I have some old codebase that still uses C++03. I am trying to write a template that evaluates to true if a class has a member function called some_function, to be used inside enable_if statements. I cannot make my example work, i.e. the output is always zero. Can anyone spot the error and explain why this fails, and how to fix it?
#include <iostream>
template< typename T >
struct has_some_function
{
typedef char yes[1];
typedef char no[2];
template< typename C > static yes& test(typename C::some_function*);
template< typename C > static no& test(...);
static const bool value = (sizeof(test< T >(0)) == sizeof(yes));
};
struct Test
{
void some_function()
{
}
};
int main()
{
std::cout << has_some_function< Test >::value << std::endl;
}
With
g++ -std=c++03 test.cpp
I get
0
