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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fusion.quick_start"></a><a class="link" href="quick_start.html" title="Quick Start">Quick Start</a>
</h2></div></div></div>
<p>
I assume the reader is already familiar with tuples (<a href="http://www.boost.org/libs/tuple/doc/tuple_users_guide.html" target="_top">Boost.Tuple</a>)
and its ancestor <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code>. The tuple is a generalization of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code>
for multiple heterogeneous elements (triples, quadruples, etc.). The tuple
is more or less a synonym for fusion's <code class="computeroutput"><a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a></code>.
</p>
<p>
For starters, we shall include all of Fusion's <a class="link" href="sequence.html" title="Sequence">Sequence</a>(s)
<sup>[<a name="id873237" href="#ftn.id873237" class="footnote">2</a>]</sup>:
</p>
<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">sequence</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">sequence</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
Let's begin with a <code class="computeroutput"><a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a></code> <sup>[<a name="id873352" href="#ftn.id873352" class="footnote">3</a>]</sup>:
</p>
<pre class="programlisting"><a class="link" href="container/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">char</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">stuff</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="char">'x'</span><span class="special">,</span> <span class="string">"howdy"</span><span class="special">);</span>
<span class="keyword">int</span> <span class="identifier">i</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">stuff</span><span class="special">);</span>
<span class="keyword">char</span> <span class="identifier">ch</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">stuff</span><span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">s</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">2</span><span class="special">>(</span><span class="identifier">stuff</span><span class="special">);</span>
</pre>
<p>
Just replace <code class="computeroutput"><span class="identifier">tuple</span></code> for <code class="computeroutput"><a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a></code>
and <code class="computeroutput"><span class="identifier">get</span></code> for <code class="computeroutput"><a class="link" href="sequence/intrinsic/functions/at_c.html" title="at_c"><code class="computeroutput"><span class="identifier">at_c</span></code></a></code> and this is exactly like
<a href="http://www.boost.org/libs/tuple/doc/tuple_users_guide.html" target="_top">Boost.Tuple</a>.
Actually, either names can be used interchangeably. Yet, the similarity ends
there. You can do a lot more with Fusion <code class="computeroutput"><a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a></code> or <code class="computeroutput"><span class="identifier">tuple</span></code>.
Let's see some examples.
</p>
<a name="fusion.quick_start.print_the_vector_as_xml"></a><h4>
<a name="id873667"></a>
<a class="link" href="quick_start.html#fusion.quick_start.print_the_vector_as_xml">Print the vector
as XML</a>
</h4>
<p>
First, let's include the algorithms:
</p>
<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">algorithm</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">algorithm</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
Now, let's write a function object that prints XML of the form <type>data</type>
for each member in the tuple.
</p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">print_xml</span>
<span class="special">{</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="keyword">const</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span>
<span class="special"><<</span> <span class="char">'<'</span> <span class="special"><<</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">x</span><span class="special">).</span><span class="identifier">name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'>'</span>
<span class="special"><<</span> <span class="identifier">x</span>
<span class="special"><<</span> <span class="string">"</"</span> <span class="special"><<</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">x</span><span class="special">).</span><span class="identifier">name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'>'</span>
<span class="special">;</span>
<span class="special">}</span>
<span class="special">};</span>
</pre>
<p>
Now, finally:
</p>
<pre class="programlisting"><a class="link" href="algorithm/iteration/functions/for_each.html" title="for_each"><code class="computeroutput"><span class="identifier">for_each</span></code></a><span class="special">(</span><span class="identifier">stuff</span><span class="special">,</span> <span class="identifier">print_xml</span><span class="special">());</span>
</pre>
<p>
That's it! <code class="computeroutput"><a class="link" href="algorithm/iteration/functions/for_each.html" title="for_each"><code class="computeroutput"><span class="identifier">for_each</span></code></a></code> is a fusion algorithm.
It is a generic algorithm similar to <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>'s.
It iterates over the sequence and calls a user supplied function. In our case,
it calls <code class="computeroutput"><span class="identifier">print_xml</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special">()</span></code> for
each element in <code class="computeroutput"><span class="identifier">stuff</span></code>.
</p>
<div class="caution"><table border="0" summary="Caution">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../doc/src/images/caution.png"></td>
<th align="left">Caution</th>
</tr>
<tr><td align="left" valign="top"><p>
The result of <code class="computeroutput"><span class="keyword">typeid</span><span class="special">(</span><span class="identifier">x</span><span class="special">).</span><span class="identifier">name</span><span class="special">()</span></code> is platform specific. The code here is
just for exposition. Of course you already know that :-)
</p></td></tr>
</table></div>
<p>
<code class="computeroutput"><a class="link" href="algorithm/iteration/functions/for_each.html" title="for_each"><code class="computeroutput"><span class="identifier">for_each</span></code></a></code> is generic. With
<code class="computeroutput"><span class="identifier">print_xml</span></code>, you can use it to
print just about any Fusion <a class="link" href="sequence.html" title="Sequence">Sequence</a>.
</p>
<a name="fusion.quick_start.print_only_pointers"></a><h4>
<a name="id874129"></a>
<a class="link" href="quick_start.html#fusion.quick_start.print_only_pointers">Print only pointers</a>
</h4>
<p>
Let's get a little cleverer. Say we wish to write a <span class="emphasis"><em>generic</em></span>
function that takes in an arbitrary sequence and XML prints only those elements
which are pointers. Ah, easy. First, let's include the <code class="computeroutput"><span class="identifier">is_pointer</span></code>
boost type trait:
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_pointer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<p>
Then, simply:
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span>
<span class="keyword">void</span> <span class="identifier">xml_print_pointers</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>
<span class="special">{</span>
<a class="link" href="algorithm/iteration/functions/for_each.html" title="for_each"><code class="computeroutput"><span class="identifier">for_each</span></code></a><span class="special">(</span><a class="link" href="algorithm/transformation/functions/filter_if.html" title="filter_if"><code class="computeroutput"><span class="identifier">filter_if</span></code></a><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_pointer</span><span class="special"><</span><span class="identifier">_</span><span class="special">></span> <span class="special">>(</span><span class="identifier">seq</span><span class="special">),</span> <span class="identifier">print_xml</span><span class="special">());</span>
<span class="special">}</span>
</pre>
<p>
<code class="computeroutput"><a class="link" href="algorithm/transformation/functions/filter_if.html" title="filter_if"><code class="computeroutput"><span class="identifier">filter_if</span></code></a></code> is another Fusion
algorithm. It returns a <a class="link" href="view/filter_view.html" title="filter_view"><code class="computeroutput"><span class="identifier">filter_view</span></code></a>, a conforming Fusion sequence.
This view reflects only those elements that pass the given predicate. In this
case, the predicate is <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_pointer</span><span class="special"><</span><span class="identifier">_</span><span class="special">></span></code>.
This "filtered view" is then passed to the <a class="link" href="algorithm/iteration/functions/for_each.html" title="for_each"><code class="computeroutput"><span class="identifier">for_each</span></code></a> algorithm, which then prints
the "filtered view" as XML.
</p>
<p>
Easy, right?
</p>
<a name="fusion.quick_start.associative_tuples"></a><h4>
<a name="id874403"></a>
<a class="link" href="quick_start.html#fusion.quick_start.associative_tuples">Associative tuples</a>
</h4>
<p>
Ok, moving on...
</p>
<p>
Apart from <code class="computeroutput"><a class="link" href="container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a></code>,
fusion has a couple of other sequence types to choose from. Each sequence has
its own characteristics. We have <code class="computeroutput"><a class="link" href="container/list.html" title="list"><code class="computeroutput"><span class="identifier">list</span></code></a></code>, <code class="computeroutput"><a class="link" href="container/set.html" title="set"><code class="computeroutput"><span class="identifier">set</span></code></a></code>, <code class="computeroutput"><a class="link" href="container/map.html" title="map"><code class="computeroutput"><span class="identifier">map</span></code></a></code>, plus a multitude of <code class="computeroutput"><span class="identifier">views</span></code> that provide various ways to present
the sequences.
</p>
<p>
Fusion's <code class="computeroutput"><a class="link" href="container/map.html" title="map"><code class="computeroutput"><span class="identifier">map</span></code></a></code>
associate types with elements. It can be used as a cleverer replacement of
the <code class="computeroutput"><span class="keyword">struct</span></code>. Example:
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">fields</span>
<span class="special">{</span>
<span class="keyword">struct</span> <span class="identifier">name</span><span class="special">;</span>
<span class="keyword">struct</span> <span class="identifier">age</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">typedef</span> <a class="link" href="container/map.html" title="map"><code class="computeroutput"><span class="identifier">map</span></code></a><span class="special"><</span>
<a class="link" href="support/pair.html" title="pair"><code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">pair</span></code></a><span class="special"><</span><span class="identifier">fields</span><span class="special">::</span><span class="identifier">name</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span>
<span class="special">,</span> <a class="link" href="support/pair.html" title="pair"><code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">pair</span></code></a><span class="special"><</span><span class="identifier">fields</span><span class="special">::</span><span class="identifier">age</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="special">></span>
<span class="identifier">person</span><span class="special">;</span>
</pre>
<p>
<code class="computeroutput"><a class="link" href="container/map.html" title="map"><code class="computeroutput"><span class="identifier">map</span></code></a></code>
is an associative sequence. Its elements are Fusion pairs which differ somewhat
from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code>. Fusion pairs only contain one member,
with the type of their second template parameter. The first type parameter
of the pair is used as an index to the associated element in the sequence.
For example, given a <code class="computeroutput"><span class="identifier">a_person</span></code>
of type, <code class="computeroutput"><span class="identifier">person</span></code>, you can do:
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">fields</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">person_name</span> <span class="special">=</span> <a class="link" href="sequence/intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a><span class="special"><</span><span class="identifier">name</span><span class="special">>(</span><span class="identifier">a_person</span><span class="special">);</span>
<span class="keyword">int</span> <span class="identifier">person_age</span> <span class="special">=</span> <a class="link" href="sequence/intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a><span class="special"><</span><span class="identifier">age</span><span class="special">>(</span><span class="identifier">a_person</span><span class="special">);</span>
</pre>
<p>
Why go through all this trouble, you say? Well, for one, unlike the <code class="computeroutput"><span class="keyword">struct</span></code>, we are dealing with a generic data structure.
There are a multitude of facilities available at your disposal provided out
of the box with fusion or written by others. With these facilities, introspection
comes for free, for example. We can write one serialization function (well,
two, if you consider loading and saving) that will work for all your fusion
<code class="computeroutput"><a class="link" href="container/map.html" title="map"><code class="computeroutput"><span class="identifier">map</span></code></a></code>s.
Example:
</p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">saver</span>
<span class="special">{</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Pair</span><span class="special">></span>
<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Pair</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">data</span><span class="special">)</span> <span class="keyword">const</span>
<span class="special">{</span>
<span class="identifier">some_archive</span> <span class="special"><<</span> <span class="identifier">data</span><span class="special">.</span><span class="identifier">second</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">};</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Stuff</span><span class="special">></span>
<span class="keyword">void</span> <span class="identifier">save</span><span class="special">(</span><span class="identifier">Stuff</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">stuff</span><span class="special">)</span>
<span class="special">{</span>
<a class="link" href="algorithm/iteration/functions/for_each.html" title="for_each"><code class="computeroutput"><span class="identifier">for_each</span></code></a><span class="special">(</span><span class="identifier">stuff</span><span class="special">,</span> <span class="identifier">saver</span><span class="special">());</span>
<span class="special">}</span>
</pre>
<p>
The <code class="computeroutput"><span class="identifier">save</span></code> function is generic
and will work for all types of <code class="computeroutput"><span class="identifier">stuff</span></code>
regardless if it is a <code class="computeroutput"><span class="identifier">person</span></code>,
a <code class="computeroutput"><span class="identifier">dog</span></code> or a whole <code class="computeroutput"><span class="identifier">alternate_universe</span></code>.
</p>
<a name="fusion.quick_start.tip_of_the_iceberg"></a><h4>
<a name="id876221"></a>
<a class="link" href="quick_start.html#fusion.quick_start.tip_of_the_iceberg">Tip of the Iceberg</a>
</h4>
<p>
And... we've barely scratched the surface! You can compose and expand the data
structures, remove elements from the structures, find specific data types,
query the elements, filter out types for inspection, transform data structures,
etc. What you've seen is just the tip of the iceberg.
</p>
<div class="footnotes">
<br><hr width="100" align="left">
<div class="footnote"><p><sup>[<a name="ftn.id873237" href="#id873237" class="para">2</a>] </sup>
There are finer grained header files available if you wish to have more control
over which components to include (see section <a class="link" href="organization.html" title="Organization">Orgainization</a>
for details).
</p></div>
<div class="footnote"><p><sup>[<a name="ftn.id873352" href="#id873352" class="para">3</a>] </sup>
Unless otherwise noted, components are in namespace <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span></code>.
For the sake of simplicity, code in this quick start implies <code class="computeroutput"><span class="keyword">using</span></code> directives for the fusion components
we will be using.
</p></div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
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>)
</p>
</div></td>
</tr></table>
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