1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Struct deduce_domain</title> 6<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../../proto/reference.html#header.boost.proto.domain_hpp" title="Header <boost/proto/domain.hpp>"> 10<link rel="prev" href="basic_default_domain.html" title="Struct basic_default_domain"> 11<link rel="next" href="is_domain.html" title="Struct template is_domain"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> 16<td align="center"><a href="../../../../index.html">Home</a></td> 17<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="basic_default_domain.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.domain_hpp"><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="is_domain.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="refentry"> 27<a name="boost.proto.deduce_domain"></a><div class="titlepage"></div> 28<div class="refnamediv"> 29<h2><span class="refentrytitle">Struct deduce_domain</span></h2> 30<p>boost::proto::deduce_domain — A pseudo-domain for use in functions and metafunctions that require a domain parameter. 31 It indicates that the domain of the parent node should be inferred from the domains of the child nodes.</p> 32</div> 33<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> 34<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../proto/reference.html#header.boost.proto.domain_hpp" title="Header <boost/proto/domain.hpp>">boost/proto/domain.hpp</a>> 35 36</span> 37<span class="keyword">struct</span> <a class="link" href="deduce_domain.html" title="Struct deduce_domain">deduce_domain</a> <span class="special">{</span> 38<span class="special">}</span><span class="special">;</span></pre></div> 39<div class="refsect1"> 40<a name="id-1.3.33.5.9.7.4"></a><h2>Description</h2> 41<p> 42 When <code class="computeroutput">proto::deduce_domain</code> is used as a domain — either 43 explicitly or implicitly by 44 <code class="computeroutput"><a class="link" href="make_expr.html" title="Function make_expr">proto::make_expr</a>()</code>, 45 <code class="computeroutput"><a class="link" href="unpack_expr.html" title="Function unpack_expr">proto::unpack_expr</a>()</code>, 46 or Proto's operator overloads — Proto will use the domains of the child expressions to 47 compute the domain of the parent. It is done in such a way that (A) expressions in domains 48 that share a common super-domain are interoperable, and (B) expressions that are in 49 the default domain (or a sub-domain thereof) are interoperable with <span class="emphasis"><em>all</em></span> 50 expressions. The rules are as follows: 51 </p> 52<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 53<li class="listitem"> 54 A sub-domain is <span class="emphasis"><em>stronger</em></span> than its super-domain. 55 </li> 56<li class="listitem"> 57<code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code>, 58 <code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code> 59 and all their sub-domains are <span class="emphasis"><em>weaker</em></span> than all other domains. 60 </li> 61<li class="listitem"> 62<code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code> 63 is weaker than 64 <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code>. 65 </li> 66<li class="listitem"> 67 For each child, define a set of domains <span class="emphasis"><em>S<sub>N</sub></em></span> 68 that includes the child's domain and all its super-domains. 69 </li> 70<li class="listitem"> 71 Define a set <span class="emphasis"><em>I<sub>S</sub></em></span> that is the intersection of 72 all the individual sets <span class="emphasis"><em>S<sub>N</sub></em></span> that don't contain 73 <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> or 74 <code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code>. 75 </li> 76<li class="listitem"> 77 Define a set <span class="emphasis"><em>I<sub>W</sub></em></span> that is the intersection of 78 all the individual sets <span class="emphasis"><em>S<sub>N</sub></em></span> that contain 79 <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> or 80 <code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code>. 81 </li> 82<li class="listitem"> 83 Define a set <span class="emphasis"><em>P</em></span> that is the union of 84 <span class="emphasis"><em>I<sub>S</sub></em></span> and 85 <span class="emphasis"><em>I<sub>W</sub></em></span>. 86 </li> 87<li class="listitem"> 88 The common domain is the strongest domain in set <span class="emphasis"><em>P</em></span>, with the 89 following caveats. 90 </li> 91<li class="listitem"> 92 Let <span class="emphasis"><em>U</em></span> be the union of all sets 93 <span class="emphasis"><em>S<sub>N</sub></em></span>. If the result is 94 <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> or 95 <code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code> 96 and <span class="emphasis"><em>U</em></span> contains an element that is <span class="emphasis"><em>not </em></span><code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> or 97 <code class="computeroutput"><a class="link" href="basic_default_domain.html" title="Struct basic_default_domain">proto::basic_default_domain</a></code>, 98 it is an error. 99 </li> 100</ul></div> 101<p> 102 </p> 103<p> 104 Note: the above description sounds like it would be expensive to compute at compile time. 105 In fact, it can all be done using C++ function overloading. 106 </p> 107</div> 108</div> 109<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 110<td align="left"></td> 111<td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p> 112 Distributed under the Boost Software License, Version 1.0. (See accompanying 113 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>) 114 </p> 115</div></td> 116</tr></table> 117<hr> 118<div class="spirit-nav"> 119<a accesskey="p" href="basic_default_domain.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.domain_hpp"><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="is_domain.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 120</div> 121</body> 122</html> 123
