_if_i, hash);
    }
    return hash;
}
key(value) → key or nil click to toggle source

Returns the key for the first-found entry with the given value (see Entry Order):

h = {foo: 0, bar: 2, baz: 2}
h.key(0) # => :foo
h.key(2) # => :bar

Returns nil if so such value is found:

h.key(:nosuch) # => nil
static VALUE
rb_hash_key(VALUE hash, VALUE value)
{
    VALUE args[2];

    args[0] = value;
    args[1] = Qnil;

    rb_hash_foreach(hash, key_i, (VALUE)args);

    return args[1];
}
key?(key) → true or false click to toggle source

Methods has_key?, key?, and member? are aliases for #include?.

Returns true if key is a key in self, otherwise false:

h = {foo: 0, bar: 1, baz: 2}
h.include?(:bar) # => true
h.include?(:nosuch) # => false

Raises an exception if key is invalid (see Invalid Hash Keys):

# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.include?(BasicObject.new)
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
keys → new_array click to toggle source

Returns a new Array containing all keys in self:

h = {foo: 0, bar: 1, baz: 2}
h.keys # => [:foo, :bar, :baz]
MJIT_FUNC_EXPORTED VALUE
rb_hash_keys(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    VALUE keys =  rb_ary_new_capa(size);

    if (size == 0) return keys;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        RARRAY_PTR_USE_TRANSIENT(keys, ptr, {
            if (RHASH_AR_TABLE_P(hash)) {
                size = ar_keys(hash, ptr, size);
            }
            else {
                st_table *table = RHASH_ST_TABLE(hash);
                size = st_keys(table, ptr, size);
            }
        });
        rb_gc_writebarrier_remember(keys);
        rb_ary_set_len(keys, size);
    }
    else {
        rb_hash_foreach(hash, keys_i, keys);
    }

    return keys;
}
length → integer click to toggle source

Returns the count of entries in self:

h = {foo: 0, bar: 1, baz: 2}
h.length # => 3

Hash#length is an alias for Hash#size.

VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}
member?(key) → true or false click to toggle source

Methods has_key?, key?, and member? are aliases for #include?.

Returns true if key is a key in self, otherwise false:

h = {foo: 0, bar: 1, baz: 2}
h.include?(:bar) # => true
h.include?(:nosuch) # => false

Raises an exception if key is invalid (see Invalid Hash Keys):

# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.include?(BasicObject.new)
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
merge → copy_of_self click to toggle source
merge(*other_hashes) → new_hash
merge(*other_hashes) { |key, old_value, new_value| ... } → new_hash

Returns the new Hash formed by merging each of other_hashes into a copy of self.

Each argument in other_hashes must be a Hash-convertible object.


With arguments and no block:

  • Returns the new Hash object formed by merging each successive Hash in other_hashes into self.

  • Each new-key entry is added at the end.

  • Each duplicate-key entry's value overwrites the previous value.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge(h1, h2)
h3 # => {:foo=>0, :bar=>4, :baz=>2, :bat=>6, :bam=>5}
h3.equal?(h) # => false # Identity check

With arguments and a block:

  • Returns a new Hash object that is the merge of self and each given hash.

  • The given hashes are merged left to right.

  • Each new-key entry is added at the end.

  • For each duplicate key:

    • Calls the block with the key and the old and new values.

    • The block's return value becomes the new value for the entry.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge(h1, h2) { |key, old_value, new_value| old_value + new_value }
h3 # => {:foo=>0, :bar=>5, :baz=>2, :bat=>9, :bam=>5}
h3.equal?(h) # => false # Identity check

Ignores an attempt in the block to add a new key:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge(h1, h2) { |key, old_value, new_value| h[:new_key] = 10 }
h3 # => {:foo=>0, :bar=>10, :baz=>2, :bat=>10, :bam=>5}
h3.equal?(h) # => false # Identity check

With no arguments:

  • Returns a copy of self.

  • The block, if given, is ignored.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.merge
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => false # Identity check
h2 = h.merge { |key, old_value, new_value| raise 'Cannot happen' }
h2 # => {:foo=>0, :bar=>1, :baz=>2}
h2.equal?(h) # => false # Identity check

Raises an exception if any given argument is not a Hash-convertible object:

h = {}
# Raises TypeError (no implicit conversion of Integer into Hash):
h.merge(1)
static VALUE
rb_hash_merge(int argc, VALUE *argv, VALUE self)
{
    return rb_hash_update(argc, argv, rb_hash_dup(self));
}
merge! → self click to toggle source
merge!(*other_hashes) → self
merge!(*other_hashes) { |key, old_value, new_value| ... } → self

Merges each of other_hashes into self; returns self.

Each argument in other_hashes must be a Hash-convertible object.

Method update is an alias for #merge!.


With arguments and no block:

  • Returns self, after the given hashes are merged into it.

  • The given hashes are merged left to right.

  • Each new entry is added at the end.

  • Each duplicate-key entry's value overwrites the previous value.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) # => {:foo=>0, :bar=>4, :baz=>2, :bat=>6, :bam=>5}
h3.equal?(h) # => true # Identity check

With arguments and a block:

  • Returns self, after the given hashes are merged.

  • The given hashes are merged left to right.

  • Each new-key entry is added at the end.

  • For each duplicate key:

    • Calls the block with the key and the old and new values.

    • The block's return value becomes the new value for the entry.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) { |key, old_value, new_value| old_value + new_value }
h3 # => {:foo=>0, :bar=>5, :baz=>2, :bat=>9, :bam=>5}
h3.equal?(h) # => true # Identity check

Allows the block to add a new key:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) { |key, old_value, new_value| h[:new_key] = 10 }
h3 # => {:foo=>0, :bar=>10, :baz=>2, :bat=>10, :new_key=>10, :bam=>5}
h3.equal?(h) # => true # Identity check

With no arguments:

  • Returns self, unmodified.

  • The block, if given, is ignored.

Example:

h = {foo: 0, bar: 1, baz: 2}
h.merge # => {:foo=>0, :bar=>1, :baz=>2}
h1 = h.merge! { |key, old_value, new_value| raise 'Cannot happen' }
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check

Raises an exception if any given argument is not a Hash-convertible object:

h = {}
# Raises TypeError (no implicit conversion of Integer into Hash):
h.merge!(1)
static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();

    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
       VALUE hash = to_hash(argv[i]);
       if (block_given) {
           rb_hash_foreach(hash, rb_hash_update_block_i, self);
       }
       else {
           rb_hash_foreach(hash, rb_hash_update_i, self);
       }
    }
    return self;
}
rassoc(value) → new_array or nil click to toggle source

Returns a new 2-element Array consisting of the key and value of the first-found entry whose value is == to value (see Entry Order):

h = {foo: 0, bar: 1, baz: 1}
h.rassoc(1) # => [:bar, 1]

Returns nil if no such value found:

h = {foo: 0, bar: 1, baz: 2}
h.rassoc(3) # => nil
VALUE
rb_hash_rassoc(VALUE hash, VALUE obj)
{
    VALUE args[2];

    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, rassoc_i, (VALUE)args);
    return args[1];
}
rehash → self click to toggle source

Rebuilds the hash table by recomputing the hash index for each key; returns self.

The hash table will have become invalid if the hash value of a key has changed since the entry was created. See Modifying an Active Hash Key.


Raises an exception if called while an iterator is traversing the hash:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (rehash during iteration):
h.each { |x| h.rehash }
VALUE
rb_hash_rehash(VALUE hash)
{
    VALUE tmp;
    st_table *tbl;

    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "rehash during iteration");
    }
    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        tmp = hash_alloc(0);
        ar_alloc_table(tmp);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        ar_free_and_clear_table(hash);
        ar_copy(hash, tmp);
        ar_free_and_clear_table(tmp);
    }
    else if (RHASH_ST_TABLE_P(hash)) {
        st_table *old_tab = RHASH_ST_TABLE(hash);
        tmp = hash_alloc(0);
        tbl = st_init_table_with_size(old_tab->type, old_tab->num_entries);
        RHASH_ST_TABLE_SET(tmp, tbl);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        st_free_table(old_tab);
        RHASH_ST_TABLE_SET(hash, tbl);
        RHASH_ST_CLEAR(tmp);
    }
    hash_verify(hash);
    return hash;
}
reject {|key, value| ... } → new_hash click to toggle source
reject → new_enumerator

Returns a new Hash object whose entries are all those from self for which the block returns false or nil:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.reject {|key, value| key.start_with?('b') }
h1 # => {:foo=>0}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.reject # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:reject>
h1 = e.each {|key, value| key.start_with?('b') }
h1 # => {:foo=>0}
VALUE
rb_hash_reject(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (RTEST(ruby_verbose)) {
        VALUE klass;
        if (HAS_EXTRA_STATES(hash, klass)) {
            rb_warn("extra states are no longer copied: %+"PRIsVALUE, hash);
        }
    }
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, reject_i, result);
    }
    return result;
}
reject! {|key, value| ... } → self or nil click to toggle source
reject! → new_enumerator

Returns self, whose remaining entries are those for which the block returns false or nil:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.reject! {|key, value| value < 2 }
h1 # => {:baz=>2}
h1.equal?(h) # => true # Identity check

Returns nil if no entries are removed:

h = {foo: 0, bar: 1, baz: 2}
h.reject! {|key, value| value > 2 } # => nil
h # => {:foo=>0, :bar=>1, :baz=>2}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.reject! # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:reject!>
h1 = e.each {|key, value| key.start_with?('b') }
h1 # => {:foo=>0}
h1.equal?(h) # => true # Identity check

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.reject! { |key, value| h[:new_Key] = 3 }
VALUE
rb_hash_reject_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, delete_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}
replace(other_hash) → self click to toggle source

Replaces the entire contents of self with the contents of other_hash; returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.replace({bat: 3, bam: 4})
h1 # => {:bat=>3, :bam=>4}
h1.equal?(h) # => true # Identity check

Raises an exception if other_hash is not a Hash-convertible object:

h = {}
# Raises TypeError (no implicit conversion of Symbol into Hash):
h.replace(:not_a_hash)
static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);

    COPY_DEFAULT(hash, hash2);

    if (RHASH_AR_TABLE_P(hash)) {
        if (RHASH_AR_TABLE_P(hash2)) {
            ar_clear(hash);
        }
        else {
            ar_free_and_clear_table(hash);
            RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), RHASH_SIZE(hash2)));
        }
    }
    else {
        if (RHASH_AR_TABLE_P(hash2)) {
            st_free_table(RHASH_ST_TABLE(hash));
            RHASH_ST_CLEAR(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
        }
    }
    rb_hash_foreach(hash2, rb_hash_rehash_i, (VALUE)hash);

    rb_gc_writebarrier_remember(hash);

    return hash;
}
select {|key, value| ... } → new_hash click to toggle source
select → new_enumerator

Hash#filter is an alias for Hash#select.

Returns a new Hash object whose entries are those for which the block returns a truthy value:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.select {|key, value| value < 2 }
h1 # => {:foo=>0, :bar=>1}
h1.equal?(h) # => false

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.select # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select>
h1 = e.each {|key, value| value < 2 }
h1 # => {:foo=>0, :bar=>1}
h1.equal?(h) # => false

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.select {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_foreach(hash, select_i, result);
    }
    return result;
}
select! {|key, value| ... } → self or nil click to toggle source
select! → new_enumerator

Hash#filter! is an alias for Hash#select!.

Returns self, whose entries are those for which the block returns a truthy value:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.select! {|key, value| value < 2 }
h # => {:foo=>0, :bar=>1}
h1.equal?(h) # => true

Returns nil if no entries were removed:

h = {foo: 0, bar: 1, baz: 2}
h.select! {|key, value| value < 3} # => nil
h # => {:foo=>0, :bar=>1, :baz=>2}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.select!  # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select!>
h1 = e.each { |key, value| value < 2 }
h1 # => {:foo=>0, :bar=>1}
h1.equal?(h) # => true

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration)
h.select! {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}
shift → [key, value] or default_value click to toggle source

Removes the first hash entry (see Entry Order); returns a 2-element Array containing the removed key and value:

h = {foo: 0, bar: 1, baz: 2}
h.shift # => [:foo, 0]
h # => {:bar=>1, :baz=>2}

Returns the default value if the hash is empty (see Default Values):

h = {}
h.shift # => nil
static VALUE
rb_hash_shift(VALUE hash)
{
    struct shift_var var;

    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 0) {
            if (ar_shift(hash, &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (var.key != Qundef) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    if (RHASH_ST_TABLE_P(hash)) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 0) {
            if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (var.key != Qundef) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    return rb_hash_default_value(hash, Qnil);
}
size → integer click to toggle source

Returns the count of entries in self:

h = {foo: 0, bar: 1, baz: 2}
h.length # => 3

Hash#length is an alias for Hash#size.

VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}
slice(*keys) → new_hash click to toggle source

Returns a new Hash object containing the entries for the given keys:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.slice(:baz, :foo)
h1 # => {:baz=>2, :foo=>0}
h1.equal?(h) # => false

Raises an exception if any given key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.slice(:foo, BasicObject.new)
static VALUE
rb_hash_slice(int argc, VALUE *argv, VALUE hash)
{
    int i;
    VALUE key, value, result;

    if (argc == 0 || RHASH_EMPTY_P(hash)) {
        return rb_hash_new();
    }
    result = rb_hash_new_with_size(argc);

    for (i = 0; i < argc; i++) {
        key = argv[i];
        value = rb_hash_lookup2(hash, key, Qundef);
        if (value != Qundef)
            rb_hash_aset(result, key, value);
    }

    return result;
}
store(key, value) click to toggle source

Associates the given value with the given key, and returns value.

If the given key exists, replaces its value with the given value; the ordering is not affected (see Entry Order):

h = {foo: 0, bar: 1}
h[:foo] = 2 # => 2
h.store(:bar, 3) # => 3
h # => {:foo=>2, :bar=>3}

If key does not exist, adds the key and value; the new entry is last in the order (see Entry Order):

h = {foo: 0, bar: 1}
h[:baz] = 2 # => 2
h.store(:bat, 3) # => 3
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}

Raises an exception if key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h[BasicObject.new] = 2
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.store(BasicObject.new, 2)
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);

    rb_hash_modify(hash);

    if (RHASH_TABLE_NULL_P(hash)) {
        if (iter_lev > 0) no_new_key();
        ar_alloc_table(hash);
    }

    if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}
to_a → new_array click to toggle source

Returns a new Array of 2-element Array objects; each nested Array contains the key and value for a hash entry:

h = {foo: 0, bar: 1, baz: 2}
h.to_a # => [[:foo, 0], [:bar, 1], [:baz, 2]]
static VALUE
rb_hash_to_a(VALUE hash)
{
    VALUE ary;

    ary = rb_ary_new_capa(RHASH_SIZE(hash));
    rb_hash_foreach(hash, to_a_i, ary);

    return ary;
}
to_h → self or new_hash click to toggle source
to_h {|key, value| ... } → new_hash

For an instance of Hash, returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.to_h
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) #  => true # Identity check

For a subclass of Hash, returns a new Hash containing the content of self:

class MyHash < Hash; end
h = MyHash[foo: 0, bar: 1, baz: 2]
h # => {:foo=>0, :bar=>1, :baz=>2}
h.class # => MyHash
h1 = h.to_h
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.class # => Hash

When a block is given, returns a new Hash object whose content is based on the block; the block should return a 2-element Array object specifying the key-value pair to be included in the returned Array:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.to_h {|key, value| [value, key] }
h1 # => {0=>:foo, 1=>:bar, 2=>:baz}

Raises an exception if the block does not return an Array:

h = {foo: 0, bar: 1, baz: 2}
# Raises TypeError (wrong element type Symbol (expected array)):
h1 = h.to_h {|key, value| :array }

Raises an exception if the block returns an Array of size different from 2:

h = {foo: 0, bar: 1, baz: 2}
# Raises ArgumentError (element has wrong array length (expected 2, was 3)):
h1 = h.to_h {|key, value| [0, 1, 2] }

Raises an exception if the block returns an invalid key (see Invalid Hash Keys):

 h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>)
 h1 = h.to_h {|key, value| [BasicObject.new, 0] }

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration):
h.to_h {|key, value| h[:new_key] = 3 }
static VALUE
rb_hash_to_h(VALUE hash)
{
    if (rb_block_given_p()) {
        return rb_hash_to_h_block(hash);
    }
    if (rb_obj_class(hash) != rb_cHash) {
        const VALUE flags = RBASIC(hash)->flags;
        hash = hash_dup(hash, rb_cHash, flags & RHASH_PROC_DEFAULT);
    }
    return hash;
}
to_hash → self click to toggle source

Returns self:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.to_hash
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check
static VALUE
rb_hash_to_hash(VALUE hash)
{
    return hash;
}
to_proc → proc click to toggle source

Returns a Proc object that maps a key to its value:

h = {foo: 0, bar: 1, baz: 2}
proc = h.to_proc
proc.class # => Proc
proc.call(:foo) # => 0
proc.call(:bar) # => 1
proc.call(:nosuch) # => nil
static VALUE
rb_hash_to_proc(VALUE hash)
{
    return rb_func_proc_new(hash_proc_call, hash);
}
to_s()
Alias for: inspect
transform_keys {|key| ... } → new_hash click to toggle source
transform_keys → new_enumerator

Returns a new Hash object; each entry has:

  • A key provided by the block.

  • The value from self.

Transform keys:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys {|key| key.to_s }
h1 # => {"foo"=>0, "bar"=>1, "baz"=>2}

Overwrites values for duplicate keys:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys {|key| :bat }
h1 # => {:bat=>2}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.transform_keys # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:transform_keys>
h1 = e.each { |key| key.to_s }
h1 # => {"foo"=>0, "bar"=>1, "baz"=>2}

Raises an exception if the block returns an invalid key (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>)
h.transform_keys {|key| BasicObject.new }

Raises an exception if the block attempts to add a new key:

h = {foo: 0, bar: 1, baz: 2}
# Raises RuntimeError (can't add a new key into hash during iteration)
h.transform_keys {|key| h[:new_key] = 3 }
static VALUE
rb_hash_transform_keys(int argc, VALUE *argv, VALUE hash)
{
    VALUE result;
    struct transform_keys_args transarg = {0};

    argc = rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        transarg.trans = to_hash(argv[0]);
        transarg.block_given = rb_block_given_p();
    }
    else {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    }
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        if (transarg.trans) {
            transarg.result = result;
            rb_hash_foreach(hash, transform_keys_hash_i, (VALUE)&transarg);
        }
        else {
            rb_hash_foreach(hash, transform_keys_i, result);
        }
    }

    return result;
}
transform_keys! {|key| ... } → self click to toggle source
transform_keys! → new_enumerator

Returns self with new keys provided by the block:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys! {|key| key.to_s }
h1 # => {"foo"=>0, "bar"=>1, "baz"=>2}
h1.equal?(h) # => true # Identity check

Overwrites values for duplicate keys:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys! {|key| :bat }
h1 # => {:bat=>2}

Allows the block to add a new entry:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys! {|key| h[:new_key] = key.to_s }
h1 # => {:new_key=>"baz", "foo"=>0, "bar"=>1, "baz"=>2}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.transform_keys! # => #<Enumerator: {"foo"=>0, "bar"=>1, "baz"=>2}:transform_keys!>
h1 = e.each { |key| key.to_s }
h1 # => {"foo"=>0, "bar"=>1, "baz"=>2}

Raises an exception if the block returns an invalid key (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>)
h.transform_keys! {|key| BasicObject.new }
static VALUE
rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
{
    VALUE trans = 0;
    int block_given = 0;

    argc = rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        trans = to_hash(argv[0]);
        block_given = rb_block_given_p();
    }
    else {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    }
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        long i;
        VALUE pairs = rb_hash_flatten(0, NULL, hash);
        rb_hash_clear(hash);
        for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
            VALUE key = RARRAY_AREF(pairs, i), new_key, val;

            if (!trans) {
                new_key = rb_yield(key);
            }
            else if ((new_key = rb_hash_lookup2(trans, key, Qundef)) != Qundef) {
                /* use the transformed key */
            }
            else if (block_given) {
                new_key = rb_yield(key);
            }
            else {
                new_key = key;
            }
            val = RARRAY_AREF(pairs, i+1);
            rb_hash_aset(hash, new_key, val);
        }
    }
    return hash;
}
transform_values {|value| ... } → new_hash click to toggle source
transform_values → new_enumerator

Returns a new Hash object; each entry has:

  • A key from self.

  • A value provided by the block.

Transform values:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_values {|value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}

Ignores an attempt in the block to add a new key:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_values {|value| h[:new_key] = 3; value * 100 }
h1 # => {:foo=>0, :bar=>100, :baz=>200}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.transform_values # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:transform_values>
h1 = e.each { |value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}
static VALUE
rb_hash_transform_values(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = hash_copy(hash_alloc(rb_cHash), hash);

    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(result, transform_values_foreach_func, transform_values_foreach_replace, result);
    }

    return result;
}
transform_values! {|value| ... } → self click to toggle source
transform_values! → new_enumerator

Returns self, whose keys are unchanged, and whose values are determined by the given block.

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_values! {|value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}
h1.equal?(h) # => true # Identity check

Allows the block to add a new entry:

h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_values! {|value| h[:new_key] = 3; value * 100 }
h1 # => {:foo=>0, :bar=>100, :baz=>200, :new_key=>3}

Returns a new Enumerator if no block given:

h = {foo: 0, bar: 1, baz: 2}
e = h.transform_values! # => #<Enumerator: {:foo=>0, :bar=>100, :baz=>200}:transform_values!>
h1 = e.each {|value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}
static VALUE
rb_hash_transform_values_bang(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);

    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(hash, transform_values_foreach_func, transform_values_foreach_replace, hash);
    }

    return hash;
}
merge! → self click to toggle source
merge!(*other_hashes) → self
merge!(*other_hashes) { |key, old_value, new_value| ... } → self

Merges each of other_hashes into self; returns self.

Each argument in other_hashes must be a Hash-convertible object.

Method update is an alias for #merge!.


With arguments and no block:

  • Returns self, after the given hashes are merged into it.

  • The given hashes are merged left to right.

  • Each new entry is added at the end.

  • Each duplicate-key entry's value overwrites the previous value.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) # => {:foo=>0, :bar=>4, :baz=>2, :bat=>6, :bam=>5}
h3.equal?(h) # => true # Identity check

With arguments and a block:

  • Returns self, after the given hashes are merged.

  • The given hashes are merged left to right.

  • Each new-key entry is added at the end.

  • For each duplicate key:

    • Calls the block with the key and the old and new values.

    • The block's return value becomes the new value for the entry.

Example:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) { |key, old_value, new_value| old_value + new_value }
h3 # => {:foo=>0, :bar=>5, :baz=>2, :bat=>9, :bam=>5}
h3.equal?(h) # => true # Identity check

Allows the block to add a new key:

h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) { |key, old_value, new_value| h[:new_key] = 10 }
h3 # => {:foo=>0, :bar=>10, :baz=>2, :bat=>10, :new_key=>10, :bam=>5}
h3.equal?(h) # => true # Identity check

With no arguments:

  • Returns self, unmodified.

  • The block, if given, is ignored.

Example:

h = {foo: 0, bar: 1, baz: 2}
h.merge # => {:foo=>0, :bar=>1, :baz=>2}
h1 = h.merge! { |key, old_value, new_value| raise 'Cannot happen' }
h1 # => {:foo=>0, :bar=>1, :baz=>2}
h1.equal?(h) # => true # Identity check

Raises an exception if any given argument is not a Hash-convertible object:

h = {}
# Raises TypeError (no implicit conversion of Integer into Hash):
h.merge!(1)
static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();

    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
       VALUE hash = to_hash(argv[i]);
       if (block_given) {
           rb_hash_foreach(hash, rb_hash_update_block_i, self);
       }
       else {
           rb_hash_foreach(hash, rb_hash_update_i, self);
       }
    }
    return self;
}
has_value?(value) → true or false click to toggle source

Returns true if value is a value in self, otherwise false:

h = {foo: 0, bar: 1, baz: 2}
h.has_value?(1) # => true
h.has_value?(123) # => false
static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}
values → new_array click to toggle source

Returns a new Array containing all values in self:

h = {foo: 0, bar: 1, baz: 2}
h.values # => [0, 1, 2]
VALUE
rb_hash_values(VALUE hash)
{
    VALUE values;
    st_index_t size = RHASH_SIZE(hash);

    values = rb_ary_new_capa(size);
    if (size == 0) return values;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        if (RHASH_AR_TABLE_P(hash)) {
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = ar_values(hash, ptr, size);
            });
        }
        else if (RHASH_ST_TABLE_P(hash)) {
            st_table *table = RHASH_ST_TABLE(hash);
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = st_values(table, ptr, size);
            });
        }
        rb_ary_set_len(values, size);
    }

    else {
        rb_hash_foreach(hash, values_i, values);
    }

    return values;
}
values_at(*keys) → new_array click to toggle source

Returns a new Array containing values for the given keys:

h = {foo: 0, bar: 1, baz: 2}
h.values_at(:foo, :baz) # => [0, 2]

Returns an empty Array if no arguments given:

h = {foo: 0, bar: 1, baz: 2}
h.values_at # => []

Raises an exception if any given key is invalid (see Invalid Hash Keys):

h = {foo: 0, bar: 1, baz: 2}
# Raises NoMethodError (undefined method `hash' for #<BasicObject>):
h.values_at(BasicObject.new)
VALUE
rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
        rb_ary_push(result, rb_hash_aref(hash, argv[i]));
    }
    return result;
}