issue13162.go

     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
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