var my_list = [1, 2, 3];
my_list[2] = 16;
my_list[1] += 2;
print(my_list); # expect: [1, 4, 16]

class MyClass {

    __init__() {
        this.x = 1;
        this.y = 2;
    }

    __setitem__(prop, val) {
        if (prop == 0) {
            this.x = val;
            return;
        }
        if (prop == 1) {
            this.y = val;
        }
    }

    __getitem__(a) {
        if (a == 0) {
            return this.x;
        }
        if (a == 1) {
            return this.y;
        }
        return nil;
    }
}

var my_object = MyClass();
my_object[0] = "X";
my_object[1] += 2;
print(my_object.x); # expect: X
print(my_object.y); # expect: 4

class BadClass {}

var bad_object = BadClass();
bad_object[1] = 2; # expect runtime error: Undefined property '__setitem__'.