Function extend_to 

pub fn extend_to<P: Blend>(
    knots: &KnotVector,
    control: &[P],
    at_end: bool,
    target: P,
    span: f64,
    continuity: usize,
    tol: Tolerances,
) -> OgeomResult<Spline<P>>

Continue a clamped B-spline past one end to target, over span in parameter: a Bézier piece whose first continuity + 1 controls carry the curve’s own end derivatives (as extend does) and whose last is target, joined on. The curve is raised a degree first where the piece needs one more than it has.

Errors

As extend.