1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Modifiers and the single-element sequence</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. The Variadic Macro Data Library 1.9"> 8<link rel="up" href="../vmd_modifiers.html" title="Macros with modifiers"> 9<link rel="prev" href="vmd_modifiers_index.html" title="Index modifiers"> 10<link rel="next" href="../vmd_identifier_subtype.html" title="Identifier subtypes"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="vmd_modifiers_index.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../vmd_modifiers.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../vmd_identifier_subtype.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="variadic_macro_data.vmd_modifiers.vmd_modifiers_single"></a><a class="link" href="vmd_modifiers_single.html" title="Modifiers and the single-element sequence">Modifiers 28 and the single-element sequence</a> 29</h3></div></div></div> 30<p> 31 A single element sequence is what we normally think of when working with 32 macro data. It is a single type of macro data passed as an input parameter 33 to some macro and processed as such. 34 </p> 35<p> 36 In its basic form without modifiers BOOST_VMD_ELEM serves to just return 37 a particular element of a sequence. For a single element sequence BOOST_VMD_ELEM 38 with element number 0, just returns the single-element sequence itself. This 39 does not offer much functionality for our simple sequence. However with modifiers 40 we can do things generically with our single-element sequence which correspond 41 to working with a single type of data and extracting information about it. 42 </p> 43<p> 44 With the return type modifier we can get the type of the data along with 45 the data. Of course we can also use BOOST_VMD_GET_TYPE to retrieve just the 46 type of data. 47 </p> 48<p> 49 With our filter modifier we can retrieve the data only if it is a particular 50 type, else retrieve emptiness. 51 </p> 52<p> 53 With the identifier modifier we can retrieve an identifier only if it matches 54 one or more other identifiers, else retrieve emptiness. 55 </p> 56<p> 57 With our index modifier we can retrieve both our identifier and its numeric 58 index if it matches one or more other identifiers, else retrieve a tuple 59 of two empty elements if no match is found. 60 </p> 61</div> 62<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 63<td align="left"></td> 64<td align="right"><div class="copyright-footer">Copyright © 2010-2017 Tropic Software 65 East Inc</div></td> 66</tr></table> 67<hr> 68<div class="spirit-nav"> 69<a accesskey="p" href="vmd_modifiers_index.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../vmd_modifiers.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../vmd_identifier_subtype.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 70</div> 71</body> 72</html> 73
