Using SFINAE, i can detect wether a given class has a certain member function. But what if i want to test for inherited member functions?
The following does not work in VC8 and GCC4 (i.e. detects that A
has a member function foo()
, but not that B
inherits one):
#include <iostream>
template<typename T, typename Sig>
struct has_foo {
template <typename U, U> struct type_check;
template <typename V> static char (& chk(type_check<Sig, &V::foo>*))[1];
template <typename > static char (& chk(...))[2];
static bool const value = (sizeof(chk<T>(0)) == 1);
};
struct A {
void foo();
};
struct B : A {};
int main()
{
using namespace std;
cout << boolalpha << has_foo<A, void (A::*)()>::value << endl; // true
cout << boolalpha << has_foo<B, void (B::*)()>::value << endl; // false
}
So, is there a way to test for inherited member functions?
Take a look at this thread:
http://lists.boost.org/boost-users/2009/01/44538.php
Derived from the code linked to in that discussion:
#include <iostream>
template <typename Type>
class has_foo
{
class yes { char m;};
class no { yes m[2];};
struct BaseMixin
{
void foo(){}
};
struct Base : public Type, public BaseMixin {};
template <typename T, T t> class Helper{};
template <typename U>
static no deduce(U*, Helper<void (BaseMixin::*)(), &U::foo>* = 0);
static yes deduce(...);
public:
static const bool result = sizeof(yes) == sizeof(deduce((Base*)(0)));
};
struct A {
void foo();
};
struct B : A {};
struct C {};
int main()
{
using namespace std;
cout << boolalpha << has_foo<A>::result << endl;
cout << boolalpha << has_foo<B>::result << endl;
cout << boolalpha << has_foo<C>::result;
}
Result:
true
true
false