Hands-On Design Patterns with Swift

Range as Sequence

When using Range<Int> or ClosedRange<Int>, in addition to others, the Standard Library provides conditional conformance to the Sequence type, as follows:

extension Range: Sequence where Bound: Strideable, Bound.Stride : SignedInteger {    public typealias Element = Bound    public typealias Iterator = IndexingIterator<Range<Bound>>}

Extract from Swift Core source code (https://github.com/apple/swift/blob/master/stdlib/public/core/Range.swift).

This means that you can use this range as the source for iterating on it, as shown in the following example:

let doubles = (1..<10).map { $0 * 2 } // [2,4,6,8,10,12,14,16,18]for i in 1..<10 {   // do something with i}

Because the Sequence conformance is provided as a conditional conformance, ...