compose10.hpp

stl自带源码

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * 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 <functional>
#include "nullary.hpp"

/* class for the compose_f_g adapter
 */
template <class OP1, class OP2>
class compose_f_g_t
 : public boost::nullary_function<typename OP1::result_type>
{
  private:
    OP1 op1;    // process: op1(op2())
    OP2 op2;
  public:
    // constructor
    compose_f_g_t(const OP1& o1, const OP2& o2)
     : op1(o1), op2(o2) {
    }

    // function call
    typename OP1::result_type
    operator()() const {
        return op1(op2());
    }
};

/* convenience function for the compose_f_g adapter
 */
template <class OP1, class OP2>
inline compose_f_g_t<OP1,OP2>
compose_f_g (const OP1& o1, const OP2& o2) {
    return compose_f_g_t<OP1,OP2>(o1,o2);
}