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| 26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
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| 27 | <a name="hash.disable"></a> Disabling The Extensions</h2></div></div></div> |
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| 28 | <p> |
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| 29 | While <code class="computeroutput"><a href="../boost/hash.html" title="Struct template hash">boost::hash</a></code>'s extensions are |
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| 30 | generally useful, you might want to turn them of in order to check that your |
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| 31 | code will work with other implementations of TR1. To do this define the macro |
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| 32 | <code class="computeroutput"><span class="identifier">BOOST_HASH_NO_EXTENSIONS</span></code>. When |
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| 33 | this macro is defined, only the specialisations detailed in TR1 will be declared. |
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| 34 | But, if you later undefine the macro and include <<code class="computeroutput"><a href="reference.html#header.boost.functional.hash.hpp" title="Header <boost/functional/hash.hpp>">boost/functional/hash.hpp</a></code>> |
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| 35 | then the non-specialised form will be defined - activating the extensions. |
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| 36 | </p> |
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| 37 | <p> |
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| 38 | It is strongly recommended that you never undefine the macro - and only define |
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| 39 | it so that it applies to the complete translation unit, either by defining |
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| 40 | it at the beginning of the main source file or, preferably, by using a compiler |
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| 41 | switch or preference. And you really should never define it in header files. |
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| 42 | </p> |
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| 43 | <p> |
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| 44 | If you are writing a library which has code in the header which requires the |
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| 45 | extensions, then the best action is to tell users not to define the macro. |
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| 46 | Their code won't <span class="emphasis"><em>require</em></span> the macro. |
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| 47 | </p> |
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| 48 | <p> |
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| 49 | Translation units that are compiled with the macro defined will link with units |
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| 50 | that were compiled without it. This feature has been designed to avoid ODR |
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| 51 | violations. |
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| 52 | </p> |
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| 56 | <td align="right"><small>Copyright © 2005, 2006 Daniel James</small></td> |
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