Golang勉強会

• Java, Node.js Golang
/
• Golang
2

Golang
• 2009 Google
• Robert C. Pike, Kenneth Lane Thompson UNIX
C
• :
• C , Limbo, Modul, Newsqueak, Oberon,
Pascal[3], Python
[Go ( ) - Wikipedia 3

Golang
•
•
•
•
• *
4

$ brew install golang
$ go version
go version go1.8 darwin/amd64
$ mkdir -p {golang } && cd $_
$ cat << _EOF_ >> ~/.bashrc
# Golang
export GOPATH=$(pwd)
export PATH=$PATH:$GOPATH/bin
_EOF_
$ exec $SHELL -l
5

Hello, World ...
Golang
$ tree -L 3
.
!"" bin # go build
#   !"" dep
#   $"" golint
!"" pkg # go get (vendor )
#   $"" darwin_amd64
#      $"" github.com
$"" src # ( / / )
!"" ghe.ca-tools.org
#   $"" montblanc
$"" mb2-shuffle
$"" github.com
   $"" seka
   $"" bbs-sample
6

Hello, World!
$ mkdir -p $GOPATH/src/github.com/{github }/helloworld && cd $_
main.go
package main
import "fmt"
func main() {
fmt.Println("Hello, World!")
}
main.go
$ go run main.go
Hello, World!
7

: Go -Qiita
: github.com/seka/bbs-sample
Golang !
8

(1/2)
//
var [, ... ]
:=
//
const =
note: (
)
var num1 int32 = 10
var num2 int64 = 10
fmt.Println(num1 + num2) // mismatched types int32 and int64
fmt.Println(1 + "10") // mismatched types int and string
9

(2/2)
[n]T {}
[]T nil
error nil
struct{} {}
*T nil
interface{} nil
chan T nil message passing
note: The Go Programming Language Speciﬁcation
10

(1/3)
//
a := [...]T{} //
b := [2][3]int{
{1, 2, 3},
{4, 5, 6},
}
//
a := make([]T,len) // a := []T{}
b := [][]int{
{1, 2, 3},
{4, 5, 6},
}
c := make([]T, len, cap)
11

(2/3)
Go Slice - Qiita
a := make([]int, 2)
a[0] = 0
a[1] = 1
b := a
fmt.Println(a) // [0 1]
fmt.Println(b) // [0 1]
b[0] = 10
fmt.Println(b) // [10 1]
b = append(b, 10)
fmt.Println(b) // [10 1 10]
b[0] = 20
fmt.Println(b) // [20 1 10]
12

(3/3)
size capacity
• capacity
• capacity size == capacity
note: capacity ...??
a := make([]int, 0, 1)
a = append(1)
fmt.Println(a) // [1] ...!
b := make([]int, 1)
b = append(a, 1)
fmt.Println(a) // [0, 1] ...??
13

(1/3)
func main() {
tmpfile, err := ioutil.TempFile("/tmp", "example-prefix")
if err != nil {
log.Fatal(err)
}
defer os.Remove(tmpfile.Name())
if _, err := tmpfile.Write([]byte("temporary file's content")); err != nil {
log.Fatal(err)
}
if err := tmpfile.Close(); err != nil {
log.Fatal(err)
}
}
Golang
err
( bool )
14

(2/3)
...
!
Golang Error Handling lesson by Rob Pike - Block Rockin’ Codes
Golang pkg/errors | SOTA
note: Error func Error() string
15

(3/3)
panic/recover
func main() {
panicFunc()
}
func panicFunc() {
defer func() {
err := recover() //
log.Infoln("recover: ", err)
}()
panic("Panic!")
}
16

(1/2)
var struct {
[ ]
[ ]
}
type struct {
[ ]
[ ]
}
• :
• :
• : / ( )
17

(2/3)
struct
type Response struct {
Page int `json:"page"`
Fruits []string `json:"fruits"`
}
r := &Response{
Page: 1,
Fruits: []string{"apple", "peach", "pear"}
}
byts, _ := json.Marshal(r)
res2 := Response{}
if err := json.Unmarshal(byts, &res2); err != nil {
panic(err)
}
fmt.Println(dat)
18

(3/3)
•
• New[ ], new[ ]
func main() {
sample := newSampleStruct()
fmt.Println(sample.getNum())
fmt.Println(sample.Name)
}
type SampleStruct struct {
num int
Name string
}
func newSampleStruct() SampleStruct {
return SampleStruct{
num: 10,
Name: "Name field",
}
}
func (s SampleStruct) getNum() int {
return s.num
}
func (SampleStruct) sayHello() {
fmt.Println("Hello, World")
}
19

(1/3)
*T T &
var p *int
i := 42
p = &i
fmt.Println(i) // 42
fmt.Println(*p) // 42
*p = 100
fmt.Println(i) // 100
fmt.Println(*p) //100
note: C Golang C
20

(2/3)
func main() {
sample := newSampleStruct()
fmt.Println(sample.getNum())
fmt.Println(sample.Name)
}
type SampleStruct struct {
num int
Name string
}
func newSampleStruct() *SampleStruct {
return &SampleStruct{
num: 10,
Name: "Name field",
}
}
func (s *SampleStruct) getNum() int {
return s.num
}
func (*SampleStruct) sayHello() {
fmt.Println("Hello, World")
}
21

(3/3)
?
Go | Step by Step
...
•
•
• ( / / )
•
22

(1/5)
type interface {
( [, ...])
( [, ...]) ( [, ...]]])
}
•
• Golang
23

(2/5)
func main() {
var r geometry = &rect{width: 3, height: 4}
fmt.Println(r.area())
}
type geometry interface {
area() float64
}
type rect struct {
width, height float64
}
func (r rect) area() float64 {
return r.width * r.height
}
var _ geometry = (*rect)(nil) // TIPS
24

(3/5)
interface{}
func main() {
f("string") // string
f(100) // 100
f(true) // true
}
func f(x interface{}){
fmt.Println(x)
}
Golang interface{}
25

(4/5)
:
seka/mutexmaps: a utility mutex maps for Golang.
type StringMutexMap struct {
m *mutexmap.MutexMap
}
func newStringMutexMap() *StringMutexMap {
return &StringMutexMap{mutexmap.New(0)}
}
func (s *StringMutexMap) Get(key string) string {
item := s.m.Get(key)
return item.(string) // interface{} string
}
func (s *StringMutexMap) Put(key string, item string) {
s.m.Put(key, item) // string put
}
26

(4/5)
interface{}
func main() {
var i interface{} = "hello"
s := i.(string)
fmt.Println(s) // hello
f, ok := i.(float64)
fmt.Println(f, ok) // 0, false
switch t := i.(type) {
case string:
fmt.Println("string: ", i) // string: hello
default:
panic()
}
}
27

Golang (extends) (embedding)
type Model struct {
db database.Database
}
func NewModel(db database.Database) *Model {
return &Model{
db: db,
}
}
func (m *Model) Save(userID, msg string) error {
query := `INSERT INTO messages(user_id, message) VALUES (?, ?)`
_, err := m.db.Execute(query, userID, msg)
return err
}
28

Golang (1/3)
go func([ , ...]) {
}( )
go ([ , ...])
Golang goroutine
goroutine Golang
29

Golang (2/3)
ch := make(chan , )
ch <- // ch
:= <-ch // ch
close(ch) //
goroutine channel Message-passing
make
• : 0
• :
chan <- <-
30

Golang (3/3)
seka/bbs-sample
goroutine
goroutine <-sigs
os
func (m *Main) createSignalHandler() (context.Context, context.CancelFunc) {
sigs := make(chan os.Signal)
signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
ctx, cancel := context.WithCancel(context.Background())
go func() {
s := <-sigs
m.logger.Info("Got signal", "sigs", s)
cancel()
}()
return ctx, cancel
}
31

select
select {
case msg := <-ch2:
fmt.Println("received", msg)
case <-ch2:
fmt.Println("received")
}
select
( )
32

Golang勉強会

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