CopyOnWriteWorkaroundTests.swift

import XCTest

class CopyOnWriteWorkaroundTests: XCTestCase {
    func testFirst() {
        self.measure { //0.272 sec
            var dict = ["a":[]]
            for i in 0..<10000 {
                if dict["a"] != nil {
                    dict["a"]!.append(i)
                } else {
                    dict["a"] = []
                }
            }
        }
    }
    
    func testSecond() {
        self.measure { // 0.254 sec
            var dict = ["a":[]]
            for i in 0..<10000 {
                var arr = dict["a"] ?? []
                arr.append(i)
                dict["a"] = arr
            }
        }
    }
    
    func testCorrect() {
        var dict: Dictionary<String, [Int]> = ["a":[]]
        for i in 0..<5 {
            if dict["a"] != nil {
                dict["a"]!.append(i)
            } else {
                dict["a"] = []
            }
        }
        let arr = dict["a"]!
        XCTAssert(arr == [0, 1, 2, 3, 4])
    }
}