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removed constraints on reference from Readable Iterator
[SVN r21641]
This commit is contained in:
Jeremy Siek
@ -802,12 +802,14 @@ object. Is all this mechanism really necessary?
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c++std-lib-12333:
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N1550 requires that for a Readable Iterator a of type X, ``*a`` returns an object of type
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iterator_traits<X>::reference. ``istreambuf_iterator::operator*`` returns charT, but
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istreambuf_iterator::reference is charT&. So am I overlooking something, or is
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istreambuf_iterator not Readable
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``iterator_traits<X>::reference``. ``istreambuf_iterator::operator*`` returns ``charT``, but
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``istreambuf_iterator::reference`` is ``charT&``. So am I overlooking something, or is
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``istreambuf_iterator`` not Readable.
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:Proposed resolution: **Needs language** (Jeremy)
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Remove requirements on the reference type from Readable Iterator.
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:Proposed resolution:
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Remove all constraints on ``iterator_traits<X>::reference`` in Readable Iterator
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and Lvalue Iterator. Change Lvalue Iterator to refer to ``T&`` instead of
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``iterator_traits<X>::reference``.
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@ -384,24 +384,12 @@ type <tt class="literal"><span class="pre">T</span></tt>.</p>
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<td>Any non-reference,
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non-cv-qualified type</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">iterator_traits<X>::reference</span></tt></td>
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<td><tt class="literal"><span class="pre">R</span></tt>, Convertible to
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<tt class="literal"><span class="pre">T</span></tt></td>
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<td> </td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">*a</span></tt></td>
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<td>Convertible to <tt class="literal"><span class="pre">R</span></tt>,
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Convertible to <tt class="literal"><span class="pre">T</span></tt></td>
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<td>Convertible to <tt class="literal"><span class="pre">T</span></tt></td>
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<td>pre: <tt class="literal"><span class="pre">a</span></tt> is
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dereferenceable. If <tt class="literal"><span class="pre">a</span>
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<span class="pre">==</span> <span class="pre">b</span></tt> then <tt class="literal"><span class="pre">*a</span></tt> is
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equivalent to <tt class="literal"><span class="pre">*b</span></tt></td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">static_cast<T>(</span>
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<span class="pre">static_cast<R>(*a)</span> <span class="pre">)</span></tt></td>
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<td><tt class="literal"><span class="pre">T</span></tt></td>
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<td>equivalent to
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<tt class="literal"><span class="pre">static_cast<T>(*a)</span></tt></td>
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equivalent to <tt class="literal"><span class="pre">*b</span></tt>.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre">a->m</span></tt></td>
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<td><tt class="literal"><span class="pre">U&</span></tt></td>
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@ -411,10 +399,8 @@ to <tt class="literal"><span class="pre">(*a).m</span></tt></td>
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</tr>
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</tbody>
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</table>
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<!-- TR1: the originally-proposed requirement that typeof(*a) == R
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was too restrictive. Now we just require that it's
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convertible to R and that accessing a T through that conversion
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is equivalent to accessing a T directly. -->
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<!-- We won't say anything about iterator_traits<X>::reference until
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the DR is resolved. -->
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<a class="target" id="writable-iterator" name="writable-iterator"></a></div>
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<div class="section" id="writable-iterators-lib-writable-iterators">
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<h4><a class="toc-backref" href="#id12" name="writable-iterators-lib-writable-iterators">Writable Iterators [lib.writable.iterators]</a></h4>
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@ -480,8 +466,9 @@ exchanged</td>
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</div>
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<div class="section" id="lvalue-iterators-lib-lvalue-iterators">
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<h4><a class="toc-backref" href="#id14" name="lvalue-iterators-lib-lvalue-iterators">Lvalue Iterators [lib.lvalue.iterators]</a></h4>
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<p>The <em>Lvalue Iterator</em> concept adds the requirement that the
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<tt class="literal"><span class="pre">reference</span></tt> type be a reference to the value type of the iterator.</p>
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<p>The <em>Lvalue Iterator</em> concept adds the requirement that the return
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type of <tt class="literal"><span class="pre">operator*</span></tt> type be a reference to the value type of the
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iterator.</p>
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<table class="table" frame="border" rules="all">
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<colgroup>
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<col width="42%" />
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@ -493,16 +480,20 @@ exchanged</td>
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</tr>
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<tr><th>Expression</th>
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<th>Return Type</th>
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<th>Assertion</th>
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<th>Note/Assertion</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="literal"><span class="pre">iterator_traits<X>::reference</span></tt></td>
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<tr><td><tt class="literal"><span class="pre">*a</span></tt></td>
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<td><tt class="literal"><span class="pre">T&</span></tt></td>
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<td><tt class="literal"><span class="pre">T</span></tt> is <em>cv</em>
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<tt class="literal"><span class="pre">iterator_traits<X>::value_type</span></tt>
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where <em>cv</em> is an optional
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cv-qualification</td>
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cv-qualification.
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pre: <tt class="literal"><span class="pre">a</span></tt> is
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dereferenceable. If <tt class="literal"><span class="pre">a</span>
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<span class="pre">==</span> <span class="pre">b</span></tt> then <tt class="literal"><span class="pre">*a</span></tt> is
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equivalent to <tt class="literal"><span class="pre">*b</span></tt>.</td>
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</tr>
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</tbody>
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</table>
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@ -889,7 +880,7 @@ LocalWords: TraversalTag typename lvalues DWA Hmm JGS mis enum -->
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<hr class="footer"/>
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<div class="footer">
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<a class="reference" href="new-iter-concepts.rst">View document source</a>.
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Generated on: 2004-01-12 18:37 UTC.
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Generated on: 2004-01-12 19:53 UTC.
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Generated by <a class="reference" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
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</div>
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</body>
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@ -368,26 +368,18 @@ type ``T``.
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|``iterator_traits<X>::value_type`` |``T`` |Any non-reference, |
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| | |non-cv-qualified type |
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+-----------------------------------+------------------------+-------------------------+
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|``iterator_traits<X>::reference`` |``R``, Convertible to | |
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| |``T`` | |
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+-----------------------------------+------------------------+-------------------------+
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|``*a`` |Convertible to ``R``, |pre: ``a`` is |
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| |Convertible to ``T`` |dereferenceable. If ``a |
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|``*a`` | Convertible to ``T`` |pre: ``a`` is |
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| | |dereferenceable. If ``a |
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| | |== b`` then ``*a`` is |
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| | |equivalent to ``*b`` |
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+-----------------------------------+------------------------+-------------------------+
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|``static_cast<T>( |``T`` |equivalent to |
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|static_cast<R>(*a) )`` | |``static_cast<T>(*a)`` |
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| | |equivalent to ``*b``. |
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+-----------------------------------+------------------------+-------------------------+
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|``a->m`` |``U&`` |pre: ``(*a).m`` is |
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| | |well-defined. Equivalent|
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| | |to ``(*a).m`` |
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+-----------------------------------+------------------------+-------------------------+
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.. TR1: the originally-proposed requirement that typeof(*a) == R
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was too restrictive. Now we just require that it's
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convertible to R and that accessing a T through that conversion
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is equivalent to accessing a T directly.
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.. We won't say anything about iterator_traits<X>::reference until
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the DR is resolved.
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.. _Writable Iterator:
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@ -432,21 +424,27 @@ expressions are valid and respect the stated semantics.
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Lvalue Iterators [lib.lvalue.iterators]
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---------------------------------------
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The *Lvalue Iterator* concept adds the requirement that the
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``reference`` type be a reference to the value type of the iterator.
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The *Lvalue Iterator* concept adds the requirement that the return
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type of ``operator*`` type be a reference to the value type of the
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iterator.
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+---------------------------------------------------------------------------------+
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| Lvalue Iterator Requirements |
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+---------------------------------+-----------+-----------------------------------+
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|Expression |Return Type|Assertion |
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|Expression |Return Type|Note/Assertion |
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+=================================+===========+===================================+
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|``iterator_traits<X>::reference``|``T&`` |``T`` is *cv* |
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|``*a`` | ``T&`` |``T`` is *cv* |
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| | |``iterator_traits<X>::value_type`` |
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| | |where *cv* is an optional |
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| | |cv-qualification |
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| | |cv-qualification. |
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| | |pre: ``a`` is |
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| | |dereferenceable. If ``a |
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| | |== b`` then ``*a`` is |
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| | |equivalent to ``*b``. |
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+---------------------------------+-----------+-----------------------------------+
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Iterator Traversal Concepts [lib.iterator.traversal]
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++++++++++++++++++++++++++++++++++++++++++++++++++++
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