https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113064
--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to m.cencora from comment #4)
> This also might be a just another symptom of the same root cause:
>
> struct bar
> {
> bar() = default;
>
> bar(const bar&);
> bar(bar&&);
>
> bar& operator=(const bar&);
> bar& operator=(bar&&);
> };
>
> struct foo
> {
> operator const bar& () const &;
>
> operator bar& () &;
>
> operator bar&&() &&;
> };
>
> void test()
> {
> bar a = foo{}; // ok
>
> a = foo{}; // not ok - ambiguous call, but why? &&-qualified looks like
> a better match
>
> foo f;
> a = f; // ok
>
> a = static_cast<const foo&>(foo{}); // ok
> }
Here the error showed up in r9-6486:
commit c7e936dbc7f59ad09c28ef57e5399a4256061747
Author: Jason Merrill <[email protected]>
Date: Mon Mar 11 23:19:22 2019 -0400
PR c++/86521 - wrong overload resolution with ref-qualifiers.
Here we were wrongly treating binding a const lvalue ref to an xvalue as
direct binding, which is wrong under [dcl.init.ref] and [over.match.ref].
