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26 <div class=
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"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>
32 Whenever we see a constant in a partially applied function, an
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>
37 (where T is the type of the constant) is automatically created for us.
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>
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>.
47 <pre class=
"programlisting"><span class=
"identifier">val
</span><span class=
"special">(
</span><span class=
"identifier">v
</span><span class=
"special">)
</span>
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.
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
62 Like arguments, values are also actors. As such, values can be evaluated.
63 Invoking a value gives the value's identity. Example:
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>
68 prints out
"3 Hello World".
71 <table xmlns:
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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>)
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