signselect.hpp

C++ Templates 完全导引范例

/* 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.
 */
#include "ifthenelse.hpp"

template <int S, typename NegT, typename ZeroT, typename PosT>
struct SignSelectT {
  typedef typename
      IfThenElse<(S<0),
                 NegT, 
                 typename IfThenElse<(S>0),
                                     PosT,
                                     ZeroT
                                    >::ResultT
                >::ResultT
      ResultT;
};