This document provides an overview of the Go programming language including: - A brief history of Go from its origins at Google in 2007 to current widespread usage. - Key features of Go like functions, structs, interfaces, methods, slices, pointers, go-routines and channels. - Examples of basic Go code demonstrating functions, structs, methods, interfaces, concurrency with go-routines and channels. - Discussion of things missing from Go like classes, generics and exceptions. - Quotes from developers commenting both positively and negatively on Go's simplicity and tradeoffs. - Links to further resources like the Go tour to learn more.

1. #golang

2. Pascal C/Asm Perl Java
Evolution of a software developer
PaintGo

3. A little bit of history…
2007 2009 2012 2013 2015
The beginning
Open sourced
1.0 1.1 1.5

4. Where used?
https://github.com/golang/go/wiki/GoUsers
Google, Docker, Heroku, Cloud Foundry, CoreOS,
InfluxDB, Dropbox, OpenShift, SoundCloud,
Toggl, etc.
In the clouds!

5. “Can't reach the pedals. no brakes.
gaining speed. eyes bulging in horror.
technical debt crash eminent. “
— Tim Dysinger, @dysinger

6. Paul Phillips
@extempore2
“go is a terrible, terrible language, yet
still a major productivity boost.
Amdahl's law in another context.”
“You often see languages which are
fighting the last war. Go is fighting
the War of 1812.”

7. “reduce: what you will do with your
expectations after you start with Go”
“Rust and Scala drown you in
complexity. Go drowns you in
simplicity.”
Paul Phillips
@extempore2

8. Tour of Go
tour.golang.org

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

10. package main
import "fmt"
func main() {
fmt.Println("Hello, Devclub!")
}
Java-developers reaction to the capital
letter in a function name

16. Missing stuff
No classes
No generics
No inheritance
No method overriding
No exceptions
etc

17. No generics? No exceptions? Wut!?

18. Features
Functions
Structures
Interfaces
Methods
Slices
Pointers
Go-routines
Channels

19. func main() {
fmt.Println("1 + 2 =", add(1, 2))
}
func add(a int, b int) int {
return a + b
}
Functions

20. func main() {
fmt.Println("1 + 2 =", add(1, 2))
}
func add(a int, b int) int {
return a + b
}
Functions

21. func main() {
fmt.Println("1 + 2 =", add(1, 2))
}
func add(a, b int) int {
return a + b
}
Functions

22. func main() {
s, p := calculate(1, 2)
fmt.Printf("1+2=%d, 1*2=%d", s, p)
}
func calculate(a, b int) (int, int) {
return a + b, a * b
}
Functions

23. func main() {
s, p := calculate(1, 2)
fmt.Printf("1+2=%d, 1*2=%d", s, p)
}
func calculate(a, b int) (int, int) {
return a + b, a * b
}
Functions

24. func main() {
s, p := calculate(1, 2)
fmt.Printf("1+2=%d, 1*2=%d", s, p)
}
func calculate(a, b int) (s, p int) {
s := a + b
p := a * b
return
}
Functions

25. func main() {
double := func(a int) int {
return a * 2
}
double(14)
}
Functions as values

26. func main() {
double := factory()
double(14)
}
func factory() func(a int) int {
return func(a int) int {
return a * 2
}
}
Functions as values

27. Arrays
var a [4]int
a[0] = 1
i := a[0]
http://blog.golang.org/go-slices-usage-and-internals
arr := [2]string{"Foo", "Bar"}
arr := […]string{"Foo", "Bar"}

28. Slices
a := []int{1, 2, 3} // [1 2 3]
No size definition
b := append(a, 4, 5) // [1 2 3 4 5]
c := make(c, 3) // [0 0 0]
d := b[1:3] // [2 3]
e := b[:3] // [1 2 3]

29. Maps
monthdays := map[string]int{
"Jan": 31, "Feb": 28, "Mar": 31,
"Apr": 30, "May": 31, "Jun": 30,
"Jul": 31, "Aug": 31, "Sep": 30,
"Oct": 31, "Nov": 30, "Dec": 31,
}
for month, days := range monthdays {
fmt.Println(month, days)
}

30. Maps
monthdays := map[string]int{
"Jan": 31, "Feb": 28, "Mar": 31,
"Apr": 30, "May": 31, "Jun": 30,
"Jul": 31, "Aug": 31, "Sep": 30,
"Oct": 31, "Nov": 30, "Dec": 31,
}
for month, days := range monthdays {
fmt.Println(month, days)
}
Obligatory comma!?

31. Maps
monthdays := map[string]int{
"Jan": 31, "Feb": 28, "Mar": 31,
"Apr": 30, "May": 31, "Jun": 30,
"Jul": 31, "Aug": 31, "Sep": 30,
"Oct": 31, "Nov": 30, "Dec": 31,
}
value, ok := monthdays["Jan"]
fmt.Println(value) // 31
fmt.Println(ok) // true

32. Pointers
var p *int
i := 42
p = &i
fmt.Println(*p)
*p = 21
fmt.Println(i)
42
21

33. Pointers
var p *int
i := 42
p = &i
fmt.Println(*p)
*p = 21
fmt.Println(i)

34. Pointers
var p *int
i := 42
p = &i
fmt.Println(*p)
*p = 21
fmt.Println(i)
No pointer
arithmetics

35. Structures
type Vertex struct {
X int
Y int
}

36. Structures
type Vertex struct {
X int
Y int
}
func main() {
fmt.Println(Vertex{1, 2})
}

37. Methods
type Vertex struct {
X int
Y int
}
func (v Vertex) Total() int {
return v.X + v.Y
}

38. Methods
type Vertex struct {
X int
Y int
}
func (v Vertex) Total() int {
return v.X + v.Y
}
v := Vertex{1, 2}
v.Total()

39. Interfaces
type Entity interface {
Total() int
}

40. Interfaces
type Entity interface {
Total() int
}
Vertex implements Entity
func (v Vertex) Total() int {
return v.X + v.Y
}

41. Interfaces
v := Vertex {1, 2}
blah(v)
func blah(e Entity) {
e.Total()
}

42. Interfaces
func foo(x interface{}) int {
x.(Vertex).Total()
}

43. Interfaces
func foo(x interface{}) int {
x.(Vertex).Total()
}
panic: interface conversion: interface is main.Vertex2, not main.Vertex
goroutine 1 [running]:
main.main()
main.go:25 +0xcd
exit status 2
foo(Vertex2{1,2})

44. A programmer had a problem. He
thought to solve it with threads.
two Now problems. he has

45. Go-routines
foo(Vertex2{1,2})
go foo(Vertex2{1,2})
Usual function call
Function call in a go-routine

46. func ready(w string, sec int) {
time.Sleep(time.Duration(sec) * time.Second)
fmt.Println(w, "is ready!")
}
func main() {
go ready("Tea", 2)
go ready("Coffee", 1)
fmt.Println("I'm waiting")
time.Sleep(5 * time.Second)
}
I’m waiting
Coffee is ready
Tea is ready

47. Channels
ci := make(chan int)
cs := make(chan string)
cf := make(chan interface{})
ci <- 1 ← send value 1 into channel ci
i := <-ci ← read int from channel ci

48. var c chan int
func ready(w string, sec int) {
time.Sleep(time.Duration(sec) * time.Second)
fmt.Println(w, "is ready!”)
с <-­‐ 1
}
func main() {
go ready("Tea", 2)
go ready("Coffee", 1)
fmt.Println("I'm waiting")
<-­‐c
<-­‐c
}

49. var done = make(chan bool)
var msgs = make(chan int)
func produce() {
for i := 0; i < 10; i++ {
msgs <-­‐ i
}
done <-­‐ true
}
func consume() {
for {
msg := <-­‐msgs
println(msg)
}
}
func main() {
go produce()
go consume()
<-­‐ done
}

50. var done = make(chan bool)
var msgs = make(chan int)
func produce() {
for i := 0; i < 10; i++ {
msgs <-­‐ i
}
done <-­‐ true
}
func consume() {
for {
msg := <-­‐msgs
println(msg)
}
}
func main() {
go produce()
go consume()
<-­‐ done
}
Start go-­‐routines

51. var done = make(chan bool)
var msgs = make(chan int)
func produce() {
for i := 0; i < 10; i++ {
msgs <-­‐ i
}
done <-­‐ true
}
func consume() {
for {
msg := <-­‐msgs
println(msg)
}
}
func main() {
go produce()
go consume()
<-­‐ done
}
Send values

52. var done = make(chan bool)
var msgs = make(chan int)
func produce() {
for i := 0; i < 10; i++ {
msgs <-­‐ i
}
done <-­‐ true
}
func consume() {
for {
msg := <-­‐msgs
println(msg)
}
}
func main() {
go produce()
go consume()
<-­‐ done
}
Receive values and print

53. var done = make(chan bool)
var msgs = make(chan int)
func produce() {
for i := 0; i < 10; i++ {
msgs <-­‐ i
}
done <-­‐ true
}
func consume() {
for {
msg := <-­‐msgs
println(msg)
}
}
func main() {
go produce()
go consume()
<-­‐ done
}
Done!

55. Environment
https://golang.org/doc/code.html#Workspaces

56. Environment

57. Environment

58. Tooling
• go (version, build, test, get, install, …)
• gofmt
• godoc
• Editors (vim, atom, IntelliJ IDEA,
Sublime Text)

59. My choice

60. What’s missing?
Debugger
IntelliJ IDEA plugin is still in development
Can use GDB, but better do something else instead
Dependency management
A lot of different solutions, no de facto standard
-vendor option in 1.5

61. Cross-compilation
http://dave.cheney.net/2015/03/03/cross-compilation-just-got-
a-whole-lot-better-in-go-1-5
env GOOS=linux GOARCH=386 go build hello.go
1. Build on Mac for Linux
2. Run the binary without installing
extra dependencies or runtime on Linux host

62. Testing
package math
func Add(a, b int) int {
return a + b
} package math
import "testing"
func TestAdd(t *testing.T){
if Add(1, 3) != 4 {
t.Error("Expecting 4")
}
}

63. Testing
package math
func Add(a, b int) int {
return a + b
} package math
import "testing"
func TestAdd(t *testing.T){
if Add(1, 3) != 4 {
t.Error("Expecting 4")
}
}
/usr/local/go/bin/go test -­‐v ./... -­‐run ^TestAdd$
Testing started at 03:35 ...
? _/Users/anton/work-­‐src/mygo [no test files]PASS
ok _/Users/anton/work-­‐src/mygo/math 0.007s

64. Q: Can you build the enterprise apps in Go?
And now a million $$ question
https://www.youtube.com/watch?v=cFJkLfujOts
Building bank in Go:
A: Apparently, you can :)

65. Can I haz
decimal type?
https://github.com/shopspring/decimal
import "github.com/shopspring/decimal"
…
x, _ := decimal.NewFromString("0.1")
sum := x.Add(x).Add(x) // 0.3

66. import (
"net/http"
"fmt"
)
func handler(w http.ResponseWriter,
r *http.Request) {
fmt.Fprintf(w, "Welcome!")
}
func main() {
http.HandleFunc("/", handler)
http.ListenAndServe(":8080", nil)
}
Compare to Java?

67. Frameworks
Gorilla web toolkit http://www.gorillatoolkit.org/
Go-Kit http://gokit.io
List of various frameworks and libraries:
https://github.com/avelino/awesome-go

68. Resources
http://www.miek.nl/downloads/Go/Learning-Go-latest.pdf
https://tour.golang.org
http://blog.golang.org
https://www.youtube.com/playlist?
list=PLMW8Xq7bXrG58Qk-9QSy2HRh2WVeIrs7e
https://www.youtube.com/channel/
UCx9QVEApa5BKLw9r8cnOFEA
Gopher Academy:
dotGo:
https://gist.github.com/kachayev/21e7fe149bc5ae0bd878
Channels are not enough:
http://dave.cheney.net/2015/08/08/performance-
without-the-event-loop
Performance without event loop:

69. @antonarhipov
http://www.slideshare.net/arhan
https://speakerdeck.com/antonarhipov