diff options
| author | Jonathan Wakely <jwakely@redhat.com> | 2021-07-20 15:20:41 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2021-07-20 16:22:26 +0100 |
| commit | 89ec3b67dbe856a447d068b053bc19559f136f43 (patch) | |
| tree | 095bc49b129d27b0523b87be0e941583a56a020e /libstdc++-v3/include/bits/hashtable.h | |
| parent | 1ef9b135793a528c05c4a3e22649744955aa2dfb (diff) | |
libstdc++: fix is_default_constructible for hash containers [PR 100863]
The recent change to _Hashtable_ebo_helper for this PR broke the
is_default_constructible trait for a hash container with a non-default
constructible allocator. That happens because the constructor needs to
be user-provided in order to initialize the member, and so is not
defined as deleted when the type is not default constructible.
By making _Hashtable derive from _Enable_special_members we can ensure
that the default constructor for the std::unordered_xxx containers is
deleted when it would be ill-formed. This makes the trait give the
correct answer.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/100863
* include/bits/hashtable.h (_Hashtable): Conditionally delete
default constructor by deriving from _Enable_special_members.
* testsuite/23_containers/unordered_map/cons/default.cc: New test.
* testsuite/23_containers/unordered_set/cons/default.cc: New test.
Diffstat (limited to 'libstdc++-v3/include/bits/hashtable.h')
| -rw-r--r-- | libstdc++-v3/include/bits/hashtable.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h index dfc2a2a7800..adb59213f2d 100644 --- a/libstdc++-v3/include/bits/hashtable.h +++ b/libstdc++-v3/include/bits/hashtable.h @@ -33,6 +33,7 @@ #pragma GCC system_header #include <bits/hashtable_policy.h> +#include <bits/enable_special_members.h> #if __cplusplus > 201402L # include <bits/node_handle.h> #endif @@ -48,6 +49,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Mandatory to have erase not throwing. __is_nothrow_invocable<const _Hash&, const _Tp&>>>; + // Helper to conditionally delete the default constructor. + // The _Hash_node_base type is used to distinguish this specialization + // from any other potentially-overlapping subobjects of the hashtable. + template<typename _Equal, typename _Hash, typename _Allocator> + using _Hashtable_enable_default_ctor + = _Enable_special_members<__and_<is_default_constructible<_Equal>, + is_default_constructible<_Hash>, + is_default_constructible<_Allocator>>{}, + true, true, true, true, true, + __detail::_Hash_node_base>; + /** * Primary class template _Hashtable. * @@ -183,7 +195,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION private __detail::_Hashtable_alloc< __alloc_rebind<_Alloc, __detail::_Hash_node<_Value, - _Traits::__hash_cached::value>>> + _Traits::__hash_cached::value>>>, + private _Hashtable_enable_default_ctor<_Equal, _Hash, _Alloc> { static_assert(is_same<typename remove_cv<_Value>::type, _Value>::value, "unordered container must have a non-const, non-volatile value_type"); |