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Filename : cdesc-Singleton.ri
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U:RDoc::NormalModule[iI"Singleton:EF@0o:RDoc::Markup::Document:@parts[o;;[o:RDoc::Markup::Paragraph;[I";The Singleton module implements the Singleton pattern.;To:RDoc::Markup::BlankLine�S:RDoc::Markup::Heading:
leveli:	textI"
Usage;T@o;	;[I"8To use Singleton, include the module in your class.;T@o:RDoc::Markup::Verbatim;[	I"class Klass
;TI"   include Singleton
;TI"   # ...
;TI"	end
;T:@format0o;	;[I"AThis ensures that only one instance of Klass can be created.;T@o;;[I"+a,b  = Klass.instance, Klass.instance
;TI"
;TI"a == b
;TI"# => true
;TI"
;TI"Klass.new
;TI"-# => NoMethodError - new is private ...
;T;0o;	;[I"HThe instance is created at upon the first call of Klass.instance().;T@o;;[I"class OtherKlass
;TI"  include Singleton
;TI"
  # ...
;TI"	end
;TI"
;TI"+ObjectSpace.each_object(OtherKlass){}
;TI"# => 0
;TI"
;TI"OtherKlass.instance
;TI"+ObjectSpace.each_object(OtherKlass){}
;TI"# => 1
;T;0o;	;[I">This behavior is preserved under inheritance and cloning.;T@S;;i;
I"Implementation;T@o;	;[I"This above is achieved by:;T@o:RDoc::Markup::List:
@type:BULLET:@items[
o:RDoc::Markup::ListItem:@label0;[o;	;[I"1Making Klass.new and Klass.allocate private.;T@o;;0;[o;	;[I"POverriding Klass.inherited(sub_klass) and Klass.clone() to ensure that the ;TI"=Singleton properties are kept when inherited and cloned.;T@o;;0;[o;	;[I"MProviding the Klass.instance() method that returns the same object each ;TI"time it is called.;T@o;;0;[o;	;[I":Overriding Klass._load(str) to call Klass.instance().;T@o;;0;[o;	;[I"IOverriding Klass#clone and Klass#dup to raise TypeErrors to prevent ;TI"cloning or duping.;T@S;;i;
I"Singleton and Marshal;T@o;	;[
I"SBy default Singleton's #_dump(depth) returns the empty string. Marshalling by ;TI"Mdefault will strip state information, e.g. instance variables and taint ;TI"Jstate, from the instance. Classes using Singleton can provide custom ;TI"Q_load(str) and _dump(depth) methods to retain some of the previous state of ;TI"the instance.;T@o;;["I"require 'singleton'
;TI"
;TI"class Example
;TI"  include Singleton
;TI"#  attr_accessor :keep, :strip
;TI"  def _dump(depth)
;TI"@    # this strips the @strip information from the instance
;TI"$    Marshal.dump(@keep, depth)
;TI"  end
;TI"
;TI"  def self._load(str)
;TI"+    instance.keep = Marshal.load(str)
;TI"    instance
;TI"  end
;TI"	end
;TI"
;TI"a = Example.instance
;TI"a.keep = "keep this"
;TI"!a.strip = "get rid of this"
;TI"
a.taint
;TI"
;TI"$stored_state = Marshal.dump(a)
;TI"
;TI"a.keep = nil
;TI"a.strip = nil
;TI"$b = Marshal.load(stored_state)
;TI"p a == b  #  => true
;TI"!p a.keep  #  => "keep this"
;TI"p a.strip #  => nil;T;0:
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