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159 lines
14 KiB
HTML
Executable File
159 lines
14 KiB
HTML
Executable File
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Boost.Range Introduction </title>
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<table border="0" >
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<tr>
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<td ><img src="../../../boost.png" border="0" ></td>
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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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<h2>Introduction</h2>
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<p>
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Generic algorithms have so far been specified in terms of two or more
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iterators. Two iterators would together form a range of values that the
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algorithm could work on. This leads to a very general interface, but also
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to a somewhat clumsy use of the algorithms with redundant specification
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of container names. Therefore we would like to raise the abstraction level
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for algorithms so they specify their interface in terms of <a
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href=range.html>Ranges</a> as much as possible.
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</p>
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<p>
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The most common form of ranges we are used to work with is standard library
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containers. However, one
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often finds it desirable to extend that code to work with other types that
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offer
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enough functionality to satisfy the needs of the generic code
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<i>if a suitable layer of indirection is applied </i>. For
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example, raw arrays are often suitable for use with generic code that
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works with containers, provided a suitable adapter is used.
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</p>
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<p>
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This library therefore provides the means to adapt standard-like
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containers, <code>std::pairs</code> of iterators, and raw arrays (and
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more), such that
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the same generic code can work with them all.
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The basic idea is to add another layer of indirection using <a
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href="../../mpl/doc/refmanual/metafunction.html">metafunctions</a> and
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free-standing functions so syntactic and/or semantic differences can be removed.
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</p>
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<p >
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The main advantages are
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<ul >
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<li >
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simpler implementation and specification of generic range algorithms
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</li>
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<li >
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more flexible, compact and maintainable client code
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</li>
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<li >
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safe use of built-in arrays
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</li>
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</ul>
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</p>
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<p >
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Below are given a small example (the complete example can be found <a
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href="../test/algorithm_example.cpp" target="_self" >here</a>): <blockquote>
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<pre >
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<span class=comment>
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//
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// example: extracting bounds in a generic algorithm
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//
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</span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>ForwardReadableRange</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>inline </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_iterator</span><span class=special>< </span><span class=identifier>ForwardReadableRange </span><span class=special>>::</span><span class=identifier>type
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</span><span class=identifier>find</span><span class=special>( </span><span class=identifier>ForwardReadableRange</span><span class=special>& </span><span class=identifier>c</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>value </span><span class=special>)
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</span><span class=special>{
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</span><span class=keyword>return </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>find</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>value </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>ForwardReadableRange</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>inline </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_iterator</span><span class=special>< </span><span class=keyword>const </span><span
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class=identifier>ForwardReadableRange </span><span class=special>>::</span><span class=identifier>type
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</span><span class=identifier>find</span><span class=special>( </span><span class=keyword>const </span><span class=identifier>ForwardReadableRange</span><span class=special>& </span><span class=identifier>c</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>value </span><span class=special>)
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</span><span class=special>{
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</span><span class=keyword>return </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>find</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>value </span><span class=special>);
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</span><span class=special>}
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</span><span class=comment>//
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// replace first value and return its index
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//
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</span><span class=keyword>template</span><span class=special>< </span><span class=keyword>class </span><span class=identifier>ForwardReadableWriteableRange</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>inline </span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_difference</span><span class=special>< </span><span class=identifier>ForwardReadableWriteableRange </span><span class=special>>::</span><span class=identifier>type
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</span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>ForwardReadableWriteableRange</span><span class=special>& </span><span class=identifier>c</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>value</span><span class=special>, </span><span class=keyword>const </span><span class=identifier>T</span><span class=special>& </span><span class=identifier>replacement </span><span class=special>)
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</span><span class=special>{
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</span><span class=keyword>typename </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>range_iterator</span><span class=special>< </span><span class=identifier>ForwardReadableWriteableRange </span><span class=special>>::</span><span class=identifier>type </span><span class=identifier>found </span><span class=special>= </span><span class=identifier>find</span><span class=special>( </span><span class=identifier>c</span><span class=special>, </span><span class=identifier>value </span><span class=special>);
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</span><span class=keyword>if</span><span class=special>( </span><span class=identifier>found </span><span class=special>!= </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>c </span><span class=special>) </span><span class=special>)
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</span><span class=special>*</span><span class=identifier>found </span><span class=special>= </span><span class=identifier>replacement</span><span class=special>;
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</span><span class=keyword>return </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>distance</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>c </span><span class=special>), </span><span class=identifier>found </span><span class=special>);
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</span><span class=special>}
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</span><span class=comment>//
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// usage
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//
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</span><span class=keyword>const </span><span class=keyword>int </span><span class=identifier>N </span><span class=special>= </span><span class=number>5</span><span class=special>;
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</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>vector</span><span class=special><</span><span class=keyword>int</span><span class=special>> </span><span class=identifier>my_vector</span><span class=special>;
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</span><span class=keyword>int </span><span class=identifier>values</span><span class=special>[] </span><span class=special>= </span><span class=special>{ </span><span class=number>1</span><span class=special>,</span><span class=number>2</span><span class=special>,</span><span class=number>3</span><span class=special>,</span><span class=number>4</span><span class=special>,</span><span class=number>5</span><span class=special>,</span><span class=number>6</span><span class=special>,</span><span class=number>7</span><span class=special>,</span><span class=number>8</span><span class=special>,</span><span class=number>9 </span><span class=special>};
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</span>
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<span class=identifier>my_vector</span><span class=special>.</span><span
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class=identifier>assign</span><span class=special>( </span><span class=identifier>values</span><span class=special>, </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>end</span><span class=special>( </span><span class=identifier>values </span><span class=special>) </span><span class=special>);</span>
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</span><span class=keyword>typedef </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>vector</span><span class=special><</span><span class=keyword>int</span><span class=special>>::</span><span class=identifier>iterator </span><span class=identifier>iterator</span><span class=special>;
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</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>pair</span><span class=special><</span><span class=identifier>iterator</span><span class=special>,</span><span class=identifier>iterator</span><span class=special>> </span><span class=identifier>my_view</span><span class=special>( </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>my_vector </span><span class=special>),
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</span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>begin</span><span class=special>( </span><span class=identifier>my_vector </span><span class=special>) </span><span class=special>+ </span><span class=identifier>N </span><span class=special>);
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</span><span class=keyword>char </span><span class=identifier>str_val</span><span class=special>[] </span><span class=special>= </span><span class=string>"a string"</span><span class=special>;
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</span><span class=keyword>char</span><span class=special>* </span><span class=identifier>str </span><span class=special>= </span><span class=identifier>str_val</span><span class=special>;
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</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>my_vector</span><span class=special>, </span><span class=number>4</span><span class=special>, </span><span class=number>2 </span><span class=special>);
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</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>my_view</span><span class=special>, </span><span class=number>4</span><span class=special>, </span><span class=number>2 </span><span class=special>);
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</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>cout </span><span class=special><< </span><span class=identifier>my_generic_replace</span><span class=special>( </span><span class=identifier>str</span><span class=special>, </span><span class=literal>'a'</span><span class=special>, </span><span class=literal>'b' </span><span class=special>);
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</span>
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<span class=comment>// prints '3', '5' and '0' </span>
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</pre>
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</blockquote>
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By using the free-standing functions and <a
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href="../../mpl/doc/refmanual/metafunction.html">metafunctions</a>, the code automatically
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works for all the types supported by this library; now and in the future.
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Notice that we have to
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provide two version of <code >find()</code> since we cannot forward a non-const
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rvalue with reference arguments (see this article about <a href="http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_self" >The
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Forwarding Problem</a> ).
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</p>
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<hr>
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<p>
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(C) Copyright Thorsten Ottosen 2003-2007
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</p>
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