George Sakkis wrote: > "Jacob Page" <[EMAIL PROTECTED]> wrote: > >>I think I will keep Interval exposed. It sort of raises a bunch of >>hard-to-answer design questions having two class interfaces, though. >>For example, would Interval.between(2, 3) + Interval.between(5, 7) raise >>an error (as it currently does) because the intervals are disjoint or >>yield an IntervalSet, or should it not even be implemented? How about >>subtraction, xoring, and anding? An exposed class should have a more >>complete interface. >> >>I think that IntervalSet.between(5, 7) | IntervalSet.between(2, 3) is >>more intuitive than IntervalSet(Interval.between(5, 7), >>Interval.between(2, 3)), but I can understand the reverse. I think I'll >>just support both. > > As I see it, there are two main options you have: > > 1. Keep Intervals immutable and pass all the responsibility of > combining them to IntervalSet. In this case Interval.__add__ would have > to go. This is simple to implement, but it's probably not the most > convenient to the user. > > 2. Give Interval the same interface with IntervalSet, at least as far > as interval combinations are concerned, so that Interval.between(2,3) | > Interval.greaterThan(7) returns an IntervalSet. Apart from being user > friendlier, an extra benefit is that you don't have to support > factories for IntervalSets, so I am more in favor of this option.
I selected option one; Intervals are immutable. However, this doesn't mean that __add__ has to go, as that function has no side-effects. The reason I chose option one was because it's uncommon for a mathematical operation on two objects to return a different type altogether. > Another hard design problem is how to combine intervals when > inheritance comes to play. Say that you have FrozenInterval and > FrozenIntervalSet subclasses. What should "Interval.between(2,3) | > FrozenInterval.greaterThan(7)" return ? For now, operations will return mutable instances. They can always be frozen later if needs be. -- http://mail.python.org/mailman/listinfo/python-list
