2004-08-05 19:37:40 +00:00
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Boost.Range FAQ </title>
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<table border="0" >
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<tr>
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2004-10-05 15:45:52 +00:00
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<td ><img src="../../../boost.png" border="0" ></td>
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2004-08-05 19:37:40 +00:00
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<td ><h1 align="center">Boost.Range</h1></td>
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</tr>
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</table>
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<p>
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2004-08-10 09:56:55 +00:00
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<h2 >FAQ</h2> <a name="FAQ" ></a>
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<ol >
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<li >
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2005-08-12 13:02:37 +00:00
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<i>Why is there no difference between <code >range_iterator<C>::type</code>
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2004-08-16 22:47:16 +00:00
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and <code >range_const_iterator<C>::type</code> for <code>std::pair<iterator, iterator></code></i>.
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2004-08-05 19:37:40 +00:00
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</li>
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<p >
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2005-08-12 13:02:37 +00:00
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In general it is not possible nor desirable to find a corresponding <code >const_iterator</code>.
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When it is possible to come up with one, the client might choose to construct a <code >std::pair<const_iterator,const_iterator></code>
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2004-08-05 19:37:40 +00:00
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object.
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</p>
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2004-08-12 10:58:13 +00:00
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<p>
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2005-08-12 13:02:37 +00:00
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Note that an <a href="utility_class.html#iter_range">iterator_range</a>
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is somewhat more convenient than a <code>pair</code> and that a <a
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href="utility_class.html#sub_range"><code>sub_range</code></a> does
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2004-08-24 15:58:01 +00:00
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propagate const-ness. </p>
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<li >
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<i>Why is there not supplied more types or more functions?</i>
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2004-08-05 19:37:40 +00:00
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<p >
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2005-08-12 13:02:37 +00:00
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The library has been kept small because its current interface will
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serve most
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purposes. If and when a genuine need arises for more functionality, it can be
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implemented.
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</p>
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</li>
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<li >
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<i>How should I implement generic algorithms for ranges?</i>
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<p >
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2005-08-12 13:02:37 +00:00
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One should always start with a generic algorithm that takes two iterators (or
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more) as input. Then use Boost.Range to build handier versions on top of the
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iterator based algorithm. Please notice that once the range version of the
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algorithm is done, it makes sense <i>not</i> to expose the iterator version in
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the public interface.
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</p>
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</li>
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<li>
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<i>Why is there no Incrementable Range concept?</i>
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<p>
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Even though we speak of incrementable iterators, it would not make
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much sense for ranges; for example, we cannot determine the size and
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emptiness of a range since we cannot even compare
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its iterators.
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</p>
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2004-08-24 15:58:01 +00:00
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<p>
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2005-08-12 13:02:37 +00:00
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Note also that incrementable iterators are derived from output
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iterators and so there exist no output range.
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</p>
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</li>
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2004-08-24 15:58:01 +00:00
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<!--
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<li>
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<i>Should I use qualified syntax, for example
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2004-08-12 10:58:13 +00:00
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<blockquote><pre>
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<span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>r </span><span class=special>); </span>
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</pre></blockquote>
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instead of
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<blockquote>
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<pre><span class=keyword>using </span><span class=keyword>namespace </span><span class=identifier>boost</span><span class=special>;</span>
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<span class=identifier>begin</span><span class=special>( </span><span class=identifier>r </span><span class=special>)</span></pre></blockquote>
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when calling functions in this library? If so, can I still rely on argument
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2004-08-10 09:56:55 +00:00
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dependent lookup (ADL) to kick in?</i>
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<p>
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2005-08-12 13:02:37 +00:00
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The answer to the first question is that "it's up to you". The
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answer to the second question is Yes. Normally qualified syntax
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disables ADL, but the functions are implemented in a special
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manner that preserves ADL properties. The trick was explained by
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Daniel Frey on comp.lang.std.c++ in the thread "Whence Swap" and
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it is best explained by some code: <blockquote>
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<pre>
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2004-08-12 10:58:13 +00:00
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<span class=keyword>namespace </span><span class=identifier>boost</span>
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<span class=special>{
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</span><span class=keyword>namespace </span><span class=identifier>range_detail
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</span><span class=special>{
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</span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>T </span><span class=special>>
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2004-08-16 22:47:16 +00:00
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</span><span class=keyword>typename </span><span class=identifier>range_iterator</span><span class=special><</span><span class=identifier>T</span><span class=special>>:</span><span class=identifier>type </span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>r </span><span class=special>)
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</span><span class=special>{ </span><span class=comment>/* normal implementation */ </span><span class=special>}
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</span><span class=special>}
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</span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>T </span><span class=special>>
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</span><span class=keyword>typename </span><span class=identifier>range_iterator</span><span class=special><</span><span class=identifier>T</span><span class=special>>::</span><span class=identifier>type </span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>r </span><span class=special>)
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</span><span class=special>{
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</span><span class=comment>//
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// Create ADL hook
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//
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</span><span class=keyword>using </span><span class=identifier>range_detail</span><span class=special>::</span><span class=identifier>begin</span><span class=special>;
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</span><span class=keyword>return </span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>r </span><span class=special>);
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</span><span class=special>}</span>
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<span class=special>} </span>
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</pre>
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</blockquote>
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Cool indeed!
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</p>
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-->
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2004-08-05 19:37:40 +00:00
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</ol>
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<hr>
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<p>
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2007-11-25 18:38:02 +00:00
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(C) Copyright Thorsten Ottosen 2003-2004
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</p>
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<br>
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