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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="core.scoped_enum"></a><a class="link" href="scoped_enum.html" title="scoped_enum">scoped_enum</a> |
| </h2></div></div></div> |
| <div class="toc"><dl class="toc"> |
| <dt><span class="section"><a href="scoped_enum.html#core.scoped_enum.overview">Overview</a></span></dt> |
| <dt><span class="section"><a href="scoped_enum.html#core.scoped_enum.deprecated_syntax">Deprecated syntax</a></span></dt> |
| <dt><span class="section"><a href="scoped_enum.html#core.scoped_enum.acquiring_the_underlying_type_of">Acquiring |
| the underlying type of the enum</a></span></dt> |
| <dt><span class="section"><a href="scoped_enum.html#core.scoped_enum.acknowledgments">Acknowledgments</a></span></dt> |
| </dl></div> |
| <div class="simplesect"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="idp87383984"></a>Authors</h3></div></div></div> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| Beman Dawes |
| </li> |
| <li class="listitem"> |
| Vicente J. Botet Escriba |
| </li> |
| <li class="listitem"> |
| Anthony Williams |
| </li> |
| </ul></div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="core.scoped_enum.overview"></a><a class="link" href="scoped_enum.html#core.scoped_enum.overview" title="Overview">Overview</a> |
| </h3></div></div></div> |
| <p> |
| The <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">scoped_enum</span><span class="special">.</span><span class="identifier">hpp</span></code> header |
| contains a number of macros that can be used to generate C++11 scoped enums |
| (7.2 [dcl.enum]) if the feature is supported by the compiler, otherwise emulate |
| it with C++03 constructs. The <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_SCOPED_ENUMS</span></code> |
| macro from Boost.Config is used to detect the feature support in the compiler. |
| </p> |
| <p> |
| Some of the enumerations defined in the standard library are scoped enums. |
| </p> |
| <pre class="programlisting"><span class="keyword">enum</span> <span class="keyword">class</span> <span class="identifier">future_errc</span> |
| <span class="special">{</span> |
| <span class="identifier">broken_promise</span><span class="special">,</span> |
| <span class="identifier">future_already_retrieved</span><span class="special">,</span> |
| <span class="identifier">promise_already_satisfied</span><span class="special">,</span> |
| <span class="identifier">no_state</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| The user can portably declare such enumeration as follows: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_SCOPED_ENUM_DECLARE_BEGIN</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">broken_promise</span><span class="special">,</span> |
| <span class="identifier">future_already_retrieved</span><span class="special">,</span> |
| <span class="identifier">promise_already_satisfied</span><span class="special">,</span> |
| <span class="identifier">no_state</span> |
| <span class="special">}</span> |
| <span class="identifier">BOOST_SCOPED_ENUM_DECLARE_END</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">)</span> |
| </pre> |
| <p> |
| These macros allows to use <code class="computeroutput"><span class="identifier">future_errc</span></code> |
| in almost all the cases as an scoped enum. |
| </p> |
| <pre class="programlisting"><span class="identifier">future_errc</span> <span class="identifier">ev</span> <span class="special">=</span> <span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">no_state</span><span class="special">;</span> |
| </pre> |
| <p> |
| It is possible to specify the underlying type of the enumeration: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_SCOPED_ENUM_UT_DECLARE_BEGIN</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">,</span> <span class="keyword">unsigned</span> <span class="keyword">int</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">broken_promise</span><span class="special">,</span> |
| <span class="identifier">future_already_retrieved</span><span class="special">,</span> |
| <span class="identifier">promise_already_satisfied</span><span class="special">,</span> |
| <span class="identifier">no_state</span> |
| <span class="special">}</span> |
| <span class="identifier">BOOST_SCOPED_ENUM_DECLARE_END</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">)</span> |
| </pre> |
| <p> |
| The enumeration supports explicit conversion from the underlying type. |
| </p> |
| <p> |
| The enumeration can be forward declared: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_SCOPED_ENUM_FORWARD_DECLARE</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">);</span> |
| </pre> |
| <p> |
| There are however some limitations. First, the emulated scoped enum is not |
| a C++ enum, so <code class="computeroutput"><span class="identifier">is_enum</span><span class="special"><</span> |
| <span class="identifier">future_errc</span> <span class="special">></span></code> |
| will be <code class="computeroutput"><span class="identifier">false_type</span></code>. |
| </p> |
| <p> |
| Second, the emulated scoped enum can not be used in switch nor in template |
| arguments. For these cases the user needs to use some helpers. Instead of |
| </p> |
| <pre class="programlisting"><span class="keyword">switch</span> <span class="special">(</span><span class="identifier">ev</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">case</span> <span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">broken_promise</span><span class="special">:</span> |
| <span class="comment">// ...</span> |
| </pre> |
| <p> |
| use |
| </p> |
| <pre class="programlisting"><span class="keyword">switch</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">native_value</span><span class="special">(</span><span class="identifier">ev</span><span class="special">))</span> |
| <span class="special">{</span> |
| <span class="keyword">case</span> <span class="identifier">future_errc</span><span class="special">::</span><span class="identifier">broken_promise</span><span class="special">:</span> |
| <span class="comment">// ...</span> |
| </pre> |
| <p> |
| and instead of |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><></span> |
| <span class="keyword">struct</span> <span class="identifier">is_error_code_enum</span><span class="special"><</span> <span class="identifier">future_errc</span> <span class="special">></span> <span class="special">:</span> |
| <span class="keyword">public</span> <span class="identifier">true_type</span> |
| <span class="special">{</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| use |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><></span> |
| <span class="keyword">struct</span> <span class="identifier">is_error_code_enum</span><span class="special"><</span> <span class="identifier">BOOST_SCOPED_ENUM_NATIVE</span><span class="special">(</span><span class="identifier">future_errc</span><span class="special">)</span> <span class="special">></span> <span class="special">:</span> |
| <span class="keyword">public</span> <span class="identifier">true_type</span> |
| <span class="special">{</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| Lastly, explicit conversion to the underlying type should be performed with |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">underlying_cast</span></code> instead of <code class="computeroutput"><span class="keyword">static_cast</span></code>: |
| </p> |
| <pre class="programlisting"><span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">underlying_cast</span><span class="special"><</span> <span class="keyword">unsigned</span> <span class="keyword">int</span> <span class="special">>(</span><span class="identifier">ev</span><span class="special">);</span> |
| </pre> |
| <p> |
| Here is usage example: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_SCOPED_ENUM_UT_DECLARE_BEGIN</span><span class="special">(</span><span class="identifier">algae</span><span class="special">,</span> <span class="keyword">char</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">green</span><span class="special">,</span> |
| <span class="identifier">red</span><span class="special">,</span> |
| <span class="identifier">cyan</span> |
| <span class="special">}</span> |
| <span class="identifier">BOOST_SCOPED_ENUM_DECLARE_END</span><span class="special">(</span><span class="identifier">algae</span><span class="special">)</span> |
| <span class="special">...</span> |
| <span class="identifier">algae</span> <span class="identifier">sample</span><span class="special">(</span> <span class="identifier">algae</span><span class="special">::</span><span class="identifier">red</span> <span class="special">);</span> |
| <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">(</span> <span class="identifier">algae</span> <span class="identifier">color</span> <span class="special">);</span> |
| <span class="special">...</span> |
| <span class="identifier">sample</span> <span class="special">=</span> <span class="identifier">algae</span><span class="special">::</span><span class="identifier">green</span><span class="special">;</span> |
| <span class="identifier">foo</span><span class="special">(</span> <span class="identifier">algae</span><span class="special">::</span><span class="identifier">cyan</span> <span class="special">);</span> |
| </pre> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="core.scoped_enum.deprecated_syntax"></a><a class="link" href="scoped_enum.html#core.scoped_enum.deprecated_syntax" title="Deprecated syntax">Deprecated syntax</a> |
| </h3></div></div></div> |
| <p> |
| In early versions of the header there were two ways to declare scoped enums, |
| with different pros and cons to each. The other way used a different set |
| of macros: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_SCOPED_ENUM_START</span><span class="special">(</span><span class="identifier">algae</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">green</span><span class="special">,</span> |
| <span class="identifier">red</span><span class="special">,</span> |
| <span class="identifier">cyan</span> |
| <span class="special">};</span> |
| <span class="identifier">BOOST_SCOPED_ENUM_END</span> |
| <span class="special">...</span> |
| <span class="identifier">BOOST_SCOPED_ENUM</span><span class="special">(</span><span class="identifier">algae</span><span class="special">)</span> <span class="identifier">sample</span><span class="special">(</span> <span class="identifier">algae</span><span class="special">::</span><span class="identifier">red</span> <span class="special">);</span> |
| <span class="keyword">void</span> <span class="identifier">foo</span><span class="special">(</span> <span class="identifier">BOOST_SCOPED_ENUM</span><span class="special">(</span><span class="identifier">algae</span><span class="special">)</span> <span class="identifier">color</span> <span class="special">);</span> |
| <span class="special">...</span> |
| <span class="identifier">sample</span> <span class="special">=</span> <span class="identifier">algae</span><span class="special">::</span><span class="identifier">green</span><span class="special">;</span> |
| <span class="identifier">foo</span><span class="special">(</span> <span class="identifier">algae</span><span class="special">::</span><span class="identifier">cyan</span> <span class="special">);</span> |
| </pre> |
| <p> |
| Here <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM_START</span></code> |
| corresponds to <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM_DECLARE_BEGIN</span></code>, |
| <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM_END</span></code> to |
| <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM_DECLARE_END</span></code> |
| and <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM</span></code> to |
| <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM_NATIVE</span></code>. |
| Note also the semicolon before <code class="computeroutput"><span class="identifier">BOOST_SCOPED_ENUM_END</span></code>. |
| </p> |
| <p> |
| In the current version these macros produce equivalent result to the ones |
| described above and are considered deprecated. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="core.scoped_enum.acquiring_the_underlying_type_of"></a><a class="link" href="scoped_enum.html#core.scoped_enum.acquiring_the_underlying_type_of" title="Acquiring the underlying type of the enum">Acquiring |
| the underlying type of the enum</a> |
| </h3></div></div></div> |
| <p> |
| The header <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">underlying_type</span><span class="special">.</span><span class="identifier">hpp</span></code> defines |
| the metafunction <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">underlying_type</span></code> which can be used to obtain |
| the underlying type of the scoped enum. This metafunction has support for |
| emulated scoped enums declared with macros in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">scoped_enum</span><span class="special">.</span><span class="identifier">hpp</span></code>. When native scoped enums are supported |
| by the compiler, this metafunction is equivalent to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">underlying_type</span></code>. |
| </p> |
| <p> |
| Unfortunately, there are configurations which implement scoped enums but |
| not <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">underlying_type</span></code>. In this case <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">underlying_type</span></code> has to be specialized by |
| user. The macro <code class="computeroutput"><span class="identifier">BOOST_NO_UNDERLYING_TYPE</span></code> |
| is defined to indicate such cases. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="core.scoped_enum.acknowledgments"></a><a class="link" href="scoped_enum.html#core.scoped_enum.acknowledgments" title="Acknowledgments">Acknowledgments</a> |
| </h3></div></div></div> |
| <p> |
| This scoped enum emulation was developed by Beman Dawes, Vicente J. Botet |
| Escriba and Anthony Williams. |
| </p> |
| <p> |
| Helpful comments and suggestions were also made by Kjell Elster, Phil Endecott, |
| Joel Falcou, Mathias Gaunard, Felipe Magno de Almeida, Matt Calabrese, Daniel |
| James and Andrey Semashev. |
| </p> |
| </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 © 2014 Peter Dimov<br>Copyright © 2014 Glen Fernandes<br>Copyright © 2014 Andrey Semashev<p> |
| Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost |
| Software License, Version 1.0</a>. |
| </p> |
| </div></td> |
| </tr></table> |
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