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| <div class="section" lang="en"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="math_toolkit.using_udt.archetypes"></a><a class="link" href="archetypes.html" title="Conceptual Archetypes for Reals and Distributions">Conceptual Archetypes |
| for Reals and Distributions</a> |
| </h3></div></div></div> |
| <p> |
| There are a few concept archetypes available: |
| </p> |
| <div class="itemizedlist"><ul type="disc"> |
| <li> |
| Real concept for floating-point types. |
| </li> |
| <li> |
| distribution Concept for statistical distributions. |
| </li> |
| </ul></div> |
| <a name="math_toolkit.using_udt.archetypes.real_concept"></a><h6> |
| <a name="id1411511"></a> |
| <a class="link" href="archetypes.html#math_toolkit.using_udt.archetypes.real_concept">Real concept</a> |
| </h6> |
| <p> |
| <code class="computeroutput"><span class="identifier">std_real_concept</span></code> is an archetype |
| for theReal types, including the built-in float, double, long double. |
| </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">concepts</span><span class="special">/</span><span class="identifier">std_real_concept</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">concepts</span> |
| <span class="special">{</span> |
| <span class="keyword">class</span> <span class="identifier">std_real_concept</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">}}</span> <span class="comment">// namespaces |
| </span></pre> |
| <p> |
| The main purpose in providing this type is to verify that standard library |
| functions are found via a using declaration - bringing those functions into |
| the current scope - and not just because they happen to be in global scope. |
| </p> |
| <p> |
| In order to ensure that a call to say <code class="computeroutput"><span class="identifier">pow</span></code> |
| can be found either via argument dependent lookup, or failing that then in |
| the std namespace: all calls to standard library functions are unqualified, |
| with the std:: versions found via a <code class="computeroutput"><span class="keyword">using</span></code> |
| declaration to make them visible in the current scope. Unfortunately it's |
| all to easy to forget the <code class="computeroutput"><span class="keyword">using</span></code> |
| declaration, and call the double version of the function that happens to |
| be in the global scope by mistake. |
| </p> |
| <p> |
| For example if the code calls ::pow rather than std::pow, the code will cleanly |
| compile, but truncation of long doubles to double will cause a significant |
| loss of precision. In contrast a template instantiated with std_real_concept |
| will <span class="bold"><strong>only</strong></span> compile if the all the standard |
| library functions used have been brought into the current scope with a using |
| declaration. |
| </p> |
| <a name="math_toolkit.using_udt.archetypes.testing_the_real_concept"></a><h4> |
| <a name="id1411690"></a> |
| <a class="link" href="archetypes.html#math_toolkit.using_udt.archetypes.testing_the_real_concept">Testing |
| the real concept</a> |
| </h4> |
| <p> |
| There is a test program <a href="../../../../../test/std_real_concept_check.cpp" target="_top">libs/math/test/std_real_concept_check.cpp</a> |
| that instantiates every template in this library with type <code class="computeroutput"><span class="identifier">std_real_concept</span></code> to verify its usage of |
| standard library functions. |
| </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">concepts</span><span class="special">/</span><span class="identifier">real_concept</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">concepts</span><span class="special">{</span> |
| |
| <span class="keyword">class</span> <span class="identifier">real_concept</span><span class="special">;</span> |
| |
| <span class="special">}}}</span> <span class="comment">// namespaces |
| </span></pre> |
| <p> |
| <code class="computeroutput"><span class="identifier">real_concept</span></code> is an archetype |
| for <a class="link" href="concepts.html" title="Conceptual Requirements for Real Number Types">user defined real types</a>, |
| it declares its standard library functions in its own namespace: these will |
| only be found if they are called unqualified allowing argument dependent |
| lookup to locate them. In addition this type is useable at runtime: this |
| allows code that would not otherwise be exercised by the built-in floating |
| point types to be tested. There is no std::numeric_limits<> support |
| for this type, since numeric_limits is not a conceptual requirement for |
| <a class="link" href="concepts.html" title="Conceptual Requirements for Real Number Types">RealType</a>s. |
| </p> |
| <p> |
| NTL RR is an example of a type meeting the requirements that this type models, |
| but note that use of a thin wrapper class is required: refer to <a class="link" href="use_ntl.html" title="Using With NTL - a High-Precision Floating-Point Library">"Using |
| With NTL - a High-Precision Floating-Point Library"</a>. |
| </p> |
| <p> |
| There is no specific test case for type <code class="computeroutput"><span class="identifier">real_concept</span></code>, |
| instead, since this type is usable at runtime, each individual test case |
| as well as testing <code class="computeroutput"><span class="keyword">float</span></code>, <code class="computeroutput"><span class="keyword">double</span></code> and <code class="computeroutput"><span class="keyword">long</span> |
| <span class="keyword">double</span></code>, also tests <code class="computeroutput"><span class="identifier">real_concept</span></code>. |
| </p> |
| <a name="math_toolkit.using_udt.archetypes.distribution_concept"></a><h4> |
| <a name="id1411912"></a> |
| <a class="link" href="archetypes.html#math_toolkit.using_udt.archetypes.distribution_concept">Distribution |
| Concept</a> |
| </h4> |
| <p> |
| Distribution Concept models statistical distributions. |
| </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">concepts</span><span class="special">/</span><span class="identifier">distribution</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">concepts</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">RealType</span><span class="special">></span> |
| <span class="keyword">class</span> <span class="identifier">distribution_archetype</span><span class="special">;</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Distribution</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">DistributionConcept</span><span class="special">;</span> |
| |
| <span class="special">}}}</span> <span class="comment">// namespaces |
| </span></pre> |
| <p> |
| The class template <code class="computeroutput"><span class="identifier">distribution_archetype</span></code> |
| is a model of the <a class="link" href="dist_concept.html" title="Conceptual Requirements for Distribution Types">Distribution |
| concept</a>. |
| </p> |
| <p> |
| The class template <code class="computeroutput"><span class="identifier">DistributionConcept</span></code> |
| is a <a href="../../../../../../../libs/concept_check/index.html" target="_top">concept checking |
| class</a> for distribution types. |
| </p> |
| <a name="math_toolkit.using_udt.archetypes.testing_the_distribution_concept"></a><h4> |
| <a name="id1412138"></a> |
| <a class="link" href="archetypes.html#math_toolkit.using_udt.archetypes.testing_the_distribution_concept">Testing |
| the distribution concept</a> |
| </h4> |
| <p> |
| The test program <a href="../../../../../test/compile_test/distribution_concept_check.cpp" target="_top">distribution_concept_check.cpp</a> |
| is responsible for using <code class="computeroutput"><span class="identifier">DistributionConcept</span></code> |
| to verify that all the distributions in this library conform to the <a class="link" href="dist_concept.html" title="Conceptual Requirements for Distribution Types">Distribution concept</a>. |
| </p> |
| <p> |
| The class template <code class="computeroutput"><span class="identifier">DistributionConcept</span></code> |
| verifies the existence (but not proper function) of the non-member accessors |
| required by the <a class="link" href="dist_concept.html" title="Conceptual Requirements for Distribution Types">Distribution |
| concept</a>. These are checked by calls like |
| </p> |
| <p> |
| v = pdf(dist, x); // (Result v is ignored). |
| </p> |
| <p> |
| And in addition, those that accept two arguments do the right thing when |
| the arguments are of different types (the result type is always the same |
| as the distribution's value_type). (This is implemented by some additional |
| forwarding-functions in derived_accessors.hpp, so that there is no need for |
| any code changes. Likewise boilerplate versions of the hazard/chf/coefficient_of_variation |
| functions are implemented in there too.) |
| </p> |
| </div> |
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| <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>) |
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