1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Complex - Fully Integrated</title> 5<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../index.html" title="Spirit 2.5.8"> 8<link rel="up" href="../tutorials.html" title="Tutorials"> 9<link rel="prev" href="karma_easier_complex.html" title="Complex - Made easier"> 10<link rel="next" href="num_list.html" title="Number List - Printing Numbers From a std::vector"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="karma_easier_complex.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorials.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="num_list.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="spirit.karma.tutorials.karma_adapted_complex"></a><a class="link" href="karma_adapted_complex.html" title="Complex - Fully Integrated">Complex 28 - Fully Integrated</a> 29</h4></div></div></div> 30<p> 31 Until now, we have been working around the fact that <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><></span></code> is not a native <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> 32 sequence. We have not been able to use it with the same simplicity and 33 natural grace of a <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">tuple</span><span class="special"><></span></code> or a similar <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> 34 data structure. Fortunately, starting with Boost V1.43 it is possible to 35 adapt any data structure (not only, as before, structures with publicly 36 accessible members) as a <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> 37 sequence. All we have to do is to employ one of the new <code class="computeroutput"><span class="identifier">BOOST_FUSION_ADAPT_ADT</span></code> 38 macros. 39 </p> 40<h6> 41<a name="spirit.karma.tutorials.karma_adapted_complex.h0"></a> 42 <span class="phrase"><a name="spirit.karma.tutorials.karma_adapted_complex.adapting_a_class_as_a_fusion_sequence"></a></span><a class="link" href="karma_adapted_complex.html#spirit.karma.tutorials.karma_adapted_complex.adapting_a_class_as_a_fusion_sequence">Adapting 43 a Class As a Fusion Sequence</a> 44 </h6> 45<p> 46 Let us start with the code again, following up with the explanations afterwards. 47 </p> 48<p> 49 Wouldn't it be optimal if we could pass our instance of a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><></span></code> 50 directly to <span class="emphasis"><em>Karma's</em></span> <code class="computeroutput"><span class="identifier">generate</span><span class="special">()</span></code> function: 51 </p> 52<p> 53</p> 54<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">OutputIterator</span><span class="special">></span> 55<span class="keyword">bool</span> <span class="identifier">generate_complex</span><span class="special">(</span><span class="identifier">OutputIterator</span> <span class="identifier">sink</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">c</span><span class="special">)</span> 56<span class="special">{</span> 57 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span> 58 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">bool_</span><span class="special">;</span> 59 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">true_</span><span class="special">;</span> 60 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">omit</span><span class="special">;</span> 61 <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">generate</span><span class="special">;</span> 62 63 <span class="keyword">return</span> <span class="identifier">generate</span><span class="special">(</span><span class="identifier">sink</span><span class="special">,</span> 64 65 <span class="comment">// Begin grammar</span> 66 <span class="special">(</span> 67 <span class="special">&</span><span class="identifier">true_</span> <span class="special"><<</span> <span class="char">'('</span> <span class="special"><<</span> <span class="identifier">double_</span> <span class="special"><<</span> <span class="string">", "</span> <span class="special"><<</span> <span class="identifier">double_</span> <span class="special"><<</span> <span class="char">')'</span> 68 <span class="special">|</span> <span class="identifier">omit</span><span class="special">[</span><span class="identifier">bool_</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">double_</span> <span class="special"><<</span> <span class="identifier">omit</span><span class="special">[</span><span class="identifier">double_</span><span class="special">]</span> 69 <span class="special">),</span> 70 <span class="comment">// End grammar</span> 71 72 <span class="identifier">c</span> <span class="comment">// Data to output</span> 73 <span class="special">);</span> 74<span class="special">}</span> 75</pre> 76<p> 77 </p> 78<p> 79 Indeed, this is possible! All we have to supply to make this work is a 80 magic incantation (somewhere in the global namespace): 81 </p> 82<p> 83</p> 84<pre class="programlisting"><span class="comment">// We can leave off the setters as Karma does not need them.</span> 85<span class="identifier">BOOST_FUSION_ADAPT_ADT</span><span class="special">(</span> 86 <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">>,</span> 87 <span class="special">(</span><span class="keyword">bool</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">,</span> <span class="identifier">obj</span><span class="special">.</span><span class="identifier">imag</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span><span class="special">,</span> <span class="comment">/**/</span><span class="special">)</span> 88 <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">obj</span><span class="special">.</span><span class="identifier">real</span><span class="special">(),</span> <span class="comment">/**/</span><span class="special">)</span> 89 <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">obj</span><span class="special">.</span><span class="identifier">imag</span><span class="special">(),</span> <span class="comment">/**/</span><span class="special">)</span> 90<span class="special">)</span> 91</pre> 92<p> 93 </p> 94<p> 95 Most of the formatting grammar itself has not changed from the last section. 96 We still utilize a very similar scheme. We have an alternative providing 97 the formatting rules for our both use cases: one for the full complex format 98 and one for complex numbers with a zero imaginary part. But instead of 99 selecting the required alternative by comparing the imaginary part to zero 100 in the grammar we assume to receive a boolean attribute carrying this information: 101 </p> 102<pre class="programlisting"><span class="special">&</span><span class="identifier">true_</span> <span class="special"><<</span> <span class="string">"("</span> <span class="special"><<</span> <span class="identifier">double_</span> <span class="special"><<</span> <span class="string">", "</span> <span class="special"><<</span> <span class="identifier">double_</span> <span class="special"><<</span> <span class="string">")"</span> 103</pre> 104<p> 105 This reads as: 'if the first (boolean) element of the supplied fusion sequence 106 is <code class="computeroutput"><span class="keyword">true</span></code>, proceed as specified, 107 else select the next alternative'. The next alternative now accounts for 108 the boolean element as well, but is otherwise (almost) unchanged from the 109 last section's example. 110 </p> 111<p> 112 Now it should be clear why our adapt construct above exposes a three element 113 <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a> 114 sequence: a boolean and two double values (the real and the imaginary part 115 of the complex number). We want it to match the requirements of our formatting 116 grammar, which expects those exact values. The <code class="computeroutput"><span class="identifier">BOOST_FUSION_ADAPT_ADT</span></code> 117 macro allows us to specify an arbitrary accessor construct, not necessarily 118 limited to just calling a member function of the object instance (represented 119 by <code class="computeroutput"><span class="identifier">obj</span></code> in the context of 120 this macro). This allows us to nicely encapsulate the decision logic into 121 the class adaptation. 122 </p> 123<p> 124 Here is the last new bit of information. If you look closely you realize 125 the second alternative to be 'shorter' than the first one. It consumes 126 only two elements of the supplied fusion sequence: it ignores the boolean 127 and uses the real part of the complex number to generate its output. If 128 there are more elements in our attribute than needed, we now can safely 129 omit them from the grammar (which is a new 'feature' added to <a href="http://boost-spirit.com" target="_top">Spirit</a> 130 in V1.43 as well). Note, we could have written the alternative as 131 </p> 132<pre class="programlisting"><span class="special">&</span><span class="identifier">false_</span> <span class="special"><<</span> <span class="identifier">double_</span> 133</pre> 134<p> 135 but this would have been a bit less efficient as we needed to compare the 136 boolean value again, while the final solution provided will just ignore 137 it. 138 </p> 139</div> 140<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 141<td align="left"></td> 142<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 143 Distributed under the Boost Software License, Version 1.0. (See accompanying 144 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>) 145 </p> 146</div></td> 147</tr></table> 148<hr> 149<div class="spirit-nav"> 150<a accesskey="p" href="karma_easier_complex.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorials.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="num_list.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 151</div> 152</body> 153</html> 154
