1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Operator</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. Phoenix 3.2.0"> 8<link rel="up" href="../modules.html" title="Modules"> 9<link rel="prev" href="function/adapting_functions.html" title="Adapting Functions"> 10<link rel="next" href="statement.html" title="Statement"> 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="function/adapting_functions.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="statement.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="phoenix.modules.operator"></a><a class="link" href="operator.html" title="Operator">Operator</a> 28</h3></div></div></div> 29<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="keyword">operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 30</pre> 31<p> 32 This facility provides a mechanism for lazily evaluating operators. Syntactically, 33 a lazy operator looks and feels like an ordinary C/C++ infix, prefix or postfix 34 operator. The operator application looks the same. However, unlike ordinary 35 operators, the actual operator execution is deferred. Samples: 36 </p> 37<pre class="programlisting"><span class="identifier">arg1</span> <span class="special">+</span> <span class="identifier">arg2</span> 38<span class="number">1</span> <span class="special">+</span> <span class="identifier">arg1</span> <span class="special">*</span> <span class="identifier">arg2</span> 39<span class="number">1</span> <span class="special">/</span> <span class="special">-</span><span class="identifier">arg1</span> 40<span class="identifier">arg1</span> <span class="special"><</span> <span class="number">150</span> 41</pre> 42<p> 43 We have seen the lazy operators in action (see <a class="link" href="../starter_kit/lazy_operators.html" title="Lazy Operators">Quick 44 Start - Lazy Operators</a>). Let's go back and examine them a little bit 45 further: 46 </p> 47<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">arg1</span> <span class="special">%</span> <span class="number">2</span> <span class="special">==</span> <span class="number">1</span><span class="special">)</span> 48</pre> 49<p> 50 Through operator overloading, the expression <code class="computeroutput"><span class="identifier">arg1</span> 51 <span class="special">%</span> <span class="number">2</span> <span class="special">==</span> <span class="number">1</span></code> actually 52 generates an actor. This actor object is passed on to STL's <code class="computeroutput"><span class="identifier">find_if</span></code> function. From the viewpoint of 53 STL, the expression is simply a function object expecting a single argument 54 of the containers value_type. For each element in <code class="computeroutput"><span class="identifier">c</span></code>, 55 the element is passed on as an argument <code class="computeroutput"><span class="identifier">arg1</span></code> 56 to the actor (function object). The actor checks if this is an odd value 57 based on the expression <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">%</span> <span class="number">2</span> <span class="special">==</span> 58 <span class="number">1</span></code> where arg1 is replaced by the container's 59 element. 60 </p> 61<p> 62 Like lazy functions (see <a class="link" href="function.html" title="Function">Function</a>), 63 lazy operators are not immediately executed when invoked. Instead, an actor 64 (see <a class="link" href="../actor.html" title="Actor">Actor</a>) object is created and returned 65 to the caller. Example: 66 </p> 67<pre class="programlisting"><span class="special">(</span><span class="identifier">arg1</span> <span class="special">+</span> <span class="identifier">arg2</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">arg3</span> 68</pre> 69<p> 70 does nothing more than return an actor. A second function call will evaluate 71 the actual operators. Example: 72 </p> 73<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="special">((</span><span class="identifier">arg1</span> <span class="special">+</span> <span class="identifier">arg2</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">arg3</span><span class="special">)(</span><span class="number">4</span><span class="special">,</span> <span class="number">5</span><span class="special">,</span> <span class="number">6</span><span class="special">);</span> 74</pre> 75<p> 76 will print out "54". 77 </p> 78<p> 79 Operator expressions are lazily evaluated following four simple rules: 80 </p> 81<div class="orderedlist"><ol class="orderedlist" type="1"> 82<li class="listitem"> 83 A binary operator, except <code class="computeroutput"><span class="special">->*</span></code> 84 will be lazily evaluated when <span class="emphasis"><em>at least</em></span> one of its 85 operands is an actor object (see <a class="link" href="../actor.html" title="Actor">Actor</a>). 86 </li> 87<li class="listitem"> 88 Unary operators are lazily evaluated if their argument is an actor object. 89 </li> 90<li class="listitem"> 91 Operator <code class="computeroutput"><span class="special">->*</span></code> is lazily 92 evaluated if the left hand argument is an actor object. 93 </li> 94<li class="listitem"> 95 The result of a lazy operator is an actor object that can in turn allow 96 the applications of rules 1, 2 and 3. 97 </li> 98</ol></div> 99<p> 100 For example, to check the following expression is lazily evaluated: 101 </p> 102<pre class="programlisting"><span class="special">-(</span><span class="identifier">arg1</span> <span class="special">+</span> <span class="number">3</span> <span class="special">+</span> <span class="number">6</span><span class="special">)</span> 103</pre> 104<div class="orderedlist"><ol class="orderedlist" type="1"> 105<li class="listitem"> 106 Following rule 1, <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> <span class="number">3</span></code> is 107 lazily evaluated since <code class="computeroutput"><span class="identifier">arg1</span></code> 108 is an actor (see <a class="link" href="core/arguments.html" title="Arguments">Arguments</a>). 109 </li> 110<li class="listitem"> 111 The result of this <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> <span class="number">3</span></code> expression 112 is an actor object, following rule 4. 113 </li> 114<li class="listitem"> 115 Continuing, <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> 116 <span class="number">3</span> <span class="special">+</span> <span class="number">6</span></code> is again lazily evaluated. Rule 2. 117 </li> 118<li class="listitem"> 119 By rule 4 again, the result of <code class="computeroutput"><span class="identifier">arg1</span> 120 <span class="special">+</span> <span class="number">3</span> <span class="special">+</span> <span class="number">6</span></code> is 121 an actor object. 122 </li> 123<li class="listitem"> 124 As <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> 125 <span class="number">3</span> <span class="special">+</span> <span class="number">6</span></code> is an actor, <code class="computeroutput"><span class="special">-(</span><span class="identifier">arg1</span> <span class="special">+</span> <span class="number">3</span> <span class="special">+</span> <span class="number">6</span><span class="special">)</span></code> is lazily evaluated. Rule 2. 126 </li> 127</ol></div> 128<p> 129 Lazy-operator application is highly contagious. In most cases, a single 130 <code class="computeroutput"><span class="identifier">argN</span></code> actor infects all its 131 immediate neighbors within a group (first level or parenthesized expression). 132 </p> 133<p> 134 Note that at least one operand of any operator must be a valid actor for 135 lazy evaluation to take effect. To force lazy evaluation of an ordinary expression, 136 we can use <code class="computeroutput"><span class="identifier">ref</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code>, <code class="computeroutput"><span class="identifier">val</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">cref</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> 137 to transform an operand into a valid actor object (see <a class="link" href="core.html" title="Core">Core</a>). 138 For example: 139 </p> 140<pre class="programlisting"><span class="number">1</span> <span class="special"><<</span> <span class="number">3</span><span class="special">;</span> <span class="comment">// Immediately evaluated</span> 141<span class="identifier">val</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special"><<</span> <span class="number">3</span><span class="special">;</span> <span class="comment">// Lazily evaluated</span> 142</pre> 143<h5> 144<a name="phoenix.modules.operator.h0"></a> 145 <span class="phrase"><a name="phoenix.modules.operator.supported_operators"></a></span><a class="link" href="operator.html#phoenix.modules.operator.supported_operators">Supported 146 operators</a> 147 </h5> 148<h5> 149<a name="phoenix.modules.operator.h1"></a> 150 <span class="phrase"><a name="phoenix.modules.operator.unary_operators"></a></span><a class="link" href="operator.html#phoenix.modules.operator.unary_operators">Unary 151 operators</a> 152 </h5> 153<pre class="programlisting"><span class="identifier">prefix</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="special">&</span> <span class="special">(</span><span class="identifier">reference</span><span class="special">),</span> <span class="special">*</span> <span class="special">(</span><span class="identifier">dereference</span><span class="special">)</span> 154<span class="identifier">postfix</span><span class="special">:</span> <span class="special">++,</span> <span class="special">--</span> 155</pre> 156<h5> 157<a name="phoenix.modules.operator.h2"></a> 158 <span class="phrase"><a name="phoenix.modules.operator.binary_operators"></a></span><a class="link" href="operator.html#phoenix.modules.operator.binary_operators">Binary 159 operators</a> 160 </h5> 161<pre class="programlisting"><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="special">|=,</span> <span class="special">^=,</span> <span class="special"><<=,</span> <span class="special">>>=</span> 162<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="special"><<,</span> <span class="special">>></span> 163<span class="special">==,</span> <span class="special">!=,</span> <span class="special"><,</span> <span class="special">>,</span> <span class="special"><=,</span> <span class="special">>=</span> 164<span class="special">&&,</span> <span class="special">||,</span> <span class="special">->*</span> 165</pre> 166<h5> 167<a name="phoenix.modules.operator.h3"></a> 168 <span class="phrase"><a name="phoenix.modules.operator.ternary_operator"></a></span><a class="link" href="operator.html#phoenix.modules.operator.ternary_operator">Ternary 169 operator</a> 170 </h5> 171<pre class="programlisting"><span class="identifier">if_else</span><span class="special">(</span><span class="identifier">c</span><span class="special">,</span> <span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span> 172</pre> 173<p> 174 The ternary operator deserves special mention. Since C++ does not allow us 175 to overload the conditional expression: <code class="computeroutput"><span class="identifier">c</span> 176 <span class="special">?</span> <span class="identifier">a</span> <span class="special">:</span> <span class="identifier">b</span></code>, the 177 if_else pseudo function is provided for this purpose. The behavior is identical, 178 albeit in a lazy manner. 179 </p> 180<h5> 181<a name="phoenix.modules.operator.h4"></a> 182 <span class="phrase"><a name="phoenix.modules.operator.member_pointer_operator"></a></span><a class="link" href="operator.html#phoenix.modules.operator.member_pointer_operator">Member 183 pointer operator</a> 184 </h5> 185<pre class="programlisting"><span class="identifier">a</span><span class="special">->*</span><span class="identifier">member_object_pointer</span> 186<span class="identifier">a</span><span class="special">->*</span><span class="identifier">member_function_pointer</span> 187</pre> 188<p> 189 The left hand side of the member pointer operator must be an actor returning 190 a pointer type. The right hand side of the member pointer operator may be 191 either a pointer to member object or pointer to member function. 192 </p> 193<p> 194 If the right hand side is a member object pointer, the result is an actor 195 which, when evaluated, returns a reference to that member. For example: 196 </p> 197<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> 198<span class="special">{</span> 199 <span class="keyword">int</span> <span class="identifier">member</span><span class="special">;</span> 200<span class="special">};</span> 201 202<span class="identifier">A</span><span class="special">*</span> <span class="identifier">a</span> <span class="special">=</span> <span class="keyword">new</span> <span class="identifier">A</span><span class="special">;</span> 203<span class="special">...</span> 204 205<span class="special">(</span><span class="identifier">arg1</span><span class="special">->*&</span><span class="identifier">A</span><span class="special">::</span><span class="identifier">member</span><span class="special">)(</span><span class="identifier">a</span><span class="special">);</span> <span class="comment">// returns member a->member</span> 206</pre> 207<p> 208 If the right hand side is a member function pointer, the result is an actor 209 which, when invoked, calls the specified member function. For example: 210 </p> 211<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> 212<span class="special">{</span> 213 <span class="keyword">int</span> <span class="identifier">func</span><span class="special">(</span><span class="keyword">int</span><span class="special">);</span> 214<span class="special">};</span> 215 216<span class="identifier">A</span><span class="special">*</span> <span class="identifier">a</span> <span class="special">=</span> <span class="keyword">new</span> <span class="identifier">A</span><span class="special">;</span> 217<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> 218 219<span class="special">(</span><span class="identifier">arg1</span><span class="special">->*&</span><span class="identifier">A</span><span class="special">::</span><span class="identifier">func</span><span class="special">)(</span><span class="identifier">arg2</span><span class="special">)(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">i</span><span class="special">);</span> <span class="comment">// returns a->func(i)</span> 220</pre> 221<h5> 222<a name="phoenix.modules.operator.h5"></a> 223 <span class="phrase"><a name="phoenix.modules.operator.include_files"></a></span><a class="link" href="operator.html#phoenix.modules.operator.include_files">Include 224 Files</a> 225 </h5> 226<div class="informaltable"><table class="table"> 227<colgroup> 228<col> 229<col> 230</colgroup> 231<thead><tr> 232<th> 233 <p> 234 Operators 235 </p> 236 </th> 237<th> 238 <p> 239 File 240 </p> 241 </th> 242</tr></thead> 243<tbody> 244<tr> 245<td> 246 <p> 247 <code class="computeroutput"><span class="special">-</span></code>, <code class="computeroutput"><span class="special">+</span></code>, 248 <code class="computeroutput"><span class="special">++</span></code>, <code class="computeroutput"><span class="special">--</span></code>, <code class="computeroutput"><span class="special">+=</span></code>, 249 <code class="computeroutput"><span class="special">-=</span></code>, <code class="computeroutput"><span class="special">*=</span></code>, <code class="computeroutput"><span class="special">/=</span></code>, 250 <code class="computeroutput"><span class="special">%=</span></code>, <code class="computeroutput"><span class="special">*</span></code>, <code class="computeroutput"><span class="special">/</span></code>, 251 <code class="computeroutput"><span class="special">%</span></code> 252 </p> 253 </td> 254<td> 255 <p> 256 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">arithmetic</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 257 </p> 258 </td> 259</tr> 260<tr> 261<td> 262 <p> 263 <code class="computeroutput"><span class="special">&=</span></code>, <code class="computeroutput"><span class="special">|=</span></code>, <code class="computeroutput"><span class="special">^=</span></code>, 264 <code class="computeroutput"><span class="special"><<=</span></code>, <code class="computeroutput"><span class="special">>>=</span></code>, <code class="computeroutput"><span class="special">&</span></code>, 265 <code class="computeroutput"><span class="special">|</span></code>, <code class="computeroutput"><span class="special">^</span></code>, 266 <code class="computeroutput"><span class="special"><<</span></code>, <code class="computeroutput"><span class="special">>></span></code> 267 </p> 268 </td> 269<td> 270 <p> 271 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">bitwise</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 272 </p> 273 </td> 274</tr> 275<tr> 276<td> 277 <p> 278 <code class="computeroutput"><span class="special">==</span></code>, <code class="computeroutput"><span class="special">!=</span></code>, <code class="computeroutput"><span class="special"><</span></code>, 279 <code class="computeroutput"><span class="special"><=</span></code>, <code class="computeroutput"><span class="special">></span></code>, <code class="computeroutput"><span class="special">>=</span></code> 280 </p> 281 </td> 282<td> 283 <p> 284 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">comparison</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 285 </p> 286 </td> 287</tr> 288<tr> 289<td> 290 <p> 291 <code class="computeroutput"><span class="special"><<</span></code>, <code class="computeroutput"><span class="special">>></span></code> 292 </p> 293 </td> 294<td> 295 <p> 296 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 297 </p> 298 </td> 299</tr> 300<tr> 301<td> 302 <p> 303 <code class="computeroutput"><span class="special">!</span></code>, &&, <code class="computeroutput"><span class="special">||</span></code> 304 </p> 305 </td> 306<td> 307 <p> 308 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">logical</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 309 </p> 310 </td> 311</tr> 312<tr> 313<td> 314 <p> 315 <code class="computeroutput"><span class="special">&</span><span class="identifier">x</span></code>, 316 <code class="computeroutput"><span class="special">*</span><span class="identifier">p</span></code>, 317 <code class="computeroutput"><span class="special">=</span></code>, <code class="computeroutput"><span class="special">[]</span></code> 318 </p> 319 </td> 320<td> 321 <p> 322 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 323 </p> 324 </td> 325</tr> 326<tr> 327<td> 328 <p> 329 <code class="computeroutput"><span class="identifier">if_else</span><span class="special">(</span><span class="identifier">c</span><span class="special">,</span> 330 <span class="identifier">a</span><span class="special">,</span> 331 <span class="identifier">b</span><span class="special">)</span></code> 332 </p> 333 </td> 334<td> 335 <p> 336 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">if_else</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 337 </p> 338 </td> 339</tr> 340<tr> 341<td> 342 <p> 343 <code class="computeroutput"><span class="special">->*</span></code> 344 </p> 345 </td> 346<td> 347 <p> 348 <code class="computeroutput"><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="keyword">operator</span><span class="special">/</span><span class="identifier">member</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 349 </p> 350 </td> 351</tr> 352</tbody> 353</table></div> 354</div> 355<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 356<td align="left"></td> 357<td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas 358 Heller, John Fletcher<p> 359 Distributed under the Boost Software License, Version 1.0. (See accompanying 360 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>) 361 </p> 362</div></td> 363</tr></table> 364<hr> 365<div class="spirit-nav"> 366<a accesskey="p" href="function/adapting_functions.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="statement.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 367</div> 368</body> 369</html> 370
