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diff --git a/libs/phoenix/doc/html/phoenix/modules/function.html b/libs/phoenix/doc/html/phoenix/modules/function.html new file mode 100644 index 0000000000..c9a0a40612 --- /dev/null +++ b/libs/phoenix/doc/html/phoenix/modules/function.html @@ -0,0 +1,150 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Function</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="Chapter 1. Phoenix 3.0"> +<link rel="up" href="../modules.html" title="Modules"> +<link rel="prev" href="core/nothing.html" title="Nothing"> +<link rel="next" href="function/adapting_functions.html" title="Adapting Functions"> +</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="core/nothing.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../modules.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="function/adapting_functions.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="phoenix.modules.function"></a><a class="link" href="function.html" title="Function">Function</a> +</h3></div></div></div> +<div class="toc"><dl><dt><span class="section"><a href="function/adapting_functions.html">Adapting + Functions</a></span></dt></dl></div> +<p> + The <code class="computeroutput"><span class="identifier">function</span></code> class template + provides a mechanism for implementing lazily evaluated functions. Syntactically, + a lazy function looks like an ordinary C/C++ function. The function call + looks familiar and feels the same as ordinary C++ functions. However, unlike + ordinary functions, the actual function execution is deferred. + </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">phoenix</span><span class="special">/</span><span class="identifier">function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> +</pre> +<p> + Unlike ordinary function pointers or functor objects that need to be explicitly + bound through the bind function (see <a class="link" href="bind.html" title="Bind">Bind</a>), + the argument types of these functions are automatically lazily bound. + </p> +<p> + In order to create a lazy function, we need to implement a model of the + <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/functional/concepts/poly.html" target="_top">Polymorphic + Function Object</a> concept. For a function that takes <code class="computeroutput"><span class="identifier">N</span></code> arguments, a model of <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/functional/concepts/poly.html" target="_top">Polymorphic + Function Object</a> must provide: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + An <code class="computeroutput"><span class="keyword">operator</span><span class="special">()</span></code> + that takes <code class="computeroutput"><span class="identifier">N</span></code> arguments, + and implements the function logic. This is also true for ordinary function + pointers. + </li> +<li class="listitem"> + A nested metafunction <code class="computeroutput"><span class="identifier">result</span><span class="special"><</span><span class="identifier">Signature</span><span class="special">></span></code> or nested typedef <code class="computeroutput"><span class="identifier">result_type</span></code>, + following the <a href="http://www.boost.org/doc/libs/release/libs/utility/utility.htm#result_of" target="_top">Boost.Result + Of</a> Protocol + </li> +</ul></div> +<p> + For example, the following type implements the FunctionEval concept, in order + to provide a lazy factorial function: + </p> +<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">factorial_impl</span> +<span class="special">{</span> + <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">></span> + <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span> + + <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">This</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></span> + <span class="keyword">struct</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span><span class="special">(</span><span class="identifier">Arg</span> <span class="keyword">const</span> <span class="special">&)></span> + <span class="special">{</span> + <span class="keyword">typedef</span> <span class="identifier">Arg</span> <span class="identifier">type</span><span class="special">;</span> + <span class="special">};</span> + + <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></span> + <span class="identifier">Arg</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Arg</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span> + <span class="special">{</span> + <span class="keyword">return</span> <span class="special">(</span><span class="identifier">n</span> <span class="special"><=</span> <span class="number">0</span><span class="special">)</span> <span class="special">?</span> <span class="number">1</span> <span class="special">:</span> <span class="identifier">n</span> <span class="special">*</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)(</span><span class="identifier">n</span><span class="special">-</span><span class="number">1</span><span class="special">);</span> + <span class="special">}</span> +<span class="special">};</span> +</pre> +<p> + (See <a href="../../../../example/factorial.cpp" target="_top">factorial.cpp</a>) + </p> +<p> + Having implemented the <code class="computeroutput"><span class="identifier">factorial_impl</span></code> + type, we can declare and instantiate a lazy <code class="computeroutput"><span class="identifier">factorial</span></code> + function this way: + </p> +<pre class="programlisting"><span class="identifier">function</span><span class="special"><</span><span class="identifier">factorial_impl</span><span class="special">></span> <span class="identifier">factorial</span><span class="special">;</span> +</pre> +<p> + Invoking a lazy function such as <code class="computeroutput"><span class="identifier">factorial</span></code> + does not immediately execute the function object <code class="computeroutput"><span class="identifier">factorial_impl</span></code>. + Instead, an <a class="link" href="../actor.html" title="Actor">actor</a> object is created + and returned to the caller. Example: + </p> +<pre class="programlisting"><span class="identifier">factorial</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">)</span> +</pre> +<p> + does nothing more than return an actor. A second function call will invoke + the actual factorial function. Example: + </p> +<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">)(</span><span class="number">4</span><span class="special">);</span> +</pre> +<p> + will print out "24". + </p> +<p> + Take note that in certain cases (e.g. for function objects with state), an + instance of the model of <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/functional/concepts/poly.html" target="_top">Polymorphic + Function Object</a> may be passed on to the constructor. Example: + </p> +<pre class="programlisting"><span class="identifier">function</span><span class="special"><</span><span class="identifier">factorial_impl</span><span class="special">></span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">ftor</span><span class="special">);</span> +</pre> +<p> + where ftor is an instance of factorial_impl (this is not necessary in this + case as <code class="computeroutput"><span class="identifier">factorial_impl</span></code> does + not require any state). + </p> +<div class="important"><table border="0" summary="Important"> +<tr> +<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../../doc/src/images/important.png"></td> +<th align="left">Important</th> +</tr> +<tr><td align="left" valign="top"><p> + Take care though when using function objects with state because they are + often copied repeatedly, and state may change in one of the copies, rather + than the original. + </p></td></tr> +</table></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 © 2002-2005, 2010 Joel de Guzman, Dan Marsden, Thomas Heller<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="core/nothing.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../modules.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="function/adapting_functions.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |