@classmethod
def from_sdl(cls, s, d, length):
    """Initialize a line segment from a start point, direction, and length.

        Args:
            s: A Point2D representing the start point of the line segment.
            d: A Vector2D representing the direction of the line segment.
            length: A number representing the length of the line segment.
        """
    return cls(s, d * length / d.magnitude)
