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Pattern Matching

match performs typed dispatch on a value, with each case Type binding -> { ... } arm matching when the runtime type is compatible.

Basic Form​

match (s) {
    case Circle c -> {
        print("Circle r=" + c.getRadius() + " area=" + s.area());
    }
    case Rectangle r -> {
        print("Rect " + r.getWidth() + "x" + r.getHeight());
    }
    case Triangle t -> {
        print("Triangle area=" + s.area());
    }
    default -> {
        print("Unknown shape");
    }
}
  • The case Circle c introduces a new local c of type Circle, bound to s if the runtime type matches.
  • Arms are checked top-to-bottom; the first compatible match runs.
  • A default -> arm catches anything not matched above.

When to Use match vs switch​

NeedUse
Branch on a primitive value (int, string)switch
Branch on the runtime type of an objectmatch

Sealed-Class-Style Hierarchies​

Combine match with abstract base classes to express closed sets of variants:

abstract class Shape {
    abstract function area(): float;
}

class Circle    extends Shape { /* ... */ }
class Rectangle extends Shape { /* ... */ }
class Triangle  extends Shape { /* ... */ }

function describe(Shape s): void {
    match (s) {
        case Circle c    -> print("circle");
        case Rectangle r -> print("rect");
        case Triangle t  -> print("tri");
        default          -> print("other");
    }
}

See Also​