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| 26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
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| 27 | <a name="boost_tr1.implementation"></a> Implementation</h2></div></div></div> |
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| 28 | <p> |
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| 29 | When Boost.TR1 is <a href="config.html" title=" Configuration">configured</a> to make |
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| 30 | use of your standard library's native TR1 implementation, then it doesn't do |
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| 31 | very much: it just includes the appropriate header. |
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| 32 | </p> |
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| 33 | <p> |
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| 34 | When Boost.TR1 is using the Boost implementation of a particular component, |
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| 35 | then it includes the appropriate Boost header(s) and imports the necessary |
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| 36 | declarations in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code> |
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| 37 | with using declarations. Note that only those declarations that are part of |
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| 38 | the standard are imported: the implementation is deliberately quite strict |
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| 39 | about not including any Boost-specific extensions in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code>, |
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| 40 | in order to catch any portability errors in user code. If you really need to |
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| 41 | use Boost-specific extensions then you should include the Boost headers directly |
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| 42 | and use the declarations in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span></code> instead. |
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| 43 | Note that this style of implementation is not completely standards-conforming, |
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| 44 | in particular it is not possible to add user-defined template specializations |
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| 45 | of TR1 components into <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code>. |
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| 46 | There are also one or two Boost libraries that are not yet fully standards |
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| 47 | conforming, any such non-conformities are documented in <a href="subject_list.html" title=" TR1 By Subject">the |
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| 48 | TR1 by subject section</a>. Hopefully, occurrences of non-standard behavior |
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| 49 | should be extremely rare in practice however. |
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| 50 | </p> |
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| 51 | <p> |
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| 52 | If you use the standard conforming header includes (in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tr1</span><span class="special">/</span><span class="identifier">tr1</span></code>) then these header names can sometimes |
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| 53 | conflict with existing standard library headers (for example <code class="computeroutput"><span class="identifier">shared_ptr</span></code> is added to the existing standard |
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| 54 | library header <code class="computeroutput"><span class="special"><</span><span class="identifier">memory</span><span class="special">></span></code> rather than it's own header). These headers |
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| 55 | forward on to your existing standard library header in one of two ways: for |
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| 56 | gcc it uses <code class="computeroutput"><span class="preprocessor">#include_next</span></code>, |
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| 57 | and for other compilers it uses the macro <code class="computeroutput"><span class="identifier">BOOST_TR1_STD_HEADER</span><span class="special">(</span><span class="identifier">header</span><span class="special">)</span></code> |
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| 58 | (defined in <a href="../../../boost/tr1/detail/config.hpp%22" target="_top">boost/tr1/detail/config.hpp</a>) |
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| 59 | which evaluates to <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><../</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">header</span><span class="special">></span></code>. |
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| 60 | This should work "straight out the box" for most compilers, but does |
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| 61 | mean that these headers should <span class="bold"><strong>never</strong></span> be placed |
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| 62 | inside a directory called "include" that is already in your compiler's |
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| 63 | search path. |
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| 64 | </p> |
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| 65 | </div> |
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| 66 | <table width="100%"><tr> |
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| 67 | <td align="left"></td> |
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| 68 | <td align="right"><small>Copyright © 2005 John Maddock</small></td> |
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