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| author | Jonathan Wakely <jwakely@redhat.com> | 2025-09-02 22:30:46 +0100 |
|---|---|---|
| committer | Jonathan Wakely <redi@gcc.gnu.org> | 2025-09-03 10:49:12 +0100 |
| commit | 0bb0d1d2880d562298eeec8eee4ab4e8ba943260 (patch) | |
| tree | 42715b93ffa73c1a5058ef623bb770841366049a | |
| parent | 381dbd4a9564525d930737a790c9b7d31dfc181f (diff) | |
| download | gcc-0bb0d1d2880d562298eeec8eee4ab4e8ba943260.zip gcc-0bb0d1d2880d562298eeec8eee4ab4e8ba943260.tar.gz gcc-0bb0d1d2880d562298eeec8eee4ab4e8ba943260.tar.bz2 | |
libstdc++: Make CTAD ignore pair(const T1&, const T2&) constructor [PR110853]
For the pair(T1, T2) explicit deduction type to decay its arguments as
intended, we need the pair(const T1&, const T2&) constructor to not be
used for CTAD. Otherwise we try to instantiate pair<T1, T2> without
decaying, which is ill-formed for function lvalues.
Use std::type_identity_t<T1> to make the constructor unusable for an
implicit deduction guide.
libstdc++-v3/ChangeLog:
PR libstdc++/110853
* include/bits/stl_pair.h [C++20] (pair(const T1&, const T2&)):
Use std::type_identity_t<T1> for first parameter.
* testsuite/20_util/pair/cons/110853.cc: New test.
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
| -rw-r--r-- | libstdc++-v3/include/bits/stl_pair.h | 2 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/20_util/pair/cons/110853.cc | 10 |
2 files changed, 11 insertions, 1 deletions
diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h index 393f6a0..2de7439 100644 --- a/libstdc++-v3/include/bits/stl_pair.h +++ b/libstdc++-v3/include/bits/stl_pair.h @@ -445,7 +445,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// Constructor accepting lvalues of `first_type` and `second_type` constexpr explicit(!_S_convertible<const _T1&, const _T2&>()) - pair(const _T1& __x, const _T2& __y) + pair(const type_identity_t<_T1>& __x, const _T2& __y) noexcept(_S_nothrow_constructible<const _T1&, const _T2&>()) requires (_S_constructible<const _T1&, const _T2&>()) : first(__x), second(__y) diff --git a/libstdc++-v3/testsuite/20_util/pair/cons/110853.cc b/libstdc++-v3/testsuite/20_util/pair/cons/110853.cc new file mode 100644 index 0000000..57ebfb8 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/pair/cons/110853.cc @@ -0,0 +1,10 @@ +// { dg-do compile { target c++17 } } +// PR libstdc++/110853 +// Bad interaction between deduction guide with decay and constraints +// (CTAD, std::pair and function lvalue) + +#include <utility> + +void func() {} +std::pair p(1, func); +std::pair<int, void (*)()>& r = p; |