issue5373.go

     1  // run
     2  
     3  // Copyright 2015 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 zeroing range loops have the requisite side-effects.
     8  
     9  package main
    10  
    11  import (
    12  	"fmt"
    13  	"os"
    14  )
    15  
    16  func check(n int) {
    17  	// When n == 0, i is untouched by the range loop.
    18  	// Picking an initial value of -1 for i makes the
    19  	// "want" calculation below correct in all cases.
    20  	i := -1
    21  	s := make([]byte, n)
    22  	for i = range s {
    23  		s[i] = 0
    24  	}
    25  	if want := n - 1; i != want {
    26  		fmt.Printf("index after range with side-effect = %d want %d\n", i, want)
    27  		os.Exit(1)
    28  	}
    29  
    30  	i = n + 1
    31  	// i is shadowed here, so its value should be unchanged.
    32  	for i := range s {
    33  		s[i] = 0
    34  	}
    35  	if want := n + 1; i != want {
    36  		fmt.Printf("index after range without side-effect = %d want %d\n", i, want)
    37  		os.Exit(1)
    38  	}
    39  
    40  	// Index variable whose evaluation has side-effects
    41  	var x int
    42  	f := func() int {
    43  		x++
    44  		return 0
    45  	}
    46  	var a [1]int
    47  	for a[f()] = range s {
    48  		s[a[f()]] = 0
    49  	}
    50  	if want := n * 2; x != want {
    51  		fmt.Printf("index function calls = %d want %d\n", x, want)
    52  		os.Exit(1)
    53  	}
    54  
    55  	// Range expression whose evaluation has side-effects
    56  	x = 0
    57  	b := [1][]byte{s}
    58  	for i := range b[f()] {
    59  		b[f()][i] = 0
    60  	}
    61  	if want := n + 1; x != n+1 {
    62  		fmt.Printf("range expr function calls = %d want %d\n", x, want)
    63  		os.Exit(1)
    64  	}
    65  }
    66  
    67  func main() {
    68  	check(0)
    69  	check(1)
    70  	check(15)
    71  }
    72
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