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 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.

Constants

VERSION: The version string

Public Class Methods

new (obj)

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

# File lib/delegate.rb, line 76
def initialize(obj)
  __setobj__(obj)
end

Public Instance Methods

! ()

Delegates ! to the __getobj__

# File lib/delegate.rb, line 181
def !
  !__getobj__
end

!= (obj)

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

# File lib/delegate.rb, line 165
def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

== (obj)

Returns true if two objects are considered of equal value.

# File lib/delegate.rb, line 157
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.

# File lib/delegate.rb, line 189
def __getobj__
  __raise__ ::NotImplementedError, "need to define '__getobj__'"
end

__raise__ ()

Alias for: raise

__setobj__ (obj)

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

# File lib/delegate.rb, line 197
def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define '__setobj__'"
end

eql? (obj)

Returns true if two objects are considered of equal value.

# File lib/delegate.rb, line 173
def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

freeze ()

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

Calls superclass method

# File lib/delegate.rb, line 238
def freeze
  __getobj__.freeze
  super()
end

marshal_dump ()

Serialization support for the object returned by __getobj__.

# File lib/delegate.rb, line 204
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.

# File lib/delegate.rb, line 216
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)

Calls superclass method

# File lib/delegate.rb, line 83
               def method_missing(m, *args, &block)
  r = true
  target = self.__getobj__ {r = false}

  if r && target_respond_to?(target, m, false)
    target.__send__(m, *args, &block)
  elsif ::Kernel.method_defined?(m) || ::Kernel.private_method_defined?(m)
    ::Kernel.instance_method(m).bind_call(self, *args, &block)
  else
    super(m, *args, &block)
  end
end

methods (all=true)

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 132
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.

Calls superclass method

# File lib/delegate.rb, line 148
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.

Calls superclass method

# File lib/delegate.rb, line 140
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.

# File lib/delegate.rb, line 67

Also aliased as: __raise__

respond_to_missing? (m, include_private)

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

# File lib/delegate.rb, line 100
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