StringVSNSString.swift

import XCTest

class PerformanceTest: XCTestCase {
    func testString() { // 0.265s on iPhone X
        var array = [String]()
        let strings = Array(1 ... 1_000_000).map { String($0) }
        measure {
            strings.forEach {
                array.append($0)
            }
        }
        print(array.count)
    }

    func testNSString() { // 0.508 s on iPhone X
        var array = [NSString]()
        let strings = Array(1 ... 1_000_000).map { String($0) }
        measure {
            strings.forEach {
                array.append($0 as NSString)
            }
        }
        print(array.count)
    }
}