09 / Fundamentals

Enums

Nyx enums are algebraic data types (ADTs): each variant can carry different data, and match expressions destructure them exhaustively. This makes it impossible to forget a case at compile time.

09-enums.nxSource →

// Enums: definición, variantes con datos, match exhaustivo

enum Shape {
    Circle(int),
    Square(int),
    Rectangle(int, int)
}

fn area(s: Shape) -> int {
    return match s {
        Shape.Circle(r)        => r * r * 3,
        Shape.Square(l)        => l * l,
        Shape.Rectangle(w, h)  => w * h
    }
}

fn describe(s: Shape) -> String {
    return match s {
        Shape.Circle(r)        => "circulo de radio " + int_to_string(r),
        Shape.Square(l)        => "cuadrado de lado " + int_to_string(l),
        Shape.Rectangle(w, h)  => "rectangulo " + int_to_string(w) + "x" + int_to_string(h)
    }
}

fn main() -> int {
    let c: Shape = Shape.Circle(5)
    let sq: Shape = Shape.Square(4)
    let rect: Shape = Shape.Rectangle(3, 7)

    print(describe(c) + " -> area aprox " + int_to_string(area(c)))
    print(describe(sq) + " -> area " + int_to_string(area(sq)))
    print(describe(rect) + " -> area " + int_to_string(area(rect)))

    return 0
}

Outputstdout

circulo de radio 5 -> area aprox 75
cuadrado de lado 4 -> area 16
rectangulo 3x7 -> area 21

How it works

An enum is declared with the enum keyword followed by a name and a list of variants. Each variant can carry zero or more typed values in parentheses: Circle(int) carries one integer (the radius), Rectangle(int, int) carries two (width and height). Variants without parentheses would be simple tags.

Enum values are constructed with dot notation: Shape.Circle(5). Note that Nyx uses Shape.Circle, not Shape::Circle — the dot is the variant separator throughout the language.

The match expression destructures an enum value and binds the inner data to local names. Each arm has the form Pattern => expression. The compiler enforces exhaustiveness: if any variant is missing from a match, the program will not compile.

The area formula for the circle uses integer arithmetic (r * r * 3 as an approximation of π·r²), which is why the result is labeled "aprox". Real programs would use float and the math standard library for precise results.

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