| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Examples</title> |
| <link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> |
| <link rel="home" href="../index.html" title="Chapter 1. Boost.LocalFunction 1.0.0"> |
| <link rel="up" href="../index.html" title="Chapter 1. Boost.LocalFunction 1.0.0"> |
| <link rel="prev" href="advanced_topics.html" title="Advanced Topics"> |
| <link rel="next" href="alternatives.html" title="Annex: Alternatives"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="advanced_topics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="alternatives.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <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 non-standard <a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html" target="_top">statement |
| expression</a> extension of the GCC compiler, 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 GCC statement expression |
| extension or that support <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a>. |
| </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_cxx11_lambda.cpp" target="_top"><code class="literal">gcc_cxx11_lambda.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">-></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> |
| The GCC lambda function macros are implemented using local functions (see |
| also <a href="../../../example/gcc_lambda.hpp" target="_top"><code class="literal">gcc_lambda.hpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor"># define</span> <span class="identifier">GCC_LAMBDA_</span><span class="special">(</span><span class="identifier">binds</span><span class="special">,</span> <span class="identifier">params</span><span class="special">,</span> <span class="identifier">results</span><span class="special">)</span> <span class="special">\</span> |
| <span class="special">({</span> <span class="comment">/* open statement expression (GCC extension only) */</span> <span class="special">\</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_LIST_ENUM</span><span class="special">(</span><span class="identifier">BOOST_PP_LIST_APPEND</span><span class="special">(</span><span class="identifier">binds</span><span class="special">,</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_LIST_APPEND</span><span class="special">(</span><span class="identifier">params</span><span class="special">,</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_IIF</span><span class="special">(</span><span class="identifier">BOOST_PP_LIST_IS_NIL</span><span class="special">(</span><span class="identifier">results</span><span class="special">),</span> <span class="special">\</span> |
| <span class="special">(</span><span class="keyword">return</span> <span class="keyword">void</span><span class="special">,</span> <span class="identifier">BOOST_PP_NIL</span><span class="special">)</span> <span class="comment">/* default for lambdas */</span> <span class="special">\</span> |
| <span class="special">,</span> <span class="special">\</span> |
| <span class="identifier">results</span> <span class="special">\</span> |
| <span class="special">)\</span> |
| <span class="special">)</span> <span class="special">\</span> |
| <span class="special">))</span> <span class="special">\</span> |
| <span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">GCC_LAMBDA_END_</span><span class="special">(</span><span class="identifier">id</span><span class="special">)</span> <span class="special">\</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">gcc_lambda_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">))</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">gcc_lambda_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">);</span> <span class="special">\</span> |
| <span class="special">})</span> <span class="comment">/* close statement expression (GCC extension only) */</span> |
| </pre> |
| <p> |
| </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 functions</a> in which case the implementation uses native lambdas |
| instead of local functions in GCC statement expressions. However, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> 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 <code class="computeroutput"><span class="special">=</span><span class="identifier">variable</span></code> |
| for <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a>) and <code class="computeroutput"><span class="identifier">bind</span><span class="special">&</span> <span class="identifier">variable</span></code> |
| (same as <code class="computeroutput"><span class="special">&</span><span class="identifier">variable</span></code> |
| for <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a>') because these have the exact same semantic between |
| the local function and the native lambda implementations. Furthermore, local |
| functions allow to bind data members directly while <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> require to access data members via binding the object |
| <code class="computeroutput"><span class="keyword">this</span></code>. Unfortunately, the short-hand |
| binds <code class="computeroutput"><span class="special">&</span></code> and <code class="computeroutput"><span class="special">=</span></code> of <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> (which automatically bind all variables in scope |
| either by reference or value) are not supported by these GCC lambda function |
| macros because they are not supported by local functions. 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 functions</a>). |
| </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 concept 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> |
| The constant block macros are implemented using local functions (see also |
| <a href="../../../example/const_block.hpp" target="_top"><code class="literal">const_block.hpp</code></a>): |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">CONST_BLOCK_</span><span class="special">(</span><span class="identifier">variables</span><span class="special">)</span> <span class="special">\</span> |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_IIF</span><span class="special">(</span><span class="identifier">BOOST_PP_LIST_IS_NIL</span><span class="special">(</span><span class="identifier">variables</span><span class="special">,</span> <span class="special">\</span> |
| <span class="keyword">void</span> <span class="identifier">BOOST_PP_TUPLE_EAT</span><span class="special">(</span><span class="number">3</span><span class="special">)</span> <span class="special">\</span> |
| <span class="special">,</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_LIST_FOR_EACH_I</span> <span class="special">\</span> |
| <span class="special">)(</span><span class="identifier">CONST_BLOCK_BIND_</span><span class="special">,</span> <span class="special">~,</span> <span class="identifier">variables</span><span class="special">)</span> <span class="special">\</span> |
| <span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">CONST_BLOCK_END_</span><span class="special">(</span><span class="identifier">id</span><span class="special">)</span> <span class="special">\</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">const_block_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">))</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">const_block_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">)();</span> <span class="comment">/* call local function immediately */</span> |
| </pre> |
| <p> |
| </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">&</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 and it 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 functions</a> because these do not support constant binding. Variables |
| bound by value using <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> (<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">29</a>]</sup> Of course it is always possible to introduce extra constant variables |
| and bind these variables to the <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> but the constant block code will then have to manage |
| the declaration and initialization of these extra variables plus it will |
| have to use the extra variable names instead of the original variable names: |
| </p> |
| <p> |
| </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="keyword">const</span> <span class="identifier">decltype</span><span class="special">(</span><span class="identifier">x</span><span class="special">)&</span> <span class="identifier">const_x</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">;</span> <span class="comment">// Constant so cannot be modified</span> |
| <span class="keyword">const</span> <span class="identifier">decltype</span><span class="special">(</span><span class="identifier">y</span><span class="special">)&</span> <span class="identifier">const_y</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">;</span> <span class="comment">// and reference so no copy.</span> |
| <span class="special">[&</span><span class="identifier">const_x</span><span class="special">,</span> <span class="special">&</span><span class="identifier">const_y</span><span class="special">]()</span> <span class="special">{</span> <span class="comment">// Lambda functions (C++11 only).</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">const_x</span> <span class="special">=</span> <span class="identifier">const_y</span><span class="special">);</span> <span class="comment">// Unfortunately, `const_` names.</span> |
| <span class="special">}();</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| In many cases the use of an extra constant variable <code class="computeroutput"><span class="identifier">const_x</span></code> |
| can be acceptable but in other cases it might be preferable to maintain the |
| same variable name <code class="computeroutput"><span class="identifier">x</span></code> within |
| the function body. |
| </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). |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| 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 by this example whenever possible (because |
| <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a> |
| is a library deliberately designed to support the scope exit construct). |
| </p></td></tr> |
| </table></div> |
| <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">&</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">&</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">-></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> |
| <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">&</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">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="identifier">checkpoint</span><span class="special">,</span> <span class="special">&</span><span class="identifier">p</span><span class="special">,</span> <span class="identifier">this_</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Or extra variable `const_p`.</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">-></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">BOOST_SCOPE_EXIT_END</span> |
| </pre> |
| <p> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <p> |
| The scope exit macros are implemented by passing a local function when constructing |
| an object of the following class (see also <a href="../../../example/scope_exit.hpp" target="_top"><code class="literal">scope_exit.hpp</code></a>): |
| </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"><</span><span class="keyword">void</span> <span class="special">(</span><span class="keyword">void</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="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"><</span><span class="keyword">void</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)></span> <span class="identifier">f_</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor"># define</span> <span class="identifier">SCOPE_EXIT</span><span class="special">(...)</span> <span class="special">\</span> |
| <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">__VA_ARGS__</span><span class="special">)</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">SCOPE_EXIT_END_</span><span class="special">(</span><span class="identifier">id</span><span class="special">)</span> <span class="special">\</span> |
| <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">scope_exit_func_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">))</span> <span class="special">\</span> |
| <span class="identifier">scope_exit</span> <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">scope_exit_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">)(</span> <span class="special">\</span> |
| <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">scope_exit_func_</span><span class="special">,</span> <span class="identifier">id</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="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</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"><=</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"><</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)></span> <span class="special">></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_TEST</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_TEST</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="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</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"><</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span> |
| |
| <span class="keyword">template</span><span class="special"><</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">></span> |
| <span class="keyword">struct</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span><span class="special">)></span> <span class="special">:</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span> <span class="keyword">const</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">This</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span><span class="special">&)></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"><</span><span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></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"><=</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="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</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"><</span><span class="identifier">factorial_impl</span><span class="special">></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_TEST</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_TEST</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="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</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">30</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 useful. |
| </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 as a non-standard extension under |
| the name of <a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html" target="_top">nested |
| functions</a>. Note that 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 local functions: |
| </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 different C++ "N-papers" |
| and programmed using local functions: |
| </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 functions</a>): 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 functions</a>): 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">29</a>] </sup> |
| Ideally, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 |
| lambda functions</a> would allow to bind variables also using <code class="computeroutput"><span class="keyword">const</span><span class="special">&</span> <span class="identifier">variable</span></code> (constant reference) and <code class="computeroutput"><span class="keyword">const</span><span class="special">&</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">30</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 © 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> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="advanced_topics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="alternatives.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
