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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - <version> header is missing __cpp_lib_type_identity and other macros"
href="https://bugs.llvm.org/show_bug.cgi?id=47261">47261</a>
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<th>Summary</th>
<td><version> header is missing __cpp_lib_type_identity and other macros
</td>
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<th>Product</th>
<td>libc++
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<th>Version</th>
<td>11.0
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>llvm@marehr.dialup.fu-berlin.de
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>Hi clang-team,
the following code doesn't compile, even thought it can compile
`std::type_identity` and `std::unwrap_reference` just fine since clang 9.0.0.
```c++
#include <type_traits>
using a = std::type_identity<int>; // works fine
using b = std::unwrap_reference_t<int>; // works fine
#ifndef __cpp_lib_type_identity
#error "Not defined?"
#endif
#ifndef __cpp_lib_unwrap_ref
#error "Not defined?"
#endif
```
<a href="https://godbolt.org/z/6vaa6x">https://godbolt.org/z/6vaa6x</a>
I thought <a href="https://eel.is/c++draft/version.syn">https://eel.is/c++draft/version.syn</a> suggests that
__cpp_lib_type_identity should be defined if it was implemented.
Thank you!</pre>
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