Generic Instance Method

starts(with:by:)

Returns a Boolean value indicating whether the initial elements of the sequence are equivalent to the elements in another sequence, using the given predicate as the equivalence test.

Declaration

func starts<PossiblePrefix>(with possiblePrefix: PossiblePrefix, by areEquivalent: (Self.Element, PossiblePrefix.Element) throws -> Bool) rethrows -> Bool where PossiblePrefix : Sequence

Parameters

possiblePrefix

A sequence to compare to this sequence.

areEquivalent

A predicate that returns true if its two arguments are equivalent; otherwise, false.

Return Value

true if the initial elements of the sequence are equivalent to the elements of possiblePrefix; otherwise, false. If possiblePrefix has no elements, the return value is true.

Discussion

The predicate must be a equivalence relation 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 possiblePrefix.

  • areEquivalent(a, a) is always true. (Reflexivity)

  • areEquivalent(a, b) implies areEquivalent(b, a). (Symmetry)

  • If areEquivalent(a, b) and areEquivalent(b, c) are both true, then areEquivalent(a, c) is also true. (Transitivity)