Generic Instance Method


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


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



A sequence to compare to this sequence.


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.


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:

Complexity: O(m), where m is the lesser of the length of the sequence and the length of other.

  • 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)