Re: passing functor or function to template class

Zoltan Juhasz <>
Wed, 18 Jul 2012 07:17:49 -0700 (PDT)
Excellent solution, thanks for sharing this.

-- Zoltan

On Wednesday, 18 July 2012 07:15:01 UTC-4, Christof Warlich wrote:

After the inspiring discussion, and particularly encouraged by Zoltan&#39;s SFINAE example, I finally found the solution myself. I&#39;m sharing it here for the record and in case someone else might be interested.

#include &lt;iostream&gt;
template&lt;typename T&gt; struct isFunctionPointer {
    template&lt;typename U&gt; static char is_ptr(U (*)());
    static double is_ptr(...);
    static T t;
    enum {value = sizeof(is_ptr(t)) == sizeof(char)};
template&lt;typename T, bool = isFunctionPointer&lt;T&gt;::value&gt; struct Type {typedef T &amp; U;};
template&lt;typename T&gt; struct Type&lt;T, true&gt; {typedef T U;};
// A function.
void *function() {
    std::cout &lt;&lt; &quot;function&quot; &lt;&lt; std::endl;
    return 0;
// A functor.
class Functor {
    Functor() {}
    void *operator()() {
        std::cout &lt;&lt; &quot;functor&quot; &lt;&lt; std::endl;
        return 0;
    Functor(const Functor &amp;);
} functor;
template&lt;typename T&gt; struct Reference {
    Reference(typename Type&lt;T&gt;::U t):f(t) {}
    typename Type&lt;T&gt;::U f;
// Test if it works.
int main() {
    Reference&lt;void *(*)()&gt; rf(function);
    Reference&lt;Functor&gt; rF(functor);
    return 0;

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