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149 lines
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HTML
149 lines
4.9 KiB
HTML
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<!DOCTYPE html>
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<html>
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<head>
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<title>Compile-time usage - Better Enums</title>
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<link rel="canonical" href="http://aantron.github.io/better-enums/tutorial/CompileTimeUsage.html" />
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<meta name="description" content="Better Enums can be used entirely at compile time in C++11. All
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conversion functions are available for constexpr functions or templates." />
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<meta name="author" content="Anton Bachin" />
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<link rel="stylesheet" href="../better-enums.css" />
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<body class="">
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<nav>
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<div class="container">
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<a class="first" href="https://raw.githubusercontent.com/aantron/better-enums/0.11.3/enum.h"
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download>Download</a>
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<a href="https://github.com/aantron/better-enums">GitHub</a>
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<a href="../index.html">Home</a>
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<a href="../tutorial/HelloWorld.html">Tutorial</a>
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<a href="../ApiReference.html">Reference</a>
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</nav>
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<div class="spacer"> </div>
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<header>
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<div class="container">
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<section>
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<h1><a href="../index.html">Better Enums</a></h1>
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<h2>Reflective compile-time enums for <span class="cpp">C++</span></h2>
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<h3>Open-source under the BSD license</h3>
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</section>
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<section class="notes">
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<p>Version 0.11.3</p>
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<p>To install, just add <code>enum.h</code> to your project.</p>
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<p>
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Visit the GitHub repo for issues, feedback, and the latest development.
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</p>
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</section>
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<section class="buttons">
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<a href="https://raw.githubusercontent.com/aantron/better-enums/0.11.3/enum.h"
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download>Download <code>enum.h</code></a>
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<a href="https://github.com/aantron/better-enums">GitHub</a>
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</section>
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</header>
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<div class="main">
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<div class="container">
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<p>
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Welcome to the Better Enums tutorials! The code in this tutorial forms a
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valid program, which you can <a href="https://github.com/aantron/better-enums/blob/0.11.3/example/9-constexpr.cc">download</a> and play with. The
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program runs as part of the automated test suite.
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</p>
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<h2>Compile-time usage</h2>
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<p>When used with <span class="cpp">C++</span><span class="eleven">11</span>, Better Enums are generated entirely during compilation.
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All the data is available for use by your own <code>constexpr</code> functions. The
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examples in <em>this</em> tutorial aren't very useful, but look at the
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<a href="../index.html#CompileTimeDemos">demos</a> at the bottom of the main page to
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get an idea of what can be done. Here, you will see the basics.</p>
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<pre>#include <iostream>
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// The reason for this is explained below.
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#ifndef BETTER_ENUMS_CONSTEXPR_TO_STRING
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#define BETTER_ENUMS_CONSTEXPR_TO_STRING
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#endif
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<em>#include <enum.h></em>
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<em>BETTER_ENUM</em>(<em>Channel</em>, <em>int</em>, <em>Red</em> = <em>1</em>, <em>Green</em> = <em>2</em>, <em>Blue</em> = <em>3</em>)
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<em>constexpr</em> Channel channel = <em>Channel::_from_integral(2)</em>;
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<em>constexpr</em> int value = <em>channel._to_integral()</em>;
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<em>constexpr</em> const char *name = <em>channel._to_string()</em>;
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<em>constexpr</em> Channel parsed = <em>Channel::_from_string("Red")</em>;</pre><p>All of the above are computed during compilation. The reason for the macro
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definition at the top of the file is explained on the
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<a href="../OptInFeatures.html#CompileTimeNameTrimming">opt-in features page</a>.
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Basically, it makes <code>_to_string</code> <code>constexpr</code>, but slows down compilation.</p>
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<p>You can also do things such as:</p>
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<pre><em>constexpr size_t length</em>(<em>const char *s</em>, <em>size_t index = 0</em>)
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{
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return <em>s[index] == '\0'</em> ? <em>index</em> : <em>length(s, index + 1)</em>;
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}
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<em>constexpr</em> size_t <em>length_of_name_of_second_constant</em> =
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<em>length(Channel::_names()[1])</em>;
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int main()
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{
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std::cout << <em>length_of_name_of_second_constant</em> << std::endl;
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return 0;
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}</pre><p>Which prints "5", the length of "Green". That 5 was also computed during
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compilation.</p>
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<section class="tutorial-footer">
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<p class="up">
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This is the last tutorial! Return to the
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<a href="../index.html">main page</a> for other resources.
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</p>
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</section>
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</div>
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</div>
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<footer>
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<div class="container">
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Copyright © 2015-2019 Anton Bachin. Released under the BSD 2-clause
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license. See
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<a href="https://github.com/aantron/better-enums/blob/0.11.3/doc/LICENSE">
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LICENSE</a>.
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<br />
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This page is part of the documentation for Better Enums 0.11.3.
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