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| <div class="section boost_icl_implementation_inplace_and_infix_operators" lang="en"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_icl.implementation.inplace_and_infix_operators"></a><a class="link" href="inplace_and_infix_operators.html" title="Inplace and infix operators">Inplace |
| and infix operators</a> |
| </h3></div></div></div> |
| <p> |
| For the major operations <span class="emphasis"><em>addition, subtraction, intersection</em></span> |
| of <span class="bold"><strong>icl</strong></span> containers and for <span class="emphasis"><em>symmetric |
| difference</em></span> inplace <code class="computeroutput"><span class="keyword">operator</span></code>s |
| <code class="computeroutput"><span class="special">+=</span> <span class="special">|=,</span> |
| <span class="special">-=,</span> <span class="special">&=</span></code> |
| and <code class="computeroutput"><span class="special">^=</span></code> are provided. |
| </p> |
| <p> |
| For every <span class="emphasis"><em><span class="bold"><strong>inplace</strong></span></em></span> operator |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">T</span><span class="special">&</span> <span class="keyword">operator</span> <span class="identifier">o</span><span class="special">=</span> <span class="special">(</span><span class="identifier">T</span><span class="special">&</span> <span class="identifier">object</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">P</span><span class="special">&</span> <span class="identifier">operand</span><span class="special">)</span> |
| </pre> |
| <p> |
| the <span class="bold"><strong>icl</strong></span> provides corresponding <span class="emphasis"><em><span class="bold"><strong>infix</strong></span></em></span> operators. |
| </p> |
| <pre class="programlisting"><span class="identifier">T</span> <span class="keyword">operator</span> <span class="identifier">o</span> <span class="special">(</span><span class="identifier">T</span> <span class="identifier">object</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">P</span><span class="special">&</span> <span class="identifier">operand</span><span class="special">){</span> <span class="keyword">return</span> <span class="identifier">object</span> <span class="identifier">o</span><span class="special">=</span> <span class="identifier">operand</span><span class="special">;</span> <span class="special">}</span> |
| <span class="identifier">T</span> <span class="keyword">operator</span> <span class="identifier">o</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">P</span><span class="special">&</span> <span class="identifier">operand</span><span class="special">,</span> <span class="identifier">T</span> <span class="identifier">object</span><span class="special">){</span> <span class="keyword">return</span> <span class="identifier">object</span> <span class="identifier">o</span><span class="special">=</span> <span class="identifier">operand</span><span class="special">;</span> <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| From this implementation of the infix <code class="computeroutput"><span class="keyword">operator</span> |
| <span class="identifier">o</span></code> the compiler will hopefully use |
| return value optimization <a href="http://en.wikipedia.org/wiki/Return_value_optimization" target="_top">(RVO)</a> |
| creating no temporary object and performing one copy of the first argument |
| <code class="computeroutput"><span class="identifier">object</span></code>. |
| </p> |
| <div class="caution"><table border="0" summary="Caution"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../doc/src/images/caution.png"></td> |
| <th align="left">Caution</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Compared to the <span class="emphasis"><em>inplace</em></span> <code class="computeroutput"><span class="keyword">operator</span> |
| <span class="identifier">o</span><span class="special">=</span></code> |
| every use of an <span class="emphasis"><em>infix</em></span> <code class="computeroutput"><span class="keyword">operator</span> |
| <span class="identifier">o</span></code> requires <span class="emphasis"><em><span class="bold"><strong>one extra copy</strong></span></em></span> of the first argument |
| <code class="computeroutput"><span class="identifier">object</span></code> that passes a container. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Use infix operators only, if |
| </p> |
| <div class="itemizedlist"><ul type="disc"> |
| <li> |
| efficiency is not crucial, e.g. the containers copied are small. |
| </li> |
| <li> |
| a concise and short notation is more important than efficiency in your |
| context. |
| </li> |
| <li> |
| you need the result of operator <code class="computeroutput"><span class="identifier">o</span><span class="special">=</span></code> as a copy anyway. |
| </li> |
| </ul></div> |
| <a name="boost_icl.implementation.inplace_and_infix_operators.time_complexity_of_infix__code__phrase_role__identifier__operators__phrase___phrase_role__identifier__o__phrase___code_"></a><h6> |
| <a name="id1133408"></a> |
| <a class="link" href="inplace_and_infix_operators.html#boost_icl.implementation.inplace_and_infix_operators.time_complexity_of_infix__code__phrase_role__identifier__operators__phrase___phrase_role__identifier__o__phrase___code_">Time |
| Complexity of infix <code class="computeroutput"><span class="identifier">operators</span> <span class="identifier">o</span></code></a> |
| </h6> |
| <p> |
| The time complexity of all infix operators of the <span class="bold"><strong>icl</strong></span> |
| is biased by the extra copy of the <code class="computeroutput"><span class="identifier">object</span></code> |
| argument. So all infix <code class="computeroutput"><span class="identifier">operators</span> |
| <span class="identifier">o</span></code> are at least <span class="emphasis"><em>linear</em></span> |
| in <code class="computeroutput"><span class="identifier">n</span> <span class="special">=</span> |
| <span class="identifier">object</span><span class="special">.</span><span class="identifier">iterative_size</span><span class="special">()</span></code>. |
| Taking this into account, the complexities of all infix operators can be |
| determined from the corresponding inplace <code class="computeroutput"><span class="identifier">operators</span> |
| <span class="identifier">o</span><span class="special">=</span></code> |
| they depend on. |
| </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 © 2007 -2010 Joachim Faulhaber<br>Copyright © 1999 -2006 Cortex Software GmbH<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>) |
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