devn00b
/
EQ2EMu


			
				
					
						
						
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081
							<html>
<head>
        <title>BOOST_PP_SEQ_NIL</title>
		<link rel="stylesheet" type="text/css" href="../styles.css">
</head>
<body>
		<div style="margin-left: 0px;">
			The <b>BOOST_PP_SEQ_NIL</b> macro is a placeholder macro for an empty <i>seq</i>.&nbsp; 
			It is only valid if it's elements are appended to the end of this empty 
			"seq."&nbsp;
		</div>
		<h4>
			Usage
		</h4>
		<div class="code">
			<b>BOOST_PP_SEQ_NIL</b>
		</div>
		<h4>
			Remarks
		</h4>
		<div>
			This macro is a utility macro intended as a empty starting point for appending 
			to the tail.&nbsp; It is <i>not</i> a nil <i>seq</i>.&nbsp; When an element is 
			appended to this macro, it expands on the element and to the element--thereby 
			removing itself.&nbsp; For example, both <b>BOOST_PP_SEQ_NIL</b>(<i>x</i>) and <b>BOOST_PP_SEQ_PUSH_BACK</b>(<b>BOOST_PP_SEQ_NIL</b>,
			<i>x</i>) expand to <i>x</i>.
		</div>
		<div>
			If any <b>BOOST_PP_SEQ_</b>* macro (other than <b>BOOST_PP_SEQ_PUSH_BACK</b>) 
			is invoked with an argument that contains <b>BOOST_PP_SEQ_NIL</b>, the behavior 
			is undefined and in most cases will result in obscure errors.
		</div>
		<div>
			The closest thing available to <b>BOOST_PP_SEQ_NIL</b> for appending to the 
			head is <b>BOOST_PP_EMPTY</b>.&nbsp; After all the elements have been 
			prepended, empty parenthesis can be invoked on the tail to remove the <b>BOOST_PP_EMPTY</b>.&nbsp; 
			As with <b>BOOST_PP_SEQ_NIL</b>, passing an argument that contains <b>BOOST_PP_EMPTY</b>
			to any <b>BOOST_PP_SEQ_</b>* macro (other than <b>BOOST_PP_SEQ_PUSH_FRONT</b>) 
			is undefined.&nbsp;
		</div>
		<div>
			(It is also possible to start with an extra element and pop it off when you 
			have finished appending to it.)
		</div>
		<div>
			In C99, neither of these macros are necessary since it is legal to pass empty 
			arguments.
		</div>
		<h4>
			See Also
		</h4>
		<ul>
			<li>
				<a href="empty.html">BOOST_PP_EMPTY</a></li>
		</ul>
		<h4>
			Requirements
		</h4>
		<div>
			<b>Header:</b> &nbsp;<a href="../headers/seq/seq.html">&lt;boost/preprocessor/seq/seq.hpp&gt;</a>
		</div>
		<h4>
			Sample Code
		</h4>
		<div>
			<pre>#include &lt;<a href="../headers/facilities/empty.html">boost/preprocessor/facilities/empty.hpp</a>&gt;<br>#include &lt;<a href="../headers/seq/push_back.html">boost/preprocessor/seq/push_back.hpp</a>&gt;<br>#include &lt;<a href="../headers/seq/push_front.html">boost/preprocessor/seq/push_front.hpp</a>&gt;<br>#include &lt;<a href="../headers/seq/seq.html">boost/preprocessor/seq/seq.hpp</a>&gt;<br><br>#define SEQ_L <a href="seq_nil.html">BOOST_PP_SEQ_NIL</a>
#define SEQ_R <a href="empty.html">BOOST_PP_EMPTY</a>
<a href="seq_push_back.html">BOOST_PP_SEQ_PUSH_BACK</a>(<br>   <a href="seq_push_back.html">BOOST_PP_SEQ_PUSH_BACK</a>(SEQ_L, a), b<br>)<br><br>// expands to (a)(b)<br><br><a href="seq_push_front.html">BOOST_PP_SEQ_PUSH_FRONT</a>(<br>   <a href="seq_push_front.html">BOOST_PP_SEQ_PUSH_FRONT</a>(SEQ_R, a), b<br>)()<br><br>// expands to (b)(a)<br></pre>
		</div>
	<hr size="1">
	<div style="margin-left: 0px;">
		<i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
		<br><i>© Copyright Paul Mensonides 2002</i>
	</div>
	<div style="margin-left: 0px;">
		<p><small>Distributed under the Boost Software License, Version 1.0. (See
		accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
		copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
	</div>
</body>
</html>