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<html>
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<title>Functional</title>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fusion.functional"></a><a class="link" href="functional.html" title="Functional">Functional</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="functional/concepts.html">Concepts</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/concepts/callable.html">Callable Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/reg_callable.html">Regular Callable
Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/def_callable.html">Deferred Callable
Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/poly.html">Polymorphic Function
Object</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/invocation.html">Invocation</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/invocation/functions.html">Functions</a></span></dt>
<dt><span class="section"><a href="functional/invocation/metafunctions.html">Metafunctions</a></span></dt>
<dt><span class="section"><a href="functional/invocation/limits.html">Limits</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/adapters.html">Adapters</a></span></dt>
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<dt><span class="section"><a href="functional/adapters/fused.html">fused</a></span></dt>
<dt><span class="section"><a href="functional/adapters/fused_procedure.html">fused_procedure</a></span></dt>
<dt><span class="section"><a href="functional/adapters/fused_function_object.html">fused_function_object</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused.html">unfused</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused_typed.html">unfused_typed</a></span></dt>
<dt><span class="section"><a href="functional/adapters/limits.html">Limits</a></span></dt>
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<dt><span class="section"><a href="functional/generation.html">Generation</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/generation/functions.html">Functions</a></span></dt>
<dt><span class="section"><a href="functional/generation/metafunctions.html">Metafunctions</a></span></dt>
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<p>
Components to call functions and function objects and to make Fusion code callable
through a function object interface.
</p>
<a name="fusion.functional.header"></a><h4>
<a name="id1033473"></a>
<a class="link" href="functional.html#fusion.functional.header">Header</a>
</h4>
<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>
</pre>
<a name="fusion.functional.fused_and_unfused_forms"></a><h4>
<a name="id1033528"></a>
<a class="link" href="functional.html#fusion.functional.fused_and_unfused_forms">Fused and unfused
forms</a>
</h4>
<p>
What is a function call?
</p>
<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>
</pre>
<p>
It is a name and a tuple written next to each other, left-to-right.
</p>
<p>
Although the C++ syntax does not allow to replace <code class="literal">(a,b,c)</code>
with some Fusion <a class="link" href="sequence.html" title="Sequence">Sequence</a>, introducing
yet another function provides a solution:
</p>
<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>
</pre>
<p>
Alternatively it is possible to apply a simple transformation to <code class="literal">f</code>
in order to achieve the same effect:
</p>
<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>
</pre>
<p>
Now, <code class="literal">f'</code> is an unary function that takes the arguments to
<code class="computeroutput"><span class="identifier">f</span></code> as a tuple; <code class="literal">f'</code>
is the <span class="emphasis"><em>fused</em></span> form of <code class="computeroutput"><span class="identifier">f</span></code>.
Reading the above equivalence right-to-left to get the inverse transformation,
<code class="computeroutput"><span class="identifier">f</span></code> is the <span class="emphasis"><em>unfused</em></span>
form of <code class="literal">f'</code>.
</p>
<a name="fusion.functional.calling_functions_and_function_objects"></a><h4>
<a name="id1033713"></a>
<a class="link" href="functional.html#fusion.functional.calling_functions_and_function_objects">Calling
functions and function objects</a>
</h4>
<p>
Having generic C++ code call back arbitrary functions provided by the client
used to be a heavily repetitive task, as different functions can differ in
arity, invocation syntax and other properties that might be part of the type.
Transporting arguments as Fusion sequences and factoring out the invocation
makes Fusion algorithms applicable to function arguments and also reduces the
problem to one invocation syntax and a fixed arity (instead of an arbitrary
number of arbitrary arguments times several syntactic variants times additional
properties).
</p>
<p>
Transforming an unfused function into its fused counterpart allows n-ary calls
from an algorithm that invokes an unary <a class="link" href="functional/concepts/poly.html" title="Polymorphic Function Object">Polymorphic
Function Object</a> with <a class="link" href="sequence.html" title="Sequence">Sequence</a>
arguments.
</p>
<p>
The library provides several function templates to invoke different kinds of
functions and adapters to transform them into fused form, respectively. Every
variant has a corresponding generator function template that returns an adapter
instance for the given argument.
</p>
<p>
Constructors can be called applying <a href="http://www.boost.org/libs/functional/factory/doc/html/index.html" target="_top">Boost.Functional/Factory</a>.
</p>
<a name="fusion.functional.making_fusion_code_callable_through_a_function_object_interface"></a><h4>
<a name="id1033757"></a>
<a class="link" href="functional.html#fusion.functional.making_fusion_code_callable_through_a_function_object_interface">Making
Fusion code callable through a function object interface</a>
</h4>
<p>
Transforming a fused function into its unfused counterpart allows to create
function objects to accept arbitrary calls. In other words, an unary function
object can be implemented instead of (maybe heavily overloaded) function templates
or function call operators.
</p>
<p>
The library provides both a strictly typed and a generic variant for this transformation.
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>
to attack <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
Forwarding Problem</a>.
</p>
<p>
Both variants have a corresponding generator function template that returns
an adapter instance for the given argument.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="right"><div class="copyright-footer">Copyright &#169; 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>
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