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| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Values</title> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h4 class="title"> | |
| 27 | <a name="phoenix.modules.core.values"></a><a class="link" href="values.html" title="Values">Values</a> | |
| 28 | </h4></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="identifier">core</span><span class="special">/</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 30 | </pre> | |
| 31 | <p> | |
| 32 | Whenever we see a constant in a partially applied function, an | |
| 33 | </p> | |
| 34 | <pre class="programlisting"><span class="identifier">expression</span><span class="special">::</span><span class="identifier">value</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> | |
| 35 | </pre> | |
| 36 | <p> | |
| 37 | (where T is the type of the constant) is automatically created for us. | |
| 38 | For instance: | |
| 39 | </p> | |
| 40 | <pre class="programlisting"><span class="identifier">add</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">,</span> <span class="number">6</span><span class="special">)</span> | |
| 41 | </pre> | |
| 42 | <p> | |
| 43 | Passing a second argument, <code class="computeroutput"><span class="number">6</span></code>, | |
| 44 | an <code class="computeroutput"><span class="identifier">expression</span><span class="special">::</span><span class="identifier">value</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span></code> is implicitly created behind the | |
| 45 | scenes. This is also equivalent to <code class="computeroutput"><span class="identifier">add</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">,</span> <span class="identifier">val</span><span class="special">(</span><span class="number">6</span><span class="special">))</span></code>. | |
| 46 | </p> | |
| 47 | <pre class="programlisting"><span class="identifier">val</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> | |
| 48 | </pre> | |
| 49 | <p> | |
| 50 | generates an <code class="computeroutput"><span class="identifier">expression</span><span class="special">::</span><span class="identifier">value</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 51 | where <code class="computeroutput"><span class="identifier">T</span></code> is the type of | |
| 52 | <code class="computeroutput"><span class="identifier">x</span></code>. In most cases, there's | |
| 53 | no need to explicitly use <code class="computeroutput"><span class="identifier">val</span></code>, | |
| 54 | but, as we'll see later on, there are situations where this is unavoidable. | |
| 55 | </p> | |
| 56 | <h3> | |
| 57 | <a name="phoenix.modules.core.values.h0"></a> | |
| 58 | <span><a name="phoenix.modules.core.values.evaluating_a_value"></a></span><a class="link" href="values.html#phoenix.modules.core.values.evaluating_a_value">Evaluating | |
| 59 | a Value</a> | |
| 60 | </h3> | |
| 61 | <p> | |
| 62 | Like arguments, values are also actors. As such, values can be evaluated. | |
| 63 | Invoking a value gives the value's identity. Example: | |
| 64 | </p> | |
| 65 | <pre class="programlisting"><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">val</span><span class="special">(</span><span class="number">3</span><span class="special">)()</span> <span class="special"><<</span> <span class="identifier">val</span><span class="special">(</span><span class="string">"Hello World"</span><span class="special">)();</span> | |
| 66 | </pre> | |
| 67 | <p> | |
| 68 | prints out "3 Hello World". | |
| 69 | </p> | |
| 70 | </div> | |
| 71 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 72 | <td align="left"></td> | |
| 73 | <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas | |
| 74 | Heller, John Fletcher<p> | |
| 75 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 76 | 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>) | |
| 77 | </p> | |
| 78 | </div></td> | |
| 79 | </tr></table> | |
| 80 | <hr> | |
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| 83 | </div> | |
| 84 | </body> | |
| 85 | </html> |