class SimpleDelegator
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 require 'delegate' 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
Public Instance Methods
Returns the current object method calls are being delegated to.
# File delegate.rb, line 318 def __getobj__ unless defined?(@delegate_sd_obj) return yield if block_given? __raise__ ::ArgumentError, "not delegated" end @delegate_sd_obj end
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 delegate.rb, line 340 def __setobj__(obj) __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj) @delegate_sd_obj = obj end