https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107340
Bug ID: 107340
Summary: std::unordered_map and completeness of nested classes
Product: gcc
Version: 11.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jens.maurer at gmx dot net
Target Milestone: ---
Consider:
#include <unordered_map>
struct X
{
struct Key
{
int x = 0;
bool operator==(const Key&) const = default;
std::size_t operator()(const Key& k) const noexcept
{
return k.x;
}
};
int a[sizeof(Key)];
std::unordered_map<Key, std::size_t, Key> m;
};
X x;
When compiled with "g++ -std=c++20", it yields:
a1.cc:24:3: error: use of deleted function ‘X::X()’
(plus lots of details)
since gcc 11.3 and 12.x; gcc 11.2 compiled this code fine.
Analysis: The nested class "X::Key" is complete at its closing brace, also
evidenced by the array data member declaration. Yet, "m" attains a deleted
default constructor for no apparent reason.
Moving class "Key" to namespace scope or providing a separate, but still
nested, "X::KeyHash" class works around the issue.
