Re: Some issues with using sizeof() in template definitions

The first one just baffles me, it makes no sense at all. I
was creating an allocator to be used with a std::map. When
using sizeof inside my allocator, such as to assign to an
enum value defined in the class, the compiler complains
about errors in <xtree>. Here's the code:
[...]

My other issue occured when trying to call a
memberfunction on an object when it exists, or do nothing
otherwise. I was using SFINAE for that:

-------------------------------------
#include <iostream>

template<unsigned> struct MemberCheck
{
   MemberCheck(int) { }
};

template<class T>
void callFoo(T * t, MemberCheck<sizeof(&T::foo)> = 0)
{
   t->foo();
}

void callFoo(void *)
{
}

struct A
{
   void foo() { std::cout << "foo()" << std::endl; }
};

struct B
{
};

int main()
{
   A a;
   B b;
   callFoo(&a);
   callFoo(&b);
}
-------------------------------------

This gives me the following error:
1>c:\...\main.cpp(31) : error C2070:
'overloaded-function': illegal sizeof operand

Comeau accepts both code snippets just fine. I haven't
tested other compilers though... And there's nothing in
the C++ standard saying that using sizeof in a template
function declaration is prohibited.