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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">&lt;</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">&gt;</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</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">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</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<a name="phoenix.modules.core.values.evaluating_a_value"></a><h3>
57<a name="id807608"></a>
58          <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">&lt;&lt;</span> <span class="identifier">val</span><span class="special">(</span><span class="number">3</span><span class="special">)()</span> <span class="special">&lt;&lt;</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>
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73<td align="right"><div class="copyright-footer">Copyright &#169; 2002-2005, 2010 Joel de Guzman, Dan Marsden, Thomas Heller<p>
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