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