How to access map values in GO?

Question

How do I access the map value for the following code? The code snippet is auto generated, so I can't modify it. I have tried OpType_name[OpType_UNKNOWN] but I am getting error from the golang compiler.

type OpType int32

const (
    OpType_UNKNOWN OpType = 0
    OpType_CREATE OpType = 1
    OpType_DELETE OpType = 3
)

var OpType_name = map[int32]string{
    0: "UNKNOWN",
    1: "CREATE",
    2: "DELETE",
}
var OpType_value = map[string]int32{
    "UNKNOWN": 0,
    "CREATE": 1,
    "DELETE": 2,
}

Error: cannot use int(api.OpType_UNKNOWN) (type int) as type int32 in map index

Andreas Wederbrand · Accepted Answer · 2015-12-13 19:30:10Z

7

Go is very strict on types. Your maps all have keys with typ int32 and you are trying to access them using a value of type OpType. It doesn't matter that OpType is an int32.

You can cast your OpType to int32 and make it work

func main() {
  fmt.Println(OpType_name[int32(OpType_UNKNOWN)])
}

The comment from @nos is a good way to go, it's probably what you want in this case.

https://play.golang.org/p/dum5GiB3zS

edited Dec 13, 2015 at 19:30

answered Dec 13, 2015 at 16:29

Andreas Wederbrand

40.5k12 gold badges71 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

nos Over a year ago

Alternatively, make the map use OpType instead of int32, map[OpType]string{

kostix Over a year ago

I think it worth to do a bit of nit-picking: OpType is not int32: it only shares the internal representation of the values of its type with int32. The crucial point is that type B A does not make B "inherit" any methods of A. This does not matter for int32, which does not have methods, but is important to know when dealing with custom types.

kostix Over a year ago

I mean, that's the reason why Go does allow type-conversion from int32 to OpType (the internal representation of the value is the same) but does not allow to assign a value of OpType to a receiver of type int32: if it would be allowed, the receiver might want to call a method defined for its type but the value passed to it would not have it in its (different) type.

Collectives™ on Stack Overflow

How to access map values in GO?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related