Guide: Singletons

Overview

Singletons are a means of ensuring a single, unique copy of an object can ever exist. There are various ways of implementing singletons, the wikipedia has a surprisingly good article on singletons and provides a snippet that utilises the curiously recurring template pattern which is used as the derivation for this form of the singleton.

CompilingLinking

Include the following at the top of any translation unit that requires compilation of a singleton derived class.

  #include <ecl/utilities.hpp>

  using ecl::Singleton;

Since it is a template class, no linking is required if you are only using this class.

Usage

Inheriting

This singleton is intended to be inherited by a deriving class - this saves the work of actually reinventing the singleton mechanisms whenever you wish to use a singleton.

  class TestObject : public ecl::Singleton<TestObject>
  {
     friend class ecl::Singleton<TestObject>;

     public:
         int value() { return data; }

     protected:
         TestObject() : data(32) {}

     private:
         int data;
  };

Calling

If you use a macro as shown below, the instance can be conveniently and readably accessed,

  #define Test TestObject::instance()

  ...

  cout << Test.value() << endl;