68 lines
3.9 KiB
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68 lines
3.9 KiB
HTML
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Values</b></font>
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<p>
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Whenever we see a constant in a curryable-function such as the plus above, an actor<value<T> > (where T is the type of the constant) is, by default, automatically created for us. For instance, the example plus above is actually equivalent to:</p>
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<code><pre>
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<span class=identifier>plus</span><span class=special>(</span><span class=identifier>arg1</span><span class=special>, </span><span class=identifier>actor</span><span class=special><</span><span class=identifier>value</span><span class=special><</span><span class=keyword>int</span><span class=special>> >(</span><span class=identifier>value</span><span class=special><</span><span class=keyword>int</span><span class=special>>(</span><span class=number>6</span><span class=special>)))
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</span></pre></code>
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<p>
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A nifty shortcut is the val(v) utility function. The expression above is also equivalent to:</p>
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<code><pre>
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<span class=identifier>plus</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>))
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</span></pre></code>
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<p>
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actor<value<int> >(value<int>(6)) is implicitly created behind the scenes, so there's really no need to explicitly type everything but:</p>
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<code><pre>
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<span class=identifier>plus</span><span class=special>(</span><span class=identifier>arg1</span><span class=special>, </span><span class=number>6</span><span class=special>)
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</span></pre></code>
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<p>
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There are situations though, as we'll see later on, where we might want to explicily write val(x).</p>
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<p>
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Like arguments, values are also actors. As such, values can be evaluated through the actor's operator(). Such invocation gives the value's identity. Example:</p>
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<code><pre>
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<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=identifier>val</span><span class=special>(</span><span class=string>"Hello World"</span><span class=special>)();
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</span><span class=identifier>prints </span><span class=identifier>out </span><span class=string>"3 Hello World"</span><span class=special>.
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</span></pre></code>
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<p class="copyright">Copyright © 2001-2002 Joel de Guzman<br>
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<br>
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<font size="2">Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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