Applies the contained diff to the supplied set.
Returns a diff that, if applied to a set, undoes the effects of this diff.
Same as apply, but fails to None if the diff's removal set has
any items that aren't present in previous
.
Same as apply, but fails to None if the diff's removal set has
any items that aren't present in previous
.
Returns Some(_) if and only if invert will undo.
SetDiff
is a class that represents changes applied to a set. It is in fact a Set[T] => Set[T], but doesn't extend Function1 since that brings in a pack of methods that we don't necessarily want.