Erik McCue

sealed interface Shape
{}
record Square(int x) implements Shape
{}
record Rectangle(int l, int w) implements Shape
{}
record Circle(int r) implements Shape
{}

double getArea(Shape s)
{
// Exhaustively checks for all alternatives.
return switch (s)
{
case Square(var x) -> x * x;
case Rectangle(var l, var w) -> l * w;
case Circle(var r) -> Math.PI * r * r;
}
}

This is a good article: https://mccue.dev/pages/11-1-21-smuggling-checked-exceptions