Course of Raku / Advanced / More about built-in types / Enumerations 🆕

Values and keys

Each enum constant carries both a name and a number. The .value method gives the number, and the .key method gives the name as a string:

enum Colour <red green blue>;

say green.value; # 1
say green.key;   # green

You do not have to accept the automatic numbering from zero. Write the constants as pairs to choose the values yourself:

enum Day (Mon => 1, Tue => 2, Wed => 3, Thu => 4, Fri => 5);

say Tue.value; # 2
say Fri.value; # 5

Here the working week is numbered from one instead of zero.

The enum type itself can list all of its constants. The .enums method returns a map from each name to its value:

enum Colour <red green blue>;

say Colour.enums;       # Map.new((blue => 2, green => 1, red => 0))
say Colour.enums.elems; # 3

Between .value, .key, and .enums, you can move freely from a constant to its number, from a number back to data, and over the whole set — which is what makes enums useful for things like menus, states, and lookup tables.

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