<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/132133>132133</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++][ranges] `ranges::to` can have non-class return type
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++,
            accepts-invalid,
            ranges
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          frederick-vs-ja
      </td>
    </tr>
</table>

<pre>
    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.
</pre>
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