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| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="phoenix.modules.operator"></a><a class="link" href="operator.html" title="Operator">Operator</a> |
| </h3></div></div></div> |
| <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> |
| </pre> |
| <p> |
| This facility provides a mechanism for lazily evaluating operators. Syntactically, |
| a lazy operator looks and feels like an ordinary C/C++ infix, prefix or postfix |
| operator. The operator application looks the same. However, unlike ordinary |
| operators, the actual operator execution is deferred. Samples: |
| </p> |
| <pre class="programlisting"><span class="identifier">arg1</span> <span class="special">+</span> <span class="identifier">arg2</span> |
| <span class="number">1</span> <span class="special">+</span> <span class="identifier">arg1</span> <span class="special">*</span> <span class="identifier">arg2</span> |
| <span class="number">1</span> <span class="special">/</span> <span class="special">-</span><span class="identifier">arg1</span> |
| <span class="identifier">arg1</span> <span class="special"><</span> <span class="number">150</span> |
| </pre> |
| <p> |
| We have seen the lazy operators in action (see <a class="link" href="../starter_kit/lazy_operators.html" title="Lazy Operators">Quick |
| Start - Lazy Operators</a>). Let's go back and examine them a little bit |
| further: |
| </p> |
| <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> |
| </pre> |
| <p> |
| Through operator overloading, the expression <code class="computeroutput"><span class="identifier">arg1</span> |
| <span class="special">%</span> <span class="number">2</span> <span class="special">==</span> <span class="number">1</span></code> actually |
| 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 |
| STL, the expression is simply a function object expecting a single argument |
| of the containers value_type. For each element in <code class="computeroutput"><span class="identifier">c</span></code>, |
| the element is passed on as an argument <code class="computeroutput"><span class="identifier">arg1</span></code> |
| to the actor (function object). The actor checks if this is an odd value |
| 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> |
| <span class="number">1</span></code> where arg1 is replaced by the container's |
| element. |
| </p> |
| <p> |
| Like lazy functions (see <a class="link" href="function.html" title="Function">Function</a>), |
| lazy operators are not immediately executed when invoked. Instead, an actor |
| (see <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="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> |
| </pre> |
| <p> |
| does nothing more than return an actor. A second function call will evaluate |
| the actual operators. 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="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> |
| </pre> |
| <p> |
| will print out "54". |
| </p> |
| <p> |
| Operator expressions are lazily evaluated following four simple rules: |
| </p> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| A binary operator, except <code class="computeroutput"><span class="special">->*</span></code> |
| will be lazily evaluated when <span class="emphasis"><em>at least</em></span> one of its |
| operands is an actor object (see <a class="link" href="../actor.html" title="Actor">Actor</a>). |
| </li> |
| <li class="listitem"> |
| Unary operators are lazily evaluated if their argument is an actor object. |
| </li> |
| <li class="listitem"> |
| Operator <code class="computeroutput"><span class="special">->*</span></code> is lazily |
| evaluated if the left hand argument is an actor object. |
| </li> |
| <li class="listitem"> |
| The result of a lazy operator is an actor object that can in turn allow |
| the applications of rules 1, 2 and 3. |
| </li> |
| </ol></div> |
| <p> |
| For example, to check the following expression is lazily evaluated: |
| </p> |
| <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> |
| </pre> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| Following rule 1, <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> <span class="number">3</span></code> is |
| lazily evaluated since <code class="computeroutput"><span class="identifier">arg1</span></code> |
| is an actor (see <a class="link" href="core/arguments.html" title="Arguments">Arguments</a>). |
| </li> |
| <li class="listitem"> |
| The result of this <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> <span class="number">3</span></code> expression |
| is an actor object, following rule 4. |
| </li> |
| <li class="listitem"> |
| Continuing, <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> |
| <span class="number">3</span> <span class="special">+</span> <span class="number">6</span></code> is again lazily evaluated. Rule 2. |
| </li> |
| <li class="listitem"> |
| By rule 4 again, the result of <code class="computeroutput"><span class="identifier">arg1</span> |
| <span class="special">+</span> <span class="number">3</span> <span class="special">+</span> <span class="number">6</span></code> is |
| an actor object. |
| </li> |
| <li class="listitem"> |
| As <code class="computeroutput"><span class="identifier">arg1</span> <span class="special">+</span> |
| <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. |
| </li> |
| </ol></div> |
| <p> |
| Lazy-operator application is highly contagious. In most cases, a single |
| <code class="computeroutput"><span class="identifier">argN</span></code> actor infects all its |
| immediate neighbors within a group (first level or parenthesized expression). |
| </p> |
| <p> |
| Note that at least one operand of any operator must be a valid actor for |
| lazy evaluation to take effect. To force lazy evaluation of an ordinary expression, |
| 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> |
| to transform an operand into a valid actor object (see <a class="link" href="core.html" title="Core">Core</a>). |
| For example: |
| </p> |
| <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> |
| <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> |
| </pre> |
| <h5> |
| <a name="phoenix.modules.operator.h0"></a> |
| <span class="phrase"><a name="phoenix.modules.operator.supported_operators"></a></span><a class="link" href="operator.html#phoenix.modules.operator.supported_operators">Supported |
| operators</a> |
| </h5> |
| <h5> |
| <a name="phoenix.modules.operator.h1"></a> |
| <span class="phrase"><a name="phoenix.modules.operator.unary_operators"></a></span><a class="link" href="operator.html#phoenix.modules.operator.unary_operators">Unary |
| operators</a> |
| </h5> |
| <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> |
| <span class="identifier">postfix</span><span class="special">:</span> <span class="special">++,</span> <span class="special">--</span> |
| </pre> |
| <h5> |
| <a name="phoenix.modules.operator.h2"></a> |
| <span class="phrase"><a name="phoenix.modules.operator.binary_operators"></a></span><a class="link" href="operator.html#phoenix.modules.operator.binary_operators">Binary |
| operators</a> |
| </h5> |
| <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> |
| <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> <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> |
| </pre> |
| <h5> |
| <a name="phoenix.modules.operator.h3"></a> |
| <span class="phrase"><a name="phoenix.modules.operator.ternary_operator"></a></span><a class="link" href="operator.html#phoenix.modules.operator.ternary_operator">Ternary |
| operator</a> |
| </h5> |
| <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> |
| </pre> |
| <p> |
| The ternary operator deserves special mention. Since C++ does not allow us |
| to overload the conditional expression: <code class="computeroutput"><span class="identifier">c</span> |
| <span class="special">?</span> <span class="identifier">a</span> <span class="special">:</span> <span class="identifier">b</span></code>, the |
| if_else pseudo function is provided for this purpose. The behavior is identical, |
| albeit in a lazy manner. |
| </p> |
| <h5> |
| <a name="phoenix.modules.operator.h4"></a> |
| <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 |
| pointer operator</a> |
| </h5> |
| <pre class="programlisting"><span class="identifier">a</span><span class="special">->*</span><span class="identifier">member_object_pointer</span> |
| <span class="identifier">a</span><span class="special">->*</span><span class="identifier">member_function_pointer</span> |
| </pre> |
| <p> |
| The left hand side of the member pointer operator must be an actor returning |
| a pointer type. The right hand side of the member pointer operator may be |
| either a pointer to member object or pointer to member function. |
| </p> |
| <p> |
| If the right hand side is a member object pointer, the result is an actor |
| which, when evaluated, returns a reference to that member. For example: |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">member</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <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> |
| <span class="special">...</span> |
| |
| <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> |
| </pre> |
| <p> |
| If the right hand side is a member function pointer, the result is an actor |
| which, when invoked, calls the specified member function. For example: |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">func</span><span class="special">(</span><span class="keyword">int</span><span class="special">);</span> |
| <span class="special">};</span> |
| |
| <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> |
| <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> |
| |
| <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> |
| </pre> |
| <h5> |
| <a name="phoenix.modules.operator.h5"></a> |
| <span class="phrase"><a name="phoenix.modules.operator.include_files"></a></span><a class="link" href="operator.html#phoenix.modules.operator.include_files">Include |
| Files</a> |
| </h5> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Operators |
| </p> |
| </th> |
| <th> |
| <p> |
| File |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">-</span></code>, <code class="computeroutput"><span class="special">+</span></code>, |
| <code class="computeroutput"><span class="special">++</span></code>, <code class="computeroutput"><span class="special">--</span></code>, <code class="computeroutput"><span class="special">+=</span></code>, |
| <code class="computeroutput"><span class="special">-=</span></code>, <code class="computeroutput"><span class="special">*=</span></code>, <code class="computeroutput"><span class="special">/=</span></code>, |
| <code class="computeroutput"><span class="special">%=</span></code>, <code class="computeroutput"><span class="special">*</span></code>, <code class="computeroutput"><span class="special">/</span></code>, |
| <code class="computeroutput"><span class="special">%</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">&=</span></code>, <code class="computeroutput"><span class="special">|=</span></code>, <code class="computeroutput"><span class="special">^=</span></code>, |
| <code class="computeroutput"><span class="special"><<=</span></code>, <code class="computeroutput"><span class="special">>>=</span></code>, <code class="computeroutput"><span class="special">&</span></code>, |
| <code class="computeroutput"><span class="special">|</span></code>, <code class="computeroutput"><span class="special">^</span></code>, |
| <code class="computeroutput"><span class="special"><<</span></code>, <code class="computeroutput"><span class="special">>></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">==</span></code>, <code class="computeroutput"><span class="special">!=</span></code>, <code class="computeroutput"><span class="special"><</span></code>, |
| <code class="computeroutput"><span class="special"><=</span></code>, <code class="computeroutput"><span class="special">></span></code>, <code class="computeroutput"><span class="special">>=</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special"><<</span></code>, <code class="computeroutput"><span class="special">>></span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">!</span></code>, &&, <code class="computeroutput"><span class="special">||</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">&</span><span class="identifier">x</span></code>, |
| <code class="computeroutput"><span class="special">*</span><span class="identifier">p</span></code>, |
| <code class="computeroutput"><span class="special">=</span></code>, <code class="computeroutput"><span class="special">[]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><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></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="special">->*</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </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, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas |
| Heller, John Fletcher<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> |
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