https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98388
Bug ID: 98388
Summary: Throwing move-only parameter results in hard error in
SFINAE context
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ensadc at mailnesia dot com
Target Milestone: ---
https://godbolt.org/z/xn8fYz
====
struct moveonly {
moveonly() = default;
moveonly(moveonly&&) = default;
};
template<class T>
constexpr auto is_throwable(T t) -> decltype(throw t, true) {
return true;
}
template<class T>
constexpr bool is_throwable(...) { return false; }
constexpr bool b = is_throwable<moveonly>(moveonly{});
====
<source>: In substitution of 'template<class T> constexpr decltype
((<throw-expression>, true)) is_throwable(T) [with T = moveonly]':
<source>:13:43: required from here
<source>:7:46: error: use of deleted function 'constexpr
moveonly::moveonly(const moveonly&)'
7 | constexpr auto is_throwable(T t) -> decltype(throw t, true) {
| ^~~~~~~
<source>:1:8: note: 'constexpr moveonly::moveonly(const moveonly&)' is
implicitly declared as deleted because 'moveonly' declares a move constructor
or move assignment operator
1 | struct moveonly {
| ^~~~~~~~
<source>:7:52: note: in thrown expression
7 | constexpr auto is_throwable(T t) -> decltype(throw t, true) {
| ^
====
I'm not sure what the value of `b` should be, but I believe that it should not
be a hard error. (Clang and MSVC initialize `b` to `true`.)
