Instance Method

index(_:offsetBy:limitedBy:)

Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index.

Declaration

func index(_ i: Bound, offsetBy distance: Int, limitedBy limit: Bound) -> Bound?

Parameters

i

A valid index of the array.

distance

The distance to offset i.

limit

A valid index of the collection to use as a limit. If distance > 0, limit should be greater than i to have any effect. Likewise, if distance < 0, limit should be less than i to have any effect.

Return Value

An index offset by distance from the index i, unless that index would be beyond limit in the direction of movement. In that case, the method returns nil.

Discussion

The following example obtains an index advanced four positions from an array’s starting index and then prints the element at that position. The operation doesn’t require going beyond the limiting numbers.endIndex value, so it succeeds.

let numbers = [10, 20, 30, 40, 50]
let i = numbers.index(numbers.startIndex, offsetBy: 4)
print(numbers[i])
// Prints "50"

The next example attempts to retrieve an index ten positions from numbers.startIndex, but fails, because that distance is beyond the index passed as limit.

let j = numbers.index(numbers.startIndex,
                      offsetBy: 10,
                      limitedBy: numbers.endIndex)
print(j)
// Prints "nil"

The value passed as distance must not offset i beyond the bounds of the collection, unless the index passed as limit prevents offsetting beyond those bounds.

Complexity: O(1)

See Also

Manipulating Indices

var startIndex: Bound

The position of the first element in a nonempty collection.

var endIndex: Bound

The collection’s “past the end” position—that is, the position one greater than the last valid subscript argument.

var indices: Range<Bound>

The indices that are valid for subscripting the collection, in ascending order.

var indices: Range<Bound>

The indices that are valid for subscripting the range, in ascending order.

func index(after: Range<Bound>.Index) -> Range<Bound>.Index

Returns the position immediately after the given index.

func formIndex(after: inout Bound)

Replaces the given index with its successor.

func index(before: Range<Bound>.Index) -> Range<Bound>.Index

Returns the position immediately before the given index.

func formIndex(before: inout Bound)

Replaces the given index with its predecessor.

func formIndex(inout Bound, offsetBy: Int)

Offsets the given index by the specified distance.

func index(Range<Bound>.Index, offsetBy: Int) -> Range<Bound>.Index

Returns an index that is the specified distance from the given index.

func formIndex(inout Bound, offsetBy: Int, limitedBy: Bound) -> Bool

Offsets the given index by the specified distance, or so that it equals the given limiting index.

func distance(from: Range<Bound>.Index, to: Range<Bound>.Index) -> Int

Returns the distance between two indices.

func hash(into: inout Hasher)

Hashes the essential components of this value by feeding them into the given hasher.