| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Setting Polices at Namespace Scope</title> |
| <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.74.0"> |
| <link rel="home" href="../../../index.html" title="Math Toolkit"> |
| <link rel="up" href="../pol_ref.html" title="Policy Reference"> |
| <link rel="prev" href="policy_defaults.html" title="Using macros to Change the Policy Defaults"> |
| <link rel="next" href="pol_ref_ref.html" title="Policy Class Reference"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="policy_defaults.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../pol_ref.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="pol_ref_ref.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="section" lang="en"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="math_toolkit.policy.pol_ref.namespace_pol"></a><a class="link" href="namespace_pol.html" title="Setting Polices at Namespace Scope"> Setting |
| Polices at Namespace Scope</a> |
| </h4></div></div></div> |
| <p> |
| Sometimes what you really want to do is bring all the special functions, |
| or all the distributions into a specific namespace-scope, along with a |
| specific policy to use with them. There are two macros defined to assist |
| with that: |
| </p> |
| <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> |
| </pre> |
| <p> |
| and: |
| </p> |
| <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> |
| </pre> |
| <p> |
| You can use either of these macros after including any special function |
| or distribution header. For example: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| <span class="comment">//using boost::math::tgamma; |
| </span><span class="comment">// Need not declare using boost::math::tgamma here, |
| </span><span class="comment">// because will define tgamma in myspace using macro below. |
| </span> |
| <span class="keyword">namespace</span> <span class="identifier">myspace</span> |
| <span class="special">{</span> |
| <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> |
| |
| <span class="comment">// Define a policy that does not throw on overflow: |
| </span> <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> |
| |
| <span class="comment">// Define the special functions in this scope to use the policy: |
| </span> <span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">my_policy</span><span class="special">)</span> |
| <span class="special">}</span> |
| |
| <span class="comment">// Now we can use myspace::tgamma etc. |
| </span><span class="comment">// They will automatically use "my_policy": |
| </span><span class="comment">// |
| </span><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><span class="comment">// despite the large value of factorial 30 = 265252859812191058636308480000000 |
| </span><span class="comment">// unlike default policy boost::math::tgamma; |
| </span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| In this example, using BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS results in |
| a set of thin inline forwarding functions being defined: |
| </p> |
| <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> |
| <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> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <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> |
| </pre> |
| <p> |
| and so on. Note that while a forwarding function is defined for all the |
| special functions, however, unless you include the specific header for |
| the special function you use (or boost/math/special_functions.hpp to include |
| everything), you will get linker errors from functions that are forward |
| declared, but not defined. |
| </p> |
| <p> |
| We can do the same thing with the distributions, but this time we need |
| to specify the floating-point type to use: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <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> |
| |
| <span class="keyword">namespace</span> <span class="identifier">myspace</span> |
| <span class="special">{</span> <span class="comment">// using namespace boost::math::policies; // May be convenient in myspace. |
| </span> |
| <span class="comment">// Define a policy called my_policy to use. |
| </span> <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> |
| |
| <span class="comment">// In this case we want all the distribution accessor functions to compile, |
| </span><span class="comment">// even if they are mathematically undefined, so |
| </span><span class="comment">// make the policy assert_undefined. |
| </span> <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> |
| |
| <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> |
| |
| <span class="comment">// Finally apply this policy to type double. |
| </span><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> |
| <span class="special">}</span> <span class="comment">// namespace myspace |
| </span> |
| <span class="comment">// Now we can use myspace::cauchy etc, which will use policy |
| </span><span class="comment">// myspace::mypolicy: |
| </span><span class="comment">// |
| </span><span class="comment">// This compiles but throws a domain error exception at runtime. |
| </span><span class="comment">// Caution! If you omit the try'n'catch blocks, |
| </span><span class="comment">// it will just silently terminate, giving no clues as to why! |
| </span><span class="comment">// So try'n'catch blocks are very strongly recommended. |
| </span> |
| <span class="keyword">void</span> <span class="identifier">test_cauchy</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">try</span> |
| <span class="special">{</span> |
| <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> <span class="special">}</span> |
| <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> |
| <span class="special">{</span> |
| <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> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| In this example the result of BOOST_MATH_DECLARE_DISTRIBUTIONS is to declare |
| a typedef for each distribution like this: |
| </p> |
| <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> |
| <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> |
| </pre> |
| <p> |
| and so on. The name given to each typedef is the name of the distribution |
| with the "_distribution" suffix removed. |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2006 , 2007, 2008, 2009, 2010 John Maddock, Paul A. Bristow, |
| Hubert Holin, Xiaogang Zhang, Bruno Lalande, Johan Råde, Gautam Sewani and |
| Thijs van den Berg<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="policy_defaults.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../pol_ref.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="pol_ref_ref.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |