Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index.
func index(_ i: Self.Index, offsetBy distance: Int, limitedBy limit: Self.Index) -> Self.Index?
A valid index of the array.
The distance to offset
A valid index of the collection to use as a limit. If
distance > 0,
limitshould be greater than
ito have any effect. Likewise, if
distance < 0,
limitshould be less than
ito have any effect.
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
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
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.