Re: SFINAE

From:
"peter koch" <peter.koch.larsen@gmail.com>
Newsgroups:
comp.lang.c++
Date:
26 Apr 2006 05:39:23 -0700
Message-ID:
<1146055163.496152.310130@e56g2000cwe.googlegroups.com>
kaalus@gmail.com wrote:

Is it possible to use SFINAE to provide different implementations of
some function depending on the fact that operator << is overloaded for
some type?


It should be: what is your problem?

For example:

template<class T>
void output1(const T &t)
{
    // This implementation should be in effect for types that support
<<
    std::cout << t;
}

template<class T>
void output2(const T &t)
{
    // This implementation should be in effect for types that do not
support <<
    my_output(t);
}

So that this usage is possible:

T t;
output(t); // uses output1 or output2 depending on << operator
defined for T


I do not really see the reason to do it with SFINAE (Substitution
Failure Is Not An Error). The most obvious way to do solve your problem
would be to provide operator<< for those classes. If that is not
appropriate, I believe I would simply provide:

template <typename T>
void my_output(T const& t) { std::cout << t; }

/Peter

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