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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Ambiguous constructor call error when calling std::span<T>(T*, 0)"
href="https://bugs.llvm.org/show_bug.cgi?id=49295">49295</a>
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<th>Summary</th>
<td>Ambiguous constructor call error when calling std::span<T>(T*, 0)
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</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>
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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>schottm@google.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>[1] shows libstdc++ compiles just fine here.
There are a lot of reasons libc++'s std::span isn't in accord with
[views.span], most stemming from the lack of concepts and ranges support
elsewhere, but [span.cons] ¶ 7.4 explicitly mandates that
"is_convertible_v<End, size_t> is false" but the ambiguous constructors [2]
actually have no constraints at all (same with the ones above that on the
primary template).
And while you're at it, [span.cons] ¶ 3.2 and 7.1 ("is_convertible_v<U(*)[],
element_type(*)[]> is true") should be there too and that doesn't require your
concepts support to be there.
[1]: <a href="https://godbolt.org/z/7E14Pa">https://godbolt.org/z/7E14Pa</a>
[2]: <a href="https://github.com/llvm/llvm-project/blob/main/libcxx/include/span#L386">https://github.com/llvm/llvm-project/blob/main/libcxx/include/span#L386</a></pre>
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