Source file test/convert4.go

     1  // run
     2  
     3  // Copyright 2020 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 conversion from slice to array pointer.
     8  
     9  package main
    10  
    11  func wantPanic(fn func(), s string) {
    12  	defer func() {
    13  		err := recover()
    14  		if err == nil {
    15  			panic("expected panic")
    16  		}
    17  		if got := err.(error).Error(); got != s {
    18  			panic("expected panic " + s + " got " + got)
    19  		}
    20  	}()
    21  	fn()
    22  }
    23  
    24  func main() {
    25  	s := make([]byte, 8, 10)
    26  	for i := range s {
    27  		s[i] = byte(i)
    28  	}
    29  	if p := (*[8]byte)(s); &p[0] != &s[0] {
    30  		panic("*[8]byte conversion failed")
    31  	}
    32  	if [8]byte(s) != *(*[8]byte)(s) {
    33  		panic("[8]byte conversion failed")
    34  	}
    35  	wantPanic(
    36  		func() {
    37  			_ = (*[9]byte)(s)
    38  		},
    39  		"runtime error: cannot convert slice with length 8 to array or pointer to array with length 9",
    40  	)
    41  	wantPanic(
    42  		func() {
    43  			_ = [9]byte(s)
    44  		},
    45  		"runtime error: cannot convert slice with length 8 to array or pointer to array with length 9",
    46  	)
    47  
    48  	var n []byte
    49  	if p := (*[0]byte)(n); p != nil {
    50  		panic("nil slice converted to *[0]byte should be nil")
    51  	}
    52  	_ = [0]byte(n)
    53  
    54  	z := make([]byte, 0)
    55  	if p := (*[0]byte)(z); p == nil {
    56  		panic("empty slice converted to *[0]byte should be non-nil")
    57  	}
    58  	_ = [0]byte(z)
    59  
    60  	var p *[]byte
    61  	wantPanic(
    62  		func() {
    63  			_ = [0]byte(*p) // evaluating *p should still panic
    64  		},
    65  		"runtime error: invalid memory address or nil pointer dereference",
    66  	)
    67  
    68  	// Test with named types
    69  	type Slice []int
    70  	type Int4 [4]int
    71  	type PInt4 *[4]int
    72  	ii := make(Slice, 4)
    73  	if p := (*Int4)(ii); &p[0] != &ii[0] {
    74  		panic("*Int4 conversion failed")
    75  	}
    76  	if p := PInt4(ii); &p[0] != &ii[0] {
    77  		panic("PInt4 conversion failed")
    78  	}
    79  }
    80  
    81  // test static variable conversion
    82  
    83  var (
    84  	ss  = make([]string, 10)
    85  	s5  = (*[5]string)(ss)
    86  	s10 = (*[10]string)(ss)
    87  
    88  	ns  []string
    89  	ns0 = (*[0]string)(ns)
    90  
    91  	zs  = make([]string, 0)
    92  	zs0 = (*[0]string)(zs)
    93  )
    94  
    95  func init() {
    96  	if &ss[0] != &s5[0] {
    97  		panic("s5 conversion failed")
    98  	}
    99  	if &ss[0] != &s10[0] {
   100  		panic("s5 conversion failed")
   101  	}
   102  	if ns0 != nil {
   103  		panic("ns0 should be nil")
   104  	}
   105  	if zs0 == nil {
   106  		panic("zs0 should not be nil")
   107  	}
   108  }
   109  

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