import Foundation

let iteration = 10_000

let year = 2019
let month = 11
let day = 10
let hour = 10
let minute = 10
let second = 10
let microsecond = 101010

func testDateComponents() {
    var comps = DateComponents(
        calendar:  Calendar(identifier: .gregorian),
        timeZone: TimeZone(secondsFromGMT: 0)!
    )
    comps.year = year
    comps.month = month
    comps.day = day
    comps.hour = hour
    comps.minute = minute
    comps.second = second
    comps.nanosecond = microsecond*1000
    let start = Date()
    var total: TimeInterval = 0
    for _ in 0..<iteration {
        total += comps.date?.timeIntervalSinceNow ?? 0
    }
    print("DateComponents: \(Date().timeIntervalSince(start))sec, \(total)")
}

func testDateFormatter() {
    let df = DateFormatter()
    df.dateFormat = "yyyy/MM/dd HH:mm:ss.SSSSSSS"
    let start = Date()
    var total: TimeInterval = 0
    for _ in 0..<iteration {
        let date = df.date(from: "\(year)/\(month)/\(day) \(hour):\(minute):\(second).\(microsecond)")
        total += date?.timeIntervalSinceNow ?? 0
    }
    print("DateFormatter: \(Date().timeIntervalSince(start))sec, \(total)")
}

testDateComponents()
testDateFormatter()

$ swift --version
Apple Swift version 5.1 (swiftlang-1100.0.270.13 clang-1100.0.33.7)
Target: x86_64-apple-darwin18.7.0
$ swiftc -O main.swift
$ ./main
DateComponents: 0.012930989265441895sec, 14041821731.490162
DateFormatter: 0.2265690565109253sec, 13717820468.565754

$ swift --version
Swift version 5.1.1 (swift-5.1.1-RELEASE)
Target: x86_64-unknown-linux-gnu
$ swiftc -O main.swift 
$ ./main
DateComponents: 0.5204849243164062sec, 14032373021.035366
DateFormatter: 0.28744006156921387sec, 14032368951.859718