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| 4 | <title>Setting Polices at Namespace Scope</title> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="math_toolkit.pol_ref.namespace_pol"></a><a class="link" href="namespace_pol.html" title="Setting Polices at Namespace Scope">Setting Polices at | |
| 28 | Namespace Scope</a> | |
| 29 | </h3></div></div></div> | |
| 30 | <p> | |
| 31 | Sometimes what you really want to do is bring all the special functions, | |
| 32 | or all the distributions into a specific namespace-scope, along with a specific | |
| 33 | policy to use with them. There are two macros defined to assist with that: | |
| 34 | </p> | |
| 35 | <pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">Policy</span><span class="special">)</span> | |
| 36 | </pre> | |
| 37 | <p> | |
| 38 | and: | |
| 39 | </p> | |
| 40 | <pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="identifier">Type</span><span class="special">,</span> <span class="identifier">Policy</span><span class="special">)</span> | |
| 41 | </pre> | |
| 42 | <p> | |
| 43 | You can use either of these macros after including any special function or | |
| 44 | distribution header. For example: | |
| 45 | </p> | |
| 46 | <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">/</span><span class="identifier">gamma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 47 | <span class="comment">//using boost::math::tgamma;</span> | |
| 48 | <span class="comment">// Need not declare using boost::math::tgamma here,</span> | |
| 49 | <span class="comment">// because will define tgamma in myspace using macro below.</span> | |
| 50 | ||
| 51 | <span class="keyword">namespace</span> <span class="identifier">myspace</span> | |
| 52 | <span class="special">{</span> | |
| 53 | <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">;</span> | |
| 54 | ||
| 55 | <span class="comment">// Define a policy that does not throw on overflow:</span> | |
| 56 | <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span><span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">></span> <span class="special">></span> <span class="identifier">my_policy</span><span class="special">;</span> | |
| 57 | ||
| 58 | <span class="comment">// Define the special functions in this scope to use the policy: </span> | |
| 59 | <span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">my_policy</span><span class="special">)</span> | |
| 60 | <span class="special">}</span> | |
| 61 | ||
| 62 | <span class="comment">// Now we can use myspace::tgamma etc.</span> | |
| 63 | <span class="comment">// They will automatically use "my_policy":</span> | |
| 64 | <span class="comment">//</span> | |
| 65 | <span class="keyword">double</span> <span class="identifier">t</span> <span class="special">=</span> <span class="identifier">myspace</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="number">30.0</span><span class="special">);</span> <span class="comment">// Will *not* throw on overflow,</span> | |
| 66 | <span class="comment">// despite the large value of factorial 30 = 265252859812191058636308480000000</span> | |
| 67 | <span class="comment">// unlike default policy boost::math::tgamma;</span> | |
| 68 | </pre> | |
| 69 | <p> | |
| 70 | In this example, using BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS results in a | |
| 71 | set of thin inline forwarding functions being defined: | |
| 72 | </p> | |
| 73 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> | |
| 74 | <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">a</span><span class="special">){</span> <span class="keyword">return</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">mypolicy</span><span class="special">());</span> <span class="special">}</span> | |
| 75 | ||
| 76 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> | |
| 77 | <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">lgamma</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">a</span><span class="special">)</span> <span class="special">(</span> <span class="keyword">return</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">lgamma</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">mypolicy</span><span class="special">());</span> <span class="special">}</span> | |
| 78 | </pre> | |
| 79 | <p> | |
| 80 | and so on. Note that while a forwarding function is defined for all the special | |
| 81 | functions, however, unless you include the specific header for the special | |
| 82 | function you use (or boost/math/special_functions.hpp to include everything), | |
| 83 | you will get linker errors from functions that are forward declared, but | |
| 84 | not defined. | |
| 85 | </p> | |
| 86 | <p> | |
| 87 | We can do the same thing with the distributions, but this time we need to | |
| 88 | specify the floating-point type to use: | |
| 89 | </p> | |
| 90 | <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">distributions</span><span class="special">/</span><span class="identifier">cauchy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 91 | ||
| 92 | <span class="keyword">namespace</span> <span class="identifier">myspace</span> | |
| 93 | <span class="special">{</span> <span class="comment">// using namespace boost::math::policies; // May be convenient in myspace.</span> | |
| 94 | ||
| 95 | <span class="comment">// Define a policy called my_policy to use.</span> | |
| 96 | <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special">;</span> | |
| 97 | ||
| 98 | <span class="comment">// In this case we want all the distribution accessor functions to compile,</span> | |
| 99 | <span class="comment">// even if they are mathematically undefined, so</span> | |
| 100 | <span class="comment">// make the policy assert_undefined.</span> | |
| 101 | <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">assert_undefined</span><span class="special">;</span> | |
| 102 | ||
| 103 | <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span><span class="identifier">assert_undefined</span><span class="special"><</span><span class="keyword">false</span><span class="special">></span> <span class="special">></span> <span class="identifier">my_policy</span><span class="special">;</span> | |
| 104 | ||
| 105 | <span class="comment">// Finally apply this policy to type double.</span> | |
| 106 | <span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">)</span> | |
| 107 | <span class="special">}</span> <span class="comment">// namespace myspace</span> | |
| 108 | ||
| 109 | <span class="comment">// Now we can use myspace::cauchy etc, which will use policy</span> | |
| 110 | <span class="comment">// myspace::mypolicy:</span> | |
| 111 | <span class="comment">//</span> | |
| 112 | <span class="comment">// This compiles but throws a domain error exception at runtime.</span> | |
| 113 | <span class="comment">// Caution! If you omit the try'n'catch blocks, </span> | |
| 114 | <span class="comment">// it will just silently terminate, giving no clues as to why! </span> | |
| 115 | <span class="comment">// So try'n'catch blocks are very strongly recommended.</span> | |
| 116 | ||
| 117 | <span class="keyword">void</span> <span class="identifier">test_cauchy</span><span class="special">()</span> | |
| 118 | <span class="special">{</span> | |
| 119 | <span class="keyword">try</span> | |
| 120 | <span class="special">{</span> | |
| 121 | <span class="keyword">double</span> <span class="identifier">d</span> <span class="special">=</span> <span class="identifier">mean</span><span class="special">(</span><span class="identifier">myspace</span><span class="special">::</span><span class="identifier">cauchy</span><span class="special">());</span> <span class="comment">// Cauchy does not have a mean!</span> | |
| 122 | <span class="special">}</span> | |
| 123 | <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">domain_error</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> | |
| 124 | <span class="special">{</span> | |
| 125 | <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> | |
| 126 | <span class="special">}</span> | |
| 127 | <span class="special">}</span> | |
| 128 | </pre> | |
| 129 | <p> | |
| 130 | In this example the result of BOOST_MATH_DECLARE_DISTRIBUTIONS is to declare | |
| 131 | a typedef for each distribution like this: | |
| 132 | </p> | |
| 133 | <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">cauchy_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span> <span class="identifier">cauchy</span><span class="special">;</span> | |
| 134 | <span class="identifier">tyepdef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">gamma_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span> <span class="identifier">gamma</span><span class="special">;</span> | |
| 135 | </pre> | |
| 136 | <p> | |
| 137 | and so on. The name given to each typedef is the name of the distribution | |
| 138 | with the "_distribution" suffix removed. | |
| 139 | </p> | |
| 140 | </div> | |
| 141 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 142 | <td align="left"></td> | |
| 143 | <td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal, | |
| 144 | Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert | |
| 145 | Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan Råde, Gautam Sewani, | |
| 146 | Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> | |
| 147 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 148 | file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | |
| 149 | </p> | |
| 150 | </div></td> | |
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