dsci · February 18, 2016 18:49 · Feb 18, 2016
diff --git a/singleton_cvar.rb b/singleton_cvar.rb
@@ -0,0 +1,17 @@
+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)
diff --git a/singleton_ivar.rb b/singleton_ivar.rb
@@ -0,0 +1,23 @@
+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)
diff --git a/singleton_ivar_wo_private_class_method.rb b/singleton_ivar_wo_private_class_method.rb
@@ -0,0 +1,37 @@
+# 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)
diff --git a/singleton_lib.rb b/singleton_lib.rb
@@ -0,0 +1,13 @@
+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