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
9package main
10
11import (
12	"fmt"
13	"os"
14)
15
16func 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
78func main() {
79	check(0)
80	check(1)
81	check(15)
82}
83