Smart enum

• Design goals
• Examples
• License

Header-only library for compile-time C++ enum introspection.

Design goals

C++ doesn't have reflection. It is a common technique to use macros to add compile time information about enumeration like the following:

enum class Animal {
  Dog = 1,
  Cat = 2,
  Lion = 4,
  Horse = 5,
};

DECLARE_ENUM(Animal, Animal::Dog, Animal::Cat, Animal::Lion, Animal::Horse);

This code violates DRY (don't repeat yourself) principle. The aim of smart enum library is to provide a user with macros that can be used in enum declaration and the user will not need to repeat enum elements.

Highlights

1. Smart enums can be declared in namespaces and classes.
2. Smart enum to and from string conversions.

Examples

Declaration of smart enum looks like this:

#include "smart_enum.h"

SMART_ENUM(Animal, int) {
    SM_ENUM_ELEM(Dog,    1,  "dog"  , "dog_description");
    SM_ENUM_ELEM(Cat,    2,  "cat"  );
    SM_ENUM_ELEM(Lion,   5);
    SM_ENUM_ELEM(Horse);
};

For each enum constant string representation and string description is generated. When macro with 1 or 2 arguments is used ( like SM_ENUM_ELEM(Lion, 5) and SM_ENUM_ELEM(Horse) ) string representation and description will match enum constant name. If you want to specify custom string representation and string description macro with 3 or 4 arguments should be used.

Definitions of variables:

Animal pet_cat   ={Animal::Cat};
Animal pet_dog   = Animal::Dog;
Animal pet_lion   (Animal::Lion);
Animal pet_horse  {Animal::Horse};

It is possible to convert smart enums to strings:

std::cout << "pet name: " << pet_cat.to_string() << std::endl;
//pet name: cat
std::cout << "pet name: " << pet_lion.to_string() << std::endl;
//pet name: Lion

It is possible get descriptions for smart enum values:

std::cout << "descr.: " << pet_dog.description() << std::endl;
//descr.: dog_description
std::cout << "descr.: " << pet_horse.description() << std::endl;
//descr.: hOrse

Smart enums can be used in switch statements like ordinal enums:

switch (pet_cat) {
     case Animal::Cat:
         assert(true);
         break;
     case Animal::Horse:
         assert(false);
         break;
     default:
         assert(false);
         break;
 }

It is possible to get information about number of elements declared in smart enum:

std::cout << "Elements in smart enum: " << Animal::size() << std::endl;
//Elements in smart enum: 4

It is possible to get all values, names and descriptions of smart enum:

std::cout << "smart enum names: ";
for (const auto &enum_item : Animal::values())
    std::cout << enum_item.to_string() << " ";
std::cout << std::endl;
//smart enum names: dog cat Lion Horse

std::cout << "smart enum names: ";
for (const auto &name : Animal::names())
    std::cout << name << " ";
std::cout << std::endl;
//smart enum names: dog cat Lion Horse

std::cout << "smart enum descriptions: ";
for (const auto &name : Animal::descriptions())
    std::cout << name << " ";
std::cout << std::endl;
//smart enum descriptions: dog_description cat Lion Horse

It is possible to check if smart enum value is valid:

Animal invalid;
*(reinterpret_cast<int*>(&invalid)) = 6666;
assert(invalid.is_valid() == false);

Installation

Include smart_enum.h in your source code.

License

The MIT license