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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - std::ranges::size incorrectly uses perfect forwarding"
href="https://bugs.llvm.org/show_bug.cgi?id=50717">50717</a>
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<th>Summary</th>
<td>std::ranges::size incorrectly uses perfect forwarding
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>12.0
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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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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</tr>
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<th>Reporter</th>
<td>zilla@kayari.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>test/std/ranges/range.access/range.prim/size.pass.cpp has this check:
assert(std::ranges::size(MoveOnlySizeFunction()) == 42);
which relies on this function being called with an rvalue:
friend constexpr size_t size(MoveOnlySizeFunction) { return 42; }
However, the relevant part of the standard says an lvalue should be used:
"then ranges::size(E) is expression-equivalent to decay-copy(size(t))"
where 't' is an lvalue, i.e. it should not be forwarded.
As a result, the test fails for libstdc++ trunk (since I fixed the same bug
earlier this month).
The spec was changed by <a href="https://wg21.link/p2091r0">https://wg21.link/p2091r0</a> to use lvalues everywhere
except ranges::cdata.</pre>
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