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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - reverse_iterator::operator[] calls const operator[]"
href="http://llvm.org/bugs/show_bug.cgi?id=17883">17883</a>
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<th>Summary</th>
<td>reverse_iterator::operator[] calls const operator[]
</td>
</tr>
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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>Linux
</td>
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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
</td>
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<th>Component</th>
<td>All Bugs
</td>
</tr>
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<th>Assignee</th>
<td>hhinnant@apple.com
</td>
</tr>
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<th>Reporter</th>
<td>timo@tbingmann.de
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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</tr>
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=11517" name="attach_11517" title="reverse_iterator_bug">attachment 11517</a> <a href="attachment.cgi?id=11517&action=edit" title="reverse_iterator_bug">[details]</a></span>
reverse_iterator_bug
We have a larger library (<a href="http://stxxl.sourceforge.net">http://stxxl.sourceforge.net</a>) that constructs reverse
iterators using std::reverse_iterator from normal forward random access
iterator classes.
Compiling with libc++ r194397 yields an error similar to:
/software/libcxx-debug/include/c++/v1/iterator:568:17: error: binding of
reference to type 'value_type' (aka 'double') to a value of type
'const value_type' (aka 'const double') drops qualifiers
{return current[-__n-1];}
^~~~~~~~~~~~~~~
Our iterator implements both mutable operator[] and const operator[]. Const
returns a const value_type&.
The current implementation of
"std::reverse_iterator<>::operator[] const"
makes the operation "current[]" call the const operator[], because the method
is const. The problem is that the "operator[] const" returning a const
value_type&, which cannot be cast back to value_type&.
Comparing libc++
reference operator[](difference_type __n) const {return current[-__n-1];}
against the gcc implementation
reference operator[](difference_type __n) const { return *(*this + __n); }
makes the problem more clear. The gcc implementation copies the iterator first.
Attached is a bad excuse of an iterator example, which implements both
operator[]s. It compiles with gcc-4.6, but not with clang-3.3
Cheers,
Timo</pre>
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