1<html> 2<head> 3<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc --> 4<title>Values</title> 5<link rel="stylesheet" href="theme/style.css" type="text/css"> 6<link rel="prev" href="arguments.html"> 7<link rel="next" href="variables.html"> 8</head> 9<body> 10<table width="100%" height="48" border="0" background="theme/bkd2.gif" cellspacing="2"> 11 <tr> 12 <td width="10"> 13 </td> 14 <td width="85%"> 15 <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Values</b></font> 16 </td> 17 <td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" align="right" border="0"></a></td> 18 </tr> 19</table> 20<br> 21<table border="0"> 22 <tr> 23 <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> 24 <td width="30"><a href="arguments.html"><img src="theme/l_arr.gif" border="0"></a></td> 25 <td width="20"><a href="variables.html"><img src="theme/r_arr.gif" border="0"></a></td> 26 </tr> 27</table> 28<p> 29Whenever 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> 30<code><pre> 31 <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>))) 32</span></pre></code> 33<p> 34A nifty shortcut is the val(v) utility function. The expression above is also equivalent to:</p> 35<code><pre> 36 <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>)) 37</span></pre></code> 38<p> 39actor<value<int> >(value<int>(6)) is implicitly created behind the scenes, so there's really no need to explicitly type everything but:</p> 40<code><pre> 41 <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>) 42</span></pre></code> 43<p> 44There are situations though, as we'll see later on, where we might want to explicitly write val(x).</p> 45<p> 46Like 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> 47<code><pre> 48 <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>)(); 49 50 </span><span class=identifier>prints </span><span class=identifier>out </span><span class=string>"3 Hello World"</span><span class=special>. 51</span></pre></code> 52<table border="0"> 53 <tr> 54 <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> 55 <td width="30"><a href="arguments.html"><img src="theme/l_arr.gif" border="0"></a></td> 56 <td width="20"><a href="variables.html"><img src="theme/r_arr.gif" border="0"></a></td> 57 </tr> 58</table> 59<br> 60<hr size="1"> 61<p class="copyright">Copyright © 2001-2002 Joel de Guzman<br> 62 <br> 63<font size="2">Use, modification and distribution is subject to the Boost Software 64 License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at 65 http://www.boost.org/LICENSE_1_0.txt) </font> </p> 66</body> 67</html> 68
