<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/112856>112856</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++] Questionable extension `packaged_task::result_type`
        </td>
    </tr>

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

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

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

<pre>
    libc++ provides `packaged_task::result_type` as an extension:

https://github.com/llvm/llvm-project/blob/7eaf92b3e4db5e3be9e9ee137866090d66dd08fb/libcxx/include/future#L325
https://github.com/llvm/llvm-project/blob/7eaf92b3e4db5e3be9e9ee137866090d66dd08fb/libcxx/include/future#L1603
https://github.com/llvm/llvm-project/blob/7eaf92b3e4db5e3be9e9ee137866090d66dd08fb/libcxx/include/future#L1697

However, the extension doens't seem conforming - as it can change behavior in SFINAE or cause ambiguity in name lookup.

It seems that the extension was added by @HowardHinnant when `packaged_task` was initially implemented. Should we
- just remove it, or
- deprecated and then remove it, or
- keep it as-is (possibly with more comments)?
</pre>
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