ifthenelse.hpp

C++ Templates 完全导引范例asics

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#ifndef IFTHENELSE_HPP
#define IFTHENELSE_HPP

// primary template: yield second or third argument depending on first argument
template<bool C, typename Ta, typename Tb>
class IfThenElse;

// partial specialization: true yields second argument
template<typename Ta, typename Tb>
class IfThenElse<true, Ta, Tb> {
  public:
    typedef Ta ResultT;
};

// partial specialization: false yields third argument
template<typename Ta, typename Tb>
class IfThenElse<false, Ta, Tb> {
  public:
    typedef Tb ResultT;
};

#endif // IFTHENELSE_HPP