Function not found from global namespace if there's an overload with different argument types

Question

If we have a function in the global namespace and an overload with different argument types in another namespace, it seems that C++Builder compiler doesn't find the function from the global namespace.

namespace A
{
    class a {
        friend void swap(a& first, a& second) { }
    };
}

class b {
    friend void swap(b& first, b& second) { }
};

namespace C
{
    class c {
        A::a dataA;
        b dataB;

        friend void swap(c& first, c& second)
        {
            swap(first.dataA, second.dataA); // no problem
            swap(first.dataB, second.dataB); // VC++12 compiles, C++Builder XE doesn't
        }

        friend void swap2(c& first, c& second) // no problem with a different name
        {
            swap(first.dataA, second.dataA);
            swap(first.dataB, second.dataB);
        }
    };
}

C++Builder gives the following errors:

E2357 Reference initialized with 'b', needs lvalue of type 'c'
E2342 Type mismatch in parameter 'first' (wanted 'c &', got 'b')

Visual C++ 2012 compiles this without errors.

I have understood that the function in global namespace should be found even when there exists a function with the same name and different argument types.

Have I missed something, or is this a bug in C++Builder?

Compiles with MinGW, too. – johnchen902 Jul 12 '13 at 09:48 — johnchen902, Jul 12 '13 at 09:48

score 2 · Accepted Answer · answered Jul 12 '13 at 10:01

It looks like a compiler bug to me. In both cases, ADL should kick in. In the first case, it looks in namespace A, including names in namespace A that were only declared in class a, and finds A::swap. In the second case, it looks in the global namespace (since that is where b is defined), including names in the global namespace that were only declare in class b, and finds ::swap.

Of course, it starts with unqualified name lookup, which will only find C::swap in both cases. Apparently, C++Builder somehow marks ::swap as hidden in this case, and fails to consider it in ADL. In the case of ADL, however, both the global namespace and namespace A should be treated equally.

The full rules are in §3.4.2. It's pretty heavy going, but for simple cases like yours, the implications are clear.

XE is several versions old. If this has not already been fixed in a later version, then it needs to be filed in QC so it can get fixed. — Remy Lebeau, Jul 13 '13 at 08:45
@RemyLebeau I don't have access to any version of CodeBuilder, so I can't test. It's up to the compiler's user community to verify this with the latest version, and send in a bug report if the error is still there. — James Kanze, Jul 13 '13 at 17:31

score 0 · Answer 2 · answered Jul 12 '13 at 09:48

0

Members of local scope with same name as global always hide global one so Call it like,A::a::swap(first.dataA, second.dataA);.

answered Jul 12 '13 at 09:48

Hitesh Vaghani

1,342
12
31

1

There are no members with the same name in his code, however. – James Kanze Jul 12 '13 at 09:51

Function not found from global namespace if there's an overload with different argument types

2 Answers2