func swap<T>(inout a: T, inout _ b: T) { let tmp = a a = b b = tmp}var n1 = 5var n2 = 7swap(&n1, &n2)//n1 is 7 and n2 is 5var s1 = "cat"var s2 = "dog"swap(&s1, &s2)//s1 is "dog" and s2 is "cat"