<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/143613>143613</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            C23 Clang rejects valid code involving compound literal and typeof
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          dcawley15
      </td>
    </tr>
</table>

<pre>
    I was attempting to create a generic bit cast macro using the new C23 typeof feature. Clang appears to reject the following code with "_error: initializer element is not a compile-time constant_" even though I believe this code is valid in C23. Both GCC and MSVC (with /std:clatest) accept this code.

``` c
#include <stdint.h>

#define bitcast(type, value) \
 (((union{ typeof(value) src; type dst; }){ (value) }).dst)

int main(void)
{
    int64_t foo = 4;
    double bar = bitcast(double, foo); // ok
    foo = bitcast(int64_t, bar); // ok
    foo = bitcast(int64_t, bitcast(double, foo)); // error
    return 0;
}
```

Compiler Flags: -std=c23 -pedantic

https://godbolt.org/z/zsfErTo1e



</pre>
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