2006-08-22 15:57:13 +00:00
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2007-02-15 23:11:24 +00:00
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2006-08-22 15:57:13 +00:00
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<link rel="start" href="../../../../index.html" title="Chapter<65>1.<2E>Fusion 2.0">
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<div class="titlepage"><div><div><h5 class="title">
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<a name="fusion.sequences.intrinsics.functions.at"></a><a href="at.html" title="at">at</a></h5></div></div></div>
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<a name="fusion.sequences.intrinsics.functions.at.description"></a><h6>
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2007-02-15 23:11:24 +00:00
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<a name="id1008089"></a>
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<a href="at.html#fusion.sequences.intrinsics.functions.at.description">Description</a>
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</h6>
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<p>
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Returns the N-th element from the beginning of the sequence.
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</p>
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<a name="fusion.sequences.intrinsics.functions.at.synopsis"></a><h6>
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<a name="id1008118"></a>
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<a href="at.html#fusion.sequences.intrinsics.functions.at.synopsis">Synopsis</a>
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</h6>
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<pre class="programlisting">
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">N</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span>
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<span class="keyword">typename</span> <a href="../metafunctions/at.html" title="at"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">N</span><span class="special">>::</span><span class="identifier">type</span>
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<span class="identifier">at</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span>
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<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">N</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span>
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<span class="keyword">typename</span> <a href="../metafunctions/at.html" title="at"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at</span></code></a><span class="special"><</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">,</span> <span class="identifier">N</span><span class="special">>::</span><span class="identifier">type</span>
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<span class="identifier">at</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span>
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</pre>
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<a name="fusion.sequences.intrinsics.functions.at.parameters"></a><h6>
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<a name="id1008409"></a>
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<a href="at.html#fusion.sequences.intrinsics.functions.at.parameters">Parameters</a>
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</h6>
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2006-10-30 01:20:23 +00:00
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>Parameter</th>
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<th>Requirement</th>
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<th>Description</th>
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</tr></thead>
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<tbody>
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<tr>
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<td><code class="computeroutput"><span class="identifier">seq</span></code></td>
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<td>Model
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of <a href="../../concepts/random_access_sequence.html" title="Random
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Access Sequence">Random
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Access Sequence</a>
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</td>
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<td>The sequence we wish to investigate.</td>
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</tr>
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<tr>
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<td><code class="computeroutput"><span class="identifier">N</span></code></td>
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<td>An
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<a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>
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integral constant</td>
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<td>An index from the beginning of
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the sequence.</td>
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</tr>
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</tbody>
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2006-10-30 01:20:23 +00:00
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</table></div>
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2006-08-22 15:57:13 +00:00
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<a name="fusion.sequences.intrinsics.functions.at.expression_semantics"></a><h6>
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2007-02-15 23:11:24 +00:00
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<a name="id1008512"></a>
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2006-08-22 15:57:13 +00:00
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<a href="at.html#fusion.sequences.intrinsics.functions.at.expression_semantics">Expression
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Semantics</a>
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</h6>
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<pre class="programlisting">
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<span class="identifier">at</span><span class="special"><</span><span class="identifier">N</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">);</span>
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</pre>
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<p>
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<span class="bold"><strong>Return type</strong></span>: Returns a reference to
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the N-th element from the beginning of the sequence <code class="computeroutput"><span class="identifier">seq</span></code>
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if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and
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<code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
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<span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code>
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is the N-th element from the beginning of the sequence, is a valid expression.
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Else, returns a type convertable to the N-th element from the beginning
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of the sequence.
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</p>
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<p>
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<span class="bold"><strong>Precondition</strong></span>: <code class="computeroutput"><span class="number">0</span>
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<span class="special"><=</span> <span class="identifier">N</span><span class="special">::</span><span class="identifier">value</span> <span class="special"><</span> <a href="size.html" title="size"><code class="computeroutput"><span class="identifier">size</span></code></a><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code>
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</p>
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<p>
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<span class="bold"><strong>Semantics</strong></span>: Equivalent to
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</p>
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<pre class="programlisting">
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<a href="../../../iterators/functions/deref.html" title="deref"><code class="computeroutput"><span class="identifier">deref</span></code></a><span class="special">(</span><a href="../../../iterators/functions/advance.html" title="advance"><code class="computeroutput"><span class="identifier">advance</span></code></a><span class="special"><</span><span class="identifier">N</span><span class="special">>(</span><a href="begin.html" title="begin"><code class="computeroutput"><span class="identifier">begin</span></code></a><span class="special">(</span><span class="identifier">s</span><span class="special">)))</span>
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</pre>
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<a name="fusion.sequences.intrinsics.functions.at.header"></a><h6>
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2007-02-15 23:11:24 +00:00
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<a name="id1008784"></a>
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2006-08-22 15:57:13 +00:00
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<a href="at.html#fusion.sequences.intrinsics.functions.at.header">Header</a>
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</h6>
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<pre class="programlisting">
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<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">sequence</span><span class="special">/</span><span class="identifier">intrinsic</span><span class="special">/</span><span class="identifier">at</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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</pre>
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<a name="fusion.sequences.intrinsics.functions.at.example"></a><h6>
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2007-02-15 23:11:24 +00:00
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<a name="id1008874"></a>
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2006-08-22 15:57:13 +00:00
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<a href="at.html#fusion.sequences.intrinsics.functions.at.example">Example</a>
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</h6>
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<pre class="programlisting">
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<a href="../../containers/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span>
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<span class="identifier">assert</span><span class="special">(</span><span class="identifier">at</span><span class="special"><</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
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</pre>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><small>Copyright <20> 2001-2005 Joel de Guzman, Dan Marsden</small></td>
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