<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/91268>91268</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++] Libc++ implements `std::from_chars` with default argument as one more overload, is it allowed?
        </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>
    https://eel.is/c++draft/charconv#from.chars-1 say the signature should be
```c++
constexpr from_chars_result from_chars(const char* first, const char* last,
 integer-type& value, int base = 10);
```
But is implemented as
https://github.com/llvm/llvm-project/blob/fcf341d3ddfe2289ac88aa3c122b25df8732cc8e/libcxx/include/__charconv/from_chars_integral.h#L222-L233

I'm not should if there's any legal ways to inspect this. And if the following code is well-formed, it does make a difference.
https://godbolt.org/z/va1MbrK68
```c++
#include <charconv>

static_assert(std::is_same_v<
 decltype(static_cast<std::from_chars_result(*)(const char*, const char*, int&)>(std::from_chars)),
 decltype(static_cast<std::from_chars_result(*)(const char*, const char*, int&)>(std::from_chars))
    >);
```
</pre>
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