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diff --git a/doc/html/boost/proto/pack.html b/doc/html/boost/proto/pack.html new file mode 100644 index 0000000000..0845704f10 --- /dev/null +++ b/doc/html/boost/proto/pack.html @@ -0,0 +1,159 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Struct pack</title> +<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> +<link rel="home" href="../../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../../proto/reference.html#header.boost.proto.transform.impl_hpp" title="Header <boost/proto/transform/impl.hpp>"> +<link rel="prev" href="transform_impl.html" title="Struct template transform_impl"> +<link rel="next" href="integral_c.html" title="Struct template integral_c"> +</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="transform_impl.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.transform.impl_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="integral_c.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="refentry"> +<a name="boost.proto.pack"></a><div class="titlepage"></div> +<div class="refnamediv"> +<h2><span class="refentrytitle">Struct pack</span></h2> +<p>boost::proto::pack — To turn an expression into a pseudo-parameter pack containing the + expression's children, for the purpose of expanding the pack expression within + a <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a> or + <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>.</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.transform.impl_hpp" title="Header <boost/proto/transform/impl.hpp>">boost/proto/transform/impl.hpp</a>> + +</span> +<span class="keyword">struct</span> <a class="link" href="pack.html" title="Struct pack">pack</a> <span class="special">{</span> +<span class="special">}</span><span class="special">;</span></pre></div> +<div class="refsect1"> +<a name="id2924760"></a><h2>Description</h2> +<p> + <code class="computeroutput">proto::pack</code> is useful within + <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a>s and + <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>s when one wishes to unpack an expression + into a function call or an object constructor. <code class="computeroutput">proto::pack</code> + turns a Proto expression into a pseudo-parameter pack, which may appear in an unpacking + pattern to be expanded with the "<code class="computeroutput">...</code>" syntax. + </p> +<p> + <span class="bold"><strong>Example:</strong></span> + </p> +<p> + </p> +<pre class="programlisting"><span class="comment">// The following demonstrates how to use a pseudo-pack expansion</span> +<span class="comment">// to unpack an expression into a function call.</span> + +<span class="keyword">struct</span> <span class="identifier">do_sum</span> <span class="special">:</span> <a class="link" href="callable.html" title="Struct callable">proto::callable</a> +<span class="special">{</span> + <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">result_type</span><span class="special">;</span> + + <span class="keyword">int</span> <span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">i</span><span class="special">;</span> <span class="special">}</span> + <span class="keyword">int</span> <span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">j</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">i</span> <span class="special">+</span> <span class="identifier">j</span><span class="special">;</span> <span class="special">}</span> + <span class="keyword">int</span> <span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">j</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">k</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">i</span> <span class="special">+</span> <span class="identifier">j</span> <span class="special">+</span> <span class="identifier">k</span><span class="special">;</span> <span class="special">}</span> +<span class="special">}</span><span class="special">;</span> + +<span class="comment">// Take any n-ary expression where the children are all int terminals and sum all the ints</span> +<span class="keyword">struct</span> <span class="identifier">sum</span> + <span class="special">:</span> <a class="link" href="when.html" title="Struct template when">proto::when</a><span class="special"><</span> + + <span class="comment">// Match any nary expression where the children are all int terminals</span> + <a class="link" href="nary_expr.html" title="Struct template nary_expr">proto::nary_expr</a><span class="special"><</span><a class="link" href="_.html" title="Struct _">_</a><span class="special">,</span> <a class="link" href="vararg.html" title="Struct template vararg">proto::vararg</a><span class="special"><</span><a class="link" href="terminal.html" title="Struct template terminal">proto::terminal</a><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="special">></span> + + <span class="comment">// Turn the current expression into a pseudo-parameter pack, then expand it,</span> + <span class="comment">// extracting the value from each child in turn.</span> + <span class="special">,</span> <span class="identifier">do_sum</span><span class="special">(</span><a class="link" href="_value.html" title="Struct _value">proto::_value</a><span class="special">(</span><span class="identifier">proto</span><span class="special">::</span><span class="identifier">pack</span><span class="special">(</span><a class="link" href="_.html" title="Struct _">_</a><span class="special">)</span><span class="special">)</span><span class="special">...</span><span class="special">)</span> + <span class="special">></span> +<span class="special">{</span><span class="special">}</span><span class="special">;</span> + +<span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="special">)</span> +<span class="special">{</span> + <a class="link" href="terminal.html" title="Struct template terminal">proto::terminal</a><span class="special"><</span><span class="keyword">int</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">{</span><span class="number">42</span><span class="special">}</span><span class="special">;</span> + <span class="keyword">int</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">sum</span><span class="special">(</span><span class="special">)</span><span class="special">(</span> <span class="identifier">i</span><span class="special">(</span><span class="number">3</span><span class="special">,</span><span class="number">5</span><span class="special">)</span> <span class="special">)</span><span class="special">;</span> <span class="comment">// Creates a ternary functional-call expression</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Sum of 42, 3, and 5 : "</span> <span class="special"><<</span> <span class="identifier">result</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> +<span class="special">}</span></pre> +<p> + </p> +<p> + The above program displays: + </p> +<p> + <code class="computeroutput">Sum of 42, 3, and 5 : 50</code> + </p> +<p> + In the above example, the type + <code class="computeroutput"> + <a class="link" href="_value.html" title="Struct _value">proto::_value</a>(proto::pack(<a class="link" href="_.html" title="Struct _">_</a>)) + </code> + is a so-called <span class="emphasis"><em>unpacking pattern</em></span>, described below. + </p> +<p> + <span class="bold"><strong>Unpacking Patterns:</strong></span> + </p> +<p> + Composite transforms (either <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a>s or + <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>s) usually have the form + <code class="computeroutput">X(A<sub>0</sub>,…A<sub>n</sub>)</code>. + However, when the argument list in a composite transform is terminated with a C-style + vararg ellipsis as in <code class="computeroutput">X(A<sub>0</sub>,…A<sub>n</sub> ...)</code>, + the final argument <code class="computeroutput">A<sub>n</sub></code> is treated + as an <span class="emphasis"><em>unpacking pattern</em></span>. + </p> +<p> + An unpacking pattern must itself be a composite transform; that is, it must be a + function type representing either a <a class="link" href="../../CallableTransform.html" title="Concept CallableTransform">CallableTransform</a> or + an <a class="link" href="../../ObjectTransform.html" title="Concept ObjectTransform">ObjectTransform</a>. The type <code class="computeroutput">proto::pack(_)</code> + must appear exactly once in the unpacking pattern. This type will receive a substitution + when the unpacking pattern is expanded. + </p> +<p> + A composite transform like <code class="computeroutput">X(A<sub>0</sub>,…A<sub>n</sub> ...)</code>, + when evaluated against a given expression <em class="replaceable"><code>E</code></em>, state and data, is evaluated as if it were + <code class="computeroutput">X(A<sub>0</sub>,…A<sub>n-1</sub>,<em class="replaceable"><code>S</code></em>)</code> + where <em class="replaceable"><code>S</code></em> is a type sequence computed as follows: + </p> +<p> + Let <code class="computeroutput"><em class="replaceable"><code>SUB</code></em>(A,B)</code> be a type function that replaces every occurence of + <code class="computeroutput">proto::pack(_)</code> within <code class="computeroutput">A</code> with <code class="computeroutput">B</code>. + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + If the expression <em class="replaceable"><code>E</code></em> is a terminal (i.e. it has arity 0), <em class="replaceable"><code>S</code></em> + is the one-element sequence containing <code class="computeroutput"><em class="replaceable"><code>SUB</code></em>(A<sub>n</sub>, <a class="link" href="_value.html" title="Struct _value">proto::_value</a>)</code>. + </li> +<li class="listitem"> + If the expression <em class="replaceable"><code>E</code></em> is a non-terminal, <em class="replaceable"><code>S</code></em> is the sequence + <code class="computeroutput"><em class="replaceable"><code>SUB</code></em>(A<sub>n</sub>, <a class="link" href="_child_c.html" title="Struct template _child_c">proto::_child_c</a><0>),… + <em class="replaceable"><code>SUB</code></em>(A<sub>n</sub>, <a class="link" href="_child_c.html" title="Struct template _child_c">proto::_child_c</a><<em class="replaceable"><code>M</code></em>-1>)</code>, where + <em class="replaceable"><code>M</code></em> is the arity of the expression <em class="replaceable"><code>E</code></em>. + </li> +</ul></div> +<p> + </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> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="transform_impl.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../proto/reference.html#header.boost.proto.transform.impl_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="integral_c.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |