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Lorenzo Caminiti 259533b62b Fixed a bug in BOOST_LOCAL_FUNCTION_DETAIL_PP_VOID_LIST: a typo VOId -> VOID. 
Fixed a bug in scope_exit.hpp: An extra trailing \ in a macro definition (compiled only when BOOST_NO_VARIADIC_MACROS is defined).
Renamed LocalFunction and ScopeExit tests and examples from _err to _error.
Updated LocalFunction docs.

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<div class="section boost_localfunction_Examples">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_localfunction.Examples"></a><a class="link" href="Examples.html" title="Examples">Examples</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.gcc_lambdas__without_c__11_">GCC
Lambdas (without C++11)</a></span></dt>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.constant_blocks">Constant
Blocks</a></span></dt>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.scope_exits">Scope Exits</a></span></dt>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.boost_phoenix_functions">Boost.Phoenix
Functions</a></span></dt>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.closures">Closures</a></span></dt>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.gcc_nested_functions">GCC
Nested Functions</a></span></dt>
<dt><span class="section"><a href="Examples.html#boost_localfunction.Examples.n_papers">N-Papers</a></span></dt>
</dl></div>
<p>
This section lists some examples that use this library.
</p>
<div class="section boost_localfunction_Examples_gcc_lambdas__without_c__11_">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.gcc_lambdas__without_c__11_"></a><a class="link" href="Examples.html#boost_localfunction.Examples.gcc_lambdas__without_c__11_" title="GCC Lambdas (without C++11)">GCC
Lambdas (without C++11)</a>
</h3></div></div></div>
<p>
Combing local functions with the <a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html" target="_top">statement
expression</a> extension of GCC compilers, it is possible to implement
lambda functions for GCC compilers even without <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a>
support.
</p>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
This code only works on compilers that support the statement expression
GCC extension or that support <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions.
</p></td></tr>
</table></div>
<p>
For example (see also <a href="../../../example/gcc_lambda.cpp" target="_top"><code class="literal">gcc_lambda.cpp</code></a>
and <a href="../../../example/gcc_lambda_cpp11.cpp" target="_top"><code class="literal">gcc_lambda_cpp11.cpp</code></a>):
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
With Local Functions (GCC only)
</p>
</th>
<th>
<p>
C++11 Lambdas
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">val</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">nums</span><span class="special">[]</span> <span class="special">=</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>
<span class="keyword">int</span><span class="special">*</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">3</span><span class="special">;</span>
<span class="keyword">int</span><span class="special">*</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span>
<span class="identifier">GCC_LAMBDA</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">val</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">,</span> <span class="keyword">return</span> <span class="keyword">bool</span><span class="special">)</span> <span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">num</span> <span class="special">==</span> <span class="identifier">val</span><span class="special">;</span>
<span class="special">}</span> <span class="identifier">GCC_LAMBDA_END</span>
<span class="special">);</span>
</pre>
<p>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">val</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">nums</span><span class="special">[]</span> <span class="special">=</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>
<span class="keyword">int</span><span class="special">*</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">3</span><span class="special">;</span>
<span class="keyword">int</span><span class="special">*</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span>
<span class="special">[</span><span class="identifier">val</span><span class="special">](</span><span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">-&gt;</span> <span class="keyword">bool</span> <span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">num</span> <span class="special">==</span> <span class="identifier">val</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">);</span>
</pre>
<p>
</p>
</td>
</tr></tbody>
</table></div>
<p>
Where the macros are defined in <a href="../../../example/gcc_lambda.hpp" target="_top"><code class="literal">gcc_lambda.hpp</code></a>.
</p>
<p>
This is possible because GCC statement expressions allow to use declaration
statements within expressions and therefore to declare a local function within
an expression. The macros automatically detect if the compiler supports
<a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions in which case the implementation uses native lambdas
instead of local functions in statement expressions. However, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions do not support constant binding so it is best to
only use <code class="computeroutput"><span class="keyword">const</span> <span class="identifier">bind</span>
<span class="identifier">variable</span></code> (same as <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> <code class="computeroutput"><span class="special">=</span><span class="identifier">variable</span></code>)
and <code class="computeroutput"><span class="identifier">bind</span><span class="special">&amp;</span>
<span class="identifier">variable</span></code> (same as <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> <code class="computeroutput"><span class="special">&amp;</span><span class="identifier">variable</span></code>)
because these have the exact same semantic between the local function and
native lambda implementation. Unfortunately, the <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> short-hand binds <code class="computeroutput"><span class="special">&amp;</span></code>
and <code class="computeroutput"><span class="special">=</span></code> (which automatically bind
all variables in scope either by reference or value) are not supported by
the macros because they are not supported by the local function implementation.
Finally, the result type <code class="computeroutput"><span class="keyword">return</span> </code><code class="literal"><span class="emphasis"><em>result-type</em></span></code>
is optional and it is assumed <code class="computeroutput"><span class="keyword">void</span></code>
when it is not specified (same as with <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions).
</p>
</div>
<div class="section boost_localfunction_Examples_constant_blocks">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.constant_blocks"></a><a class="link" href="Examples.html#boost_localfunction.Examples.constant_blocks" title="Constant Blocks">Constant
Blocks</a>
</h3></div></div></div>
<p>
It is possible to use local functions to check assertions between variables
that are made constant within the asserted expressions. This is advantageous
because assertions are not supposed to change the state of the program and
ideally the compiler will not compile assertions that modify variables.
</p>
<p>
For example, consider the following assertion where by mistake we programmed
<code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span></code>
instead of <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code>:
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">);</span> <span class="comment">// Mistakenly `=` instead of `==`.</span>
</pre>
<p>
Ideally this code will not compile instead this example not only compiles
but the assertion even passes the run-time check and no error is generated
at all. The <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2004/n1613.pdf" target="_top">[N1613]</a>
paper introduces the idea of a <span class="emphasis"><em>const-block</em></span> which could
be used to wrap the assertion above and catch the programming error at compile-time.
Similarly, the following code will generate a compile-time error when <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span></code>
is mistakenly used instead of <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> because both <code class="computeroutput"><span class="identifier">x</span></code>
and <code class="computeroutput"><span class="identifier">y</span></code> are made constants
(using local functions) within the block of code performing the assertion
(see also <a href="../../../example/const_block_error.cpp" target="_top"><code class="literal">const_block_error.cpp</code></a>):
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
With Local Functions
</p>
</th>
<th>
<p>
N1613 Const-Blocks
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span>
<span class="identifier">CONST_BLOCK</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">y</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Constant block.</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">);</span> <span class="comment">// Compiler error.</span>
<span class="special">}</span> <span class="identifier">CONST_BLOCK_END</span>
</pre>
<p>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span>
<span class="keyword">const</span> <span class="special">{</span> <span class="comment">// Constant block.</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">);</span> <span class="comment">// Compiler error.</span>
<span class="special">}</span>
</pre>
<p>
</p>
</td>
</tr></tbody>
</table></div>
<p>
Where the macros are defined in <a href="../../../example/const_block.hpp" target="_top"><code class="literal">const_block.hpp</code></a>.
</p>
<p>
The constant block macros are implemented using a local function which binds
by constant reference <code class="computeroutput"><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&amp;</span></code>
all the specified variables (so the variables are constant within the code
block but they do not need to be <code class="computeroutput"><span class="identifier">CopyConstructible</span></code>
and no extra copy is performed). The local function executes the <code class="computeroutput"><span class="identifier">assert</span></code> instruction in its body which is
called immediately after it is defined. More in general, constant blocks
can be used to evaluate any instruction (not just assertions) within a block
were all specified variables are constant.
</p>
<p>
Unfortunately, constant blocks cannot be implemented with <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions because these do not support constant binding (of
course it is always possible to introduce extra constant variables <code class="computeroutput"><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&amp;</span> <span class="identifier">const_x</span>
<span class="special">=</span> <span class="identifier">x</span></code>,
etc and use these variables in the assertion). Variables bound by value using
<a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions (<code class="computeroutput"><span class="identifier">variable</span></code>,
<code class="computeroutput"><span class="special">=</span><span class="identifier">variable</span></code>,
and <code class="computeroutput"><span class="special">=</span></code>) are constant but they
are required to be <code class="computeroutput"><span class="identifier">CopyConstructible</span></code>
and they introduce potentially expensive copy operations. <sup>[<a name="boost_localfunction.Examples.constant_blocks.f0" href="#ftn.boost_localfunction.Examples.constant_blocks.f0" class="footnote">27</a>]</sup>
</p>
</div>
<div class="section boost_localfunction_Examples_scope_exits">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.scope_exits"></a><a class="link" href="Examples.html#boost_localfunction.Examples.scope_exits" title="Scope Exits">Scope Exits</a>
</h3></div></div></div>
<p>
Scope exits allow to execute arbitrary code at the exit of the enclosing
scope and they are provided by the <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a>
library.
</p>
<p>
For curiosity, here we show how to re-implement scope exits using local functions.
One small advantage of scope exits that use local functions is that they
support constant binding. <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a>
does not directly support constant binding (however, it is always possible
to introduce an extra <code class="computeroutput"><span class="keyword">const</span></code>
local variable, assign it to the value to bind, and then bind the <code class="computeroutput"><span class="keyword">const</span></code> variable so to effectively have constant
binding with <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a>
as well). In general, the authors recommend to use <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a>
instead of the code listed here whenever possible.
</p>
<p>
The following example binds <code class="computeroutput"><span class="identifier">p</span></code>
by constant reference so this variable cannot be modified within the scope
exit body but it is not copied and it will present the value it has at the
exit of the enclosing scope and not at the scope exit declaration (see also
<a href="../../../example/scope_exit.cpp" target="_top"><code class="literal">scope_exit.cpp</code></a>):
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
With Local Functions
</p>
</th>
<th>
<p>
Boost.ScopeExit
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">person</span><span class="special">&amp;</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">back</span><span class="special">();</span>
<span class="identifier">person</span><span class="special">::</span><span class="identifier">evolution_t</span> <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution_</span><span class="special">;</span>
<span class="identifier">SCOPE_EXIT</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">checkpoint</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">bind</span> <span class="identifier">this_</span><span class="special">)</span> <span class="special">{</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution_</span><span class="special">)</span> <span class="identifier">this_</span><span class="special">-&gt;</span><span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span>
<span class="special">}</span> <span class="identifier">SCOPE_EXIT_END</span>
</pre>
<p>
</p>
</td>
<td>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting">person&amp; p = persons_.back();
person::evolution_t checkpoint = p.evolution_;
BOOST_SCOPE_EXIT(checkpoint, &amp;p, this_) { // Or extra variable <code class="computeroutput"><span class="identifier">const_p</span></code>.
if (checkpoint == p.evolution_) this_-&gt;persons_.pop_back();
} BOOST_SCOPE_EXIT_END
</pre>
</td>
</tr></tbody>
</table></div>
<p>
Where the macros are defined in <a href="../../../example/scope_exit.hpp" target="_top"><code class="literal">scope_exit.hpp</code></a>.
</p>
<p>
The scope exit macros are implemented by passing a local function when constructing
an object of the following class:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">scope_exit</span> <span class="special">{</span>
<span class="identifier">scope_exit</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span><span class="keyword">void</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)&gt;</span> <span class="identifier">f</span><span class="special">):</span> <span class="identifier">f_</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> <span class="special">{}</span>
<span class="special">~</span><span class="identifier">scope_exit</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">f_</span><span class="special">();</span> <span class="special">}</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span><span class="keyword">void</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)&gt;</span> <span class="identifier">f_</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
A local variable within the enclosing scope is used to hold the object so
the destructor will be invoked at the exit of the enclosing scope and it
will in turn call the local function executing the scope exit instructions.
The scope exit local function has no parameter and <code class="computeroutput"><span class="keyword">void</span></code>
result type but it supports binding and constant binding.
</p>
</div>
<div class="section boost_localfunction_Examples_boost_phoenix_functions">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.boost_phoenix_functions"></a><a class="link" href="Examples.html#boost_localfunction.Examples.boost_phoenix_functions" title="Boost.Phoenix Functions">Boost.Phoenix
Functions</a>
</h3></div></div></div>
<p>
Local functions can be used to create <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a>
functions. For example (see also <a href="../../../example/phoenix_factorial_local.cpp" target="_top"><code class="literal">phoenix_factorial_local.cpp</code></a>
and <a href="../../../example/phoenix_factorial.cpp" target="_top"><code class="literal">phoenix_factorial.cpp</code></a>):
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Local Functions
</p>
</th>
<th>
<p>
Global Functor
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">BOOST_AUTO_TEST_CASE</span><span class="special">(</span> <span class="identifier">test_phoenix_factorial_local</span> <span class="special">)</span> <span class="special">{</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">arg_names</span><span class="special">::</span><span class="identifier">arg1</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">n</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Unfortunately, monomorphic.</span>
<span class="keyword">return</span> <span class="special">(</span><span class="identifier">n</span> <span class="special">&lt;=</span> <span class="number">0</span><span class="special">)</span> <span class="special">?</span> <span class="number">1</span> <span class="special">:</span> <span class="identifier">n</span> <span class="special">*</span> <span class="identifier">factorial_impl</span><span class="special">(</span><span class="identifier">n</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span>
<span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">recursive</span> <span class="identifier">factorial_impl</span><span class="special">)</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)&gt;</span> <span class="special">&gt;</span>
<span class="identifier">factorial</span><span class="special">(</span><span class="identifier">factorial_impl</span><span class="special">);</span> <span class="comment">// Phoenix function from local function.</span>
<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">4</span><span class="special">;</span>
<span class="identifier">BOOST_CHECK</span><span class="special">(</span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">i</span><span class="special">)()</span> <span class="special">==</span> <span class="number">24</span> <span class="special">);</span> <span class="comment">// Call.</span>
<span class="identifier">BOOST_CHECK</span><span class="special">(</span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">)(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">==</span> <span class="number">24</span> <span class="special">);</span> <span class="comment">// Lazy call.</span>
<span class="special">}</span>
</pre>
<p>
</p>
</td>
<td>
<p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">struct</span> <span class="identifier">factorial_impl</span> <span class="special">{</span> <span class="comment">// Phoenix function from global functor.</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">This</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">result</span><span class="special">&lt;</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span><span class="special">)&gt;</span> <span class="special">:</span> <span class="identifier">result</span><span class="special">&lt;</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span> <span class="keyword">const</span><span class="special">&amp;)&gt;</span> <span class="special">{};</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">This</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">result</span><span class="special">&lt;</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span><span class="special">&amp;)&gt;</span> <span class="special">{</span> <span class="keyword">typedef</span> <span class="identifier">Arg</span> <span class="identifier">type</span><span class="special">;</span> <span class="special">};</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">&gt;</span> <span class="comment">// Polymorphic.</span>
<span class="identifier">Arg</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Arg</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span>
<span class="keyword">return</span> <span class="special">(</span><span class="identifier">n</span> <span class="special">&lt;=</span> <span class="number">0</span><span class="special">)</span> <span class="special">?</span> <span class="number">1</span> <span class="special">:</span> <span class="identifier">n</span> <span class="special">*</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)(</span><span class="identifier">n</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span>
<span class="special">}</span>
<span class="special">};</span>
<span class="identifier">BOOST_AUTO_TEST_CASE</span><span class="special">(</span> <span class="identifier">test_phoenix_factorial</span> <span class="special">)</span> <span class="special">{</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">arg_names</span><span class="special">::</span><span class="identifier">arg1</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span><span class="identifier">factorial_impl</span><span class="special">&gt;</span> <span class="identifier">factorial</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">4</span><span class="special">;</span>
<span class="identifier">BOOST_CHECK</span><span class="special">(</span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">i</span><span class="special">)()</span> <span class="special">==</span> <span class="number">24</span> <span class="special">);</span> <span class="comment">// Call.</span>
<span class="identifier">BOOST_CHECK</span><span class="special">(</span> <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">)(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">==</span> <span class="number">24</span> <span class="special">);</span> <span class="comment">// Lazy call.</span>
<span class="special">}</span>
</pre>
<p>
</p>
</td>
</tr></tbody>
</table></div>
<p>
This is presented here mainly as a curiosity because <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a>
functions created from local functions have the important limitation that
they cannot be polymorphic. <sup>[<a name="boost_localfunction.Examples.boost_phoenix_functions.f0" href="#ftn.boost_localfunction.Examples.boost_phoenix_functions.f0" class="footnote">28</a>]</sup> Therefore, in many cases creating the <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a>
function from global functors (possibly with the help of <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a>
adaptor macros) might be a more valuable option.
</p>
</div>
<div class="section boost_localfunction_Examples_closures">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.closures"></a><a class="link" href="Examples.html#boost_localfunction.Examples.closures" title="Closures">Closures</a>
</h3></div></div></div>
<p>
The following are examples of <a href="http://en.wikipedia.org/wiki/Closure_(computer_science)" target="_top">closures</a>
that illustrate how to return local functions to the calling scope (note
how extra care is taken in order to ensure that all bound variables remain
valid at the calling scope):
</p>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
<p>
Files
</p>
</th></tr></thead>
<tbody>
<tr><td>
<p>
<a href="../../../test/return_inc.cpp" target="_top"><code class="literal">return_inc.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_this.cpp" target="_top"><code class="literal">return_this.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_setget.cpp" target="_top"><code class="literal">return_setget.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_derivative.cpp" target="_top"><code class="literal">return_derivative.cpp</code></a>
</p>
</td></tr>
</tbody>
</table></div>
</div>
<div class="section boost_localfunction_Examples_gcc_nested_functions">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.gcc_nested_functions"></a><a class="link" href="Examples.html#boost_localfunction.Examples.gcc_nested_functions" title="GCC Nested Functions">GCC
Nested Functions</a>
</h3></div></div></div>
<p>
The GCC C compiler supports local functions under the name of <a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html" target="_top">nested
functions</a>. Nested functions are exclusively a C extension of the
GCC compiler (they are not supported for C++ not even by the GCC compiler,
and they are not part of any C or C++ standard, nor they are supported by
other compilers like MSVC).
</p>
<p>
The following examples are taken form the GCC nested function documentation
and programmed using this library:
</p>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
<p>
Files
</p>
</th></tr></thead>
<tbody>
<tr><td>
<p>
<a href="../../../example/gcc_square.cpp" target="_top"><code class="literal">gcc_square.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../example/gcc_access.cpp" target="_top"><code class="literal">gcc_access.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../example/gcc_store.cpp" target="_top"><code class="literal">gcc_store.cpp</code></a>
</p>
</td></tr>
</tbody>
</table></div>
</div>
<div class="section boost_localfunction_Examples_n_papers">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_localfunction.Examples.n_papers"></a><a class="link" href="Examples.html#boost_localfunction.Examples.n_papers" title="N-Papers">N-Papers</a>
</h3></div></div></div>
<p>
The following examples are taken from a number of N-papers and programmed
using this library.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Files
</p>
</th>
<th>
<p>
Notes
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a href="../../../example/n2550_find_if.cpp" target="_top"><code class="literal">n2550_find_if.cpp</code></a>
</p>
</td>
<td>
<p>
This example is adapted from <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2550.pdf" target="_top">[N2550]</a>
(<a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions): It passes a local function to the STL
algorithm <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a href="../../../example/n2529_this.cpp" target="_top"><code class="literal">n2529_this.cpp</code></a>
</p>
</td>
<td>
<p>
This example is adapted from <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2529.pdf" target="_top">[N2529]</a>
(<a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions): It binds the object in scope <code class="computeroutput"><span class="keyword">this</span></code> to a local function.
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="footnotes">
<br><hr width="100" align="left">
<div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.Examples.constant_blocks.f0" href="#boost_localfunction.Examples.constant_blocks.f0" class="para">27</a>] </sup>
Ideally, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11
lambda</a> functions would allow to bind variables also using <code class="computeroutput"><span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">variable</span></code> (constant reference) and <code class="computeroutput"><span class="keyword">const</span><span class="special">&amp;</span></code>
(all variables by constant reference).
</p></div>
<div class="footnote"><p><sup>[<a id="ftn.boost_localfunction.Examples.boost_phoenix_functions.f0" href="#boost_localfunction.Examples.boost_phoenix_functions.f0" class="para">28</a>] </sup>
<span class="bold"><strong>Rationale.</strong></span> Local functions can only be
monomorphic because they are implemented using local classes and local
classes cannot be templates in C++ (not even in <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a>).
</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 &#169; 2009-2012 Lorenzo
Caminiti<p>
Distributed under the Boost Software License, Version 1.0 (see accompanying
file LICENSE_1_0.txt or a 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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