Re: Trying to apply SFINAE

From:
Victor Bazarov <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Mon, 29 Sep 2008 13:39:53 -0400
Message-ID:
<gbr3t8$7n6$1@news.datemas.de>
Hendrik Schober wrote:

[..]
    #include <iterator>

    //template< typename T >
    //void test( T /*a1*/, T /*a2*/ ) {}

    template< typename Iter, class ItTr >
    void test( Iter /*b*/, Iter /*e*/
             , ItTr = std::iterator_traits<Iter>() ) {}

    int main()
    {
        const int fa[] = { 255, 255, 255, 255 };

        //test(0,1);
        test(fa, fa+4);

        return 0;
    }

doesn't compile.
[..]


Well, the compiler cannot deduce the type from a default argument, I
vaguely recall that it's a non-deducible context. That's why putting
the traits there won't cut it. Consider

     #include <iterator>

     template<typename Iter>
     void test(Iter, Iter, std::iterator_traits<Iter> const* = 0);

     int main ()
     {
        const int fa[] = { 1,2,3,4 };
        test(fa, fa+4);
     }

V
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