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.
The version string
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 76
def initialize(obj)
__setobj__(obj)
end
Pass in the obj to delegate method calls to. All methods supported by obj will be delegated to.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 181
def !
!__getobj__
end
Delegates ! to the __getobj__
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 165
def !=(obj)
return false if obj.equal?(self)
__getobj__ != obj
end
Returns true if two objects are not considered of equal value.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 157
def ==(obj)
return true if obj.equal?(self)
self.__getobj__ == obj
end
Returns true if two objects are considered of equal value.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 173
def eql?(obj)
return true if obj.equal?(self)
obj.eql?(__getobj__)
end
Returns true if two objects are considered of equal value.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 238
def freeze
__getobj__.freeze
super()
end
:method: freeze Freeze both the object returned by __getobj__ and self.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 189
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.
# File tmp/rubies/ruby-4.0.0/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
Serialization support for the object returned by __getobj__.
# File tmp/rubies/ruby-4.0.0/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
Reinitializes delegation from a serialized object.
# File tmp/rubies/ruby-4.0.0/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
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 132
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.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 148
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.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 140
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.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 67
# File tmp/rubies/ruby-4.0.0/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
Checks for a method provided by this the delegate object by forwarding the call through __getobj__.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 197
def __setobj__(obj)
__raise__ ::NotImplementedError, "need to define '__setobj__'"
end
This method must be overridden by subclasses and change the object delegate to obj.
# File tmp/rubies/ruby-4.0.0/lib/delegate.rb, line 115
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