issue23188.go

     1  // run
     2  
     3  // Copyright 2018 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  // Test order of evaluation of index operations.
     8  
     9  package main
    10  
    11  func main() {
    12  	arr := []int{1, 2}
    13  
    14  	// The spec says that in an assignment statement the operands
    15  	// of all index expressions and pointer indirections on the
    16  	// left, and the expressions on the right, are evaluated in
    17  	// the usual order. The usual order means function calls and
    18  	// channel operations are done first. Then the assignments are
    19  	// carried out one at a time. The operands of an index
    20  	// expression include both the array and the index. So this
    21  	// evaluates as
    22  	//   tmp1 := arr
    23  	//   tmp2 := len(arr) - 1
    24  	//   tmp3 := len(arr)
    25  	//   arr = arr[:tmp3-1]
    26  	//   tmp1[tmp2] = 3
    27  	arr, arr[len(arr)-1] = arr[:len(arr)-1], 3
    28  
    29  	if len(arr) != 1 || arr[0] != 1 || arr[:2][1] != 3 {
    30  		panic(arr)
    31  	}
    32  }
    33
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