1<html> 2<head> 3<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc --> 4<title>Lazy Construction and Conversions</title> 5<link rel="stylesheet" href="theme/style.css" type="text/css"> 6<link rel="prev" href="adaptable_closures.html"> 7<link rel="next" href="efficiency.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>Lazy Construction and Conversions</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="adaptable_closures.html"><img src="theme/l_arr.gif" border="0"></a></td> 25 <td width="20"><a href="efficiency.html"><img src="theme/r_arr.gif" border="0"></a></td> 26 </tr> 27</table> 28<a name="lazy_c___casts"></a><h2>Lazy C++ Casts</h2><p> 29The set of lazy C++ cast template classes and functions provide a way of lazily casting certain type to another during parsing. The lazy C++ templates are (syntactically) used very much like the well known C++ casts:</p> 30<code><pre> 31 <span class=identifier>A </span><span class=special>*</span><span class=identifier>a </span><span class=special>= </span><span class=identifier>static_cast_</span><span class=special><</span><span class=identifier>A </span><span class=special>*>(</span><span class=identifier>_a_lambda_expression_</span><span class=special>); 32</span></pre></code> 33<p> 34These casts parallel the ones in the C++ language. Take note however that the <i>lazy</i> versions have a trailing underscore.</p> 35<ul><li>static_cast_<T>(lambda_expression)</li><li>dynamic_cast_<T>(lambda_expression)</li><li>const_cast_<T>(lambda_expression)</li><li>reinterpret_cast_<T>(lambda_expression)</li></ul><table width="80%" border="0" align="center"> 36 <tr> 37 <td class="note_box"> 38<img src="theme/note.gif"></img> <b>Acknowledgement:</b><br><br><b>Hartmut Kaiser</b> implemented the lazy casts and constructors based on his original work on <a href="http://spirit.sourceforge.net"> 39Spirit</a> SE "semantic expressions" (the precursor of Phoenix). </td> 40 </tr> 41</table> 42<a name="lazy_object_construction"></a><h2>Lazy object construction</h2><p> 43A set of lazy constructor template classes and functions provide a way of lazily constructing an object of a type from an arbitrary set of lazy arguments in the form of lambda expressions. The construct_ templates are (syntactically) used very much like the well known C++ casts:</p> 44<code><pre> 45 <span class=identifier>A </span><span class=identifier>a </span><span class=special>= </span><span class=identifier>construct_</span><span class=special><</span><span class=identifier>A</span><span class=special>>(</span><span class=identifier>lambda_arg1</span><span class=special>, </span><span class=identifier>lambda_arg2</span><span class=special>, ..., </span><span class=identifier>lambda_argN</span><span class=special>); 46</span></pre></code> 47<p> 48where the given parameters are become the parameters to the contructor of the object of type A. (This implies, that type A is expected to have a constructor with a corresponsing set of parameter types.)</p> 49<table width="80%" border="0" align="center"> 50 <tr> 51 <td class="note_box"> 52<img src="theme/bulb.gif"></img> The ultimate maximum number of actual parameters is limited by the preprocessor constant PHOENIX_CONSTRUCT_LIMIT. Note though, that this limit should not be greater than PHOENIX_LIMIT. </td> 53 </tr> 54</table> 55<table border="0"> 56 <tr> 57 <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> 58 <td width="30"><a href="adaptable_closures.html"><img src="theme/l_arr.gif" border="0"></a></td> 59 <td width="20"><a href="efficiency.html"><img src="theme/r_arr.gif" border="0"></a></td> 60 </tr> 61</table> 62<br> 63<hr size="1"> 64<p class="copyright">Copyright © 2001-2002 Joel de Guzman<br> 65 <br> 66<font size="2">Use, modification and distribution is subject to the Boost Software 67 License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at 68 http://www.boost.org/LICENSE_1_0.txt) </font> </p> 69</body> 70</html> 71
