enums for golang with constants and iota

[Tong Sun]

Hi, 

I know that golang doesn't have enums but use the constants and iota to simulate it. 

What I feel missing and still haven't figured out is that, in C, enums and variables are associated. I.e., when associate a variable with enum values, we know for sure that such variable will take no values other than the ones from defined enums. What's the best way to establish such association in go? 

For example, can I define a groups of constants like the following, and express the idea that my variable myWeekDay takes nothing but the such constants? I know it might be hard to enforce it, so I think establishing such logical association is more important.

Thanks

const (
	Sunday = iota
	Monday
	Tuesday
	Wednesday
	Thursday
	Friday
	Saturday
	numberOfDays  // this constant is not exported
)

[Caleb Spare]

You can make your own type instead of using untyped integer constants.

http://play.golang.org/p/wHQ-tHpHVA

You could still make a bad constant -- weekday(1000) -- but it's a lot
harder to do by accident. Also if the type is not exported than
package users cannot make bad constants.

-Caleb

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[minux]

On Wed, Apr 23, 2014 at 11:55 AM, Tong Sun <sunto...@gmail.com> wrote:

I know that golang doesn't have enums but use the constants and iota to simulate it. 

What I feel missing and still haven't figured out is that, in C, enums and variables are associated. I.e., when associate a variable with enum values, we know for sure that such variable will take no values other than the ones from defined enums. What's the best way to establish such association in go? 

Actually in C you can assign an enum variable with any integer representable by the

integer type that hosts the enum.

$ gcc -c -o /dev/null -Wall -Wextra -x c - <<EOF

> enum { A, B, C } x = 10;

> EOF

$ echo $?

0

For example, can I define a groups of constants like the following, and express the idea that my variable myWeekDay takes nothing but the such constants? I know it might be hard to enforce it, so I think establishing such logical association is more important.

there really isn't a way to do this perfectly in Go, as you can always use ideal consts.

[Caleb Spare]

Oh yeah, this is a good point.

[minux]

On Wed, Apr 23, 2014 at 12:03 PM, Caleb Spare <ces...@gmail.com> wrote:

You can make your own type instead of using untyped integer constants.

http://play.golang.org/p/wHQ-tHpHVA

it seems you forgot the type in const declarations: http://play.golang.org/p/6VD1RfPcQ_ 

You could still make a bad constant -- weekday(1000) -- but it's a lot
harder to do by accident. Also if the type is not exported than
package users cannot make bad constants.

they still can make arbitrary constants typed weekday.

for example, pkg.Monday * 1000.

and with some work, you can even get arbitrary variable number typed weekday.

[Tong Sun]

On Wednesday, April 23, 2014 12:08:56 PM UTC-4, minux wrote:

Actually in C you can assign an enum variable with any integer representable by the

integer type that hosts the enum.

 I know it is hard to enforce it, and I don't care about the enforcement. Establishing a logical association is more important to me. 

 

On Wed, Apr 23, 2014 at 12:03 PM, Caleb Spare <ces...@gmail.com> wrote:

You can make your own type instead of using untyped integer constants.

http://play.golang.org/p/wHQ-tHpHVA

it seems you forgot the type in const declarations: http://play.golang.org/p/6VD1RfPcQ_ 

 Yep, that exactly expresses it. 

Thanks

[Tong Sun]

On Wednesday, April 23, 2014 12:27:41 PM UTC-4, Tong Sun wrote:

... http://play.golang.org/p/6VD1RfPcQ_ 

 Yep, that exactly expresses it. 

 

Hmm, a bit more help please -- please correct this: http://play.golang.org/p/jJpPLouAqj

[Martin Drlík]

You mean this http://play.golang.org/p/ithwq1Pgu7 ?

[dja...@gmail.com]

http://play.golang.org/p/BucsMfxn1W

[Tong Sun]

On Wednesday, April 23, 2014 12:49:32 PM UTC-4, dja...@gmail.com wrote:

http://play.golang.org/p/BucsMfxn1W

Thanks everyone, http://play.golang.org/p/gQn8b3nDaj