Delegator

Class

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.

Constants

KERNEL_RESPOND_TO

No documentation available

Class Methods

new(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 71
def initialize(obj)
  __setobj__(obj)
end

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

Instance Methods

!

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 176
def !
  !__getobj__
end

Delegates ! to the _getobj_

!=(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 160
def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

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

==(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 152
def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end

Returns true if two objects are considered of equal value.

getobj

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 184
def __getobj__
  __raise__ ::NotImplementedError, "need to define `__getobj__'"
end

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

raise

lib/delegate.rb View on GitHub

An alias for raise

setobj(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 192
def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define `__setobj__'"
end

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

eql?(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 168
def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

Returns true if two objects are considered of equal value.

freeze

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 233
def freeze
  __getobj__.freeze
  super()
end

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

marshal_dump

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 199
def marshal_dump
  ivars = instance_variables.reject {|var| /\A@delegate_/ =~ var}
  [
    :__v2__,
    ivars, ivars.map {|var| instance_variable_get(var)},
    __getobj__
  ]
end

Serialization support for the object returned by _getobj_.

marshal_load(data)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 211
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

Reinitializes delegation from a serialized object.

method_missing(m, *args, &block)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 78
               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

No documentation available

methods(all=true)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 127
def methods(all=true)
  __getobj__.methods(all) | super
end

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

protected_methods(all=true)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 143
def protected_methods(all=true)
  __getobj__.protected_methods(all) | super
end

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

public_methods(all=true)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 135
def public_methods(all=true)
  __getobj__.public_methods(all) | super
end

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

raise

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 62

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

respond_to_missing?(m, include_private)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/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

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

target_respond_to?(target, m, include_private)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.7.6/lib/delegate.rb, line 110
        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

Handle BasicObject instances