c++ - enum to string in modern C++11 / C++14 / C++17 and future C++20

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Contrary to all other similar
questions, this question is about using the new C++
features.

After reading
many answers, I did not yet find
any:

Example

An
example is often better than a long explanation.
You can compile and run this
snippet on rel="noreferrer">Coliru.
^{( href="http://coliru.stacked-crooked.com/a/bb58819257b6df50" rel="noreferrer">Another
former example is also
available)}

#include
            

Constraints

• Please
  no valueless duplication of href="https://stackoverflow.com/a/10177840/938111">other answers or href="https://stackoverflow.com/a/18791363/938111">basic
  link.


• Please avoid bloat macro-based answer, or
  try to reduce the #define overhead as minimum as possible.
  


• Please no manual enum ->
  string
  mapping.

Nice to
have

• Support
  enum values starting from a number different from
  zero


• Support negative enum
  values


• Support fragmented enum
  values


• Support class enum
  (C++11)


• Support class enum :
having any allowed
  (C++11)


• Compile-time (not run-time) conversions to a
  string,
  or at least fast execution at run-time (e.g.
  std::map is not a great
  idea...)


• href="https://en.cppreference.com/w/cpp/language/constexpr"
  rel="noreferrer">constexpr (C++11, then relaxed in
  C++14/17/20)


• href="https://en.cppreference.com/w/cpp/language/noexcept"
  rel="noreferrer">noexcept
  (C++11)



• href="https://en.wikipedia.org/wiki/C%2B%2B17" rel="noreferrer">C++17/ href="https://en.wikipedia.org/wiki/C%2B%2B20" rel="noreferrer">C++20
  friendly snippet

One
possible idea could be using the C++ compiler capabilities to generate C++ code at
compilation-time using meta-programming tricks based on variadic template
class and constexpr
functions...

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class="normal">Answer

#include
            

enum Color { RED = 2, BLUE = 4, GREEN = 8
            };


Color color = Color::RED;
auto color_name =
            magic_enum::enum_name(color);
// color_name ->
            "RED"

std::string color_name{"GREEN"};
auto color =
            magic_enum::enum_cast(color_name)
if (color.has_value())
            {
 // color.value() ->
            Color::GREEN
};

For
more examples check home repository rel="noreferrer">https://github.com/Neargye/magic_enum.

Where
is the drawback?

This library uses a
compiler-specific hack (based on __PRETTY_FUNCTION__ /
__FUNCSIG__), which works on Clang >= 5, MSVC >= 15.3 and
GCC >= 9.

Enum value must be in range
[MAGIC_ENUM_RANGE_MIN, MAGIC_ENUM_RANGE_MAX]. By default
MAGIC_ENUM_RANGE_MIN = -128, MAGIC_ENUM_RANGE_MAX =
128.

• If
  need another range for all enum types by default, redefine the macro
  MAGIC_ENUM_RANGE_MIN and
  MAGIC_ENUM_RANGE_MAX.




• If
  need another range for specific enum type, add specialization enum_range for necessary
  enum type.

  
  
  

  #include
              
  
  enum number { one = 100, two = 200, three =
              300 };
  
  namespace magic_enum {
  template
              <>
  
   struct enum_range {
   static
              constexpr int min = 100;
   static constexpr int max =
              300;
  };
  }