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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="fusion.container.cons"></a><a class="link" href="cons.html" title="cons">cons</a>
</h3></div></div></div>
<a name="fusion.container.cons.description"></a><h5>
<a name="id953163"></a>
<a class="link" href="cons.html#fusion.container.cons.description">Description</a>
</h5>
<p>
<code class="computeroutput"><span class="identifier">cons</span></code> is a simple <a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
Sequence</a>. It is a lisp style recursive list structure where <code class="computeroutput"><span class="identifier">car</span></code> is the <span class="emphasis"><em>head</em></span> and
<code class="computeroutput"><span class="identifier">cdr</span></code> is the <span class="emphasis"><em>tail</em></span>:
usually another cons structure or <code class="computeroutput"><span class="identifier">nil</span></code>:
the empty list. Fusion's <a class="link" href="list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a> is built on top of this more
primitive data structure. It is more efficient than <a class="link" href="vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a> when the target sequence
is constructed piecemeal (a data at a time). The runtime cost of access to
each element is peculiarly constant (see <a class="link" href="../notes.html#fusion.notes.recursive_inlined_functions">Recursive
Inlined Functions</a>).
</p>
<a name="fusion.container.cons.header"></a><h5>
<a name="id953244"></a>
<a class="link" href="cons.html#fusion.container.cons.header">Header</a>
</h5>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">list</span><span class="special">/</span><span class="identifier">cons</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">cons</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<a name="fusion.container.cons.synopsis"></a><h5>
<a name="id953359"></a>
<a class="link" href="cons.html#fusion.container.cons.synopsis">Synopsis</a>
</h5>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Car</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Cdr</span> <span class="special">=</span> <span class="identifier">nil</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">cons</span><span class="special">;</span>
</pre>
<a name="fusion.container.cons.template_parameters"></a><h5>
<a name="id953434"></a>
<a class="link" href="cons.html#fusion.container.cons.template_parameters">Template parameters</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Description
</p>
</th>
<th>
<p>
Default
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Car</span></code>
</p>
</td>
<td>
<p>
Head type
</p>
</td>
<td>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Cdr</span></code>
</p>
</td>
<td>
<p>
Tail type
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">nil</span></code>
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="fusion.container.cons.model_of"></a><h5>
<a name="id953557"></a>
<a class="link" href="cons.html#fusion.container.cons.model_of">Model of</a>
</h5>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
<a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward Sequence</a>
</li></ul></div>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl>
<dt><span class="term"><code class="computeroutput"><span class="identifier">nil</span></code></span></dt>
<dd><p>
An empty <code class="computeroutput"><span class="identifier">cons</span></code>
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">C</span></code></span></dt>
<dd><p>
A <code class="computeroutput"><span class="identifier">cons</span></code> type
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">l</span></code>, <code class="computeroutput"><span class="identifier">l2</span></code></span></dt>
<dd><p>
Instances of <code class="computeroutput"><span class="identifier">cons</span></code>
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">car</span></code></span></dt>
<dd><p>
An arbitrary data
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">cdr</span></code></span></dt>
<dd><p>
Another <code class="computeroutput"><span class="identifier">cons</span></code> list
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">s</span></code></span></dt>
<dd><p>
A <a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
Sequence</a>
</p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">N</span></code></span></dt>
<dd><p>
An <a href="http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL
Integral Constant</a>
</p></dd>
</dl>
</div>
<a name="fusion.container.cons.expression_semantics"></a><h5>
<a name="id953773"></a>
<a class="link" href="cons.html#fusion.container.cons.expression_semantics">Expression Semantics</a>
</h5>
<p>
Semantics of an expression is defined only where it differs from, or is not
defined in <a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
Sequence</a>.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Expression
</p>
</th>
<th>
<p>
Semantics
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">nil</span><span class="special">()</span></code>
</p>
</td>
<td>
<p>
Creates an empty list.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span><span class="special">()</span></code>
</p>
</td>
<td>
<p>
Creates a cons with default constructed elements.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span><span class="special">(</span><span class="identifier">car</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
Creates a cons with <code class="computeroutput"><span class="identifier">car</span></code>
head and default constructed tail.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span><span class="special">(</span><span class="identifier">car</span><span class="special">,</span>
<span class="identifier">cdr</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
Creates a cons with <code class="computeroutput"><span class="identifier">car</span></code>
head and <code class="computeroutput"><span class="identifier">cdr</span></code> tail.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">C</span><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
Copy constructs a cons from a <a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
Sequence</a>, <code class="computeroutput"><span class="identifier">s</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">l</span> <span class="special">=</span>
<span class="identifier">s</span></code>
</p>
</td>
<td>
<p>
Assigns to a cons, <code class="computeroutput"><span class="identifier">l</span></code>,
from a <a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
Sequence</a>, <code class="computeroutput"><span class="identifier">s</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><a class="link" href="../sequence/intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a><span class="special"><</span><span class="identifier">N</span><span class="special">>(</span><span class="identifier">l</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
The Nth element from the beginning of the sequence; see <a class="link" href="../sequence/intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a>.
</p>
</td>
</tr>
</tbody>
</table></div>
<div class="sidebar">
<p class="title"><b></b></p>
<p>
<span class="inlinemediaobject"><img src="../../images/note.png" alt="note"></span> <code class="computeroutput"><a class="link" href="../sequence/intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a><span class="special"><</span><span class="identifier">N</span><span class="special">>(</span><span class="identifier">l</span><span class="special">)</span></code> is provided
for convenience and compatibility with the original <a href="http://www.boost.org/libs/tuple/doc/tuple_users_guide.html" target="_top">Boost.Tuple</a>
library, despite <code class="computeroutput"><span class="identifier">cons</span></code> being
a <a class="link" href="../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward Sequence</a>
only (<code class="computeroutput"><span class="identifier">at</span></code> is supposed to be
a <a class="link" href="../sequence/concepts/random_access_sequence.html" title="Random Access Sequence">Random
Access Sequence</a> requirement). The runtime complexity of <a class="link" href="../sequence/intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a> is constant (see <a class="link" href="../notes.html#fusion.notes.recursive_inlined_functions">Recursive
Inlined Functions</a>).
</p>
</div>
<a name="fusion.container.cons.example"></a><h5>
<a name="id954247"></a>
<a class="link" href="cons.html#fusion.container.cons.example">Example</a>
</h5>
<pre class="programlisting"><span class="identifier">cons</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">cons</span><span class="special"><</span><span class="keyword">float</span><span class="special">></span> <span class="special">></span> <span class="identifier">l</span><span class="special">(</span><span class="number">12</span><span class="special">,</span> <span class="identifier">cons</span><span class="special"><</span><span class="keyword">float</span><span class="special">>(</span><span class="number">5.5f</span><span class="special">));</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <a class="link" href="../sequence/intrinsic/functions/at_c.html" title="at_c"><code class="computeroutput"><span class="identifier">at_c</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">l</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <a class="link" href="../sequence/intrinsic/functions/at_c.html" title="at_c"><code class="computeroutput"><span class="identifier">at_c</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">>(</span><span class="identifier">l</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
</pre>
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Schwinger<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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