extends.rts

// `extends` operator checks if the left hand side is assignable to the right
// hand side, if it was treated as a type. It can be useful for checking actual
// types at runtime.
//
// For example:
// - if `array extends any[]` is true, `array` is indexable by numbers
// - if `object extends {}` is true, `object` is indexable by strings
// - `n extends 0 | 1 | 2 | 3 | 4 | 5` can be a silly way of checking if `n` is
//   one of the values

const assign = fn (object: any, property: string, value: any) nil {
	if (not (object extends {})) {
		panic("Argument is not an object");
	}

	object[property] = value;
};

const obj: any = {};
println(obj);
assign(obj, "foo", "bar");
println(obj);
assign(obj, "baz", nil);
println(obj);

println("");

const array = [1];
println(array);
println("Next line won't fail, but the panic function will be called");
assign(array, "foo", 2);