Enums¶

Enums (enumerations) define types with a fixed set of variants. Each variant can optionally carry data.

Defining Enums¶

enum Color:
    Red: none
    Green: none
    Blue: none

enum Shape:
    Circle: float      # radius
    Rectangle: (float, float)  # width, height

Unit variants (none): No associated data
Payload variants: Carry data of the specified type

Creating Enum Values¶

Unit variants (no payload) can be used with or without parentheses:

# Both syntaxes work for unit variants
let c = Color.Red()
let c2 = Color.Red     # Parentheses optional for unit variants

Payload variants require parentheses with the value:

let shape = Shape.Circle(5.0)

Pattern Matching¶

Use match to handle enum variants:

match shape:
    Shape.Circle(r): print("Circle with radius", r)
    Shape.Rectangle(w, h): print("Rectangle", w, "x", h)

Wildcard Pattern¶

Use _ to match remaining cases:

match color:
    Color.Red(): print("Stop!")
    _: print("Go")

Public Enums¶

Use pub to export enums from modules:

pub enum Status:
    Pending: none
    Running: int
    Completed: str

Using Enums as Function Parameters¶

Enums work as function parameters like any other type:

def describe_status(s: Status) -> str:
    match s:
        Status.Pending(): "waiting"
        Status.Running(progress): f"running at {progress}%"
        Status.Completed(msg): msg

Nested Enums¶

Enums can contain other enum types:

enum Result:
    Ok: Status
    Error: str

let r = Result.Ok(Status.Completed("done"))