<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/91266>91266</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++] Falsely rejected code for `std::unique_ptr` because `__compressed_pair` requires different types.
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          SainoNamkho
      </td>
    </tr>
</table>

<pre>
    As shown in https://godbolt.org/z/4K6q9bo3e, only libc++ 
```c++
#include <memory>
#include <any>

void f(std::any) {}

std::unique_ptr<decltype(f), decltype(f)*> p(f, f);
```

I've not found anywhere in the draft saying this should be rejected.

1. Why does `__compressed_pair` require the two template arguments to be the same and the `_CanBeEmptyBase` traits? If they makes it unable to compress, then an uncompressed layout is automatically produced, with no need to be explicitly rejected. And the indices used by `__compressed_pair_elem` suggest that it handles same types correctly.
2. If it is reasonable to keep the implementation of `__compressed_pair`, is it a good solution to change `unique_ptr` into use something like `conditional_t<same_as<pointer, deleter_type>, __compressed_pair<<pointer, deleter_type>, ...>`?
</pre>
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