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example/5-map.cc

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-// This file was generated automatically.
-
-// Maps
-//
-// It is possible to create constexpr bidirectional maps between Better Enums
-// and any type. This is currently an experimental feature. Feedback is very
-// much wanted, but please don't build any mission-critical code on top of this
-// :)
-//
-// The way it works is you give Better Enums a function - say, const char*
-// describe(Channel). The library enumerates it to make a map.
-//
-// The reason for using a function is that a switch statement is, I believe, the
-// only place where a compiler will check for exhaustiveness. If you forget to
-// create a case for one of the enum's constants, the compiler can let you know.
-// Obviously, a switch statement is not data, and needs to be inside a function.
-// It can only be inside a constexpr function in C++14, so this feature is most
-// natural in C++14. When you pass the function to Better Enums, the library can
-// build up a lookup data structure at compile time.
-//
-// Actually, right now, Better Enums doesn't quite do that - it enumerates the
-// function every time you want to convert to an enum (but not from an enum). It
-// simply does a linear scan every time. This is because I haven't yet found a
-// data structure whose compile-time generation is fast enough for practical
-// use.
-
-
-#include <iostream>
-#include <enum.h>
-
-BETTER_ENUM(Channel, int, Red, Green, Blue)
-
-// We will create a map from this function:
-
-constexpr const char* describe(Channel channel)
-{
-    switch(channel) {
-        case Channel::Red:   return "the red channel";
-        case Channel::Green: return "the green channel";
-        case Channel::Blue:  return "the blue channel";
-    }
-
-    return "needed for gcc 5";
-}
-
-// Here is the map. The actual type is better_enums::map<Channel, const char*>.
-
-constexpr auto descriptions = better_enums::make_map(describe);
-
-// And the usage:
-
-int main()
-{
-    std::cout << descriptions[Channel::Red] << std::endl;
-
-    std::cout << descriptions.from_enum(Channel::Red) << std::endl;
-    std::cout << descriptions.to_enum("the green channel") << std::endl;
-
-    auto not_a_literal = std::string("the blue channel");
-    std::cout << descriptions.to_enum(not_a_literal.c_str()) << std::endl;
-
-    return 0;
-}
-
-
-// make_map above produces a value of type better_enums::map<E, T>. The full
-// signature of the template better_enums::map is
-//
-// template <typename Enum, typename T, typename Compare = map_compare<T>>
-//
-// Compare has to be a class with a static member function bool less(const T&,
-// const T&). The default implementation better_enums::map_compare simply
-// applies operator <, except when T is const char*. In that case, it does
-// lexicographic comparison.