tebeka

filePerm := Read | Write // set permission (| is bitwise OR)
if filePerm&Write != 0 { // check permission (& is bitwise AND)
    fmt.Println("can write")
}

tebeka

func (p FilePerm) String() string {
    switch p {
    case Read:
        return "read"
    case Write:
        return "write"
    case Execute:
        return "execute"
    }

tebeka

Seeking Permission or Begging Forgiveness?

A Go Brain Teaser

What do you think the following program will print?

https://gist.github.com/cd76f0d470d06005166315e3f1a81845

This program will print: 4.

When you use iota in a const group, the values of the constants will advance according to the first operation. The << operator is "left shift". It moves the bits of a number to the left, basically multiplying it by power of 2.

tebeka

type Perm struct {
    Read    bool
    Write   bool
    Execute bool
}

tebeka

fmt.Println(unsafe.Sizeof(filePerm)) // 1
var p Perm
fmt.Println(unsafe.Sizeof(p)) // 3

tebeka

filePerm := Read | Write // set permission (| is bitwise OR)
if filePerm&Write != 0 { // check permission (& is bitwise AND)
    fmt.Println("can write")
}

tebeka

type FilePerm uint8

const (
    Read FilePerm = 1 << iota
    Write
    Execute
)

func main() {
    fmt.Println(Execute) // execute

tebeka

func (p FilePerm) String() string {
    switch p {
    case Read:
        return "read"
    case Write:
        return "write"
    case Execute:
        return "execute"
    }

tebeka

fmt.Println(unsafe.Sizeof(filePerm)) // 1
var p Perm
fmt.Println(unsafe.Sizeof(p)) // 3

tebeka

type Perm struct {
    Read    bool
    Write   bool
    Execute bool
}