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| <h2><span class="refentrytitle">Struct deduce_domain</span></h2> |
| <p>boost::proto::deduce_domain — A pseudo-domain for use in functions and metafunctions that require a domain parameter. |
| It indicates that the domain of the parent node should be inferred from the domains of the child nodes.</p> |
| </div> |
| <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> |
| <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>> |
| |
| </span> |
| <span class="keyword">struct</span> <a class="link" href="deduce_domain.html" title="Struct deduce_domain">deduce_domain</a> <span class="special">{</span> |
| <span class="special">}</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="id2276149"></a><h2>Description</h2> |
| <p> |
| When <code class="computeroutput">proto::deduce_domain</code> is used as a domain — either |
| explicitly or implicitly by |
| <code class="computeroutput"><a class="link" href="make_expr_id1265715.html" title="Function make_expr">proto::make_expr</a>()</code>, |
| <code class="computeroutput"><a class="link" href="unpack_expr_id1265992.html" title="Function unpack_expr">proto::unpack_expr</a>()</code>, |
| or Proto's operator overloads — Proto will use the domains of the child expressions to |
| compute the domain of the parent. It is done in such a way that (A) expressions in domains |
| that share a common super-domain are interoperable, and (B) expressions that are in |
| the default domain (or a sub-domain thereof) are interoperable with <span class="emphasis"><em>all</em></span> |
| expressions. The rules are as follows: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| A sub-domain is <span class="emphasis"><em>stronger</em></span> than its super-domain. |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> |
| and all its sub-domains are <span class="emphasis"><em>weaker</em></span> than all other domains. |
| </li> |
| <li class="listitem"> |
| For each child, define a set of domains <span class="emphasis"><em>S<sub>N</sub></em></span> |
| that includes the child's domain and all its super-domains. |
| </li> |
| <li class="listitem"> |
| Define a set <span class="emphasis"><em>I<sub>S</sub></em></span> that is the intersection of |
| all the individual sets <span class="emphasis"><em>S<sub>N</sub></em></span> that don't contain |
| <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code>. |
| </li> |
| <li class="listitem"> |
| Define a set <span class="emphasis"><em>I<sub>W</sub></em></span> that is the intersection of |
| all the individual sets <span class="emphasis"><em>S<sub>N</sub></em></span> that contain |
| <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code>. |
| </li> |
| <li class="listitem"> |
| Define a set <span class="emphasis"><em>P</em></span> that is the union of |
| <span class="emphasis"><em>I<sub>S</sub></em></span> and |
| <span class="emphasis"><em>I<sub>W</sub></em></span>. |
| </li> |
| <li class="listitem"> |
| The common domain is the strongest domain in set <span class="emphasis"><em>P</em></span>, with the |
| following caveat. |
| </li> |
| <li class="listitem"> |
| Let <span class="emphasis"><em>U</em></span> be the union of all sets |
| <span class="emphasis"><em>S<sub>N</sub></em></span>. If the result is |
| <code class="computeroutput"><a class="link" href="default_domain.html" title="Struct default_domain">proto::default_domain</a></code> |
| 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>, |
| it is an error. |
| </li> |
| </ul></div> |
| <p> |
| </p> |
| <p> |
| Note: the above description sounds like it would be expensive to compute at compile time. |
| In fact, it can all be done using C++ function overloading. |
| </p> |
| </div> |
| </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 © 2008 Eric Niebler<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> |
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