深入理解Go 的变量和常量:零值机制、类型推导与枚举

package main
import "fmt"
func main() {
	var a int = 10
	var b = 20
	c := 30
	fmt.Println(a)
	fmt.Println(b)
	fmt.Println(c)
}

package main
import "fmt"
func main() {
	var a int
	var b bool
	var c string
	fmt.Printf("a: %d, b: %t, c: %q\n", a, b, c)
	fmt.Println("a:", a)
	fmt.Println("b:", b)
	fmt.Println("c:", c)
	fmt.Println(len(c))
}

var s []int
fmt.Println(s == nil) // true

s = append(s, 1) // 完全没问题

package main
import "fmt"
func main() {
	var s []int
	fmt.Println(s == nil)
	s = append(s, 1)
	s = append(s, 2)
	fmt.Println(s)
}

x := 10      // int
y := 3.14    // float64
z := "hello" // string

var a

a, b := 1, "go"

x := 10
x = 20      // OK
x = 3.14    // ❌ 编译错误

const Pi = 3.14

const x = 10

var a int = x
var b float64 = x

package main
func main() {
	const (
		A = iota // 0
		B        // 1
		C        // 2
	)
	println(A, B, C)
}

package main
func main() {
	const (
		A = iota // 0
		B        // 1
	)
	const (
		C = iota // 0（重新开始）
	)
	println(A, B, C)
}

1 << n  =  1 * 2^n

package main
func main() {
	const (
		Read    = 1 << iota // 1
		Write               // 2
		Execute             // 4
	)
	println(Read, Write, Execute)
}

const (
    A = iota // 0
    B        // 1
    C        // 2
)

const (
    Read    = 1 << 0
    Write   = 1 << 1
    Execute = 1 << 2
)

1 << 0

1 << 1

1 << 2

perm := Read | Write

const (
package main
func main() {
	const (
		A = iota
		_
		C
	)
	println(A, C)
}

package main
func main() {
	const (
		StatusInit = iota
		StatusRunning
		StatusSuccess
		StatusFailed
	)
	println(StatusInit, StatusRunning, StatusSuccess, StatusFailed)
}