Instance Method

prefix(_:)

Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection.

Declaration

func prefix(_ maxLength: Int) -> Substring

Parameters

maxLength

The maximum number of elements to return. maxLength must be greater than or equal to zero.

Return Value

A subsequence starting at the beginning of this collection with at most maxLength elements.

Discussion

If the maximum length exceeds the number of elements in the collection, the result contains all the elements in the collection.

let numbers = [1, 2, 3, 4, 5]
print(numbers.prefix(2))
// Prints "[1, 2]"
print(numbers.prefix(10))
// Prints "[1, 2, 3, 4, 5]"

Complexity: O(1) if the collection conforms to RandomAccessCollection; otherwise, O(k), where k is the number of elements to select from the beginning of the collection.

See Also

Getting Substrings

subscript<R>(R) -> Substring

Accesses the contiguous subrange of the collection’s elements specified by a range expression.

func prefix(through: String.Index) -> Substring

Returns a subsequence from the start of the collection through the specified position.

func prefix(upTo: String.Index) -> Substring

Returns a subsequence from the start of the collection up to, but not including, the specified position.

func prefix(while: (Character) -> Bool) -> Substring

Returns a subsequence containing the initial elements until predicate returns false and skipping the remaining elements.

func suffix(Int) -> Substring

Returns a subsequence, up to the given maximum length, containing the final elements of the collection.

func suffix(from: String.Index) -> Substring

Returns a subsequence from the specified position to the end of the collection.