template function for reference parameters : template pointer parameter « template « C++ Tutorial

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/* 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 <string>

// note: reference parameters
template <typename T>
inline T const& max (T const& a, T const& b)
{
    return  a < b  ?  b : a;
}

int main()
{
    std::string s;

    ::max("apple","peach");   // OK: same type
    //::max("apple","tomato");  // ERROR: different types
    //::max("apple",s);         // ERROR: different types
}