Re: Encapsulating related utility functions

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=?UTF-8?B?TWFyY2VsIE3DvGxsZXI=?= <news.5.maazl@spamgourmet.org>

Newsgroups:

comp.lang.c++

Date:

Sun, 22 Jun 2008 18:19:01 +0200

Message-ID:

<485e7b7a$0$6608$9b4e6d93@newsspool2.arcor-online.net>

Hi!

Erik Wikstr??m wrote:

Ask your self this (or ask your collogues):

* If you will never instantiate it why use a class, or put another way:
   how is it object-oriented to create a class but never create any
   objects from it?

* If you create a class with static functions, what relation does these
   functions have with the class (except that the class provides a
   namespace for the functions)?

There are meaningful semantics of classes with only static members.

For example something like that:

template<class T, class K>
class instance_repository
{public:
   // abstract factory interface used for object instantiation
   struct IFactory
   { virtual T* operator()(K& key) = 0;
   };

  public:
   // Get an existing instance of T or return NULL.
   static intrusive_ptr<T> FindByKey(const K&);
   // Get an existing instance of T or create a new one.
   static intrusive_ptr<T> GetByKey(K& key, IFactory& factory);
  private:
   static sorted_vector<T*, const K&> Index;
   static mutex Mtx; // protect the index above
};

Marcel