[Bug c++/95511] New: Class template argument deduction: guide generated from constructor preferred over deduction-guide.

[Bug c++/95511] New: Class template argument deduction: guide generated from constructor preferred over deduction-guide.

[okannen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95511

            Bug ID: 95511
           Summary: Class template argument deduction: guide generated
                    from constructor preferred over deduction-guide.
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: okannen at gmail dot com
  Target Milestone: ---

This bug exists since gcc 7 and all following version. It also exists on the
current GCC-10 release branch.

The following code should compile:


template <class...Ts>
struct tpl
        {
        tpl (Ts...);
        };

template <class...Ts>
struct A 
        : tpl <Ts...>
        {
        template <class...Args>
        A (Args...args)
                : tpl <Ts...> (args...)
                {}
        };

template <class...Ts>
A (Ts...) -> A <Ts...>;

A a {10}; //error: no matching function for call to 'tpl<>::tpl(int&)'


Clang compile this code.

Maybe overload resolution considers that the guide generated from the
constructor of A is a better match than the one generated from the
deduction-guide.

[Bug c++/95511] Class template argument deduction: guide generated from constructor preferred over deduction-guide.

[okannen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95511

--- Comment #1 from Olivier Kannengieser <okannen at gmail dot com> ---
Actualy it is a bug that happens during the selection of the best viable
function:

template <class...Ts>
void
func (auto...);

void
func (auto...);

void g(){
   func (10); // this should not compile
}

According to clang the call `func(10)` is ambiguous.

But GCC select fun<,int>. This is precisely what it does for the deduction
guide.

[Bug c++/95511] Class template argument deduction: guide generated from constructor preferred over deduction-guide.

[okannen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95511

Olivier Kannengieser <okannen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Olivier Kannengieser <okannen at gmail dot com> ---
The bug is not more here in GCC version 10.2.