lexicographicallyPrecedes(_:by:)

Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the given predicate to compare elements.

Declaration

func lexicographicallyPrecedes<OtherSequence>(_ other: OtherSequence, by areInIncreasingOrder: (Self.Element, Self.Element) throws -> Bool) rethrows -> Bool where OtherSequence : Sequence, Self.Element == OtherSequence.Element

Parameters

other:
A sequence to compare to this sequence.
areInIncreasingOrder:
A predicate that returns true if its first argument should be ordered before its second argument; otherwise, false.

Return Value

true if this sequence precedes other in a dictionary ordering as ordered by areInIncreasingOrder; otherwise, false.

Discussion

The predicate must be a strict weak ordering over the elements. That is, for any elements a, b, and c, the following conditions must hold:

areInIncreasingOrder(a, a) is always false. (Irreflexivity)
If areInIncreasingOrder(a, b) and areInIncreasingOrder(b, c) are both true, then areInIncreasingOrder(a, c) is also true. (Transitive comparability)
Two elements are incomparable if neither is ordered before the other according to the predicate. If a and b are incomparable, and b and c are incomparable, then a and c are also incomparable. (Transitive incomparability)