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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [span] Incorrect static_assert in span::front and span::back"
href="https://bugs.llvm.org/show_bug.cgi?id=44725">44725</a>
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<th>Summary</th>
<td>[span] Incorrect static_assert in span::front and span::back
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<th>Product</th>
<td>libc++
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<th>Version</th>
<td>10.0
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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
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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>mschellenbergercosta@googlemail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>Currently ```span<T, extent>::front()``` and ```span<T, extent>::back()``` have
a static_assert that checks whether ```extent > 0```.
However, this is an invalid requirement, as it would trigger in all evaluated
branches. Consider the following code
```
template<class R>
int get_front_or_default(R myRange, int myDefault) {
if (!myRange.empty())
return myRange.front();
else
return myDefault;
}
```
This would give a compile error when passed a span<int, 0> albeit the front()
method is never called. Consequently, the static_assert should be replaced by
an _LIBCPP_ASSERT.
There is already a PR for that (<a href="https://reviews.llvm.org/D71995">https://reviews.llvm.org/D71995</a>)</pre>
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