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Class: Delegator

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Subclasses:
Inherits: BasicObject
Defined in: lib/delegate.rb

Overview

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 of the use of Delegator:

require 'delegate'

class SimpleDelegator < Delegator
  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.

Constant Summary

Class Method Summary

Instance Method Summary

Constructor Details

.new(obj) ⇒ Delegator

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 75

def initialize(obj)
  __setobj__(obj)
end

Class Method Details

.const_missing(n)

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 60

def self.const_missing(n)
  ::Object.const_get(n)
end

.delegating_block(mid)

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 346

def Delegator.delegating_block(mid) # :nodoc:
  lambda do |*args, &block|
    target = self.__getobj__
    target.__send__(mid, *args, &block)
  end.ruby2_keywords
end

.public_api

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 243

def self.public_api # :nodoc:
  @delegator_api
end

Instance Method Details

#!

Delegates ! to the _getobj_

[ GitHub ]

  
# File 'lib/delegate.rb', line 180

def !
  !__getobj__
end

#!=(obj)

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 164

def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

#==(obj)

Returns true if two objects are considered of equal value.

[ GitHub ]

  
# File 'lib/delegate.rb', line 156

def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end

#__getobj__

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 188

def __getobj__
  __raise__ ::NotImplementedError, "need to define `__getobj__'"
end

#__setobj__(obj)

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 196

def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define `__setobj__'"
end

#eql?(obj) ⇒ Boolean

Returns true if two objects are considered of equal value.

[ GitHub ]

  
# File 'lib/delegate.rb', line 172

def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

#freeze

[ GitHub ]

  
# File 'lib/delegate.rb', line 237

RDoc directive :method: freeze

#initialize_clone(obj, freeze: nil) (private)

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 225

def initialize_clone(obj, freeze: nil) # :nodoc:
  self.__setobj__(obj.__getobj__.clone(freeze: freeze))
end

#initialize_dup(obj) (private)

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 228

def initialize_dup(obj) # :nodoc:
  self.__setobj__(obj.__getobj__.dup)
end

#marshal_dump

Serialization support for the object returned by _getobj_.

[ GitHub ]

  
# File 'lib/delegate.rb', line 203

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)

Reinitializes delegation from a serialized object.

[ GitHub ]

  
# File 'lib/delegate.rb', line 215

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

#methods(all = true)

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 131

def methods(all=true)
  __getobj__.methods(all) | super
end

#protected_methods(all = true)

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 147

def protected_methods(all=true)
  __getobj__.protected_methods(all) | super
end

#public_methods(all = true)

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 139

def public_methods(all=true)
  __getobj__.public_methods(all) | super
end

#raise

Use #__raise__ if your Delegator does not have a object to delegate the #raise method call.

[ GitHub ]

  
# File 'lib/delegate.rb', line 66

rdoc_method :method: raise

#respond_to_missing?(m, include_private) ⇒ Boolean

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 99

def respond_to_missing?(m, include_private)
  r = true
  target = self.__getobj__ {r = false}
  r &&= target_respond_to?(target, m, include_private)
  if r && include_private && !target_respond_to?(target, m, false)
    warn "delegator does not forward private method \##{m}", uplevel: 3
    return false
  end
  r
end

#target_respond_to?(target, m, include_private) ⇒ Boolean (private)

Handle BasicObject instances

[ GitHub ]

  
# File 'lib/delegate.rb', line 114

private def target_respond_to?(target, m, include_private)
  case target
  when Object
    target.respond_to?(m, include_private)
  else
    if KERNEL_RESPOND_TO.bind_call(target, :respond_to?)
      target.respond_to?(m, include_private)
    else
      KERNEL_RESPOND_TO.bind_call(target, m, include_private)
    end
  end
end