Annotations for enums in F#

Question

I have an enum in F#:

type Gender = Undisclosed = 0 | Male = 1 | Female = 2

The equivalent C# code would be

public enum Gender
{
    Undisclosed,
    Male,
    Female
}

In fact, in C#, I can go one step better. To use gender in a dropdown in a cshtml page, I can do this:

public enum Gender
{
    [Display(ResourceType = typeof(LocalisedStrings), Name = "GenderUndisclosed")] Undisclosed,
    [Display(ResourceType = typeof(LocalisedStrings), Name = "GenderMale")] Male,
    [Display(ResourceType = typeof(LocalisedStrings), Name = "GenderFemale")] Female
}

Unfortunately, the F# compiler says that "attributes are not allowed here" if I try to add similar annotations to the F# enum members. Is there a way around this? I'd like to avoid creating a duplicate class and performing Automapper voodoo if I possibly can.

Answer 1

You need a | before the attribute.

// Doesn't compile. "Attributes are not allowed here"
type Foo = [<Bar>] Baz = 0

// Compiles.
type Foo = | [<Bar>] Baz = 0

In your case, this would come out to:

type Gender = 
    | [<Display(ResourceType = typeof<LocalisedStrings>, Name = "GenderUndisclosed")>] Undisclosed = 0
    | [<Display(ResourceType = typeof<LocalisedStrings>, Name = "GenderMale")>] Male = 1
    | [<Display(ResourceType = typeof<LocalisedStrings>, Name = "GenderFemale")>] Female = 2

Answer 2

This should work:

type Gender = 
    | [<Display>] Undisclosed = 0 
    | [<Display>] Male        = 1 
    | [<Display>] Female      = 2