adl.cpp

来自「非常著名的C++ Templates 完全导引范例配套的原代码」· C++ 代码 · 共 36 行

/* 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>

namespace X {
    template<typename T> void f(T);
}

namespace N {
    using namespace X;
    enum E { e1 };
    void f(E) { 
        std::cout << "N::f(N::E) called\n"; 
    }
}

void f(int) 
{ 
    std::cout << "::f(int) called\n"; 
}

int main() 
{
    ::f(N::e1);  // qualified function name: no ADL
    f(N::e1);    // ordinary lookup finds ::f() and ADL finds N::f(),
}                //  the latter is preferred