The inability to have a type safe enum in Go has bothered me as well.
While using a struct, as Peter suggests, does prevent accidental use of
literals, it also prevents you from making your enum items constant.This
means that the values can be changed, accidentally, or intentionally, in
another package. For example:
package enum
import "fmt"
type Status struct {
s string
}
var One = Status{"one"}
var Two = Status{"two"}
func PrintIt(stat Status) {
fmt.Println("Status is", stat.s)
}
But a client of your package can then do:
func Foo() {
enum.One = enum.Two
enum.PrintIt(enum.One)
}
Which will print "two", and perminantly alter the meaning of enum.One.
On Thursday, November 7, 2019 at 8:15:20 AM UTC-5, speter wrote:
>
> Hi bsr,
>
> I'd suggest to use a struct type with a single string field. It will
> prevent conversion from untyped string constant "by mistake".
> Moreover, if you make the string field unexported, you can limit new
> instance creation to the declaring package, allowing to enforce predefined
> values.
> Unlike with some other languages, there is no memory or runtime overhead
> due to encapsulating the string within a struct.
>
> HTH,
> Peter
>
> On Thu, Nov 7, 2019 at 7:58 PM bsr <bsr...@gmail.com <javascript:>> wrote:
>
>> Hello,
>>
>> I am a long time user of go, but I always had the impression that below
>> code would not work as string and Status are different type.
>> I thought I need to explicitly convert as ```exec(Status("abc"))``` it to
>> work.
>>
>> I think, this part of the spec may be the reason
>> https://golang.org/ref/spec#Assignability
>>
>> - x is an untyped constant <https://golang.org/ref/spec#Constants>
>> representable <https://golang.org/ref/spec#Representability> by a
>> value of type T.
>>
>> Is there a way I can prevent this behavior.
>> I am using Status like an enum, and only predefined status values should
>> be allowed.
>>
>>
>>
>>
>> https://play.golang.org/p/4zsb7KtPBC6
>>
>> package main
>>
>> import (
>> "fmt"
>> )
>>
>> type Status string
>>
>> func main() {
>> exec("abc")
>> }
>>
>> func exec(s Status) {
>> fmt.Printf("Hello, %s", s)
>> }
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to golan...@googlegroups.com <javascript:>.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/golang-nuts/a20a7034-19c3-410a-bc86-25deff38534f%40googlegroups.com
>>
>> <https://groups.google.com/d/msgid/golang-nuts/a20a7034-19c3-410a-bc86-25deff38534f%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/golang-nuts/9df8504c-4309-43ab-86ee-518b52eb2e2f%40googlegroups.com.
