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.

Class Methods

new(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/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-2.3.8/lib/delegate.rb, line 151
def !
  !__getobj__
end

Delegates ! to the _getobj_

!=(obj)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 143
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-2.3.8/lib/delegate.rb, line 135
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-2.3.8/lib/delegate.rb, line 159
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-2.3.8/lib/delegate.rb, line 167
def __setobj__(obj)
  __raise__ ::NotImplementedError, "need to define `__setobj__'"
end

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

freeze

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 225

Freeze both the object returned by _getobj_ and self.

marshal_dump

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 174
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-2.3.8/lib/delegate.rb, line 186
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-2.3.8/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

Handles the magic of delegation through _getobj_.

methods(all=true)

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 110
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-2.3.8/lib/delegate.rb, line 126
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-2.3.8/lib/delegate.rb, line 118
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-2.3.8/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-2.3.8/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 "#{caller(3)[0]}: delegator does not forward private method \##{m}"
    return false
  end
  r
end

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

taint

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 215

Taint both the object returned by _getobj_ and self.

trust

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 205

Trust both the object returned by _getobj_ and self.

untaint

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 220

Untaint both the object returned by _getobj_ and self.

untrust

lib/delegate.rb View on GitHub

          
            # File tmp/rubies/ruby-2.3.8/lib/delegate.rb, line 210

Untrust both the object returned by _getobj_ and self.