https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99433
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot
gnu.org
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2021-03-17
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
I think the underlying problem here is excessive instantiation due to usage of
deduced return types, which leads to hard errors during overload resolution.
If I give the lambda in your testcase a concrete return type decltype(nucl + '
'), and apply the following change to <ranges> (giving concrete return types to
a couple of lambdas therein) then we accept the testcase.
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 1be74beb860..9fd647c144f 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -803,7 +803,11 @@ namespace views
// otherwise capture by value.
auto __closure
= [...__args(__maybe_refwrap(std::forward<_Args>(__args)))]
- <typename _Range> (_Range&& __r) {
+ <typename _Range> (_Range&& __r)
+ -> decltype(_Callable{}(std::forward<_Range>(__r),
+ (static_cast<unwrap_reference_t
+ <remove_const_t<decltype(__args)>>>
+ (__args))...)) {
// This static_cast has two purposes: it forwards a
// reference_wrapper<T> capture as a T&, and otherwise
// forwards the captured argument as an rvalue.
@@ -1655,6 +1659,7 @@ namespace views
{
inline constexpr __adaptor::_RangeAdaptor transform
= [] <viewable_range _Range, typename _Fp> (_Range&& __r, _Fp&& __f)
+ -> decltype(transform_view{std::forward<_Range>(__r),
std::forward<_Fp>(__f)})
{
return transform_view{std::forward<_Range>(__r),
std::forward<_Fp>(__f)};
};
For maximum SFINAE friendliness, all the range adaptors objects should probably
be changed to avoid using deduced return types, in a manner similar to the
above. While we're at it, we should make them conditionally noexcept.
