File: function_hooks.html

package info (click to toggle)
boost1.55 1.55.0%2Bdfsg-3
  • links: PTS, VCS
  • area: main
  • in suites: jessie, jessie-kfreebsd
  • size: 487,824 kB
  • ctags: 673,349
  • sloc: cpp: 2,098,430; xml: 106,036; ansic: 46,744; python: 32,427; sh: 11,864; cs: 2,121; asm: 1,640; makefile: 984; perl: 714; yacc: 456; php: 132; fortran: 43; sql: 13; csh: 6
file content (146 lines) | stat: -rw-r--r-- 16,244 bytes parent folder | download 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
 
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Using function hooks</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../intrusive.html" title="Chapter&#160;15.&#160;Boost.Intrusive">
<link rel="prev" href="clone_from.html" title="Cloning Boost.Intrusive containers">
<link rel="next" href="recursive.html" title="Recursive Boost.Intrusive containers">
</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="clone_from.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="recursive.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="intrusive.function_hooks"></a><a class="link" href="function_hooks.html" title="Using function hooks">Using function hooks</a>
</h2></div></div></div>
<p>
      A programmer might find that base or member hooks are not flexible enough in
      some situations. In some applications it would be optimal to put a hook deep
      inside a member of a class or just outside the class. <span class="bold"><strong>Boost.Intrusive</strong></span>
      has an easy option to allow such cases: <code class="computeroutput"><a class="link" href="../boost/intrusive/function_hook.html" title="Struct template function_hook">function_hook</a></code>.
    </p>
<p>
      This option is similar to <code class="computeroutput"><a class="link" href="../boost/intrusive/member_hook.html" title="Struct template member_hook">member_hook</a></code>
      or <code class="computeroutput"><a class="link" href="../boost/intrusive/base_hook.html" title="Struct template base_hook">base_hook</a></code>, but
      the programmer can specify a function object that tells the container how to
      obtain a hook from a value and vice versa. The programmer just needs to define
      the following function object:
    </p>
<pre class="programlisting"><span class="comment">//This functor converts between value_type and a hook_type</span>
<span class="keyword">struct</span> <span class="identifier">Functor</span>
<span class="special">{</span>
   <span class="comment">//Required types</span>
   <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span>      <span class="identifier">hook_type</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span>      <span class="identifier">hook_ptr</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span>      <span class="identifier">const_hook_ptr</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span>      <span class="identifier">value_type</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span>      <span class="identifier">pointer</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span>      <span class="identifier">const_pointer</span><span class="special">;</span>
   <span class="comment">//Required static functions</span>
   <span class="keyword">static</span> <span class="identifier">hook_ptr</span> <span class="identifier">to_hook_ptr</span> <span class="special">(</span><span class="identifier">value_type</span> <span class="special">&amp;</span><span class="identifier">value</span><span class="special">);</span>
   <span class="keyword">static</span> <span class="identifier">const_hook_ptr</span> <span class="identifier">to_hook_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span><span class="identifier">value</span><span class="special">);</span>
   <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">hook_ptr</span> <span class="identifier">n</span><span class="special">);</span>
   <span class="keyword">static</span> <span class="identifier">const_pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">const_hook_ptr</span> <span class="identifier">n</span><span class="special">);</span>
<span class="special">};</span>
</pre>
<p>
      Converting from values to hooks is generally easy, since most hooks are in
      practice members or base classes of class data members. The inverse operation
      is a bit more complicated, but <span class="bold"><strong>Boost.Intrusive</strong></span>
      offers a bit of help with the function <code class="computeroutput"><a class="link" href="../boost/intrusive/get_parent_fro_idp33907928.html" title="Function template get_parent_from_member">get_parent_from_member</a></code>,
      which allows easy conversions from the address of a data member to the address
      of the parent holding that member. Let's see a little example of <code class="computeroutput"><a class="link" href="../boost/intrusive/function_hook.html" title="Struct template function_hook">function_hook</a></code>:
    </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">parent_from_member</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>

<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive</span><span class="special">;</span>

<span class="keyword">struct</span> <span class="identifier">MyClass</span>
<span class="special">{</span>
   <span class="keyword">int</span> <span class="identifier">dummy</span><span class="special">;</span>
   <span class="comment">//This internal type has a member hook</span>
   <span class="keyword">struct</span> <span class="identifier">InnerNode</span>
   <span class="special">{</span>
      <span class="keyword">int</span> <span class="identifier">dummy</span><span class="special">;</span>
      <span class="identifier">list_member_hook</span><span class="special">&lt;&gt;</span> <span class="identifier">hook</span><span class="special">;</span>
   <span class="special">}</span> <span class="identifier">inner</span><span class="special">;</span>
<span class="special">};</span>

<span class="comment">//This functor converts between MyClass and InnerNode's member hook</span>
<span class="keyword">struct</span> <span class="identifier">Functor</span>
<span class="special">{</span>
   <span class="comment">//Required types</span>
   <span class="keyword">typedef</span> <span class="identifier">list_member_hook</span><span class="special">&lt;&gt;</span>    <span class="identifier">hook_type</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">hook_type</span><span class="special">*</span>            <span class="identifier">hook_ptr</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">hook_type</span><span class="special">*</span>      <span class="identifier">const_hook_ptr</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">MyClass</span>               <span class="identifier">value_type</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">value_type</span><span class="special">*</span>           <span class="identifier">pointer</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">value_type</span><span class="special">*</span>     <span class="identifier">const_pointer</span><span class="special">;</span>

   <span class="comment">//Required static functions</span>
   <span class="keyword">static</span> <span class="identifier">hook_ptr</span> <span class="identifier">to_hook_ptr</span> <span class="special">(</span><span class="identifier">value_type</span> <span class="special">&amp;</span><span class="identifier">value</span><span class="special">)</span>
      <span class="special">{</span>  <span class="keyword">return</span> <span class="special">&amp;</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">inner</span><span class="special">.</span><span class="identifier">hook</span><span class="special">;</span> <span class="special">}</span>
   <span class="keyword">static</span> <span class="identifier">const_hook_ptr</span> <span class="identifier">to_hook_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span><span class="identifier">value</span><span class="special">)</span>
      <span class="special">{</span>  <span class="keyword">return</span> <span class="special">&amp;</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">inner</span><span class="special">.</span><span class="identifier">hook</span><span class="special">;</span> <span class="special">}</span>
   <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">hook_ptr</span> <span class="identifier">n</span><span class="special">)</span>
   <span class="special">{</span>
      <span class="keyword">return</span> <span class="identifier">get_parent_from_member</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;</span>
         <span class="special">(</span><span class="identifier">get_parent_from_member</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">&gt;(</span><span class="identifier">n</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">::</span><span class="identifier">hook</span><span class="special">)</span>
         <span class="special">,&amp;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">inner</span>
      <span class="special">);</span>
   <span class="special">}</span>
   <span class="keyword">static</span> <span class="identifier">const_pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">const_hook_ptr</span> <span class="identifier">n</span><span class="special">)</span>
   <span class="special">{</span>
      <span class="keyword">return</span> <span class="identifier">get_parent_from_member</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;</span>
         <span class="special">(</span><span class="identifier">get_parent_from_member</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">&gt;(</span><span class="identifier">n</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">::</span><span class="identifier">hook</span><span class="special">)</span>
         <span class="special">,&amp;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">inner</span>
      <span class="special">);</span>
   <span class="special">}</span>
<span class="special">};</span>

<span class="comment">//Define a list that will use the hook accessed through the function object</span>
<span class="keyword">typedef</span> <span class="identifier">list</span><span class="special">&lt;</span> <span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">function_hook</span><span class="special">&lt;</span> <span class="identifier">Functor</span><span class="special">&gt;</span> <span class="special">&gt;</span>  <span class="identifier">List</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="identifier">MyClass</span> <span class="identifier">n</span><span class="special">;</span>
   <span class="identifier">List</span> <span class="identifier">l</span><span class="special">;</span>
   <span class="comment">//Insert the node in both lists</span>
   <span class="identifier">l</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">n</span><span class="special">);</span>
   <span class="identifier">assert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
   <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
    </p>
</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 &#169; 2005 Olaf Krzikalla<br>Copyright &#169; 2006-2013 Ion Gaztanaga<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="clone_from.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="recursive.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>