https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82262
Bug ID: 82262
Summary: std::hash<std::optional<T>>::operator() missing
remove_const_t
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: zhangxy at google dot com
Target Milestone: ---
std::hash<std::optional<T>> specialization doesn't work with const-qualified
type. I think the problem is that std::remove_const_t is missing.
For example, the following code will result in compiler error:
#include <optional>
void Foo() {
std::hash<std::optional<const int>> h;
std::optional<const int> o(1);
size_t v = h(o);
}
/opt/compiler-explorer/gcc-7.2.0/include/c++/7.2.0/optional: In instantiation
of 'std::size_t std::__optional_hash_call_base<_Tp, <anonymous>
>::operator()(const std::optional<_Tp>&) const [with _Tp = const int; bool
<anonymous> = true; std::size_t = long unsigned int]':
6 : <source>:6:19: required from here
/opt/compiler-explorer/gcc-7.2.0/include/c++/7.2.0/optional:1009:37: error:
could not convert '<brace-enclosed initializer list>()' from '<brace-enclosed
initializer list>' to 'std::__hash_enum<const int, false>'
noexcept(noexcept(hash<_Tp> {}(*__t)))
~~~~~~~~~~~~^~~~~~
