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@dsci
Created February 18, 2016 18:49
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class SingletonCvar
def self.instance
@@instance ||= new
end
private_class_method :new
end
singleton = SingletonCvar.instance
singleton_again = SingletonCvar.instance
p singleton.object_id # => 70235617244200
p singleton_again.object_id # => 70235617244200
SingletonCvar.new
# singleton_cvar.rb:15:in `<main>': private method `new' called
# for SingletonCvar:Class (NoMethodError)
module Singleton
def self.included(base)
base.class_eval do
def self.instance
@instance ||= new
end
private_class_method :new
end
end
end
class SingletonIvar
include Singleton
end
singletion = SingletonIvar.instance
p singletion.object_id # => 70242076750240
singleton_again = SingletonIvar.instance
p singleton_again.object_id # => 70242076750240
SingletonIvar.new
# singleton_ivar.rb:21:in `<main>': private method `new'
# called for SingletonIvar:Class (NoMethodError)
# No usage of private_class_method here
module Singleton
def self.included(base)
base.send(:extend, ClassMethods)
end
module ClassMethods
def instance
singleton_class.send(:private, :new) unless is_private_method?(:new)
@instance ||= new
end
private
def is_private_method?(meth_name)
self.private_methods.include?(meth_name)
end
end
end
class SingletonIvarWoPrivateClassMethods
include Singleton
def foo
12
end
end
singletion = SingletonIvarWoPrivateClassMethods.instance
p singletion.object_id #=> 70174947355600
singleton_again = SingletonIvarWoPrivateClassMethods.instance
p singleton_again.object_id #=> 70174947355600
SingletonIvarWoPrivateClassMethods.new
#=> singleton_wo_private_class_method.rb:35:in `<main>': private method `new'
# called for SingletonIvarWoPrivateClassMethods:Class (NoMethodError)
require 'singleton' # use Ruby implementation
class SingletonImp
include Singleton
end
singletion = SingletonImp.instance
p singletion.object_id #=> 70127047740700
singleton_again = SingletonImp.instance
p singleton_again.object_id #=> 70127047740700
SingletonImp.new
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