1 let str = "strengthen"
 2 
 3 //prefix
 4 print(str.prefix(5)) // "stren"
 5 //suffix
 6 print(str.suffix(5)) // "gthen"
 7 
 8 //dropFirst
 9 print(str.dropFirst()) // "trengthen"
10 //dropLast
11 print(str.dropLast()) // "strengthe"

1 var a = 1
2 var b = 2
3 (b, a) = (a, b)
4 print(a, b)

1 var a = 1
2 var b = 2
3 var c = 3
4 (a, b, c) = (b, c, a)
5 print(a, b, c)

1 var fruits = ["apple", "pear", "grape", "banana"]
2 
3 fruits.swapAt(1, 2)
4 
5 print(fruits)