How to constrain an integral type's values

[Mark]

I often create small multi-value flag types, e.g.

```go

type mode uint8

const (
argMode mode = iota
baseMode
cmdMode
)

```

The problem is that if I write, say,  `m := baseMode`, although `m` has the correct type (`mode`), there is no way to constrain its values to the consts I've declared.

In theory I could create a `NewMode(int) mode` function and have it panic if the given int isn't valid; but that won't prevent, say, `m += 99`. The next step would be to define a full type, e.g., something like:

```go

type mode struct {

    m int

}

```

This would prevent `m++` and similar since all accesses would have to go through the public functions. However, this would still do all its checking at _runtime_; whereas for this kind of use it should surely be possible to check at compile time.

In Pascal it is easy to declare a "subrange" type which might look like this in Go-like syntax:

`type mode uint8 0..2`

Is there a compile-time solution for this that I've missed?

[Jan Mercl]

On Fri, Sep 8, 2023 at 9:24 AM 'Mark' via golang-nuts
<golan...@googlegroups.com> wrote:

> Is there a compile-time solution for this that I've missed?

No. Go does not have enum types.

[Thomas Bushnell BSG]

I recommend using strings as the base type for things like this, rather than ints. There is no need to use ints, just because that's what C uses.

Thomas

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