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* [gcc r14-3902] libstdc++: Fix std::bind_front perfect forwarding [PR111327]
@ 2023-09-12 15:28 Patrick Palka
0 siblings, 0 replies; only message in thread
From: Patrick Palka @ 2023-09-12 15:28 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:4289f6ceefe74ea46e792692448c06197ac20c86
commit r14-3902-g4289f6ceefe74ea46e792692448c06197ac20c86
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Sep 12 11:23:12 2023 -0400
libstdc++: Fix std::bind_front perfect forwarding [PR111327]
In order to properly implement a perfect forwarding call wrapper (without
C++23 deducing 'this') we need a total of 8 operator() overloads, 4
enabled ones and 4 deleted ones, i.e. two for each const/ref qual pair,
as described in section 5.5 of P0847R6. Otherwise the wrapper may not
do the right thing if the underlying function object has a deleted
const/ref-qualified operator() overload. This patch fixes this issue in
std::bind_front.
PR libstdc++/111327
libstdc++-v3/ChangeLog:
* include/std/functional (_Bind_front::operator()): Add deleted
fallback overloads for each const/ref qualifier pair. Give the
enabled overloads dummy constraints to make each one more
specialized than the corresponding deleted overload.
* testsuite/20_util/function_objects/bind_front/111327.cc: New test.
Diff:
---
libstdc++-v3/include/std/functional | 16 +++++++++
.../20_util/function_objects/bind_front/111327.cc | 41 ++++++++++++++++++++++
2 files changed, 57 insertions(+)
diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
index 7d1b890bb4e9..c50b9e4d3658 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -938,6 +938,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
~_Bind_front() = default;
template<typename... _CallArgs>
+ requires true
constexpr
invoke_result_t<_Fd&, _BoundArgs&..., _CallArgs...>
operator()(_CallArgs&&... __call_args) &
@@ -948,6 +949,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename... _CallArgs>
+ requires true
constexpr
invoke_result_t<const _Fd&, const _BoundArgs&..., _CallArgs...>
operator()(_CallArgs&&... __call_args) const &
@@ -959,6 +961,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename... _CallArgs>
+ requires true
constexpr
invoke_result_t<_Fd, _BoundArgs..., _CallArgs...>
operator()(_CallArgs&&... __call_args) &&
@@ -969,6 +972,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename... _CallArgs>
+ requires true
constexpr
invoke_result_t<const _Fd, const _BoundArgs..., _CallArgs...>
operator()(_CallArgs&&... __call_args) const &&
@@ -979,6 +983,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
std::forward<_CallArgs>(__call_args)...);
}
+ template<typename... _CallArgs>
+ void operator()(_CallArgs&&...) & = delete;
+
+ template<typename... _CallArgs>
+ void operator()(_CallArgs&&...) const & = delete;
+
+ template<typename... _CallArgs>
+ void operator()(_CallArgs&&...) && = delete;
+
+ template<typename... _CallArgs>
+ void operator()(_CallArgs&&...) const && = delete;
+
private:
using _BoundIndices = index_sequence_for<_BoundArgs...>;
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
new file mode 100644
index 000000000000..fcfb9f9c7c02
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
@@ -0,0 +1,41 @@
+// PR libstdc++/111327 - std::bind_front (and std::not_fn) doesn't always
+// perfectly forward according to value category of the call wrapper object
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+#include <functional>
+#include <utility>
+
+struct F {
+ void operator()(...) & = delete;
+ void operator()(...) const &;
+};
+
+struct G {
+ void operator()(...) && = delete;
+ void operator()(...) const &&;
+};
+
+int main() {
+ auto f0 = std::bind_front(F{});
+ f0(); // { dg-error "deleted" }
+ std::move(f0)();
+ std::as_const(f0)();
+ std::move(std::as_const(f0))();
+
+ auto g0 = std::bind_front(G{});
+ g0(); // { dg-error "deleted" }
+ std::move(g0)(); // { dg-error "deleted" }
+ std::move(std::as_const(g0))();
+
+ auto f1 = std::bind_front(F{}, 42);
+ f1(); // { dg-error "deleted" }
+ std::move(f1)();
+ std::as_const(f1)();
+ std::move(std::as_const(f1))();
+
+ auto g1 = std::bind_front(G{}, 42);
+ g1(); // { dg-error "deleted" }
+ std::move(g1)(); // { dg-error "deleted" }
+ std::move(std::as_const(g1))();
+}
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