Trying to define namespace member via using-declaration

Question

Consider the following program. Is it well-formed or not according to the c++ standard (references to relevant parts of the standard needed):

namespace X { extern int i; }

namespace N { using X::i; }

int N::i = 1;

int main() {}

I'm getting different results for different compilers. I'm trying to figure out for what compiler I should file a bug report for:

Clang: Gives the following compiler error: No member named 'i' in namespace 'N'
GCC and Visual C++ compiles it without errors.

For comparison the following gives compiler error with all three compilers:

namespace X { void f(); }

namespace N { using X::f; }

void N::f() {};

int main() {}

Funny, VS2013 compiles, but IntelliSence says "Error: namespace "N" has no actual member "i" — AlexD
– AlexD, Commented Jul 18, 2015 at 23:20
@Supremum You can get your own copy of the C++ standard to read at isocpp.org/std/the-standard. — Coder
– Coder, Commented Jul 18, 2015 at 23:27
Jorj Tyron: That link does not answer this question. This question is not about best practices. — Supremum
– Supremum, Commented Jul 18, 2015 at 23:34
@Supremum I got it working with CLang by changing "using X::i" to "using namespace X;". — Coder
– Coder, Commented Jul 18, 2015 at 23:43

bogdan · Accepted Answer · 2015-07-19 00:14:14Z

11

Current working draft N4527, [8.3p1]:

[...] When the declarator-id is qualified, the declaration shall refer to a previously declared member of the class or namespace to which the qualifier refers (or, in the case of a namespace, of an element of the inline namespace set of that namespace (7.3.1)) or to a specialization thereof; the member shall not merely have been introduced by a using-declaration in the scope of the class or namespace nominated by the nested-name-specifier of the declarator-id. [...]

So, definitely ill-formed; GCC and MSVC are wrong.

answered Jul 19, 2015 at 0:14

bogdan

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