Compare performance of iterating through a UTF8View of a 79 bytes String with iterating through its Data representation.

StringPerformanceTest.swift

// Executed with optimization -Os on a MacBook Pro (15-inch, 2017) 2,8 GHz Intel Core i7
class StringPerformanceTest: XCTestCase {

    // Takes in average 0.075 secs
    func testPerformanceOfUTF8View() {
        let data = "_cqeFf~cjVf@p@fA}AtAoB`ArAx@hA`GbIvDiFv@gAh@t@X\\|@z@`@Z\\Xf@Vf@VpA\\tATJ@NBBkC".data(using: .utf8)!
        let string = String(decoding: data, as: UTF8.self)
        measure {
            for _ in 0...10_000 {
                _ = string.utf8.reduce(into: 0, { count, _ in count += 1 })
            }
        }
    }

    // Takes in average 0.040 secs
    func testPerformanceOfData() {
        let data = "_cqeFf~cjVf@p@fA}AtAoB`ArAx@hA`GbIvDiFv@gAh@t@X\\|@z@`@Z\\Xf@Vf@VpA\\tATJ@NBBkC".data(using: .utf8)!
        let string = String(decoding: data, as: UTF8.self)
        measure {
            for _ in 0...10_000 {
                _ = string.data(using: .utf8)!.reduce(into: 0, { count, _ in count += 1 })
            }
        }
    }
}