| Issue |
127095
|
| Summary |
libcxx error global operator <=> for std::set has only two template parameters(_Key, _Allocator) but need tree(_Key, Compare, Allocator)
|
| Labels |
libc++
|
| Assignees |
|
| Reporter |
leanid
|
Problem:
current libc++ include next std::set operator<=> for c++20
```cpp
template <class _Key, class _Allocator>
_LIBCPP_HIDE_FROM_ABI __synth_three_way_result<_Key>
operator<=>(const set<_Key, _Allocator>& __x, const set<_Key, _Allocator>& __y) {
return std::lexicographical_compare_three_way(
__x.begin(), __x.end(), __y.begin(), __y.end(), std::__synth_three_way<_Key, _Key>);
}
```
If we add custom allocator and custom comparator we need operator<=> with three template parameters like:
```cpp
namespace std
{
// we need three template parameters to find this if using custom _Allocator
template <class _Key, class Comparator, class _Allocator>
auto operator<=>(const set<_Key, Comparator, _Allocator>& __x,
const set<_Key, Comparator, _Allocator>& __y)
{
return std::lexicographical_compare_three_way(
__x.begin(),
__x.end(),
__y.begin(),
__y.end(),
std::__synth_three_way<_Key, _Key>);
}
} // namespace std
```
Minimal reproduction:
**main.cxx** file:
```cpp
#include <cstdlib>
#include <functional>
#include <iostream>
#include <set>
struct my_type
{
int i;
bool operator<(const my_type& other) const { return i < other.i; }
};
template <class T> class MyAllocator
{
public:
using value_type = T;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
using propagate_on_container_move_assignment = std::true_type;
T* allocate(size_type n, const void* hint = 0)
{
std::cout << "Alloc" << n << std::endl;
return static_cast<T*>(malloc(n * sizeof(T)));
}
void deallocate(T* p, size_type n) { free(p); }
size_type max_size() const
{
return size_type(std::numeric_limits<unsigned int>::max() / sizeof(T));
}
void construct(T* p, const T& value) { _construct(p, value); }
void destroy(T* p) { _destroy(p); }
};
template <class T, class U>
bool operator==(const MyAllocator<T>&, const MyAllocator<U>&) noexcept
{
return true;
}
template <class T, class U>
bool operator!=(const MyAllocator<T>&, const MyAllocator<U>&) noexcept
{
return false;
}
#if defined(FIX_LIBCXX) // 1 to fix error
namespace std
{
// we need three template parameters to find this if using custom _Allocator
template <class _Key, class Comparator, class _Allocator>
auto operator<=>(const set<_Key, Comparator, _Allocator>& __x,
const set<_Key, Comparator, _Allocator>& __y)
{
return std::lexicographical_compare_three_way(
__x.begin(),
__x.end(),
__y.begin(),
__y.end(),
std::__synth_three_way<_Key, _Key>);
}
} // namespace std
#endif
int main()
{
std::set<my_type> s01;
std::set<my_type> s02;
std::cout << "(s01 < s02): " << (s01 < s02) << std::endl; // compiles
std::set<my_type, std::less<my_type>> s11;
std::set<my_type, std::less<my_type>> s12;
std::cout << "(s11 < s12): " << (s11 < s12) << std::endl; // compiles
std::set<my_type, std::less<my_type>, std::allocator<my_type>> s21;
std::set<my_type, std::less<my_type>, std::allocator<my_type>> s22;
std::cout << "(s21 < s22): " << (s21 < s22) << std::endl; // compiles
std::set<my_type, std::less<my_type>, MyAllocator<my_type>> s31;
std::set<my_type, std::less<my_type>, MyAllocator<my_type>> s32;
std::cout << "(s31 < s32): " << (s31 < s32) << std::endl; // error
return EXIT_SUCCESS;
}
```
How to test it in terminal:
1. install latest libcxx or just install **XCode16.2**
2. in terminal go to directory with main.cxx file
3. to get error exec:> `clang++ -std=c++20 -stdlib=libc++ ./main.cxx`
4. to get fix exec:> `clang++ -std=c++20 -stdlib=libc++ -DFIX_LIBCXX ./main.cxx`
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