When does a const return type interfere with template instantiation?

Question

From Herb Sutter\'s GotW #6

Return-by-value should normally be const for non-builtin return types. ...

Note: Lakos (pg. 618) argues again

Answer 1

Here's a simple example involving function pointers:

const int f_const(int) { return 42; }
int f(int) { return 42; }

template <typename T>
void g(T(*)(T))
{
    return;
}

int main()
{
    g(&f_const); // doesn't work:  function has type "const int (*)(int)"
    g(&f);       // works: function has type "int (*)(int)"
}

Note that Visual C++ 2010 incorrectly accepts both. Comeau 4.3.10 and g++ 4.1.2 correctly do not accept the g(&f_const) call.