Class: Delegator

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:

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.

Direct Known Subclasses

SimpleDelegator

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(obj) ⇒ Delegator

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



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# File 'lib/delegate.rb', line 71

def initialize(obj)
  __setobj__(obj)
end

Class Method Details

.const_missing(n) ⇒ Object

:stopdoc:



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# File 'lib/delegate.rb', line 56

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

.delegating_block(mid) ⇒ Object

:nodoc:



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# File 'lib/delegate.rb', line 333

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

.public_api ⇒ Object

:nodoc:



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# File 'lib/delegate.rb', line 232

def self.public_api # :nodoc:
  @delegator_api
end

Instance Method Details

#! ⇒ Object

Delegates ! to the _getobj_



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# File 'lib/delegate.rb', line 169

def !
  !__getobj__
end

#!=(obj) ⇒ Object

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



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# File 'lib/delegate.rb', line 153

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

#==(obj) ⇒ Object

Returns true if two objects are considered of equal value.



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# File 'lib/delegate.rb', line 145

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

#__getobj__ ⇒ Object

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



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# File 'lib/delegate.rb', line 177

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

#__setobj__(obj) ⇒ Object

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



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# File 'lib/delegate.rb', line 185

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

#eql?(obj) ⇒ Boolean

Returns true if two objects are considered of equal value.

Returns:

  • (Boolean) 


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# File 'lib/delegate.rb', line 161

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

#freeze ⇒ Object

:method: freeze Freeze both the object returned by _getobj_ and self.



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# File 'lib/delegate.rb', line 226

def freeze
  __getobj__.freeze
  super()
end

#marshal_dump ⇒ Object

Serialization support for the object returned by _getobj_.



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# File 'lib/delegate.rb', line 192

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) ⇒ Object

Reinitializes delegation from a serialized object.



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# File 'lib/delegate.rb', line 204

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) ⇒ Object

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



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# File 'lib/delegate.rb', line 120

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

#protected_methods(all = true) ⇒ Object

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



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# File 'lib/delegate.rb', line 136

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

#public_methods(all = true) ⇒ Object

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



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# File 'lib/delegate.rb', line 128

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

#respond_to_missing?(m, include_private) ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/delegate.rb', line 95

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