1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // This file contains examples to embed in the Go 1 release notes document. 6 7 package main 8 9 import ( 10 "errors" 11 "flag" 12 "fmt" 13 "log" 14 "os" 15 "path/filepath" 16 "testing" 17 "time" 18 "unicode" 19 ) 20 21 func main() { 22 flag.Parse() 23 stringAppend() 24 mapDelete() 25 mapIteration() 26 multipleAssignment() 27 structEquality() 28 compositeLiterals() 29 runeType() 30 errorExample() 31 timePackage() 32 walkExample() 33 osIsExist() 34 } 35 36 var timeout = flag.Duration("timeout", 30*time.Second, "how long to wait for completion") 37 38 func init() { 39 // canonicalize the logging 40 log.SetFlags(0) 41 } 42 43 func mapDelete() { 44 m := map[string]int{"7": 7, "23": 23} 45 k := "7" 46 delete(m, k) 47 if m["7"] != 0 || m["23"] != 23 { 48 log.Fatal("mapDelete:", m) 49 } 50 } 51 52 func stringAppend() { 53 greeting := []byte{} 54 greeting = append(greeting, []byte("hello ")...) 55 greeting = append(greeting, "world"...) 56 if string(greeting) != "hello world" { 57 log.Fatal("stringAppend: ", string(greeting)) 58 } 59 } 60 61 func mapIteration() { 62 m := map[string]int{"Sunday": 0, "Monday": 1} 63 for name, value := range m { 64 // This loop should not assume Sunday will be visited first. 65 f(name, value) 66 } 67 } 68 69 func f(string, int) { 70 } 71 72 func assert(t bool) { 73 if !t { 74 log.Panic("assertion fail") 75 } 76 } 77 78 func multipleAssignment() { 79 sa := []int{1, 2, 3} 80 i := 0 81 i, sa[i] = 1, 2 // sets i = 1, sa[0] = 2 82 83 sb := []int{1, 2, 3} 84 j := 0 85 sb[j], j = 2, 1 // sets sb[0] = 2, j = 1 86 87 sc := []int{1, 2, 3} 88 sc[0], sc[0] = 1, 2 // sets sc[0] = 1, then sc[0] = 2 (so sc[0] = 2 at end) 89 90 assert(i == 1 && sa[0] == 2) 91 assert(j == 1 && sb[0] == 2) 92 assert(sc[0] == 2) 93 } 94 95 func structEquality() { 96 type Day struct { 97 long string 98 short string 99 } 100 Christmas := Day{"Christmas", "XMas"} 101 Thanksgiving := Day{"Thanksgiving", "Turkey"} 102 holiday := map[Day]bool{ 103 Christmas: true, 104 Thanksgiving: true, 105 } 106 fmt.Printf("Christmas is a holiday: %t\n", holiday[Christmas]) 107 } 108 109 func compositeLiterals() { 110 type Date struct { 111 month string 112 day int 113 } 114 // Struct values, fully qualified; always legal. 115 holiday1 := []Date{ 116 Date{"Feb", 14}, 117 Date{"Nov", 11}, 118 Date{"Dec", 25}, 119 } 120 // Struct values, type name elided; always legal. 121 holiday2 := []Date{ 122 {"Feb", 14}, 123 {"Nov", 11}, 124 {"Dec", 25}, 125 } 126 // Pointers, fully qualified, always legal. 127 holiday3 := []*Date{ 128 &Date{"Feb", 14}, 129 &Date{"Nov", 11}, 130 &Date{"Dec", 25}, 131 } 132 // Pointers, type name elided; legal in Go 1. 133 holiday4 := []*Date{ 134 {"Feb", 14}, 135 {"Nov", 11}, 136 {"Dec", 25}, 137 } 138 // STOP OMIT 139 _, _, _, _ = holiday1, holiday2, holiday3, holiday4 140 } 141 142 func runeType() { 143 // STARTRUNE OMIT 144 delta := '' // delta has type rune. 145 var DELTA rune 146 DELTA = unicode.ToUpper(delta) 147 epsilon := unicode.ToLower(DELTA + 1) 148 if epsilon != ''+1 { 149 log.Fatal("inconsistent casing for Greek") 150 } 151 // ENDRUNE OMIT 152 } 153 154 // START ERROR EXAMPLE OMIT 155 type SyntaxError struct { 156 File string 157 Line int 158 Message string 159 } 160 161 func (se *SyntaxError) Error() string { 162 return fmt.Sprintf("%s:%d: %s", se.File, se.Line, se.Message) 163 } 164 165 // END ERROR EXAMPLE OMIT 166 167 func errorExample() { 168 var ErrSyntax = errors.New("syntax error") 169 _ = ErrSyntax 170 se := &SyntaxError{"file", 7, "error"} 171 got := fmt.Sprint(se) 172 const expect = "file:7: error" 173 if got != expect { 174 log.Fatalf("errorsPackage: expected %q got %q", expect, got) 175 } 176 } 177 178 // sleepUntil sleeps until the specified time. It returns immediately if it's too late. 179 func sleepUntil(wakeup time.Time) { 180 now := time.Now() // A Time. 181 if !wakeup.After(now) { 182 return 183 } 184 delta := wakeup.Sub(now) // A Duration. 185 fmt.Printf("Sleeping for %.3fs\n", delta.Seconds()) 186 time.Sleep(delta) 187 } 188 189 func timePackage() { 190 sleepUntil(time.Now().Add(123 * time.Millisecond)) 191 } 192 193 func walkExample() { 194 // STARTWALK OMIT 195 markFn := func(path string, info os.FileInfo, err error) error { 196 if path == "pictures" { // Will skip walking of directory pictures and its contents. 197 return filepath.SkipDir 198 } 199 if err != nil { 200 return err 201 } 202 log.Println(path) 203 return nil 204 } 205 err := filepath.Walk(".", markFn) 206 if err != nil { 207 log.Fatal(err) 208 } 209 // ENDWALK OMIT 210 } 211 212 func initializationFunction(c chan int) { 213 c <- 1 214 } 215 216 var PackageGlobal int 217 218 func init() { 219 c := make(chan int) 220 go initializationFunction(c) 221 PackageGlobal = <-c 222 } 223 224 func BenchmarkSprintf(b *testing.B) { 225 // Verify correctness before running benchmark. 226 b.StopTimer() 227 got := fmt.Sprintf("%x", 23) 228 const expect = "17" 229 if expect != got { 230 b.Fatalf("expected %q; got %q", expect, got) 231 } 232 b.StartTimer() 233 for i := 0; i < b.N; i++ { 234 fmt.Sprintf("%x", 23) 235 } 236 } 237 238 func osIsExist() { 239 name := "go1.go" 240 f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600) 241 if os.IsExist(err) { 242 log.Printf("%s already exists", name) 243 } 244 _ = f 245 } 246
