Enums

Rice supports both C enums and newer C++ enum classes.

enum Color
{ RED,
  BLACK,
  GREEN };

enum class Season
{ Spring,
  Summer,
  Fall,
  Winter };

To expose an enum to Ruby, use define_enum like this:

Enum<Color> colors = define_enum<Color>("Color")
  .define_value("RED", RED)
  .define_value("BLACK", BLACK)
  .define_value("GREEN", GREEN);

define_enum<Color>("Color") creates a new Ruby class called Color. Each call to define_value defines a new instance of Color that is stored as a constant on the Color class. Thus from the Ruby side of things, the mapping looks like:

class Color
  RED = Color.new(RED)
  BLACK = Color.new(BLACK)
  GREEN = Color.new(GREEN)
end

Nested and Anonymous Enums

C/C++ supports the concept of anonymous enums. They used to be used as hack to define constants before C++ compilers supported member constants. For example:

class MyClass
{
  public:
    static const int SOME_CONSTANT = 42;

    enum class Season
    { Spring,
      Summer,
      Fall,
      Winter };

    // Enum hack that used to be needed by compilers
    enum
    {
        HACKED_CLASS_CONSTANT_1 = 43,
        HACKED_CLASS_CONSTANT_2 = 44
    };
};

In this case, there is one class enum and one anonymous enum. The anonymous enum should be mapped to static member constants like this:

 // Define the class. Map anonymous enums to constants
 Data_Type<MyClass> rb_cMyClass = define_class<MyClass>("MyClass").
   define_constructor(Constructor<MyClass>()).
   define_constant("SOME_CONSTANT", 42).
   define_constant("HACKED_CLASS_CONSTANT_1", (int)MyClass::HACKED_CLASS_CONSTANT_1).
   define_constant("HACKED_CLASS_CONSTANT_2", (int)MyClass::HACKED_CLASS_CONSTANT_2);

// Define the class and enum and nest it under MyClass
Enum<Season> seasons = define_enum_under<Season>("Season", rb_cMyClass)
 .define_value("Spring", Season::Spring)
 .define_value("Summer", Season::Summer)
 .define_value("Fall", Season::Fall)
 .define_value("Winter", Season::Winter);

From the Ruby side, this creates:

class MyClass
  SOME_CONSTANT = 42
  HACKED_CLASS_CONSTANT_1 = MyClass::HACKED_CLASS_CONSTANT_1
  HACKED_CLASS_CONSTANT_2 = MyClass::HACKED_CLASS_CONSTANT_2

  class Season
    Spring = Color.new(Season::Spring)
    Summer = Color.new(Season::Summer)
    Fall = Color.new(Season::Fall)
    Winter = Color.new(Season::Winter)
  end
end

Ruby API

Generated enum classes have the following Ruby API.

Enum.from_int

Enum#<=>
Enum#eql?
Enum#hash
Enum#each
Enum#inspect
Enum#to_int
Enum#to_s

Enum#&
Enum#|
Enum#^
Enum#~
Enum#<<
Enum#>>

In addition, they have the following aliases:

Enum#===
Enum#eql?
Enum#to_i
Enum#to_int

And mixin the following modules:

• Comparable

• Enumerable