1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Notes</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Fusion 2.2"> 8<link rel="up" href="../index.html" title="Chapter 1. Fusion 2.2"> 9<link rel="prev" href="functional/generation/metafunctions/mk_unfused.html" title="make_unfused"> 10<link rel="next" href="change_log.html" title="Change log"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="functional/generation/metafunctions/mk_unfused.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="change_log.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="fusion.notes"></a><a class="link" href="notes.html" title="Notes">Notes</a> 28</h2></div></div></div> 29<h4> 30<a name="fusion.notes.h0"></a> 31 <span class="phrase"><a name="fusion.notes.recursive_inlined_functions"></a></span><a class="link" href="notes.html#fusion.notes.recursive_inlined_functions">Recursive 32 Inlined Functions</a> 33 </h4> 34<p> 35 An interesting peculiarity of functions like <a class="link" href="sequence/intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a> when applied to a <a class="link" href="sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward 36 Sequence</a> like <a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a> 37 is that what could have been linear runtime complexity effectively becomes 38 constant O(1) due to compiler optimization of C++ inlined functions, however 39 deeply recursive (up to a certain compiler limit of course). Compile time complexity 40 remains linear. 41 </p> 42<h4> 43<a name="fusion.notes.h1"></a> 44 <span class="phrase"><a name="fusion.notes.overloaded_functions"></a></span><a class="link" href="notes.html#fusion.notes.overloaded_functions">Overloaded 45 Functions</a> 46 </h4> 47<p> 48 Associative sequences use function overloading to implement membership testing 49 and type associated key lookup. This amounts to constant runtime and amortized 50 constant compile time complexities. There is an overloaded function, <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>, for each key <span class="emphasis"><em>type</em></span> <code class="computeroutput"><span class="identifier">k</span></code>. The compiler chooses the appropriate function 51 given a key, <code class="computeroutput"><span class="identifier">k</span></code>. 52 </p> 53<h4> 54<a name="fusion.notes.h2"></a> 55 <span class="phrase"><a name="fusion.notes.tag_dispatching"></a></span><a class="link" href="notes.html#fusion.notes.tag_dispatching">Tag 56 Dispatching</a> 57 </h4> 58<p> 59 Tag dispatching is a generic programming technique for selecting template specializations. 60 There are typically 3 components involved in the tag dispatching mechanism: 61 </p> 62<div class="orderedlist"><ol class="orderedlist" type="1"> 63<li class="listitem"> 64 A type for which an appropriate template specialization is required 65 </li> 66<li class="listitem"> 67 A metafunction that associates the type with a tag type 68 </li> 69<li class="listitem"> 70 A template that is specialized for the tag type 71 </li> 72</ol></div> 73<p> 74 For example, the fusion <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">begin</span></code> metafunction 75 is implemented as follows: 76 </p> 77<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span> 78<span class="keyword">struct</span> <span class="identifier">begin</span> 79<span class="special">{</span> 80 <span class="keyword">typedef</span> <span class="keyword">typename</span> 81 <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">begin_impl</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span><span class="special"><</span><span class="identifier">Sequence</span><span class="special">>::</span><span class="identifier">type</span><span class="special">>::</span> 82 <span class="keyword">template</span> <span class="identifier">apply</span><span class="special"><</span><span class="identifier">Sequence</span><span class="special">>::</span><span class="identifier">type</span> 83 <span class="identifier">type</span><span class="special">;</span> 84<span class="special">};</span> 85</pre> 86<p> 87 In the case: 88 </p> 89<div class="orderedlist"><ol class="orderedlist" type="1"> 90<li class="listitem"> 91 <code class="computeroutput"><span class="identifier">Sequence</span></code> is the type for 92 which a suitable implementation of <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">begin_impl</span></code> 93 is required 94 </li> 95<li class="listitem"> 96 <code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">tag_of</span></code> is the metafunction that associates 97 <code class="computeroutput"><span class="identifier">Sequence</span></code> with an appropriate 98 tag 99 </li> 100<li class="listitem"> 101 <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">begin_impl</span></code> is the template which is specialized 102 to provide an implementation for each tag type 103 </li> 104</ol></div> 105<h4> 106<a name="fusion.notes.h3"></a> 107 <span class="phrase"><a name="fusion.notes.extensibility"></a></span><a class="link" href="notes.html#fusion.notes.extensibility">Extensibility</a> 108 </h4> 109<p> 110 Unlike <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a>, there is no 111 extensible sequence concept in fusion. This does not mean that Fusion sequences 112 are not extensible. In fact, all Fusion sequences are inherently extensible. 113 It is just that the manner of sequence extension in Fusion is different from 114 both <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a> 115 and <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a> on account of the 116 lazy nature of fusion <a class="link" href="algorithm.html" title="Algorithm">Algorithms</a>. 117 <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a> 118 containers extend themselves in place though member functions such as <a class="link" href="algorithm/transformation/functions/push_back.html" title="push_back"><code class="computeroutput"><span class="identifier">push_back</span></code></a> and <a class="link" href="algorithm/transformation/functions/insert.html" title="insert"><code class="computeroutput"><span class="identifier">insert</span></code></a>. <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a> 119 sequences, on the other hand, are extended through "intrinsic" functions 120 that actually return whole sequences. <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a> 121 is purely functional and can not have side effects. For example, <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a>'s 122 <code class="computeroutput"><span class="identifier">push_back</span></code> does not actually 123 mutate an <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span></code>. It can't do that. Instead, it returns 124 an extended <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">vector</span></code>. 125 </p> 126<p> 127 Like <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a>, Fusion too is 128 purely functional and can not have side effects. With runtime efficiency in 129 mind, Fusion sequences are extended through generic functions that return 130 <a class="link" href="view.html" title="View">Views</a>. <a class="link" href="view.html" title="View">Views</a> 131 are sequences that do not actually contain data, but instead impart an alternative 132 presentation over the data from one or more underlying sequences. <a class="link" href="view.html" title="View">Views</a> 133 are proxies. They provide an efficient yet purely functional way to work on 134 potentially expensive sequence operations. For example, given a <a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a>, Fusion's <a class="link" href="algorithm/transformation/functions/push_back.html" title="push_back"><code class="computeroutput"><span class="identifier">push_back</span></code></a> returns a <a class="link" href="view/joint_view.html" title="joint_view"><code class="computeroutput"><span class="identifier">joint_view</span></code></a>, instead of an actual extended 135 <a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a>. 136 A <a class="link" href="view/joint_view.html" title="joint_view"><code class="computeroutput"><span class="identifier">joint_view</span></code></a> 137 holds a reference to the original sequence plus the appended data --making 138 it very cheap to pass around. 139 </p> 140<h4> 141<a name="fusion.notes.h4"></a> 142 <span class="phrase"><a name="fusion.notes.element_conversion"></a></span><a class="link" href="notes.html#fusion.notes.element_conversion">Element 143 Conversion</a> 144 </h4> 145<p> 146 Functions that take in elemental values to form sequences (e.g. <a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a>) convert their arguments 147 to something suitable to be stored as a sequence element. In general, the element 148 types are stored as plain values. Example: 149 </p> 150<pre class="programlisting"><a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="char">'x'</span><span class="special">)</span> 151</pre> 152<p> 153 returns a <a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a><code class="computeroutput"><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> 154 <span class="keyword">char</span><span class="special">></span></code>. 155 </p> 156<p> 157 There are a few exceptions, however. 158 </p> 159<p> 160 <span class="bold"><strong>Arrays:</strong></span> 161 </p> 162<p> 163 Array arguments are deduced to reference to const types. For example <a href="#ftn.fusion.notes.f0" class="footnote" name="fusion.notes.f0"><sup class="footnote">[14]</sup></a>: 164 </p> 165<pre class="programlisting"><a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="string">"Donald"</span><span class="special">,</span> <span class="string">"Daisy"</span><span class="special">)</span> 166</pre> 167<p> 168 creates a <a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a> 169 of type 170 </p> 171<pre class="programlisting"><a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a><span class="special"><</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">(&)[</span><span class="number">7</span><span class="special">],</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">(&)[</span><span class="number">6</span><span class="special">]></span> 172</pre> 173<p> 174 <span class="bold"><strong>Function pointers:</strong></span> 175 </p> 176<p> 177 Function pointers are deduced to the plain non-reference type (i.e. to plain 178 function pointer). Example: 179 </p> 180<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">);</span> 181 <span class="special">...</span> 182<a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(&</span><span class="identifier">f</span><span class="special">);</span> 183</pre> 184<p> 185 creates a <a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a> 186 of type 187 </p> 188<pre class="programlisting"><a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a><span class="special"><</span><span class="keyword">void</span> <span class="special">(*)(</span><span class="keyword">int</span><span class="special">)></span> 189</pre> 190<h4> 191<a name="fusion.notes.h5"></a> 192 <span class="phrase"><a name="fusion.notes.reference_wrappers"></a></span><a class="link" href="notes.html#fusion.notes.reference_wrappers">Reference 193 Wrappers</a> 194 </h4> 195<p> 196 Fusion's generation functions (e.g. <a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a>) by default stores the element 197 types as plain non-reference types. Example: 198 </p> 199<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">A</span><span class="special">&</span> <span class="identifier">a</span><span class="special">,</span> <span class="identifier">B</span><span class="special">&</span> <span class="identifier">b</span><span class="special">)</span> <span class="special">{</span> 200 <span class="special">...</span> 201 <a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span> 202</pre> 203<p> 204 creates a <a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a> 205 of type 206 </p> 207<pre class="programlisting"><a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a><span class="special"><</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">></span> 208</pre> 209<p> 210 Sometimes the plain non-reference type is not desired. You can use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ref</span></code> 211 and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cref</span></code> to store references or const references 212 (respectively) instead. The mechanism does not compromise const correctness 213 since a const object wrapped with ref results in a tuple element with const 214 reference type (see the fifth code line below). Examples: 215 </p> 216<p> 217 For example: 218 </p> 219<pre class="programlisting"><span class="identifier">A</span> <span class="identifier">a</span><span class="special">;</span> <span class="identifier">B</span> <span class="identifier">b</span><span class="special">;</span> <span class="keyword">const</span> <span class="identifier">A</span> <span class="identifier">ca</span> <span class="special">=</span> <span class="identifier">a</span><span class="special">;</span> 220<a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="identifier">cref</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">b</span><span class="special">);</span> <span class="comment">// creates list<const A&, B></span> 221<a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">b</span><span class="special">);</span> <span class="comment">// creates list<A&, B></span> 222<a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">cref</span><span class="special">(</span><span class="identifier">b</span><span class="special">));</span> <span class="comment">// creates list<A&, const B&></span> 223<a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="identifier">cref</span><span class="special">(</span><span class="identifier">ca</span><span class="special">));</span> <span class="comment">// creates list<const A&></span> 224<a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a><span class="special">(</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">ca</span><span class="special">));</span> <span class="comment">// creates list<const A&></span> 225</pre> 226<p> 227 See <a href="http://www.boost.org/libs/core/ref.html" target="_top">Ref utility</a> 228 for details. 229 </p> 230<p> 231 Since C++11, the standard reference wrappers (<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ref</span></code> and 232 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cref</span></code>) work as well. 233 </p> 234<h4> 235<a name="fusion.notes.h6"></a> 236 <span class="phrase"><a name="fusion.notes.adt_attribute_proxy"></a></span><a class="link" href="notes.html#fusion.notes.adt_attribute_proxy">adt_attribute_proxy</a> 237 </h4> 238<p> 239 To adapt arbitrary data types that do not allow direct access to their members, 240 but allow indirect access via expressions (such as invocations of get- and 241 set-methods), fusion's <code class="literal">BOOST_FUSION_ADAPT_<span class="emphasis"><em>xxx</em></span>ADT<span class="emphasis"><em>xxx</em></span></code>-family 242 (e.g. <a class="link" href="adapted/adapt_adt.html" title="BOOST_FUSION_ADAPT_ADT"><code class="computeroutput"><span class="identifier">BOOST_FUSION_ADAPT_ADT</span></code></a>) 243 may be used. To bypass the restriction of not having actual lvalues that represent 244 the elements of the fusion sequence, but rather a sequence of paired expressions 245 that access the elements, the actual return type of fusion's intrinsic sequence 246 access functions (<a class="link" href="sequence/intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a>, <a class="link" href="sequence/intrinsic/functions/at_c.html" title="at_c"><code class="computeroutput"><span class="identifier">at_c</span></code></a>, <a class="link" href="sequence/intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a>, <a class="link" href="iterator/functions/deref.html" title="deref"><code class="computeroutput"><span class="identifier">deref</span></code></a>, and <a class="link" href="iterator/functions/deref_data.html" title="deref_data"><code class="computeroutput"><span class="identifier">deref_data</span></code></a>) is a proxy type, an instance 247 of <code class="computeroutput"><span class="identifier">adt_attribute_proxy</span></code>, that 248 encapsulates these expressions. 249 </p> 250<p> 251 <code class="computeroutput"><span class="identifier">adt_attribute_proxy</span></code> is defined 252 in the namespace <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">extension</span></code> and has three template arguments: 253 </p> 254<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">fusion</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">extension</span> 255<span class="special">{</span> 256 <span class="keyword">template</span><span class="special"><</span> 257 <span class="keyword">typename</span> <span class="identifier">Type</span> 258 <span class="special">,</span> <span class="keyword">int</span> <span class="identifier">Index</span> 259 <span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">Const</span> 260 <span class="special">></span> 261 <span class="keyword">struct</span> <span class="identifier">adt_attribute_proxy</span><span class="special">;</span> 262<span class="special">}}}</span> 263</pre> 264<p> 265 When adapting a class type, <code class="computeroutput"><span class="identifier">adt_attribute_proxy</span></code> 266 is specialized for every element of the adapted sequence, with <code class="computeroutput"><span class="identifier">Type</span></code> being the class type that is adapted, 267 <code class="computeroutput"><span class="identifier">Index</span></code> the 0-based indices of 268 the elements, and <code class="computeroutput"><span class="identifier">Const</span></code> both 269 <code class="computeroutput"><span class="keyword">true</span></code> and <code class="computeroutput"><span class="keyword">false</span></code>. 270 The return type of fusion's intrinsic sequence access functions for the <span class="emphasis"><em>N</em></span>th 271 element of an adapted class type <code class="computeroutput"><span class="identifier">type_name</span></code> 272 is <code class="literal">adt_attribute_proxy<type_name, <span class="emphasis"><em>N</em></span>, <span class="emphasis"><em>Const</em></span>></code>, 273 with <code class="literal"><span class="emphasis"><em>Const</em></span></code> being <code class="computeroutput"><span class="keyword">true</span></code> 274 for constant instances of <code class="computeroutput"><span class="identifier">type_name</span></code> 275 and <code class="computeroutput"><span class="keyword">false</span></code> for non-constant ones. 276 </p> 277<div class="variablelist"> 278<p class="title"><b>Notation</b></p> 279<dl class="variablelist"> 280<dt><span class="term"><code class="computeroutput"><span class="identifier">type_name</span></code></span></dt> 281<dd><p> 282 The type to be adapted, with M attributes 283 </p></dd> 284<dt><span class="term"><code class="computeroutput"><span class="identifier">inst</span></code></span></dt> 285<dd><p> 286 Object of type <code class="computeroutput"><span class="identifier">type_name</span></code> 287 </p></dd> 288<dt><span class="term"><code class="computeroutput"><span class="identifier">const_inst</span></code></span></dt> 289<dd><p> 290 Object of type <code class="computeroutput"><span class="identifier">type_name</span> <span class="keyword">const</span></code> 291 </p></dd> 292<dt><span class="term"><code class="literal">(attribute_type<span class="emphasis"><em>N</em></span>, attribute_const_type<span class="emphasis"><em>N</em></span>, 293 get_expr<span class="emphasis"><em>N</em></span>, set_expr<span class="emphasis"><em>N</em></span>)</code></span></dt> 294<dd><p> 295 Attribute descriptor of the <span class="emphasis"><em>N</em></span>th attribute of <code class="computeroutput"><span class="identifier">type_name</span></code> as passed to the adaption 296 macro, 0≤<span class="emphasis"><em>N</em></span><M 297 </p></dd> 298<dt><span class="term"><code class="literal">proxy_type<span class="emphasis"><em>N</em></span></code></span></dt> 299<dd><p> 300 <code class="literal">adt_attribute_proxy<type_name, <span class="emphasis"><em>N</em></span>, <code class="computeroutput"><span class="keyword">false</span></code>></code> with <span class="emphasis"><em>N</em></span> 301 being an integral constant, 0≤<span class="emphasis"><em>N</em></span><M 302 </p></dd> 303<dt><span class="term"><code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span></code></span></dt> 304<dd><p> 305 <code class="literal">adt_attribute_proxy<type_name, <span class="emphasis"><em>N</em></span>, <code class="computeroutput"><span class="keyword">true</span></code>></code> with <span class="emphasis"><em>N</em></span> 306 being an integral constant, 0≤<span class="emphasis"><em>N</em></span><M 307 </p></dd> 308<dt><span class="term"><code class="literal">proxy<span class="emphasis"><em>N</em></span></code></span></dt> 309<dd><p> 310 Object of type <code class="literal">proxy_type<span class="emphasis"><em>N</em></span></code> 311 </p></dd> 312<dt><span class="term"><code class="literal">const_proxy<span class="emphasis"><em>N</em></span></code></span></dt> 313<dd><p> 314 Object of type <code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span></code> 315 </p></dd> 316</dl> 317</div> 318<p> 319 <span class="bold"><strong>Expression Semantics</strong></span> 320 </p> 321<div class="informaltable"><table class="table"> 322<colgroup> 323<col> 324<col> 325</colgroup> 326<thead><tr> 327<th> 328 <p> 329 Expression 330 </p> 331 </th> 332<th> 333 <p> 334 Semantics 335 </p> 336 </th> 337</tr></thead> 338<tbody> 339<tr> 340<td> 341 <p> 342 <code class="literal">proxy_type<span class="emphasis"><em>N</em></span>(inst)</code> 343 </p> 344 </td> 345<td> 346 <p> 347 Creates an instance of <code class="literal">proxy_type<span class="emphasis"><em>N</em></span></code> 348 with underlying object <code class="computeroutput"><span class="identifier">inst</span></code> 349 </p> 350 </td> 351</tr> 352<tr> 353<td> 354 <p> 355 <code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span>(const_inst)</code> 356 </p> 357 </td> 358<td> 359 <p> 360 Creates an instance of <code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span></code> 361 with underlying object <code class="computeroutput"><span class="identifier">const_inst</span></code> 362 </p> 363 </td> 364</tr> 365<tr> 366<td> 367 <p> 368 <code class="literal">proxy_type<span class="emphasis"><em>N</em></span>::type</code> 369 </p> 370 </td> 371<td> 372 <p> 373 Another name for <code class="literal">attribute_type<span class="emphasis"><em>N</em></span></code> 374 </p> 375 </td> 376</tr> 377<tr> 378<td> 379 <p> 380 <code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span>::type</code> 381 </p> 382 </td> 383<td> 384 <p> 385 Another name for <code class="literal">const_attribute_type<span class="emphasis"><em>N</em></span></code> 386 </p> 387 </td> 388</tr> 389<tr> 390<td> 391 <p> 392 <code class="literal">proxy<span class="emphasis"><em>N</em></span>=t</code> 393 </p> 394 </td> 395<td> 396 <p> 397 Invokes <code class="literal">set_expr<span class="emphasis"><em>N</em></span></code>, with 398 <code class="computeroutput"><span class="identifier">t</span></code> being an arbitrary 399 object. <code class="literal">set_expr<span class="emphasis"><em>N</em></span></code> may access 400 the variables named <code class="computeroutput"><span class="identifier">obj</span></code> 401 of type <code class="computeroutput"><span class="identifier">type_name</span><span class="special">&</span></code>, which represent the corresponding 402 instance of <code class="computeroutput"><span class="identifier">type_name</span></code>, 403 and <code class="computeroutput"><span class="identifier">val</span></code> of an arbitrary 404 const-qualified reference template type parameter <code class="computeroutput"><span class="identifier">Val</span></code>, 405 which represents <code class="computeroutput"><span class="identifier">t</span></code>. 406 </p> 407 </td> 408</tr> 409<tr> 410<td> 411 <p> 412 <code class="literal">proxy<span class="emphasis"><em>N</em></span>.get()</code> 413 </p> 414 </td> 415<td> 416 <p> 417 Invokes <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> and forwards 418 its return value. <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> 419 may access the variable named <code class="computeroutput"><span class="identifier">obj</span></code> 420 of type <code class="computeroutput"><span class="identifier">type_name</span><span class="special">&</span></code> which represents the underlying 421 instance of <code class="computeroutput"><span class="identifier">type_name</span></code>. 422 <code class="literal">attribute_type<span class="emphasis"><em>N</em></span></code> may specify 423 the type that <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> denotes 424 to. 425 </p> 426 </td> 427</tr> 428<tr> 429<td> 430 <p> 431 <code class="literal">const_proxy<span class="emphasis"><em>N</em></span>.get()</code> 432 </p> 433 </td> 434<td> 435 <p> 436 Invokes <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> and forwards 437 its return value. <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> 438 may access the variable named <code class="computeroutput"><span class="identifier">obj</span></code> 439 of type <code class="computeroutput"><span class="identifier">type_name</span> <span class="keyword">const</span><span class="special">&</span></code> 440 which represents the underlying instance of <code class="computeroutput"><span class="identifier">type_name</span></code>. 441 <code class="literal">attribute_const_type<span class="emphasis"><em>N</em></span></code> may 442 specify the type that <code class="literal">get_expr<span class="emphasis"><em>N</em></span></code> 443 denotes to. 444 </p> 445 </td> 446</tr> 447</tbody> 448</table></div> 449<p> 450 Additionally, <code class="literal">proxy_type<span class="emphasis"><em>N</em></span></code> and <code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span></code> 451 are copy constructible, copy assignable and implicitly convertible to <code class="literal">proxy_type<span class="emphasis"><em>N</em></span>::type</code> 452 or <code class="literal">const_proxy_type<span class="emphasis"><em>N</em></span>::type</code>. 453 </p> 454<div class="tip"><table border="0" summary="Tip"> 455<tr> 456<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td> 457<th align="left">Tip</th> 458</tr> 459<tr><td align="left" valign="top"><p> 460 To avoid the pitfalls of the proxy type, an arbitrary class type may also 461 be adapted directly using fusion's <a class="link" href="extension.html" title="Extension">intrinsic 462 extension mechanism</a>. 463 </p></td></tr> 464</table></div> 465<div class="footnotes"> 466<br><hr style="width:100; text-align:left;margin-left: 0"> 467<div id="ftn.fusion.notes.f0" class="footnote"><p><a href="#fusion.notes.f0" class="para"><sup class="para">[14] </sup></a> 468 Note that the type of a string literal is an array of const characters, not 469 <code class="computeroutput"><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span></code>. To get <a class="link" href="container/generation/functions/make_list.html" title="make_list"><code class="computeroutput"><span class="identifier">make_list</span></code></a> to create a <a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a> with an element of a non-const 470 array type one must use the <code class="computeroutput"><span class="identifier">ref</span></code> 471 wrapper (see <a class="link" href="notes.html#fusion.notes.reference_wrappers"><code class="computeroutput"><span class="identifier">Reference</span> <span class="identifier">Wrappers</span></code></a>). 472 </p></div> 473</div> 474</div> 475<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 476<td align="left"></td> 477<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman, 478 Dan Marsden, Tobias Schwinger<p> 479 Distributed under the Boost Software License, Version 1.0. (See accompanying 480 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>) 481 </p> 482</div></td> 483</tr></table> 484<hr> 485<div class="spirit-nav"> 486<a accesskey="p" href="functional/generation/metafunctions/mk_unfused.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="change_log.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 487</div> 488</body> 489</html> 490
