// Semantics Consulting's Tyr Library
// http://www.semantics.org
//
// Copyright (c) 2003 by Stephen C. Dewhurst
//
// Permission to use, copy, modify, distribute, and sell this software
// for any purpose is hereby granted without fee, provided that the above
// copyright notice appears in all copies and that both that copyright
// notice and this permission notice appear in supporting documentation.
// The author makes no representations about the suitability of this
// software for any purpose.  It is provided "as is" without express
// or implied warranty.

// Expanding Monostate protopattern

// Described in What Are You, Anyway? C/C++ Users Journal Experts Forum, 21, 8 (August 2003).

#ifndef EXPANDINGMONOSTATE_H
#define EXPANDINGMONOSTATE_H

namespace Tyr {

//
//	Expanding Monostate
//
//	Ask for a member of a given type, creates members
//	automatically, as needed at compile time.
//
class Monostate {
  public:
	template <typename T>
	T &get() {
		static T member;
		return member;
	}
};

//
//	Indexed Expanding Monostate
//
//	Allows different members of the same type.
//
class IndexedMonostate {
  public:
	template <typename T, int i>
	T &get() {
		static T member;
		return member;
	}
};

//
//	Named Expanding Monostate
//
//	Allows named monostate members.
//
template <typename T, int n>
struct Name {
	typedef T Type;
};

typedef Name<int,1> anInt;
typedef Name<double,1> aDouble;

class NamedMonostate {
  public:
	template <typename N>
	typename N::Type &get( ) {
	    static typename N::Type member;
	    return member;
	}
};

//
//	Named Expanding Monostate with traditional get/set.
//
class GSNamedMonostate {
  public:
	template <typename N>
	void set( const typename N::Type &val ) {
		// This const_cast is actually safe, since we are
		// always actually getting a non-const object.
		// (Unless N::Type is const, then you get a compile error here.)
	    const_cast<typename N::Type &>(get<N>()) = val;
	}
	template <typename N>
	const typename N::Type &get( ) const {
	    static typename N::Type member;
	    return member;
	}
};

} // namespace Tyr

#endif