This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 114b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-05-06


1433. trailing-return-type and point of declaration

Section: 6.4.2  [basic.scope.pdecl]     Status: NAD     Submitter: Jason Merrill     Date: 2011-12-20

This seems like it should be well-formed:

    template <class T> T list(T x);

    template <class H, class ...T>
    auto list(H h, T ...args) -> decltype(list(args...));

    auto list3 = list(1, 2, 3);

but it isn't, because the second list isn't in scope in its own trailing-return-type; the point of declaration is after the declarator, which includes the trailing-return-type. And since int has no associated namespaces, the call in the return type only sees the first list. G++, EDG and Clang all reject the testcase on this basis.

But this seems like a natural pattern for writing variadic function templates, and we could support it by moving the point of declaration to the ->. This would mean having to deal with a function that only has a placeholder for a return type, but I think we can handle that.

Rationale (February, 2012):

This is a request for an extension to the language and is thus more appropriately addressed by EWG.

EWG 2022-11-11

This is a breaking change whose benefits and trade-offs need to be carefully analyzed.