functorops.cpp

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 <iostream>
#include <string>
#include <typeinfo>
#include "functorops.hpp"

bool compare (std::string debugstr, double v1, float v2)
{
    if (debugstr != "") {
        std::cout << debugstr << ": " << v1 
                                      << (v1<v2? '<' : '>') 
                                      << v2 << '\n';
    }
    return v1<v2;
}

void print_name_value (std::string name, double value) 
{
    std::cout << name << ": " << value << '\n';
}

double sub (double a, double b)
{
    return a-b;
}

double twice (double a) 
{
    return 2*a;
}

int main() 
{
    using std::cout;

    // demonstrate composition:
    cout << "Composition result: "
         << compose(func_ptr(sub), func_ptr(twice))(3.0, 7.0)
         << '\n';

    // demonstrate binding:
    cout << "Binding result:     "
         << bindfp<1>(compare, "main()->compare()")(1.02, 1.03)
         << '\n';
    cout << "Binding output:     ";
    bindfp<1>(print_name_value,
              "the ultimate answer to life")(42);

    // combine composition and binding:
    cout << "Mixing composition and binding (bind<1>): "
         << bind<1>(compose(func_ptr(sub),func_ptr(twice)),
                    7.0)(3.0)
         << '\n';
    cout << "Mixing composition and binding (bind<2>): "
         << bind<2>(compose(func_ptr(sub),func_ptr(twice)),
                    7.0)(3.0)
         << '\n';
}