didset_inout.swift

/*
 event | without didSet | have didSet
 start 0 0
 0 0
 set 1 1
 1 0
 1 0
 1 0
 end 1 1
 --- 1
 */
func f(_ v: inout Int, _ didSet: inout Int) {
    print("start", v, didSet)
    v += 1
    didSet += 1
    print("set", v, didSet)
    sleep(4)
    print("end", v, didSet)
}

var v = 0

var v_didSet = 0 {
    didSet {}
}

DispatchQueue.global().async {
    print(v, v_didSet)
}

DispatchQueue.global().asyncAfter(deadline: .now() + .seconds(1)) {
    print(v, v_didSet)
}

DispatchQueue.global().asyncAfter(deadline: .now() + .seconds(2)) {
    print(v, v_didSet)
}

DispatchQueue.global().asyncAfter(deadline: .now() + .seconds(3)) {
    print(v, v_didSet)
}

f(&v, &v_didSet)

sleep(7)

print("---", v)