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  26. <div class="titlepage"><div><div><h4 class="title">
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  27. <a name="phoenix.modules.core.values"></a><a class="link" href="values.html" title="Values">Values</a>
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  28. </h4></div></div></div>
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  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>
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  30. </pre>
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  31. <p>
    32. 

  32.           Whenever we see a constant in a partially applied function, an
    33. 

  33.         </p>
    34. 

  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. 

  35. </pre>
    36. 

  36. <p>
    37. 

  37.           (where T is the type of the constant) is automatically created for us.
    38. 

  38.           For instance:
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  39.         </p>
    40. 

  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>
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  41. </pre>
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  42. <p>
    43. 

  43.           Passing a second argument, <code class="computeroutput"><span class="number">6</span></code>,
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  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
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  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. 

  46.         </p>
    47. 

  47. <pre class="programlisting"><span class="identifier">val</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span>
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  48. </pre>
    49. 

  49. <p>
    50. 

  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>
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  51.           where <code class="computeroutput"><span class="identifier">T</span></code> is the type of
    52. 

  52.           <code class="computeroutput"><span class="identifier">x</span></code>. In most cases, there's
    53. 

  53.           no need to explicitly use <code class="computeroutput"><span class="identifier">val</span></code>,
    54. 

  54.           but, as we'll see later on, there are situations where this is unavoidable.
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  55.         </p>
    56. 

  56. <a name="phoenix.modules.core.values.evaluating_a_value"></a><h3>
    57. 

  57. <a name="id807608"></a>
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  58.           <a class="link" href="values.html#phoenix.modules.core.values.evaluating_a_value">Evaluating
    59. 

  59.           a Value</a>
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  60.         </h3>
    61. 

  61. <p>
    62. 

  62.           Like arguments, values are also actors. As such, values can be evaluated.
    63. 

  63.           Invoking a value gives the value's identity. Example:
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  64.         </p>
    65. 

  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. 

  66. </pre>
    67. 

  67. <p>
    68. 

  68.           prints out "3 Hello World".
    69. 

  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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  74.         Distributed under the Boost Software License, Version 1.0. (See accompanying
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  75.         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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