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class Delegator

Parent:
BasicObject

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.

Public Class Methods

new(obj) Show source 
# File lib/delegate.rb, line 70
def initialize(obj)
  __setobj__(obj)
end

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

Public Instance Methods

# File lib/delegate.rb, line 158
def !
  !__getobj__
end

Delegates ! to the _getobj_

!=(obj) Show source 
# File lib/delegate.rb, line 142
def !=(obj)
  return false if obj.equal?(self)
  __getobj__ != obj
end

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

==(obj) Show source 
# File lib/delegate.rb, line 134
def ==(obj)
  return true if obj.equal?(self)
  self.__getobj__ == obj
end

Returns true if two objects are considered of equal value.

__getobj__() Show source 
# File lib/delegate.rb, line 166
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__()
Alias for: raise
__setobj__(obj) Show source 
# File lib/delegate.rb, line 174
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) Show source 
# File lib/delegate.rb, line 150
def eql?(obj)
  return true if obj.equal?(self)
  obj.eql?(__getobj__)
end

Returns true if two objects are considered of equal value.

freeze() Show source 
# File lib/delegate.rb, line 236

Freeze both the object returned by _getobj_ and self.

marshal_dump() Show source 
# File lib/delegate.rb, line 181
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) Show source 
# File lib/delegate.rb, line 193
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) Show source 
# File lib/delegate.rb, line 77
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_.

Calls superclass method BasicObject#method_missing
methods(all=true) Show source 
# File lib/delegate.rb, line 109
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.

Calls superclass method
protected_methods(all=true) Show source 
# File lib/delegate.rb, line 125
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.

Calls superclass method
public_methods(all=true) Show source 
# File lib/delegate.rb, line 117
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.

Calls superclass method
raise() Show source 
# File lib/delegate.rb, line 66

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

Also aliased as: __raise__
respond_to_missing?(m, include_private) Show source 
# File lib/delegate.rb, line 94
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

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

taint() Show source 
# File lib/delegate.rb, line 226

Taint both the object returned by _getobj_ and self.

trust() Show source 
# File lib/delegate.rb, line 216

Trust both the object returned by _getobj_ and self.

untaint() Show source 
# File lib/delegate.rb, line 231

Untaint both the object returned by _getobj_ and self.

untrust() Show source 
# File lib/delegate.rb, line 221

Untrust both the object returned by _getobj_ and self.

Ruby Core © 1993–2017 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.