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authorPatrick Palka <ppalka@redhat.com>2020-03-05 10:04:06 -0500
committerPatrick Palka <ppalka@redhat.com>2020-03-06 09:22:54 -0500
commit6d082cd90131a9c0ce3142217e84194a5bf0de27 (patch)
tree412df4c8feba360c4670204a334a4eb31bde7dc8 /libstdc++-v3/include
parent4cdcb2c92a128d2a30a6110084b7ab2f9995c683 (diff)
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libstdc++: Give ranges::empty() a concrete return type (PR 93978)
This works around PR 93978 by avoiding having to instantiate the body of ranges::empty() when checking the constraints of view_interface::operator bool(). When ranges::empty() has an auto return type, then we must instantiate its body in order to determine whether the requires expression { ranges::empty(_M_derived()); } is well-formed. But this means instantiating view_interface::empty() and hence view_interface::_M_derived(), all before we've yet deduced the return type of join_view::end(). (The reason view_interface::operator bool() is needed in join_view::end() in the first place is because in this function we perform direct initialization of join_view::_Sentinel from a join_view, and so we try to find a conversion sequence from the latter to the former that goes through this conversion operator.) Giving ranges::empty() a concrete return type of bool should be safe according to [range.prim.empty]/4 which says "whenever ranges::empty(E) is a valid expression, it has type bool." This fixes the test case in PR 93978 when compiling without -Wall, but with -Wall the test case still fails due to the issue described in PR c++/94038, I think. I still don't quite understand why the test case doesn't fail without -O. libstdc++-v3/ChangeLog: PR libstdc++/93978 * include/bits/range_access.h (__cust_access::_Empty::operator()): Declare return type to be bool instead of auto. * testsuite/std/ranges/adaptors/93978.cc: New test.
Diffstat (limited to 'libstdc++-v3/include')
-rw-r--r--libstdc++-v3/include/bits/range_access.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index 8b276fd..4dd48bb 100644
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -793,7 +793,7 @@ namespace ranges
template<typename _Tp>
requires __member_empty<_Tp> || __size0_empty<_Tp>
|| __eq_iter_empty<_Tp>
- constexpr auto
+ constexpr bool
operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>())
{
if constexpr (__member_empty<_Tp>)