Generic Instance Method

starts(with:)

Returns a Boolean value indicating whether the initial elements of the sequence are the same as the elements in another sequence.

Declaration

func starts<PossiblePrefix>(with possiblePrefix: PossiblePrefix) -> Bool where PossiblePrefix : Sequence, Self.Element == PossiblePrefix.Element

Parameters

possiblePrefix

A sequence to compare to this sequence.

Return Value

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

Discussion

This example tests whether one countable range begins with the elements of another countable range.

let a = 1...3
let b = 1...10

print(b.starts(with: a))
// Prints "true"

Passing a sequence with no elements or an empty collection as possiblePrefix always results in true.

print(b.starts(with: []))
// Prints "true"

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

See Also

Testing Set Membership

func contains(IndexSet.Element) -> Bool

Returns true if self contains integer.

func contains(integersIn: IndexSet) -> Bool

Returns true if self contains all of the integers in indexSet.

func contains(integersIn: Range<IndexSet.Element>) -> Bool

Returns true if self contains all of the integers in range.

func contains(where: (Int) -> Bool) -> Bool

Returns a Boolean value indicating whether the sequence contains an element that satisfies the given predicate.

func intersects(integersIn: Range<IndexSet.Element>) -> Bool

Returns true if self intersects any of the integers in range.

func isDisjoint(with: IndexSet) -> Bool

Returns a Boolean value that indicates whether the set has no members in common with the given set.

func isStrictSubset(of: IndexSet) -> Bool

Returns a Boolean value that indicates whether this set is a strict subset of the given set.

func isStrictSuperset(of: IndexSet) -> Bool

Returns a Boolean value that indicates whether this set is a strict superset of the given set.

func isSubset(of: IndexSet) -> Bool

Returns a Boolean value that indicates whether the set is a subset of another set.

func isSuperset(of: IndexSet) -> Bool

Returns a Boolean value that indicates whether the set is a superset of the given set.