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Go: a language built for getting things done Sarah Wells Principal Engineer, Financial Times @sarahjwells

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@sarahjwells Hello

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@sarahjwells Building a microservices architecture

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@sarahjwells Running applications in containers

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@sarahjwells The JVM makes docker images bigger

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@sarahjwells Image size container memory used vs

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@sarahjwells Enthusiastic gopher on the team!

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@sarahjwells About Go Robert Griesemer, Rob Pike, and Ken Thompson

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@sarahjwells “Efficient, scalable and productive”

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@sarahjwells • Started Sept 2007 • Announced and open sourced in Nov 2009 • Go 1.0 released March 2012 • Now on version 1.7 (released 2016/08/15) • Both 1.6 and 1.7 releases were mostly changes in the implementation of the toolchain, runtime, and libraries

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@sarahjwells Built to solve Google’s problems

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@sarahjwells – Rob Pike keynote at SPLASH 2012 conference “to eliminate the slowness and clumsiness of software development at Google, and thereby to make the process more productive and scalable”

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@sarahjwells Can’t be too radical, need developers to be productive quickly

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@sarahjwells Must cope with the modern world: multicore machines, web applications

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@sarahjwells Must work at scale: large programmes, lots of developers working on them

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@sarahjwells Designed to make tools easy to write

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@sarahjwells Getting started with Go

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@sarahjwells • https://golang.org/ • Install Go • Create a workspace directory, e.g. go-workspace • set $GOPATH to point to that workspace

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@sarahjwells package main import ( "fmt" "github.com/golang/example/stringutil" ) func main() { fmt.Println(stringutil.Reverse("Hello world")) }

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@sarahjwells package main import ( "fmt" "github.com/golang/example/stringutil" ) func main() { fmt.Println(stringutil.Reverse("Hello world")) }

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@sarahjwells package main import ( "fmt" "github.com/golang/example/stringutil" ) func main() { fmt.Println(stringutil.Reverse("Hello world")) }

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@sarahjwells package main import ( "fmt" "github.com/golang/example/stringutil" ) func main() { fmt.Println(stringutil.Reverse("Hello world")) }

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No content

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@sarahjwells package main import ( "fmt" "github.com/golang/example/stringutil" ) func main() { fmt.Println(stringutil.Reverse("Hello world")) }

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@sarahjwells Go tooling

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@sarahjwells go fmt - formats your code according to specific rules • Easier to write • Easier to read • Easier to maintain • Fewer arguments!

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@sarahjwells Allows you to easily do automatic code transformations

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@sarahjwells FT-MW4708:wosr sarah.wells$ go help Go is a tool for managing Go source code. Usage: go command [arguments] The commands are: build compile packages and dependencies clean remove object files doc show documentation for package or symbol env print Go environment information fix run go tool fix on packages fmt run gofmt on package sources

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@sarahjwells … generate generate Go files by processing source get download and install packages and dependencies install compile and install packages and dependencies list list packages run compile and run Go program test test packages tool run specified go tool version print Go version vet run go tool vet on packages

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@sarahjwells Go workspace

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go get github.com/golang/example/hello

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@sarahjwells Let’s have a look at some more code

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@sarahjwells Functions

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@sarahjwells func split(sum int) (x, y int) { x = sum * 4 / 9 y = sum - x return } func main() { x, y := split(15) fmt.Printf("x=%d, y=%d\n", x, y) //outputs x=6, y=9 }

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@sarahjwells func split(sum int) (x, y int) { x = sum * 4 / 9 y = sum - x return } func main() { x, y := split(15) fmt.Printf("x=%d, y=%d\n", x, y) //outputs x=6, y=9 }

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@sarahjwells Error handling

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@sarahjwells type error interface { Error() string }

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@sarahjwells package os func Open(name string) (file *File, err error) … f, err := os.Open("filename.ext") if err != nil { log.Fatal(err) } // do something with the open *File f

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@sarahjwells Objects

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@sarahjwells type Rect struct { width int height int } func (r Rect) Area() int { return r.width * r.height } func main() { r := Rect{width: 10, height: 5} fmt.Printf("area: %d\n", r.area()) }

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@sarahjwells type Rectangle struct { width int height int } func (r Rectangle) Area() int { return r.width * r.height } func main() { r := Rectangle{width: 10, height: 5} fmt.Printf("area: %d\n", r.Area()) }

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@sarahjwells Interfaces

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@sarahjwells type Writer interface { Write(p []byte) (n int, err error) }

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@sarahjwells package os func (f *File) Write(b []byte) (n int, err error) { if f == nil { return 0, ErrInvalid } … }

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@sarahjwells type ByteCounter struct { counter int } func (c *ByteCounter) Write(p []byte) (int, error) { (*c).counter += len(p) return len(p), nil }

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@sarahjwells package fmt // writes to the supplied writer func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) { p := newPrinter() p.doPrintf(format, a) n, err = w.Write(p.buf) p.free() return }

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@sarahjwells Concurrency

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@sarahjwells func main() { fmt.Printf("Hello\n") go slowFunction() fmt.Printf("Bye!\n") } func slowFunction() { //do something slow time.Sleep(1 * time.Second) fmt.Printf("Finished slow stuff\n") }

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@sarahjwells ch := make(chan int) ch <- v // Send v to channel ch. v := <-ch // Receive from ch, and // assign value to v.

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@sarahjwells func main() { rand.Seed(time.Now().UnixNano()) responses := make(chan string, 5) for i := 1; i <= 5; i++ { go slowFunction(i, responses) } fmt.Printf("Winner was %s\n", <-responses) } func slowFunction(num int, out chan<- string) { waitSeconds := rand.Intn(10) fmt.Printf("Num %d is waiting %d seconds\n", num, waitSeconds) time.Sleep(time.Duration(waitSeconds) * time.Second) out <- fmt.Sprintf("%d", num) }

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@sarahjwells func main() { rand.Seed(time.Now().UnixNano()) responses := make(chan string, 5) for i := 1; i <= 5; i++ { go slowFunction(i, responses) } fmt.Printf("Winner was %s\n", <-responses) } func slowFunction(num int, out chan<- string) { waitSeconds := rand.Intn(10) fmt.Printf("Num %d is waiting %d seconds\n", num, waitSeconds) time.Sleep(time.Duration(waitSeconds) * time.Second) out <- fmt.Sprintf("%d", num) }

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@sarahjwells func main() { rand.Seed(time.Now().UnixNano()) responses := make(chan string, 5) for i := 1; i <= 5; i++ { go slowFunction(i, responses) } fmt.Printf("Winner was %s\n", <-responses) } func slowFunction(num int, out chan<- string) { waitSeconds := rand.Intn(10) fmt.Printf("Num %d is waiting %d seconds\n", num, waitSeconds) time.Sleep(time.Duration(waitSeconds) * time.Second) out <- fmt.Sprintf("%d", num) }

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@sarahjwells That webservice…

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@sarahjwells func main() { ah := authorHandler{newHardCodedAuthorService()} r := mux.NewRouter() r.HandleFunc("/authors/{uuid}", ah.getAuthor).Methods("GET") http.Handle("/", r) log.Fatal(http.ListenAndServe("localhost:8000", nil)) } type authorHandler struct { as authorService }

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@sarahjwells func main() { ah := authorHandler{newHardCodedAuthorService()} r := mux.NewRouter() r.HandleFunc("/authors/{uuid}", ah.getAuthor).Methods("GET") http.Handle("/", r) log.Fatal(http.ListenAndServe("localhost:8000", nil)) } type authorHandler struct { as authorService }

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@sarahjwells func (ah *authorHandler) getAuthor(writer http.ResponseWriter, req *http.Request) { vars := mux.Vars(req) uuid := vars["uuid"] requestedAuthor, found := ah.as.getAuthorByUUID(uuid) if !found { writer.WriteHeader(http.StatusNotFound) return } enc := json.NewEncoder(writer) //should have error handling here enc.Encode(requestedAuthor) }

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@sarahjwells type authorService interface { getAuthorByUUID(uuid string) (author, bool) } type simpleAuthorService struct { authors map[string]author } func (as simpleAuthorService) getAuthorByUUID(uuid string) (author, bool) { requestedAuthor, found := as.authors[uuid] return requestedAuthor, found }

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@sarahjwells type author struct { Name string `json:"name"` Email string `json:"email"` ImageURL string `json:"imageurl"` Biography string `json:"biography"` TwitterHandle string `json:"twitterhandle"` TmeIdentifier string `json:"tmeidentifier"` }

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@sarahjwells Summary

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@sarahjwells We’ve talked about: • the language aims • tooling • some of the interesting design decisions

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@sarahjwells So who’s using Go? • Docker is written in Go • Dropbox use Go (as well as Python) • Netflix rewrote their chaos monkey in Go

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@sarahjwells Resources

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@sarahjwells • https://golang.org - the home of Go, including go docs • Start with the Go tour: https://tour.golang.org/welcome/1 • Then Effective Go: https://golang.org/doc/effective_go.html • Go by Example: https://gobyexample.com/

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@sarahjwells http://www.gopl.io/ https://github.com/adonovan/ gopl.io

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@sarahjwells Code samples: https://github.com/sjwells/wosr

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@sarahjwells Thank you!