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Copyright © 2017 eureka, Inc. All rights reserved.
2019/9/28 (Sat) EngineerX.go #1
GoݴޠΛ࢝ΊΔ࣌ͷམͱ݀͠
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2
ࣗݾհ
Copyright © 2017 eureka, Inc. All rights reserved.
͓͠͝ͱ
"1*Λͭ͘Δ
Իָ׆ಈʢॕʂࣾόϯυ݁ʂʣ
ण৳ҰʢJufuku Shinichiʣ
גࣜձࣾΤϨΧ
"1*5FBNॴଐ
αʔόʔαΠυΤϯδχΞʢ(P+BWB1)1ʣ
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50 Shades of Go: Traps, Gotchas, and
Common Mistakes for New Golang Devs
IUUQEFWTDMPVEJNNVOJUZDPNHPUDIBTBOEDPNNPONJTUBLFTJOHPHPMBOH
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Copyright © 2017 eureka, Inc. All rights reserved.
4
։࢝ͷதׅހΛผͷߦʹஔͰ͖·ͤΜ
package main
import "fmt"
func main()
{ // syntax error: unexpected semicolon or newline before {
fmt.Println("hello!")
}
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func test(
i int,
s string,
) {
fmt.Println("hello!")
}
ʲ͜ΕOKʳ
func main(
i int,
s string,
) (
Response,
error,
) {
fmt.Println("hello!")
}
ʲ͜ΕOKʳ
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func test(
i int,
s string // syntax error: unexpected newline, expecting comma or )
) {
fmt.Println("hello!")
}
ʲ͜ΕNGʳ
func main(
i int,
s string,
) (
Response,
error // syntax error: unexpected newline, expecting comma or )
) {
fmt.Println("hello!")
}
ʲ͜ΕNGʳ
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Copyright © 2017 eureka, Inc. All rights reserved.
7
มͷະ༻
package main
import "fmt"
var gvar int // not an error
func main() {
var one int // error, unused variable
two := 2 // error, unused variable
var three int // error, even though it's assigned 3 on the next line
three = 3
func(unused string) {
fmt.Println("Unused arg. No compile error")
}("what?")
}
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package main
import "fmt"
func main() {
var one int
_ = one
two := 2
fmt.Println(two)
var three int
three = 3
one = three
var four int
four = four
}
ʲ͜ΕͳΒOKʳ
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Copyright © 2017 eureka, Inc. All rights reserved.
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͍มએݴͰͷೖ
package main
import "fmt"
type info struct {
result int
}
func work() (int,error) {
return 13,nil
}
func main() {
var data info
data.result, err := work() //error
fmt.Printf("info: %+v\n",data)
}
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package main
import "fmt"
type info struct {
result int
}
func work() (int, error) {
return 13, nil
}
func main() {
var data info
var err error
data.result, err = work()
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("info: %+v\n", data)
}
ʲ͜ΕͳΒOKʳ
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package main
import "fmt"
type info struct {
result int
}
func work() (int, error) {
return 13, nil
}
func main() {
res, err := work()
if err != nil {
fmt.Println(err)
return
}
data := info{result: res}
fmt.Printf("info: %+v\n", data)
}
ʲͬͪ͜ͷํ͕ΑΓεϚʔτʳ
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Copyright © 2017 eureka, Inc. All rights reserved.
12
ؔҾʹྻ
package main
import "fmt"
func main() {
x := [3]int{1,2,3}
func(arr [3]int) {
arr[0] = 7
fmt.Println(arr) //prints [7 2 3]
}(x)
fmt.Println(x) //prints [1 2 3] (not ok if you need [7 2 3])
}
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package main
import "fmt"
func main() {
x := []int{1, 2, 3}
func(arr []int) {
arr[0] = 7
fmt.Println(arr) //prints [7 2 3]
}(x)
fmt.Println(x) //prints [7 2 3]
}
ʲ͜ΕͳΒOKʳ
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package main
import "fmt"
func main() {
x := make([]int, 3)
x[0] = 1
x[1] = 2
x[2] = 3
func(arr []int) {
arr[0] = 7
fmt.Println(arr) //prints [7 2 3]
}(x)
fmt.Println(x) //prints [7 2 3]
}
ʲ͜ΕOKʳ
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Copyright © 2017 eureka, Inc. All rights reserved.
15
“range”۟ͷڍಈ
package main
import "fmt"
func main() {
x := []string{"a", "b", "c"}
for v := range x {
fmt.Println(v) //prints 0, 1, 2
}
}
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package main
import "fmt"
func main() {
x := []string{"a", "b", “c"}
for _, v := range x {
fmt.Println(v) //prints a, b, c
}
}
ʲ͜ΕͳΒOKʳ
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Copyright © 2017 eureka, Inc. All rights reserved.
17
“for range”۟ͰͷϚοϓͷॱ൪
package main
import "fmt"
func main() {
m := map[string]int{"one": 1, "two": 2, "three": 3, "four": 4}
for k, v := range m {
fmt.Println(k, v)
}
}
IUUQTQMBZHPMBOHPSHQ/-Y#+',(#
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Copyright © 2017 eureka, Inc. All rights reserved.
18
ʮswitchʯͷϑΥʔϧεϧʔಈ࡞
package main
import "fmt"
func main() {
isSpace := func(i int) bool {
switch i {
case 1:
case 2:
return true
}
return false
}
fmt.Println(isSpace(2)) //prints true (ok)
fmt.Println(isSpace(1)) //prints false (not ok)
}
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package main
import "fmt"
func main() {
isSpace := func(i int) bool {
switch i {
case 1,2:
return true
}
return false
}
fmt.Println(isSpace(2)) //prints true (ok)
fmt.Println(isSpace(1)) //prints false (not ok)
}
ʲ͜ΕͳΒOKʳ
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Copyright © 2017 eureka, Inc. All rights reserved.
͝੩ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠