https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103849
Bug ID: 103849
Summary: std::hash specializations with distinct concepts fails
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fchelnokov at gmail dot com
Target Milestone: ---
The two specialization of std::hash with distinct concepts:
```
#include <concepts>
#include <functional>
template <std::convertible_to<int> T>
struct std::hash<T> {};
template <std::convertible_to<float> U>
struct std::hash<U> {};
int main() {}
```
fails to compile in GCC with the error:
```
error: redefinition of 'struct std::hash<_Tp>'
8 | struct std::hash<U> {};
```
Clang and MSVC have no problem with it. Demo:
https://gcc.godbolt.org/z/z4f3o6bdo
Related discussion: https://stackoverflow.com/q/68885697/7325599
