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

KERNEL_RESPOND_TO
VERSION

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 delegate.rb, line 75
def initialize(obj)
  __setobj__(obj)
end

Public Instance Methods

!() click to toggle source

Delegates ! to the _getobj_

# File delegate.rb, line 180
def !
  !__getobj__
end

!=(obj) click to toggle source

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

# File delegate.rb, line 164
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 delegate.rb, line 156
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 delegate.rb, line 188
def __getobj__
  __raise__ ::NotImplementedError, "need to define '__getobj__'"
end

__raise__()

Alias for: raise

__setobj__(obj) click to toggle source

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

# File delegate.rb, line 196
def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define '__setobj__'"
end

eql?(obj) click to toggle source

Returns true if two objects are considered of equal value.

# File delegate.rb, line 172
def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

freeze() click to toggle source

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

Calls superclass method

# File delegate.rb, line 237
def freeze
  __getobj__.freeze
  super()
end

marshal_dump() click to toggle source

Serialization support for the object returned by _getobj_.

# File 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) click to toggle source

Reinitializes delegation from a serialized object.

# File 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

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

Calls superclass method

# File delegate.rb, line 82
               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) 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 delegate.rb, line 131
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 delegate.rb, line 147
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 delegate.rb, line 139
def public_methods(all=true)
  __getobj__.public_methods(all) | super
end

raise() click to toggle source

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

# File delegate.rb, line 66

Also aliased as: __raise__

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 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

Private Instance Methods

target_respond_to?(target, m, include_private) click to toggle source

Handle BasicObject instances

# File delegate.rb, line 114
        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