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<h1><a href="../Table_of_Contents.html"><img src="../mpl_logo.jpg" alt="[Home]" border=0 align="right"></a>empty</h1><h3>Synopsis</h3>
<p>
<pre>
template<
typename Sequence
>
struct empty
{
typedef <em>unspecified</em> type;
};
</pre>
<p>
<h3>Description</h3>
<p>
Returns an <a href="../Integral_Constant.html">Integral Constant</a> <code>c</code> such that <code>c::value == true</code> if and only if the sequence is empty.
<p>
<h3>Definition</h3>
<p>
<pre>
#include "<a href="../../../../../boost/mpl/empty.hpp">boost/mpl/empty.hpp</a>"
</pre>
<p>
<h3>Parameters</h3>
<table border="1">
<tr><th> Parameter </th><th> Requirement </th><th> Description </th></tr>
<tr><td><code>Sequence</code></td><td>A model of <a href="../Sequence.html">Sequence</a></td><td></td></tr>
</table>
<p>
<h3>Expression semantics</h3>
<p>
<table border="1">
<tr><th> Expression </th><th> Expression type </th><th> Precondition </th><th> Semantics </th><th> Postcondition </th></tr>
<tr><td><code>typedef empty<Sequence>::type c;</code></td><td>A model of <code>bool</code> <a href="../Integral_Constant.html">Integral Constant</a></td><td></td><td>Equivalent to <code>typedef is_same< begin<Sequence>::type,end<Sequence>::type >::type c;</code></td><td></td></tr>
</table>
<p>
<p>
<h3>Complexity</h3>
<p>
Amortized constant time.
<p>
<h3>Example</h3>
<p>
<pre>
typedef range_c<int,0,0> empty_range;
typedef list<long,float,double> types;
<p>
BOOST_STATIC_ASSERT(empty<empty_range>::value)
BOOST_STATIC_ASSERT(!empty<types>::value)
</pre>
<p>
<h3>See also</h3>
<p>
<a href="../Sequence.html">Sequence</a>, <code><a href="../Reference/size.html">size</a></code>, <code><a href="../Reference/begin.html">begin</a></code>, <code><a href="../Reference/end.html">end</a></code>
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<a href="../Table_of_Contents.html">Table of Contents</a><br>Last edited July 17, 2002 3:52 am</body></html>
