CWG Issue 1838 (original) (raw)
This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-11-05
1838. Definition via unqualified-id and using-declaration
Section: _N4868_.9.8.2.3 [namespace.memdef]Status: CD4Submitter: Richard SmithDate: 2014-01-17
[Moved to DR at the November, 2014 meeting.]
The Standard is not clear about what happens when an entity is declared but not defined in an inner namespace and declared via a_using-declaration_ in an outer namespace, and a definition of an entity with that name as an unqualified-id appears in the outer namespace. Is this a legitimate definition of the inner-namespace entity, as it would be if the definition used a qualified-id, or is the definition a member of the outer namespace and thus in conflict with the using-declaration? There is implementation divergence on the treatment of such definitions.
Notes from the February, 2014 meeting:
CWG agreed that the definition in such cases is a member of the outer namespace, not a redeclaration of the name introduced in that namespace by the using-declaration.
Proposed Resolution (July, 2014):
- Change _N4868_.9.8.2.3 [namespace.memdef] paragraph 1 as follows:
Members (including explicit specializations of templates (13.9.4 [temp.expl.spec])) of a namespace can be defined within that namespace.A declaration in a namespaceN (excluding declarations in nested scopes) whose_declarator-id_ is an unqualified-id declares (or redeclares) a member of N, and may be a definition. [_Note:_ An explicit instantiation (13.9.3 [temp.explicit]) or explicit specialization (13.9.4 [temp.expl.spec]) of a template does not introduce a name and thus may be declared using an unqualified-id in a member of the enclosing namespace set, if the primary template is declared in an inline namespace. —_end note_] [Example:namespace X { void f() { /* ... */ } // OK: introduces X::f()
namespace M { void g(); // OK: introduces X::M::g() } using M::g; void g(); // error: conflicts with X::M::g() }
—_end example_]
- Change _N4868_.9.8.2.3 [namespace.memdef] paragraph 3 as follows:
Every name first declared in a namespace is a member of that namespace.If a friend declaration...