functor1.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>

// class for function objects that return constant value
class ConstantIntFunctor {
  private:
    int value;    // value to return on ``function call''
  public:
    // constructor: initialize value to return
    ConstantIntFunctor (int c) : value(c) {
    }

    // ``function call''
    int operator() () const { 
        return value;
    }
};

// client function that uses the function object
void client (ConstantIntFunctor const& cif)
{
    std::cout << "calling back functor yields " << cif() << '\n';
}

int main() 
{
    ConstantIntFunctor seven(7);
    ConstantIntFunctor fortytwo(42);
    client(seven);
    client(fortytwo);
}