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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="id831016" href="#ftn.id831016" 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="id831131" href="#ftn.id831131" 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="id831446"></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="id833636"></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="id833910"></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="id834620"></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.id831016" href="#id831016" 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.id831131" href="#id831131" 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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