-// $G $F.go && $L $F.$A && ./$A.out
+// run
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
+// Test nil.
+
package main
+import (
+ "fmt"
+ "time"
+)
+
type T struct {
i int
}
-type IN interface {
-}
+type IN interface{}
func main() {
- var i *int;
- var f *float;
- var s *string;
- var m *map[float] *int;
- var c *chan int;
- var t *T;
- var in IN;
- var ta []IN;
-
- i = nil;
- f = nil;
- s = nil;
- m = nil;
- c = nil;
- t = nil;
- i = nil;
- ta = new([1]IN);
- ta[0] = nil;
+ var i *int
+ var f *float32
+ var s *string
+ var m map[float32]*int
+ var c chan int
+ var t *T
+ var in IN
+ var ta []IN
+
+ i = nil
+ f = nil
+ s = nil
+ m = nil
+ c = nil
+ t = nil
+ i = nil
+ ta = make([]IN, 1)
+ ta[0] = nil
+
+ _, _, _, _, _, _, _, _ = i, f, s, m, c, t, in, ta
+
+ arraytest()
+ chantest()
+ maptest()
+ slicetest()
+}
+
+func shouldPanic(f func()) {
+ defer func() {
+ if recover() == nil {
+ panic("not panicking")
+ }
+ }()
+ f()
+}
+
+func shouldBlock(f func()) {
+ go func() {
+ f()
+ panic("did not block")
+ }()
+ time.Sleep(1e7)
+}
+
+// nil array pointer
+
+func arraytest() {
+ var p *[10]int
+
+ // Looping over indices is fine.
+ s := 0
+ for i := range p {
+ s += i
+ }
+ if s != 45 {
+ panic(s)
+ }
+
+ s = 0
+ for i := 0; i < len(p); i++ {
+ s += i
+ }
+ if s != 45 {
+ panic(s)
+ }
+
+ // Looping over values is not.
+ shouldPanic(func() {
+ for i, v := range p {
+ s += i + v
+ }
+ })
+
+ shouldPanic(func() {
+ for i := 0; i < len(p); i++ {
+ s += p[i]
+ }
+ })
+}
+
+// nil channel
+// select tests already handle select on nil channel
+
+func chantest() {
+ var ch chan int
+
+ // nil channel is never ready
+ shouldBlock(func() {
+ ch <- 1
+ })
+ shouldBlock(func() {
+ <-ch
+ })
+ shouldBlock(func() {
+ x, ok := <-ch
+ println(x, ok) // unreachable
+ })
+
+ if len(ch) != 0 {
+ panic(len(ch))
+ }
+ if cap(ch) != 0 {
+ panic(cap(ch))
+ }
+}
+
+// nil map
+
+func maptest() {
+ var m map[int]int
+
+ // nil map appears empty
+ if len(m) != 0 {
+ panic(len(m))
+ }
+ if m[1] != 0 {
+ panic(m[1])
+ }
+ if x, ok := m[1]; x != 0 || ok {
+ panic(fmt.Sprint(x, ok))
+ }
+
+ for k, v := range m {
+ panic(k)
+ panic(v)
+ }
+
+ // can delete (non-existent) entries
+ delete(m, 2)
+
+ // but cannot be written to
+ shouldPanic(func() {
+ m[2] = 3
+ })
+}
+
+// nil slice
+
+func slicetest() {
+ var x []int
+
+ // nil slice is just a 0-element slice.
+ if len(x) != 0 {
+ panic(len(x))
+ }
+ if cap(x) != 0 {
+ panic(cap(x))
+ }
+
+ // no 0-element slices can be read from or written to
+ var s int
+ shouldPanic(func() {
+ s += x[1]
+ })
+ shouldPanic(func() {
+ x[2] = s
+ })
}