class Delegator

This library provides three different ways to delegate method calls to an object. The easiest to use is SimpleDelegator. Pass an object to the constructor and all methods supported by the object will be delegated. This object can be changed later.

Going a step further, the top level DelegateClass method allows you to easily setup delegation through class inheritance. This is considerably more flexible and thus probably the most common use for this library.

Finally, if you need full control over the delegation scheme, you can inherit from the abstract class Delegator and customize as needed. (If you find yourself needing this control, have a look at Forwardable which is also in the standard library. It may suit your needs better.)

SimpleDelegator's implementation serves as a nice example if the use of Delegator:

class SimpleDelegator < Delegator
  def initialize(obj)
    super                  # pass obj to Delegator constructor, required
    @delegate_sd_obj = obj # store obj for future use
  end

  def __getobj__
    @delegate_sd_obj # return object we are delegating to, required
  end

  def __setobj__(obj)
    @delegate_sd_obj = obj # change delegation object,
                           # a feature we're providing
  end
end

Notes¶ ↑

Be advised, RDoc will not detect delegated methods.

Public Class Methods

new(obj) click to toggle source

Pass in the obj to delegate method calls to. All methods supported by obj will be delegated to.

# File lib/delegate.rb, line 69
def initialize(obj)
  __setobj__(obj)
end

Public Instance Methods

!() click to toggle source

Delegates ! to the _getobj_

# File lib/delegate.rb, line 152
def !
  !__getobj__
end

!=(obj) click to toggle source

Returns true if two objects are not considered of equal value.

# File lib/delegate.rb, line 144
def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

==(obj) click to toggle source

Returns true if two objects are considered of equal value.

# File lib/delegate.rb, line 136
def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end

__getobj__() click to toggle source

This method must be overridden by subclasses and should return the object method calls are being delegated to.

# File lib/delegate.rb, line 160
def __getobj__
  __raise__ ::NotImplementedError, "need to define `__getobj__'"
end

__setobj__(obj) click to toggle source

This method must be overridden by subclasses and change the object delegate to obj.

# File lib/delegate.rb, line 168
def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define `__setobj__'"
end

freeze() click to toggle source

Freeze both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 230

marshal_dump() click to toggle source

Serialization support for the object returned by _getobj_.

# File lib/delegate.rb, line 175
def marshal_dump
  ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var}
  [
    :__v2__,
    ivars, ivars.map{|var| instance_variable_get(var)},
    __getobj__
  ]
end

marshal_load(data) click to toggle source

Reinitializes delegation from a serialized object.

# File lib/delegate.rb, line 187
def marshal_load(data)
  version, vars, values, obj = data
  if version == :__v2__
    vars.each_with_index{|var, i| instance_variable_set(var, values[i])}
    __setobj__(obj)
  else
    __setobj__(data)
  end
end

method_missing(m, *args, &block) click to toggle source

Handles the magic of delegation through _getobj_.

Calls superclass method BasicObject#method_missing

# File lib/delegate.rb, line 76
def method_missing(m, *args, &block)
  r = true
  target = self.__getobj__ {r = false}
  begin
    if r && target.respond_to?(m)
      target.__send__(m, *args, &block)
    elsif ::Kernel.respond_to?(m, true)
      ::Kernel.instance_method(m).bind(self).(*args, &block)
    else
      super(m, *args, &block)
    end
  ensure
    $@.delete_if {|t| %r"\A#{Regexp.quote(__FILE__)}:(?:#{[__LINE__-7, __LINE__-5, __LINE__-3].join('|')}):"o =~ t} if $@
  end
end

methods(all=true) click to toggle source

Returns the methods available to this delegate object as the union of this object's and _getobj_ methods.

Calls superclass method

# File lib/delegate.rb, line 111
def methods(all=true)
  __getobj__.methods(all) | super
end

protected_methods(all=true) click to toggle source

Returns the methods available to this delegate object as the union of this object's and _getobj_ protected methods.

Calls superclass method

# File lib/delegate.rb, line 127
def protected_methods(all=true)
  __getobj__.protected_methods(all) | super
end

public_methods(all=true) click to toggle source

Returns the methods available to this delegate object as the union of this object's and _getobj_ public methods.

Calls superclass method

# File lib/delegate.rb, line 119
def public_methods(all=true)
  __getobj__.public_methods(all) | super
end

respond_to_missing?(m, include_private) click to toggle source

Checks for a method provided by this the delegate object by forwarding the call through _getobj_.

# File lib/delegate.rb, line 96
def respond_to_missing?(m, include_private)
  r = true
  target = self.__getobj__ {r = false}
  r &&= target.respond_to?(m, include_private)
  if r && include_private && !target.respond_to?(m, false)
    warn "#{caller(3)[0]}: delegator does not forward private method \##{m}"
    return false
  end
  r
end

taint() click to toggle source

Taint both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 220

trust() click to toggle source

Trust both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 210

untaint() click to toggle source

Untaint both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 225

untrust() click to toggle source

Untrust both the object returned by _getobj_ and self.

# File lib/delegate.rb, line 215