https://gcc.gnu.org/g:e6e7b477bbdbfb3fee6b44087a59f94fd1e2c7a3
commit r15-7897-ge6e7b477bbdbfb3fee6b44087a59f94fd1e2c7a3
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Thu Mar 6 21:18:21 2025 +0000
libstdc++: Make std::erase for linked lists convert to bool
LWG 4135 (approved in Wrocław, November 2024) fixes the lambda
expressions used by std::erase for std::list and std::forward_list.
Previously they attempted to copy something that isn't required to be
copyable. Instead they should convert it to bool right away.
The issue resolution also changes the lambda's parameter to be const, so
that it can't modify the elements while comparing them.
libstdc++-v3/ChangeLog:
* include/std/forward_list (erase): Change lambda to have
explicit return type and const parameter type.
* include/std/list (erase): Likewise.
* testsuite/23_containers/forward_list/erasure.cc: Check lambda
is correct.
* testsuite/23_containers/list/erasure.cc: Likewise.
Reviewed-by: Patrick Palka <ppa...@redhat.com>
Diff:
---
libstdc++-v3/include/std/forward_list | 5 +++--
libstdc++-v3/include/std/list | 5 +++--
.../23_containers/forward_list/erasure.cc | 22 ++++++++++++++++++++++
.../testsuite/23_containers/list/erasure.cc | 22 ++++++++++++++++++++++
4 files changed, 50 insertions(+), 4 deletions(-)
diff --git a/libstdc++-v3/include/std/forward_list
b/libstdc++-v3/include/std/forward_list
index 6c5ad1195db9..166fdb04242a 100644
--- a/libstdc++-v3/include/std/forward_list
+++ b/libstdc++-v3/include/std/forward_list
@@ -83,8 +83,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
inline typename forward_list<_Tp, _Alloc>::size_type
erase(forward_list<_Tp, _Alloc>& __cont, const _Up& __value)
{
- using __elem_type = typename forward_list<_Tp, _Alloc>::value_type;
- return std::erase_if(__cont, [&](__elem_type& __elem) {
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4135. helper lambda of std::erase for list should specify return type
+ return std::erase_if(__cont, [&](const auto& __elem) -> bool {
return __elem == __value;
});
}
diff --git a/libstdc++-v3/include/std/list b/libstdc++-v3/include/std/list
index 51f1bc079cc2..170499d65f71 100644
--- a/libstdc++-v3/include/std/list
+++ b/libstdc++-v3/include/std/list
@@ -107,8 +107,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
inline typename list<_Tp, _Alloc>::size_type
erase(list<_Tp, _Alloc>& __cont, const _Up& __value)
{
- using __elem_type = typename list<_Tp, _Alloc>::value_type;
- return std::erase_if(__cont, [&](__elem_type& __elem) {
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4135. helper lambda of std::erase for list should specify return type
+ return std::erase_if(__cont, [&](const auto& __elem) -> bool {
return __elem == __value;
});
}
diff --git a/libstdc++-v3/testsuite/23_containers/forward_list/erasure.cc
b/libstdc++-v3/testsuite/23_containers/forward_list/erasure.cc
index 37e502039599..1ec11de6e36c 100644
--- a/libstdc++-v3/testsuite/23_containers/forward_list/erasure.cc
+++ b/libstdc++-v3/testsuite/23_containers/forward_list/erasure.cc
@@ -53,6 +53,28 @@ test02()
VERIFY( num == 0 );
}
+// LWG 4135.
+// The helper lambda of std::erase for list should specify return type as bool
+void
+test_lwg4135()
+{
+ struct Bool {
+ Bool() = default;
+ Bool(const Bool&) = delete;
+ operator bool() const { return false; }
+ };
+
+ static Bool b;
+
+ struct Int {
+ Bool& operator==(Int) const { return b; }
+ void operator==(Int) = delete;
+ };
+
+ std::forward_list<Int> l;
+ std::erase(l, Int{});
+}
+
int
main()
{
diff --git a/libstdc++-v3/testsuite/23_containers/list/erasure.cc
b/libstdc++-v3/testsuite/23_containers/list/erasure.cc
index 1a33eca77c26..9f4f8536fe64 100644
--- a/libstdc++-v3/testsuite/23_containers/list/erasure.cc
+++ b/libstdc++-v3/testsuite/23_containers/list/erasure.cc
@@ -52,6 +52,28 @@ test02()
VERIFY( num == 0 );
}
+// LWG 4135.
+// The helper lambda of std::erase for list should specify return type as bool
+void
+test_lwg4135()
+{
+ struct Bool {
+ Bool() = default;
+ Bool(const Bool&) = delete;
+ operator bool() const { return false; }
+ };
+
+ static Bool b;
+
+ struct Int {
+ Bool& operator==(Int) const { return b; }
+ void operator==(Int) = delete;
+ };
+
+ std::list<Int> l;
+ std::erase(l, Int{});
+}
+
int
main()
{
