This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 120b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2026-08-09

3214. Redeclaration of types and namespaces and their aliases

(From #9241.)

Consider:

  struct T;
  typedef struct T T;

According to 6.7 [basic.link] paragraph 8, these two declarations declare the same entity. However, type aliases are separate entities nowadays.

Possible resolution:

Add bullets and change in 6.7 [basic.link] paragraph 8 as follows:

Two declarations of entities declare the same entity if, considering declarations of unnamed types to introduce their names for linkage purposes, if any (9.2.4 [dcl.typedef], 9.8.1 [dcl.enum]),

• they correspond (6.4.1 [basic.scope.scope]),
• both have the same target scope that is not a function or template parameter scope,
• neither is a name-independent declaration, and
• if either declares a type alias, both do,
• if either declares a namespace alias, both do, and
• either one of the following holds:
  • they appear in the same translation unit, or
  • they both declare type aliases or namespace aliases that have the same underlying entity, or
  • they both declare names with module or external linkage and are attached to the same module.

[Note 3: There are other circumstances in which declarations declare the same entity (9.12 [dcl.link], 13.6 [temp.type], 13.7.6 [temp.spec.partial]). —end note]