trait BodyLike {
    def x(self) = self.body().x
    def y(self) = self.body().y
    def pos(self) = [self.x(), self.y()]
    def set_pos(self, xy) = [self.body().x, self.body().y] = xy
    def rot(self) = self.body().rot
    def set_rot(self, rot) = self.body().rot = rot
    def dx(self) = self.body().dx
    def dy(self) = self.body().dy
    def set_velocity(self, dxdy) = [self.body().dx, self.body().dy] = dxdy
    def drot(self) = self.body().drot
    def set_drot(self, drot) = self.body().drot = drot
    def radius(self) = self.body().radius
    def update(self, elapsed_time) = self.body().update(elapsed_time)
    def hits(self, other) = {
        [ax, ay] = self.pos()
        [bx, by] = other.pos()
        ar = self.radius()
        br = self.radius()
        (ax - bx) ** 2 + (ay - by) ** 2 < (ar + br) ** 2
    }
}

@class Body(BodyLike) {
    [x, y, rot, dx, dy, drot, radius]
    def body(self) = self
    def update(self, elapsed_time) {
        self.x += elapsed_time * self.dx
        self.y += elapsed_time * self.dy
        self.rot += elapsed_time * self.drot
    }
}