Getting started with Go at GDays Nigeria 2014

13 December 2014 Ge.ng Started with Go | Abiola Ibrahim

getting started with

Go Programming Language

Abiola Ibrahim @abiosoB


AGENDA

•  My Go Story •  IntroducGon to Go •  Build our applicaGon •  Go on App Engine •  AdopGon of Go •  Useful Links


My Go Story

•  Interpreted Languages have slower runGmes and no compile Gme error checks.

•  I like Java but not the JVM overhead. •  Building C++ is not as fun as desired. •  Go is compiled, single binary (no dependencies) and builds very fast.


Why Go ?

“ “Speed, reliability, or simplicity: pick

two.” (some9mes just one).

Can’t we do be@er? ” Real World Go talk -‐ Andrew Gerrand, 2011.


Scope of Talk

•  Things this talk cannot help you do – Build Drones – Create Google.com killer – Replicate Facebook

•  Things this talk can help you do – Understand the core of Go – Start wriGng Go apps


INTRODUCTION TO GO


Simple Type System Go is staGcally typed, but type inference saves repeGGon.

Java/C/C++: int i = 1;

Go: i := 1 // type int pi := 3.142 // type float64 hello := "Hello, GDays!" // type string add := func(x, y int) int { return x + y }

//type func (x, y int)


Syntax and Structure Statements are terminated with semicolons but you don’t need to include it.

var a int = 1 // valid linevar b string = “GDays”; // also valid line


iota can come handy in constants

const EVENT = “GDays” //value cannot change

const (ANDROID_SESSION = iota // 0GOLANG_SESSION // 1GIT_SESSION // 2

)


No brackets, just braces.

if a < 0 {fmt.Printf(“%d is negative”, a)

}

for i := 0; i< 10; i++ {fmt.Println(“GDays is awesome”)

}


No while, no do while, just for.

for i < 10 { ... } //while loop in other languages

for { ... } //infinite loop

// range over arrays, slices and mapsnums := [4]int{0, 1, 2, 3}for i, value := range nums {

fmt.Println(“value at %d is %d”, i, value)}

gdays := map[string]string{ “loc” : “Chams City”, ... }for key, value := range gdays {

fmt.Println(“value at %s is %s”, key, value)}


If statement supports iniGalizaGon.

file, err := os.Open(“sample.txt”)if err == nil {

fmt.Println(file.Name())}

This can be shortened to

if file, err := os.Open(“sample.txt”); err == nil {fmt.Println(file.Name())

}


MulGple return values.

func Sqrt(float64 n) (float64, err) {if (n < 0){

return 0, errors.New(“Negative number”)}return math.Sqrt(n), nil

}


MulGple assignments.

a, b, c := 1, 2, 3

func Reverse(str string) string {b := []byte(str)for i, j := 0, len(b)-1; i != j; i, j = i+1, j-1 {

b[i], b[j] = b[j], b[i]}return string(b)

}


Arrays and Slices var nums [4]int //array declarationnums := [4]int{0, 1, 2, 3} //declare and initialize

n := nums[0:2] // slice of nums from index 0 to 1n := nums[:2] // same as aboven := nums[2:] // from index 2 to max indexn := nums[:] // slice of entire array

nums[0] = 1 // assignmentn[0] = 2 // assignment

var copyOfNum = make([]int, 4) //slice allocationcopy(copyOfNum, nums[:]) //copy nums into it


Maps var gdays map[string]string //declarationgdays = make(map[string]string) //allocation

//shorter declaration with allocationvar gdays = make(map[string]string)gdays := make(map[string]string)

gdays[“location”] = “Chams City” //assignment

//declaration with valuesgdays := map[string]string {

“location” : “Chams City”}


Structs type Point struct {

X int,Y int,Z int,

}

var p = &Point{0, 1, 3}

//partial initializationvar p = &Point{

X: 1,Z: 2,

}


FuncGons //void function without return valuefunc SayHelloToMe(name string){

fmt.Printf(”Hello, %s”, name)}

//function with return valuefunc Multiply(x, y int) int {

return x * y}


type Rectangle struct {

X, Y int }

func (r Rectangle) Area() int {return r.X * r.Y

}

r := Rectangle{4, 3} // type Rectangler.Area() // == 12

Methods


You can define methods on any type.

type MyInt int

func (m MyInt) Square() int {i := int(m)return i * i

}

num := MyInt(4)num.Square() // == 16

Types and Methods


Scoping

•  Package level scope •  No classes •  A package can have mulGple source files •  Package source files reside in same directory

package main // sample package declaration


Visibility •  No use of private or public keywords. •  Visibility is defined by case

//visible to other packagesvar Name string = “”func Hello(name string) string {

return fmt.Printf(“Hello %s”, name)}

//not visible to other packagesvar name string = “”func hello(name string) string {

return fmt.Printf(“Hello %s”, name)}


Concurrency •  GorouGnes are like threads but cheaper. MulGple per threads. •  CommunicaGons between gorouGnes are done with channels

done := make(chan bool) //create channeldoSort := func(s []int) {

sort(s)done <- true //inform channel goroutine is done

}i := pivot(s)go doSort(s[:i]) go doSort(s[i:])<-done //wait for message on channel<-done //wait for message on channel


BUILDING OUR APPLICATION


InstallaGon

Download Go installer for your pladorm at hep://golang.org/doc/install


Code Session

•  Let us build a GDays Aeendance app. •  Displays total number of aeendees •  Ability to mark yourself as present

Source code will be available aBer session at hep://github.com/abiosoB/gdays-‐ae


GO ON APP ENGINE


Code Session

•  Let us modify our app to suit App Engine – Use User service to uniquely idenGfy user – Use Data Store to persist number of aeendees

Source code will be available aBer session at hep://github.com/abiosoB/gdays-‐ae-‐appengine


ADOPTION OF GO


Go in ProducGon •  Google •  Canonical •  DropBox •  SoundCloud •  Heroku •  Digital Ocean •  Docker

And many more at hep://golang.org/wiki/GoUsers


USEFUL LINKS


•  hep://golang.org/doc -‐ official documentaGon •  hep://tour.golang.org -‐ interacGve tutorials •  hep://gobyexample.com -‐ tutorials •  hep://gophercasts.io -‐ screencasts •  hep://golang.org/wiki/ArGcles -‐ lots of helpful arGcles


Community •  Blog –  hep://blog.golang.org

•  Google Group –  heps://groups.google.com/d/forum/golang-‐nuts

•  Gopher Academy –  hep://gopheracademy.com

•  Me –  hep://twieer.com/abiosoB –  [email protected]


THANK YOU

Software

Getting started with Go at GDays Nigeria 2014