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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="fusion.functional"></a><a class="link" href="functional.html" title="Functional">Functional</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="functional/concepts.html">Concepts</a></span></dt>
  31 <dd><dl>
  32 <dt><span class="section"><a href="functional/concepts/callable.html">Callable Object</a></span></dt>
  33 <dt><span class="section"><a href="functional/concepts/reg_callable.html">Regular Callable
  34         Object</a></span></dt>
  35 <dt><span class="section"><a href="functional/concepts/def_callable.html">Deferred Callable
  36         Object</a></span></dt>
  37 <dt><span class="section"><a href="functional/concepts/poly.html">Polymorphic Function
  38         Object</a></span></dt>
  39 </dl></dd>
  40 <dt><span class="section"><a href="functional/invocation.html">Invocation</a></span></dt>
  41 <dd><dl>
  42 <dt><span class="section"><a href="functional/invocation/functions.html">Functions</a></span></dt>
  43 <dt><span class="section"><a href="functional/invocation/metafunctions.html">Metafunctions</a></span></dt>
  44 <dt><span class="section"><a href="functional/invocation/limits.html">Limits</a></span></dt>
  45 </dl></dd>
  46 <dt><span class="section"><a href="functional/adapters.html">Adapters</a></span></dt>
  47 <dd><dl>
  48 <dt><span class="section"><a href="functional/adapters/fused.html">fused</a></span></dt>
  49 <dt><span class="section"><a href="functional/adapters/fused_procedure.html">fused_procedure</a></span></dt>
  50 <dt><span class="section"><a href="functional/adapters/fused_function_object.html">fused_function_object</a></span></dt>
  51 <dt><span class="section"><a href="functional/adapters/unfused.html">unfused</a></span></dt>
  52 <dt><span class="section"><a href="functional/adapters/unfused_typed.html">unfused_typed</a></span></dt>
  53 <dt><span class="section"><a href="functional/adapters/limits.html">Limits</a></span></dt>
  54 </dl></dd>
  55 <dt><span class="section"><a href="functional/generation.html">Generation</a></span></dt>
  56 <dd><dl>
  57 <dt><span class="section"><a href="functional/generation/functions.html">Functions</a></span></dt>
  58 <dt><span class="section"><a href="functional/generation/metafunctions.html">Metafunctions</a></span></dt>
  59 </dl></dd>
  60 </dl></div>
  61 <p>
  62       Components to call functions and function objects and to make Fusion code callable
  63       through a function object interface.
  64     </p>
  65 <h4>
  66 <a name="fusion.functional.h0"></a>
  67       <span class="phrase"><a name="fusion.functional.header"></a></span><a class="link" href="functional.html#fusion.functional.header">Header</a>
  68     </h4>
  69 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">functional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  70 </pre>
  71 <h4>
  72 <a name="fusion.functional.h1"></a>
  73       <span class="phrase"><a name="fusion.functional.fused_and_unfused_forms"></a></span><a class="link" href="functional.html#fusion.functional.fused_and_unfused_forms">Fused
  74       and unfused forms</a>
  75     </h4>
  76 <p>
  77       What is a function call?
  78     </p>
  79 <pre class="programlisting"><span class="identifier">f</span> <span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">,</span><span class="identifier">c</span><span class="special">)</span>
  80 </pre>
  81 <p>
  82       It is a name and a tuple written next to each other, left-to-right.
  83     </p>
  84 <p>
  85       Although the C++ syntax does not allow to replace <code class="literal">(a,b,c)</code>
  86       with some Fusion <a class="link" href="sequence.html" title="Sequence">Sequence</a>, introducing
  87       yet another function provides a solution:
  88     </p>
  89 <pre class="programlisting"><span class="identifier">invoke</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">my_sequence</span><span class="special">)</span>
  90 </pre>
  91 <p>
  92       Alternatively it is possible to apply a simple transformation to <code class="literal">f</code>
  93       in order to achieve the same effect:
  94     </p>
  95 <pre class="programlisting"><span class="identifier">f</span> <span class="identifier">tuple</span> <span class="special">&lt;=&gt;</span> f' <span class="special">(</span><span class="identifier">tuple</span><span class="special">)</span>
  96 </pre>
  97 <p>
  98       Now, <code class="literal">f'</code> is an unary function that takes the arguments to
  99       <code class="computeroutput"><span class="identifier">f</span></code> as a tuple; <code class="literal">f'</code>
 100       is the <span class="emphasis"><em>fused</em></span> form of <code class="computeroutput"><span class="identifier">f</span></code>.
 101       Reading the above equivalence right-to-left to get the inverse transformation,
 102       <code class="computeroutput"><span class="identifier">f</span></code> is the <span class="emphasis"><em>unfused</em></span>
 103       form of <code class="literal">f'</code>.
 104     </p>
 105 <h4>
 106 <a name="fusion.functional.h2"></a>
 107       <span class="phrase"><a name="fusion.functional.calling_functions_and_function_objects"></a></span><a class="link" href="functional.html#fusion.functional.calling_functions_and_function_objects">Calling
 108       functions and function objects</a>
 109     </h4>
 110 <p>
 111       Having generic C++ code call back arbitrary functions provided by the client
 112       used to be a heavily repetitive task, as different functions can differ in
 113       arity, invocation syntax and other properties that might be part of the type.
 114       Transporting arguments as Fusion sequences and factoring out the invocation
 115       makes Fusion algorithms applicable to function arguments and also reduces the
 116       problem to one invocation syntax and a fixed arity (instead of an arbitrary
 117       number of arbitrary arguments times several syntactic variants times additional
 118       properties).
 119     </p>
 120 <p>
 121       Transforming an unfused function into its fused counterpart allows n-ary calls
 122       from an algorithm that invokes an unary <a class="link" href="functional/concepts/poly.html" title="Polymorphic Function Object">Polymorphic
 123       Function Object</a> with <a class="link" href="sequence.html" title="Sequence">Sequence</a>
 124       arguments.
 125     </p>
 126 <p>
 127       The library provides several function templates to invoke different kinds of
 128       functions and adapters to transform them into fused form, respectively. Every
 129       variant has a corresponding generator function template that returns an adapter
 130       instance for the given argument.
 131     </p>
 132 <p>
 133       Constructors can be called applying <a href="http://www.boost.org/libs/functional/factory/doc/html/index.html" target="_top">Boost.Functional/Factory</a>.
 134     </p>
 135 <h4>
 136 <a name="fusion.functional.h3"></a>
 137       <span class="phrase"><a name="fusion.functional.making_fusion_code_callable_through_a_function_object_interface"></a></span><a class="link" href="functional.html#fusion.functional.making_fusion_code_callable_through_a_function_object_interface">Making
 138       Fusion code callable through a function object interface</a>
 139     </h4>
 140 <p>
 141       Transforming a fused function into its unfused counterpart allows to create
 142       function objects to accept arbitrary calls. In other words, an unary function
 143       object can be implemented instead of (maybe heavily overloaded) function templates
 144       or function call operators.
 145     </p>
 146 <p>
 147       The library provides both a strictly typed and a generic variant for this transformation.
 148       The latter should be used in combination with <a href="http://www.boost.org/libs/functional/forward/doc/html/index.html" target="_top">Boost.Functional/Forward</a>
 149       to attack <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
 150       Forwarding Problem</a>.
 151     </p>
 152 <p>
 153       Both variants have a corresponding generator function template that returns
 154       an adapter instance for the given argument.
 155     </p>
 156 </div>
 157 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 158 <td align="left"></td>
 159 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2006, 2011, 2012 Joel de Guzman,
 160       Dan Marsden, Tobias Schwinger<p>
 161         Distributed under the Boost Software License, Version 1.0. (See accompanying
 162         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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