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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:

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.

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 71
def initialize(obj)
  __setobj__(obj)
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(m, *args, &block)

Handles the magic of delegation through _getobj_.

[ GitHub ]

  
# File 'lib/delegate.rb', line 78
def method_missing(m, *args, &block)
  r = true
  target = self.__getobj__ {r = false}

  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
end

Class Method Details

.const_missing(n)

This method is for internal use only.
[ GitHub ]

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

.public_api

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 245
def self.public_api # :nodoc:
  @delegator_api
end

Instance Method Details

#!

Delegates ! to the _getobj_

[ GitHub ]

  
# File 'lib/delegate.rb', line 159
def !
  !__getobj__
end

#!=(obj)

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

[ GitHub ]

  
# File 'lib/delegate.rb', line 143
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 135
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 167
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 175
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 151
def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

#freeze

Freeze both the object returned by _getobj_ and self.

[ GitHub ]

  
# File 'lib/delegate.rb', line 238
rdoc_method :method: freeze

#initialize_clone(obj) (private)

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 204
def initialize_clone(obj) # :nodoc:
  self.__setobj__(obj.__getobj__.clone)
end

#initialize_dup(obj) (private)

This method is for internal use only.
[ GitHub ]

  
# File 'lib/delegate.rb', line 207
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 182
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 194
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 110
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 126
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 118
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 62
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 95
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 "delegator does not forward private method \##{m}", uplevel: 3
    return false
  end
  r
end

#taint

Taint both the object returned by _getobj_ and self.

[ GitHub ]

  
# File 'lib/delegate.rb', line 223
rdoc_method :method: taint

#trust

Trust both the object returned by _getobj_ and self.

[ GitHub ]

  
# File 'lib/delegate.rb', line 213
rdoc_method :method: trust

#untaint

Untaint both the object returned by _getobj_ and self.

[ GitHub ]

  
# File 'lib/delegate.rb', line 228
rdoc_method :method: untaint

#untrust

Untrust both the object returned by _getobj_ and self.

[ GitHub ]

  
# File 'lib/delegate.rb', line 218
rdoc_method :method: untrust