define default named arguments in terms of other arguments in scala -

i have case class stores 3 tied parameters. i'd define companion object may build class 2 parameters, looks sample below, incorrect:

def test(start : float = end - duration, duration : float = end - start, end : float = start + duration) {   require( abs(start + duration - end) < epsilon )   ... } val t1 = test(start = 0f, duration = 5f) val t2 = test(end = 4f, duration = 3f) val t3 = test(start = 3f, end = 5f) 

what tricks may use similar usage syntax?

you can use type-classes:

// represents no argument object noarg  // resolves start, duration, stop trait durationres[a,b,c] {   def resolve(s: a, d: b, e: c): (float, float, float) }  object durationres {   implicit object startendres extends durationres[float, noarg.type, float] {     def resolve(s: float, d: noarg.type, e: float) = (s, e-s, e)   }   implicit object startdurres extends durationres[float, float, noarg.type] {     def resolve(s: float, d: float, e: noarg.type) = (s, d, s+d)   }   // etc. }  def test[a,b,c](start: = noarg, dur: b = noarg, end: c = noarg)                (implicit res: durationres[a,b,c]) {   val (s,d,e) = res.resolve(start, dur, end)   // s start, d duration, e end }  test(start = 1f, end = 2f) 

this way type-safe , cannot call like:

test(start = 1f) 

or even

test()