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eac6afacdc
Also added a C++14 configuration to testing, but using it only for bidrectional map testing at the moment.
53 lines
2.0 KiB
Markdown
53 lines
2.0 KiB
Markdown
## Compile-time usage
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When used with $cxx11, Better Enums are generated entirely during compilation.
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All the data is available for use by your own `constexpr` functions. The
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examples in *this* tutorial aren't very useful, but look at the
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[demos](${prefix}index.html#CompileTimeDemos) 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.
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#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>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>;
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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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[opt-in features page](${prefix}OptInFeatures.html#CompileTimeNameTrimming).
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Basically, it makes `_to_string` `constexpr`, but slows down compilation.
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You can also do things such as:
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<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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}
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Which prints "5", the length of "Green". That 5 was also computed during
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compilation.
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%% description = 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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