1 // run 2 3 // Copyright 2016 The Go Authors. All rights reserved. 4 // Use of this source code is governed by a BSD-style 5 // license that can be found in the LICENSE file. 6 7 // Ensure that range loops over a string have the requisite side-effects. 8 9 package main 10 11 import ( 12 "fmt" 13 "os" 14 ) 15 16 func check(n int) { 17 var i int 18 var r rune 19 20 b := make([]byte, n) 21 for i = range b { 22 b[i] = byte(i + 1) 23 } 24 s := string(b) 25 26 // When n == 0, i is untouched by the range loop. 27 // Picking an initial value of -1 for i makes the 28 // "want" calculation below correct in all cases. 29 i = -1 30 for i = range s { 31 b[i] = s[i] 32 } 33 if want := n - 1; i != want { 34 fmt.Printf("index after range with side-effect = %d want %d\n", i, want) 35 os.Exit(1) 36 } 37 38 i = -1 39 r = '\x00' 40 for i, r = range s { 41 b[i] = byte(r) 42 } 43 if want := n - 1; i != want { 44 fmt.Printf("index after range with side-effect = %d want %d\n", i, want) 45 os.Exit(1) 46 } 47 if want := rune(n); r != want { 48 fmt.Printf("rune after range with side-effect = %q want %q\n", r, want) 49 os.Exit(1) 50 } 51 52 i = -1 53 // i is shadowed here, so its value should be unchanged. 54 for i := range s { 55 b[i] = s[i] 56 } 57 if want := -1; i != want { 58 fmt.Printf("index after range without side-effect = %d want %d\n", i, want) 59 os.Exit(1) 60 } 61 62 i = -1 63 r = -1 64 // i and r are shadowed here, so their values should be unchanged. 65 for i, r := range s { 66 b[i] = byte(r) 67 } 68 if want := -1; i != want { 69 fmt.Printf("index after range without side-effect = %d want %d\n", i, want) 70 os.Exit(1) 71 } 72 if want := rune(-1); r != want { 73 fmt.Printf("rune after range without side-effect = %q want %q\n", r, want) 74 os.Exit(1) 75 } 76 } 77 78 func main() { 79 check(0) 80 check(1) 81 check(15) 82 } 83
