A Tour of Go

Introduction to Go programming language based on tour.golang.org

Transcript

1. A Tour of Go Who? Ian Yang From? Intridea Inc. When? March 27, 2013
2. Contents 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
3. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
4. How to Write Go Code golang.org/doc/code.html
5. GOPATH 1 mkdir -p ~/go/src 2 export GOPATH =~/go
6. Directory Structure 1 go 2 |- bin 3 | `- hello 4 |- src 5 | `- github.com/doitian/studygo 6 `- pkg 7 `- linux_amd64/github.com/doitian/ studygo
7. Go Package All go files in a directory
8. Go Package All go files in a directory Do not find files recursively
9. Go Package All go files in a directory Do not find files recursively All files declare the same package
10. Package Search Search by import path
11. Package Search Search by import path Import path is relative directory path
12. Package Search Search by import path Import path is relative directory path Search paths in GOPATH one by one
13. Package Search Search by import path Import path is relative directory path Search paths in GOPATH one by one pkg first, then src
14. Executable A package that declares package main
15. Executable A package that declares package main Installed into bin
16. Executable A package that declares package main Installed into bin Run func main
17. Toolkit go build compile package
18. Toolkit go build compile package go install compile and install
19. Toolkit go build compile package go install compile and install go test run tests in *_test.go
20. Toolkit go build compile package go install compile and install go test run tests in *_test.go go get install remote packages
21. Toolkit go build compile package go install compile and install go test run tests in *_test.go go get install remote packages go help manual
22. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
23. A Tour of Go Let's rock with the online tour tour.golang.org
24. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
25. Hello World 1 package main 2 3 import "fmt" 4 5 func main() { 6 fmt.Println("Hello ,␣World") 7 }
26. package Only package main is executable Must be the same in directory Default name when imported Convention: same with the last element of the import path
27. If we do not follow the convention, foo/greeting.go 1 package bar // <-- import path is foo 2 import "fmt" 3 func Greeting () { 4 fmt.Println("Hello ,␣World") 5 }
28. User will be confused. hello/main.go 1 package main 2 import "foo" 3 func main() { 4 bar.Greeting () 5 }
29. import 1 import "fmt" 2 import m "math" 3 4 func main() { 5 fmt.Println(m.Pi) 6 }
30. in group 1 import ( 2 "fmt" 3 "math" 4 ) 5 import ( 6 fmt "fmt" 7 m "math" 8 )
31. Exported names a name is exported if it begins with a capital letter. global var, const, type and func
32. General Declaration Rules type after variable type is optional if it can be deduced
33. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
34. func 1 func sum(x int , y int) int { 2 return x + y; 3 }
35. func Cont. You can omit the type if two or more consecutive parameters share a type. 1 func sum(x, y int) int { 2 return x + y; 3 }
36. func Multiple results 1 func swap(x, y string) (string , string) { 2 return y, x; 3 } 4 func main() { 5 x, y := swap("hello", "world") 6 }
37. Comma OK pattern 1 func main() { 2 m := map[string]string{ 3 "foo": "bar" 4 } 5 6 if name , ok := m["name"]; ok { 7 fmt.Println(name) 8 } 9 }
38. Comma err pattern 1 import "os" 2 import "log" 3 4 func main() { 5 file , err := os.Open("file.go") 6 if err != nil { 7 log.Fatal(err) 8 } 9 }
39. func Named results 1 func Sqrt(f float64) (result float64 , err error) { 2 if f < 0 { 3 err = ... 4 } else { 5 result = ... 6 } 7 return 8 }
40. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
41. Variables The var statement declares a list of variables. 1 var a, b, c int
42. Variables Cont. Cross multiple lines 1 var ( 2 a int 3 b string 4 )
43. Variables initializer 1 var x, y, z = true , "foo", 3.14
44. Variables initializer Cont. Cross multiple lines 1 var ( 2 a int = 10 3 b = "foo" 4 )
45. Short Assignment Inside function, := short assignment can be used in place of var with implicit type. 1 func main() { 2 a, b, c := "foo", true , 3.14 3 }
46. Short Assignment At least one variable is newly declared in current scope 1 func parse(path string) (config map[sring] sring , err error) { 2 file , err := os.Open(path) 3 data := make ([]byte , 100) 4 count , err := file.Read(data) 5 ... 6 }
47. Variables Scope block scope (except if) parameters and named results are in the scope of function block var, := hide the variable in parent scope
48. Primitive Types bool string int int8 int16 int32 int64 uint uint8 uint16 uint32 uint64 uintptr
49. Primitive Types Cont. byte alias of uint8 rune Unicode code, alias of int32 float32 float64 complex64 complex128
50. Constants like var, but use const character, string, boolean, or numeric values. 1 const Pi = 3.14 2 func main() { 3 const World = "world" 4 }
51. First class func 1 add = func(x, y int) int { 2 return x + y 3 } 4 fmt.Println(add(10, 20)) // => 30
52. Closure 1 func adder () func(int) int { 2 sum := 0 3 return func(int x) int { 4 sum += x 5 return sum 6 } 7 }
53. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
54. for no ( ) { } are required 1 sum := 0 2 for i := 1; i <= 10; i++ { 3 sum += i 4 }
55. for Pitfalls There is no comma operator ++ and -- are statements 1 for a,b := 0,0; a<10; a,b = a+1,b+1 { 2 ... 3 }
56. for is while 1 sum , i := 0, 1 2 for i <= 10 { 3 sum += i 4 }
57. forever 1 for { 2 serve(<-req) 3 }
58. if no ( ) { } are required 1 func abs(x int) int { 2 if x < 0 { 3 return -x 4 } 5 return x 6 }
59. if initializer 1 if name , err := m["name"]; ok { 2 fmt.Println(name) 3 } Variable declared in initializer is visible in all branches
60. Switch 1 switch os := runtime.GOOS; os { 2 case "darwin": 3 fmt.Println("OS␣X.") 4 case "linux": 5 fmt.Println("Linux.") 6 default: 7 fmt.Printf("%s.", os) // freebsd , ... 8 } 9 }
61. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
62. struct 1 type Vertex struct { 2 X int 3 Y int 4 } 5 var origin = Vertex{0, 0} 6 var xUnit = Vertex{X:1} 7 var yUnit = Vertex{Y:1}
63. struct fields 1 type Vertex struct { X, Y int } 2 func main() { 3 v := Vertex {100, 200} 4 v.X = 300 5 fmt.Println(v.X, v.Y) // => 300 200 6 }
64. Pointers 1 type Vertex struct { X, Y int } 2 func main() { 3 v := Vertex {100, 200} 4 var p *Vertex = &v 5 p.X = 300 6 fmt.Println(v.X, v.Y) // => 300 200 7 }
65. new 1 var p *T = new(T) 2 p: = new(T)
66. Slices 1 p := []int{2, 3, 5, 7, 11, 13} 2 3 for i := 0; i < len(p); i++ { 4 fmt.Printf("p[%d]␣=␣%d\n", i, p[i]) 5 }
67. Slicing Slices 1 p := []int{2, 3, 5, 7, 11, 13} 2 p[1:4] // => [3,5,7] 3 p[1:] // => [3,5,7,11,13] 4 p[:4] // => [2,3,5,7]
68. Making slice 1 // make ([]T, lenth , capability) 2 p := make ([]int , 0, 10) 3 cap(p) // => 10 4 len(p) // => 0
69. Slicing beyond len 1 p := make ([]int , 5, 10) 2 p = p[3,8] // len(p)=5,cap(p)=7
70. 1 p := make ([]int , 5, 10)
71. append 1 func append(slice []Type , elems ... Type) [] Type Slice the slice if capability is enough, otherwise allocate a new array.
72. append 1 slice = append(slice , elem1 , elem2) 2 slice = append(slice , anotherSlice ...)
73. range 1 prime := []int{2,3,5,7,11,13} 2 for i, value := range pow { 3 fmt.Printf("prime [%d]=%d\n", i, value) 4 }
74. range 1 pow := make ([]int , 10) 2 for i := range pow { // only key 3 pow[i] = 1 << uint(i) 4 } 5 for _, value := range pow { // only value 6 fmt.Printf("%d\n", value) 7 }
75. map 1 type Vertex struct { 2 Lat , Long float64 3 } 4 5 var m = map[string]Vertex{ 6 "Bell␣Labs": Vertex {40.68433 , -74.39967} , 7 "Google": Vertex {37.42202 , -122.08408} , 8 }
76. map Cont. 1 var m = map[string]Vertex{ 2 "Bell␣Labs": { 3 Lat: 40.68433 , 4 Long: -74.39967 , 5 }, 6 "Google": {37.42202 , -122.08408} , 7 }
77. map functions 1 m[key] = value 2 elem = m[key] 3 delete(m, key) 4 elem , ok = m[key]
78. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
79. Methods 1 type Vertex struct{ X, Y float64 } 2 func (v *Vertex) double () { 3 v.X, v.Y = v.X*2, v.Y*2 4 } 5 6 func main() { 7 v := &Vertex{1, 2} 8 v.double () // => &Vertex {2,4} 9 }
80. Revisit Pointer 1 type Vertex struct{ X, Y float64 } 2 func (v Vertex) double () { 3 v.X, v.Y = v.X*2, v.Y*2 4 } 5 6 func main() { 7 v := &Vertex{1, 2} 8 v.double () // => &Vertex {1,2} 9 }
81. Revisit Pointer Cont. You can pass pointer when value is required You can pass value when pointer is required only as method receiver (maybe a bug)
82. Methods Cont. In fact, you can define a method on any type you define in your package, not just structs. You cannot define a method on a type from another package, or on a basic type.
83. Methods Cont. 1 type SqrtError float64 2 3 func (err SqrtError) Error () string { 4 return fmt.Sprintf("Sqrt:␣%v␣is␣nagative", float64(err)) 5 } 6 7 var err = SqrtError (-64)
84. Interfaces An interface type is defined by a set of methods. A value of interface type can hold any value that implements those methods.
85. Interfaces 1 type error interface { 2 Error () string 3 }
86. Interfaces 1 type SqrtError float64 2 func (err *SqrtError) Error () string { 3 return fmt.Sprintf("Sqrt:␣%v␣is␣nagative", float64 (*err)) 4 } 5 var err = SqrtError (3) 6 var x error = 1 // => type error 7 var y error = err // => type error 8 var z error = &err // => OK
87. Interfaces and Pointer Methods defined on value is considered defined on pointer as well Methods defined on pointer is not defined on value
88. Interfaces and Pointer 1 type SqrtError float64 2 func (err SqrtError) Error () string { 3 return fmt.Sprintf("Sqrt:␣%v␣is␣nagative", float64(err)) 4 } 5 var err = SqrtError (3) 6 var x error = 1 // => type error 7 var y error = err // => OK 8 var z error = &err // => OK
89. Interfaces Union 1 type ReadWriter interface { 2 Reader 3 Writer 4 }
90. Embedding 1 type Job struct { 2 Command string 3 *log.Logger 4 } Job has all methods defined on log.Logger.
91. Embedding Last part of the type name is defined as implicit field name 1 func main() { 2 job := Job{Logger: log.New(os.Stderr , "Job:␣ ", log.Ldate)} 3 4 fmt.Println(job) 5 }
92. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
93. Goroutines A goroutine is a lightweight thread 1 go f(x, y, z)
94. Channels Channels are a typed conduit through which you can send and receive values with the channel operator, <-. 1 ch <- v // send v to channel 2 v := <-ch // receive from ch , and assign to v
95. Making Channels 1 ch := make(chan int) 2 queue = make(chan *Request)
96. Channels Blocking sender is blocked until data is read by receiver receiver is blocked until data is placed by sender
97. Buffered Channels 1 ch := make(chan int , 10) 2 queue = make(chan *Request , 100)
98. Buffered Channels Blocking sender is blocked when buffer is full receiver is blocked when buffer is empty
99. 1 func worker(a []int , ch chan int) { 2 result := sum(a) 3 ch <- result 4 } 5 6 func main() { 7 ch := make(chan int) 8 go worker ([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, ch) 9 10 fmt.Println(<-ch) // => 3 11 }
100. select 1 select { 2 case c <- x: 3 x, y = y, x+y 4 case <-quit: 5 fmt.Println("quit") 6 return 7 }
101. non-blocking select 1 select { 2 case c <- x: 3 x, y = y, x+y 4 case <-quit: 5 fmt.Println("quit") 6 return 7 default: 8 time.Sleep (5e7) 9 }
102. Outline 1 How to Write Go Code 2 A Tour of Go Hello World Functions Variables Control Statements Data Structures Methods and Interfaces Concurrency 3 Continue Reading
103. Continue Reading Effective Go Defer, Panic, and Recover (similar to exception) Concurrency Patterns Packages Reference