Gophers! Go, google's open source language - WXG Guildford 2013

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gophers! Ben Lovell

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benlovell _j

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113581334398839860922 (thanks, google)

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sometimes we don’t get along…

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what is go? … and why does it exist

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go will be the server language of the future - Tobias Lütke, Shopify founder

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go is fast

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go is object-oriented (but not as you know it)

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go is statically typed

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go is garbage collected

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go is concurrent

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optimised for developer happiness

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a brief history of go

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started in 2007 by three googlers…

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Rob Pike

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Ken Thompson

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Robert Griesemer

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open sourced in 2009 (over 300 contributors to date)

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1.0 release March 2012

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what was left out is more important than what was put in - UNIX philosophy

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hello, world!

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package main ! import "fmt" ! func main() { fmt.Println("Hello, world!") }

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the type system

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package main ! import "fmt" ! type Person string ! func (person Person) Greet() { fmt.Printf("Hello, %s!\n", person) } ! func main() { person := Person("Ben") person.Greet() } !

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package main ! import "fmt" ! type Person struct { Name string Age int } ! func (person Person) Greet() { fmt.Println(person.Name) } ! func main() { person := Person{"Ben", 33} person.Greet() } !

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no classes…

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…no type hierarchy

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favour composition over inheritance

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arranging code in packages

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% export GOPATH=/gocode/ ! /gocode /gocode/src

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package person ! import "fmt" ! type Person struct { Name string } ! func (person Person) Greet() string { return fmt.Sprintf("Hello, %s", person.Name) } ~/gocode/src/person/person.go

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~/gocode/src/main.go ~/gocode/src % go run main.go package main ! import ( "fmt" "person" ) ! func main() { person := person.Person{"Ben"} greeting := person.Greet() fmt.Println(greeting) } !

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visibility?

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start your identifier with a lowercase letter to make it private

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function arguments are copied

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package main ! import ( "fmt" "strings" ) ! func Upcase(name string) { name = strings.ToUpper(name) } ! func main() { name := "ben" Upcase(name) ! fmt.Println(name) } ! // ben

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pointers! (scream)

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// BEN package main ! import ( "fmt" "strings" ) ! func Upcase(name *string) { *name = strings.ToUpper(*name) } ! func main() { name := "ben" Upcase(&name) ! fmt.Println(name) } !

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the same applies to function receivers

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package main ! import "fmt" ! type Person struct { Name string } ! func (p Person) SetName(name string) { p.Name = name } ! func main() { p := Person{"Ben"} p.SetName("Jim") fmt.Println(p.Name) } ! // Ben

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// Jim package main ! import "fmt" ! type Person struct { Name string } ! func (p *Person) SetName(name string) { p.Name = name } ! func main() { p := Person{"Ben"} p.SetName("Jim") fmt.Println(p.Name) } !

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pointers are not just for reference semantics

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pointers are not just for reference semantics Christmas

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representing is-a with type embedding (well, kinda)

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// I’M BEN // I’m Ben type Person struct { Name string } ! func (p Person) Greet() { fmt.Println("I'm", p.Name) } ! type Manager struct { Person } ! func (m Manager) Greet() { fmt.Println("I'M", strings.ToUpper(m.Name)) } ! func main() { m := Manager{Person{"Ben"}} m.Greet() m.Person.Greet() }

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signature based polymorphism (quack quack)

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interfaces

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type Person struct { Name string } ! func (p Person) Greet() { fmt.Println("I'm", p.Name) } ! type Manager struct { Person } ! func (m Manager) Greet() { fmt.Println("I'M", strings.ToUpper(m.Name)) } ! func greet(greeters ...Greeter) { for _, g := range greeters { g.Greet() } } ! type Greeter interface { Greet() } ! func main() { greet(Person{"Ben"}, Manager{Person{"Bob"}}, Person{"Anne"}) }

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interfaces are implicitly satisfied

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querying for support and casting

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func greet(greeters ...interface{}) { for _, g := range greeters { g.(Greeter).Greet() } }

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don’t. there are safe idioms

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func greet(greeters ...interface{}) { for _, g := range greeters { greetable, ok := g.(Greeter) if ok { greetable.Greet() } else { fmt.Println("Whoops!") } } } ! func main() { greet(Person{"Ben"}, "WHOA!", Person{"Anne"}) } ! // I’m Ben // Whoops! // I’m Anne

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error handling (the error interface!)

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type error interface { Error() string }

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// os.Open signature func Open(name string) (file *File, err error) ! ! f, err := os.Open("file.txt") if err != nil { log.Fatal(err) } // do something with the open file

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f, err := os.Open("file.txt") if err != nil { log.Fatal(err) } ! defer f.Close() // do something with the *File f

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concurrency (kind hard of is it)

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communicating sequential processes

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don’t communicate by sharing memory share memory by communicating

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three simple constructs

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go routines (lightweight threads)

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func main() { go greet() ! // hang around a while time.Sleep(2 * time.Second) } ! func greet() { fmt.Println("Hi!") }

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channels (for communication)

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//make a channel c := make(chan int) ! //send on the channel c <- 1 ! //receive from the channel val := <- c

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func ping(c chan string) { for i := 0; ; i++ { c <- "ping" } } ! func printer(c chan string) { for { msg := <- c fmt.Println(msg) time.Sleep(time.Second * 1) } } ! func main() { c := make(chan string) ! go ping(c) go printer(c) ! time.Sleep(time.Second * 10) }

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func main() { s := make(chan int) ! go greet(s) s <- 1 } ! func greet(signaller chan int) { <- signaller fmt.Println("Hi!") }

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func main() { functions := make(chan func(int, int)(int)) go executor(functions) ! functions <- add functions <- multiply functions <- subtract } ! func add(x, y int) int { return x + y } ! func multiply(x, y int) int { return x * y } ! func subtract(x, y int) int { return x - y } ! func executor(functions chan func(int, int)(int)) { for f := range functions { fmt.Println("The result is: ", f(10, 10)) } }

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select

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func printer(c chan string, d chan string) { for { select { case x := <- c: fmt.Println(x) case y := <- d: fmt.Println(y) case <- time.After(1 * time.Second): fmt.Println("Timeout!") } } } ! func main() { c := make(chan string) d := make(chan string) ! go ping(c) go ping(d) go printer(c, d) ! time.Sleep(time.Second * 10) }