https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115420
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Last reconfirmed| |2024-06-11
Status|CLOSED |NEW
Ever confirmed|0 |1
Resolution|INVALID |---
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If we add this to _Hashtable:
template<typename>
struct _Check_hash_requirements : true_type
{
static_assert(is_copy_constructible<_Hash>::value,
"custom hash function must be copy constructible");
static_assert(is_destructible<_Hash>::value,
"custom hash function must be destructible");
};
template<typename _Tp>
struct _Check_hash_requirements<hash<_Tp>> : true_type
{
static_assert(is_default_constructible<hash<_Tp>>::value,
"the std::hash<key_type> specialization is disabled");
};
static_assert(_Check_hash_requirements<_Hash>::value, "");
Then the first error is much clearer where the problem lies:
In file included from
/home/jwakely/gcc/15/include/c++/15.0.0/bits/unordered_map.h:33,
from /home/jwakely/gcc/15/include/c++/15.0.0/unordered_map:41,
from un.cc:1:
/home/jwakely/gcc/15/include/c++/15.0.0/bits/hashtable.h: In instantiation of
'struct std::_Hashtable<std::__cxx11::basic_string<char>, std::pair<const
std::__cxx11::basic_string<char>, long unsigned int>,
std::allocator<std::pair<const std::__cxx11::basic_string<char>, long unsigned
int> >, std::__detail::_Select1st,
std::equal_to<std::__cxx11::basic_string<char> >,
std::hash<std::__cxx11::basic_string<char> >,
std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash,
std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true,
false, true>
>::_Check_hash_requirements<std::hash<std::__cxx11::basic_string<char> > >':
/home/jwakely/gcc/15/include/c++/15.0.0/bits/hashtable.h:221:54: required
from 'class std::_Hashtable<std::__cxx11::basic_string<char>, std::pair<const
std::__cxx11::basic_string<char>, long unsigned int>,
std::allocator<std::pair<const std::__cxx11::basic_string<char>, long unsigned
int> >, std::__detail::_Select1st,
std::equal_to<std::__cxx11::basic_string<char> >,
std::hash<std::__cxx11::basic_string<char> >,
std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash,
std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true,
false, true> >'
221 | static_assert(_Check_hash_requirements<_Hash>::value, "");
| ^~~~~
/home/jwakely/gcc/15/include/c++/15.0.0/bits/unordered_map.h:112:18: required
from 'class std::unordered_map<std::__cxx11::basic_string<char>, long unsigned
int>'
112 | _Hashtable _M_h;
| ^~~~
un.cc:5:45: required from here
5 | std::unordered_map<std::string, uint64_t> bar;
| ^~~
/home/jwakely/gcc/15/include/c++/15.0.0/bits/hashtable.h:218:62: error: static
assertion failed: the std::hash<key_type> specialization is disabled
218 | static_assert(is_default_constructible<hash<_Tp>>::value,
| ^~~~~
So let's reopen this as a diagnostic RFE for the library.
