Class: SimpleDelegator
Relationships & Source Files | |
Super Chains via Extension / Inclusion / Inheritance | |
Class Chain:
self,
::Delegator
|
|
Instance Chain:
self,
::Delegator
|
|
Inherits: |
Delegator
|
Defined in: | lib/delegate.rb |
Overview
A concrete implementation of ::Delegator, this class provides the means to delegate all supported method calls to the object passed into the constructor and even to change the object being delegated to at a later time with #__setobj__.
class User
def born_on
Date.new(1989, 9, 10)
end
end
class UserDecorator < SimpleDelegator
def birth_year
born_on.year
end
end
decorated_user = UserDecorator.new(User.new)
decorated_user.birth_year #=> 1989
decorated_user.__getobj__ #=> #<User: ...>
A SimpleDelegator instance can take advantage of the fact that SimpleDelegator
is a subclass of ::Delegator to call super
to have methods called on the object being delegated to.
class SuperArray < SimpleDelegator
def [](*args)
super + 1
end
end
SuperArray.new([1])[0] #=> 2
Here's a simple example that takes advantage of the fact that SimpleDelegator's delegation object can be changed at any time.
class Stats
def initialize
@source = SimpleDelegator.new([])
end
def stats(records)
@source.__setobj__(records)
"Elements: #{@source.size}\n" +
" Non-Nil: #{@source.compact.size}\n" +
" Unique: #{@source.uniq.size}\n"
end
end
s = Stats.new
puts s.stats(%w{James Edward Gray II})
puts
puts s.stats([1, 2, 3, nil, 4, 5, 1, 2])
Prints:
Elements: 4
Non-Nil: 4
Unique: 4
Elements: 8
Non-Nil: 7
Unique: 6
Class Method Summary
::Delegator - Inherited
.new | Pass in the obj to delegate method calls to. |
Instance Method Summary
-
#__getobj__
Returns the current object method calls are being delegated to.
-
#__setobj__(obj)
Changes the delegate object to obj.
::Delegator - Inherited
#! | Delegates ! to the _getobj_. |
#!= | Returns true if two objects are not considered of equal value. |
#== | Returns true if two objects are considered of equal value. |
#__getobj__ | This method must be overridden by subclasses and should return the object method calls are being delegated to. |
#__setobj__ | This method must be overridden by subclasses and change the object delegate to obj. |
#freeze | Freeze both the object returned by _getobj_ and self. |
#marshal_dump | Serialization support for the object returned by _getobj_. |
#marshal_load | Reinitializes delegation from a serialized object. |
#method_missing | Handles the magic of delegation through _getobj_. |
#methods | Returns the methods available to this delegate object as the union of this object's and _getobj_ methods. |
#protected_methods | Returns the methods available to this delegate object as the union of this object's and _getobj_ protected methods. |
#public_methods | Returns the methods available to this delegate object as the union of this object's and _getobj_ public methods. |
#raise | Use __raise__ if your ::Delegator does not have a object to delegate the raise method call. |
#respond_to_missing? | Checks for a method provided by this the delegate object by forwarding the call through _getobj_. |
#taint | Taint both the object returned by _getobj_ and self. |
#trust | Trust both the object returned by _getobj_ and self. |
#untaint | Untaint both the object returned by _getobj_ and self. |
#untrust | Untrust both the object returned by _getobj_ and self. |
Constructor Details
This class inherits a constructor from Delegator
Dynamic Method Handling
This class handles dynamic methods through the method_missing method in the class Delegator
Instance Method Details
#__getobj__
Returns the current object method calls are being delegated to.
# File 'lib/delegate.rb', line 310
def __getobj__ unless defined?(@delegate_sd_obj) return yield if block_given? __raise__ ::ArgumentError, "not delegated" end @delegate_sd_obj end
#__setobj__(obj)
Changes the delegate object to obj.
It's important to note that this does not cause SimpleDelegator's methods to change. Because of this, you probably only want to change delegation to objects of the same type as the original delegate.
Here's an example of changing the delegation object.
names = SimpleDelegator.new(%w{James Edward Gray II})
puts names[1] # => Edward
names.__setobj__(%w{Gavin Sinclair})
puts names[1] # => Sinclair
# File 'lib/delegate.rb', line 332
def __setobj__(obj) __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj) @delegate_sd_obj = obj end