class Binding

Evaluates the Ruby expression(s) in string, in the binding's context. If the optional filename and lineno parameters are present, they will be used when reporting syntax errors.

def get_binding(param)
  binding
end
b = get_binding("hello")
b.eval("param")   #=> "hello"

static VALUE
bind_eval(int argc, VALUE *argv, VALUE bindval)
{
    VALUE args[4];

    rb_scan_args(argc, argv, "12", &args[0], &args[2], &args[3]);
    args[1] = bindval;
    return rb_f_eval(argc+1, args, Qnil /* self will be searched in eval */);
}

Opens an IRB session where binding.irb is called which allows for interactive debugging. You can call any methods or variables available in the current scope, and mutate state if you need to.

Given a Ruby file called potato.rb containing the following code:

class Potato
  def initialize
    @cooked = false
    binding.irb
    puts "Cooked potato: #{@cooked}"
  end
end

Potato.new

Running ruby potato.rb will open an IRB session where binding.irb is called, and you will see the following:

$ ruby potato.rb

From: potato.rb @ line 4 :

    1: class Potato
    2:   def initialize
    3:     @cooked = false
 => 4:     binding.irb
    5:     puts "Cooked potato: #{@cooked}"
    6:   end
    7: end
    8:
    9: Potato.new

irb(#<Potato:0x00007feea1916670>):001:0>

You can type any valid Ruby code and it will be evaluated in the current context. This allows you to debug without having to run your code repeatedly:

irb(#<Potato:0x00007feea1916670>):001:0> @cooked
=> false
irb(#<Potato:0x00007feea1916670>):002:0> self.class
=> Potato
irb(#<Potato:0x00007feea1916670>):003:0> caller.first
=> ".../2.5.1/lib/ruby/2.5.0/irb/workspace.rb:85:in `eval'"
irb(#<Potato:0x00007feea1916670>):004:0> @cooked = true
=> true

You can exit the IRB session with the exit command. Note that exiting will resume execution where binding.irb had paused it, as you can see from the output printed to standard output in this example:

irb(#<Potato:0x00007feea1916670>):005:0> exit
Cooked potato: true

See IRB for more information.

# File lib/irb.rb, line 948
def irb
  IRB.setup(source_location[0], argv: [])
  workspace = IRB::WorkSpace.new(self)
  STDOUT.print(workspace.code_around_binding)
  binding_irb = IRB::Irb.new(workspace)
  binding_irb.context.irb_path = File.expand_path(source_location[0])
  binding_irb.run(IRB.conf)
end

Returns true if a local variable symbol exists.

def foo
  a = 1
  binding.local_variable_defined?(:a) #=> true
  binding.local_variable_defined?(:b) #=> false
end

This method is the short version of the following code:

binding.eval("defined?(#{symbol}) == 'local-variable'")

static VALUE
bind_local_variable_defined_p(VALUE bindval, VALUE sym)
{
    ID lid = check_local_id(bindval, &sym);
    const rb_binding_t *bind;
    const rb_env_t *env;

    if (!lid) return Qfalse;

    GetBindingPtr(bindval, bind);
    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    return get_local_variable_ptr(&env, lid) ? Qtrue : Qfalse;
}

Returns the value of the local variable symbol.

def foo
  a = 1
  binding.local_variable_get(:a) #=> 1
  binding.local_variable_get(:b) #=> NameError
end

This method is the short version of the following code:

binding.eval("#{symbol}")

static VALUE
bind_local_variable_get(VALUE bindval, VALUE sym)
{
    ID lid = check_local_id(bindval, &sym);
    const rb_binding_t *bind;
    const VALUE *ptr;
    const rb_env_t *env;

    if (!lid) goto undefined;

    GetBindingPtr(bindval, bind);

    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    if ((ptr = get_local_variable_ptr(&env, lid)) != NULL) {
        return *ptr;
    }

    sym = ID2SYM(lid);
  undefined:
    rb_name_err_raise("local variable `%1$s' is not defined for %2$s",
                      bindval, sym);
    UNREACHABLE_RETURN(Qundef);
}

Set local variable named symbol as obj.

def foo
  a = 1
  bind = binding
  bind.local_variable_set(:a, 2) # set existing local variable `a'
  bind.local_variable_set(:b, 3) # create new local variable `b'
                                 # `b' exists only in binding

  p bind.local_variable_get(:a)  #=> 2
  p bind.local_variable_get(:b)  #=> 3
  p a                            #=> 2
  p b                            #=> NameError
end

This method behaves similarly to the following code:

binding.eval("#{symbol} = #{obj}")

if obj can be dumped in Ruby code.

static VALUE
bind_local_variable_set(VALUE bindval, VALUE sym, VALUE val)
{
    ID lid = check_local_id(bindval, &sym);
    rb_binding_t *bind;
    const VALUE *ptr;
    const rb_env_t *env;

    if (!lid) lid = rb_intern_str(sym);

    GetBindingPtr(bindval, bind);
    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    if ((ptr = get_local_variable_ptr(&env, lid)) == NULL) {
        /* not found. create new env */
        ptr = rb_binding_add_dynavars(bindval, bind, 1, &lid);
        env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    }

    RB_OBJ_WRITE(env, ptr, val);

    return val;
}

Returns the names of the binding's local variables as symbols.

def foo
  a = 1
  2.times do |n|
    binding.local_variables #=> [:a, :n]
  end
end

This method is the short version of the following code:

binding.eval("local_variables")

static VALUE
bind_local_variables(VALUE bindval)
{
    const rb_binding_t *bind;
    const rb_env_t *env;

    GetBindingPtr(bindval, bind);
    env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
    return rb_vm_env_local_variables(env);
}

Returns the bound receiver of the binding object.

static VALUE
bind_receiver(VALUE bindval)
{
    const rb_binding_t *bind;
    GetBindingPtr(bindval, bind);
    return vm_block_self(&bind->block);
}

Returns the Ruby source filename and line number of the binding object.

static VALUE
bind_location(VALUE bindval)
{
    VALUE loc[2];
    const rb_binding_t *bind;
    GetBindingPtr(bindval, bind);
    loc[0] = pathobj_path(bind->pathobj);
    loc[1] = INT2FIX(bind->first_lineno);

    return rb_ary_new4(2, loc);
}