This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

2783. Handling of deduction guides in global-module-fragment

[Accepted as a DR at the November, 2023 meeting.]

Consider:

  // header "S.h"
  
  template<class T>
  struct S {
    S(const T*);
  };
  template<class T>
  S(T*) -> S<T>

  // translation unit
  module;
  #include "S.h"

  export module M;
  export using ::S;

Obviously, the using-declaration referring to the class template S is exported by M, but what about the deduction guide of S?

Proposed resolution (approved by CWG 2023-08-25) [SUPERSEDED]:

Add a new bullet after 10.4 [module.global.frag] bullet 3.5.7 as follows:

• ...
• there exists a declaration M that is not a namespace-definition for which M is decl-reachable from S and either
  • ...
  • one of M and D declares a template and the other declares a partial or explicit specialization or an implicit or explicit instantiation of that template, or
  • one of M and D declares a class template and the other declares a deduction guide for that template, or

Proposed resolution (approved by CWG 2023-10-06):

Add a new bullet after 10.4 [module.global.frag] bullet 3.5.7 as follows:

• ...
• there exists a declaration M that is not a namespace-definition for which M is decl-reachable from S and either
  • ...
  • one of M and D declares a template and the other declares a partial or explicit specialization or an implicit or explicit instantiation of that template, or
  • M declares a class template and D is a deduction guide for that template, or