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138 lines
3.8 KiB
C++
138 lines
3.8 KiB
C++
// This file was generated automatically.
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// Conversions
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//
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// Let's begin by including enum.h and declaring our enum:
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#include <cassert>
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#include <iostream>
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#include <enum.h>
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BETTER_ENUM(Channel, int, Cyan = 1, Magenta, Yellow, Black)
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// We now have an int-sized enum with four constants.
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//
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// There are three groups of conversion functions: for strings, case-insensitive
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// strings, and integers. They all follow the same pattern, so I'll explain the
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// string functions in detail, and the rest can be understood by analogy.
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//
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// Strings
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//
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// There are three functions:
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//
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// 1. ._to_string
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// 2. ::_from_string
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// 3. ::_from_string_nothrow
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int main()
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{
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Channel channel = Channel::Cyan;
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std::cout << channel._to_string() << " ";
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// As you'd expect, the code above prints "Cyan".
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//
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// If channel is invalid - for example, if you simply cast the number "42" to
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// Channel - then the result of to_string is undefined.
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channel = Channel::_from_string("Magenta");
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std::cout << channel._to_string() << " ";
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// This is also straightforward. If you pass a string which is not the name of a
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// declared value, _from_string throws std::runtime_error.
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// If you don't want an exception, there is _from_string_nothrow:
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better_enums::optional<Channel> maybe_channel =
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Channel::_from_string_nothrow("Yellow");
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if (!maybe_channel)
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std::cout << "error";
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else
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std::cout << maybe_channel->_to_string() << " ";
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// This returns an optional value, in the style of boost::optional or the
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// proposed std::optional.
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//
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// What that means for the above code is:
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//
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// 1. if the conversion succeeds, maybe_channel converts to true and
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// *maybe_channel is the converted value of type Channel,
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// 2. if the conversion fails, maybe_channel converts to false.
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//
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// In C++11, you can use auto to avoid writing out the optional type:
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//
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// auto maybe_channel = Channel::_from_string_nothrow("Yellow");
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// if (!maybe_channel)
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// std::cout << "error";
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// else
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// std::cout << maybe_channel->_to_string() << " ";
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//
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// Case-insensitive strings
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//
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// The "_nocase" string conversions follow the same pattern, except for the lack
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// of a "to_string_nocase".
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//
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// 1. ::_from_string_nocase
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// 2. ::_from_string_nocase_nothrow
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channel = Channel::_from_string_nocase("cYaN");
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std::cout << channel._to_string() << " ";
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maybe_channel = Channel::_from_string_nocase_nothrow("rEeD");
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assert(!maybe_channel);
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// Integers
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//
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// And, it is similar with the representation type int:
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//
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// 1. ._to_integral
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// 2. ::_from_integral
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// 3. ::_from_integral_nothrow
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// 4. ::_from_integral_unchecked
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channel = Channel::Cyan;
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std::cout << channel._to_integral() << " ";
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channel = Channel::_from_integral(2);
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std::cout << channel._to_string() << " ";
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maybe_channel = Channel::_from_integral_nothrow(0);
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assert(!maybe_channel);
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// That prints "1 Magenta".
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//
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// _from_integral_unchecked is a no-op unchecked cast of integers to enums, so
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// use it carefully.
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channel = Channel::_from_integral_unchecked(0);
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// Invalid - better not to try converting it to string!
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// Validity checking
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//
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// For completeness, Better Enums also provides three validity checking
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// functions, one for each of the groups of conversions - string,
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// case-insensitive string, and integer:
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assert(Channel::_is_valid(3));
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assert(Channel::_is_valid("Magenta"));
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assert(Channel::_is_valid_nocase("cYaN"));
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// Almost done.
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//
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// There is one unfortunate wrinkle. You cannot convert a literal constant such
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// as Channel::Cyan directly to, for example, a string. You have to prefix it
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// with +:
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std::cout << (+Channel::Cyan)._to_string();
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// This is due to some type gymnastics in the implementation of Better Enums.
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// The reference has a full explanation.
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std::cout << std::endl;
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return 0;
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}
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