A Tour of Go

Transcript

1. 1.

   A Tour of Go Who? Ian Yang From? Intridea Inc.

   When? March 27, 2013
2. 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. 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. 4.

   How to Write Go Code golang.org/doc/code.html

5. 5.

   GOPATH 1 mkdir -p ~/go/src 2 export GOPATH =~/go

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   Directory Structure 1 go 2 |- bin 3 | `-

   hello 4 |- src 5 | `- github.com/doitian/studygo 6 `- pkg 7 `- linux_amd64/github.com/doitian/ studygo
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   Go Package All go files in a directory

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   Go Package All go files in a directory Do not

   find files recursively
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   Go Package All go files in a directory Do not

   find files recursively All files declare the same package
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    Package Search Search by import path

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    Package Search Search by import path Import path is relative

    directory path
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    Package Search Search by import path Import path is relative

    directory path Search paths in GOPATH one by one
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    Package Search Search by import path Import path is relative

    directory path Search paths in GOPATH one by one pkg first, then src
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    Executable A package that declares package main

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    Executable A package that declares package main Installed into bin

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    Executable A package that declares package main Installed into bin

    Run func main
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    Toolkit go build compile package

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    Toolkit go build compile package go install compile and install

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    Toolkit go build compile package go install compile and install

    go test run tests in *_test.go
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    Toolkit go build compile package go install compile and install

    go test run tests in *_test.go go get install remote packages
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    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. 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. 23.

    A Tour of Go Let's rock with the online tour

    tour.golang.org
24. 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. 25.

    Hello World 1 package main 2 3 import "fmt" 4

    5 func main() { 6 fmt.Println("Hello ,␣World") 7 }
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    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
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    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 }
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    User will be confused. hello/main.go 1 package main 2 import

    "foo" 3 func main() { 4 bar.Greeting () 5 }
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    import 1 import "fmt" 2 import m "math" 3 4

    func main() { 5 fmt.Println(m.Pi) 6 }
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    in group 1 import ( 2 "fmt" 3 "math" 4

    ) 5 import ( 6 fmt "fmt" 7 m "math" 8 )
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    Exported names a name is exported if it begins with

    a capital letter. global var, const, type and func
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    General Declaration Rules type after variable type is optional if

    it can be deduced
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    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. 34.

    func 1 func sum(x int , y int) int {

    2 return x + y; 3 }
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    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 }
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    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 }
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    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 }
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    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 }
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    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 }
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    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. 41.

    Variables The var statement declares a list of variables. 1

    var a, b, c int
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    Variables Cont. Cross multiple lines 1 var ( 2 a

    int 3 b string 4 )
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    Variables initializer 1 var x, y, z = true ,

    "foo", 3.14
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    Variables initializer Cont. Cross multiple lines 1 var ( 2

    a int = 10 3 b = "foo" 4 )
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    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 }
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    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 }
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    Variables Scope block scope (except if) parameters and named results

    are in the scope of function block var, := hide the variable in parent scope
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    Primitive Types bool string int int8 int16 int32 int64 uint

    uint8 uint16 uint32 uint64 uintptr
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    Primitive Types Cont. byte alias of uint8 rune Unicode code,

    alias of int32 float32 float64 complex64 complex128
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    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 }
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    First class func 1 add = func(x, y int) int

    { 2 return x + y 3 } 4 fmt.Println(add(10, 20)) // => 30
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    Closure 1 func adder () func(int) int { 2 sum

    := 0 3 return func(int x) int { 4 sum += x 5 return sum 6 } 7 }
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    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. 54.

    for no ( ) { } are required 1 sum

    := 0 2 for i := 1; i <= 10; i++ { 3 sum += i 4 }
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    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 }
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    for is while 1 sum , i := 0, 1

    2 for i <= 10 { 3 sum += i 4 }
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    forever 1 for { 2 serve(<-req) 3 }

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    if no ( ) { } are required 1 func

    abs(x int) int { 2 if x < 0 { 3 return -x 4 } 5 return x 6 }
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    if initializer 1 if name , err := m["name"]; ok

    { 2 fmt.Println(name) 3 } Variable declared in initializer is visible in all branches
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    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 }
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    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. 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}
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    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 }
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    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 }
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    new 1 var p *T = new(T) 2 p: =

    new(T)
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    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 }
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    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]
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    Making slice 1 // make ([]T, lenth , capability) 2

    p := make ([]int , 0, 10) 3 cap(p) // => 10 4 len(p) // => 0
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    Slicing beyond len 1 p := make ([]int , 5,

    10) 2 p = p[3,8] // len(p)=5,cap(p)=7
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    1 p := make ([]int , 5, 10)

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    append 1 func append(slice []Type , elems ... Type) []

    Type Slice the slice if capability is enough, otherwise allocate a new array.
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    append 1 slice = append(slice , elem1 , elem2) 2

    slice = append(slice , anotherSlice ...)
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    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 }
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    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 }
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    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 }
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    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 }
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    map functions 1 m[key] = value 2 elem = m[key]

    3 delete(m, key) 4 elem , ok = m[key]
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    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. 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 }
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    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 }
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    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)
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    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.
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    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)
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    Interfaces An interface type is defined by a set of

    methods. A value of interface type can hold any value that implements those methods.
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    Interfaces 1 type error interface { 2 Error () string

    3 }
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    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
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    Interfaces and Pointer Methods defined on value is considered defined

    on pointer as well Methods defined on pointer is not defined on value
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    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
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    Interfaces Union 1 type ReadWriter interface { 2 Reader 3

    Writer 4 }
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    Embedding 1 type Job struct { 2 Command string 3

    *log.Logger 4 } Job has all methods defined on log.Logger.
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    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 }
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    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
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    Goroutines A goroutine is a lightweight thread 1 go f(x,

    y, z)
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    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
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    Making Channels 1 ch := make(chan int) 2 queue =

    make(chan *Request)
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    Channels Blocking sender is blocked until data is read by

    receiver receiver is blocked until data is placed by sender
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    Buffered Channels 1 ch := make(chan int , 10) 2

    queue = make(chan *Request , 100)
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    Buffered Channels Blocking sender is blocked when buffer is full

    receiver is blocked when buffer is empty
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    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 }
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     select 1 select { 2 case c <- x: 3

     x, y = y, x+y 4 case <-quit: 5 fmt.Println("quit") 6 return 7 }
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     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 }
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     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. 103.

     Continue Reading Effective Go Defer, Panic, and Recover (similar to

     exception) Concurrency Patterns Packages Reference