| Issue |
132133
|
| Summary |
[libc++][ranges] `ranges::to` can have non-class return type
|
| Labels |
libc++,
accepts-invalid,
ranges
|
| Assignees |
|
| Reporter |
frederick-vs-ja
|
Currently, this ill-formed program which violates [[range.utility.conv.to]/1](https://eel.is/c++draft/range.utility.conv.to#1) and [[range.utility.conv.adaptors]/1](https://eel.is/c++draft/range.utility.conv.adaptors#1) isn't rejected when using libc++ ([Godbolt link](https://godbolt.org/z/6bce8Pj98)):
```C++
#include <concepts>
#include <ranges>
int main() {
struct R {
int* begin() const;
int* end() const;
operator int() const { return 0; }
};
std::same_as<int> auto m [[maybe_unused]] = std::ranges::to<int>(R{});
std::same_as<int> auto n [[maybe_unused]] = R{} | std::ranges::to<int>();
}
```
It's weird that the "class" part is mentioned in comments but not actually implemented.
https://github.com/llvm/llvm-project/blob/ead272460004519ccbd98d08d68c70123892cd4e/libcxx/include/__ranges/to.h#L80-L83
https://github.com/llvm/llvm-project/blob/ead272460004519ccbd98d08d68c70123892cd4e/libcxx/include/__ranges/to.h#L207-L210
Note that libstdc++ and MSVC STL also reject union types by only using `is_class_v`, despite that the term "class type" in the C++ core language specification also covers union types. Perhaps we should also only accept non-union class types here and submit an LWG issue for this.
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