How to define optional parameters in F# modules?

Question

I'm trying to re-write a tiny C# lib in F# and I've encountered an error. I'm trying to define optional parameters for a method in a module but the compiler says "Optional arguments are only permitted on type members".

I've checked why you can't use them in loose functions but when typing static member or member I get another error instead.

module Kingdom =
    let Rule (?years : int) =
        ()

I thought this was going to wor kas it's how I understood you type it, after reading the Microsoft Docs article about it.

Answer 1

By using another way to define the "static class" you can add member to it. And then you can use optional parameters. The class will show up as a normal static class in C#.

[<AbstractClass; Sealed>]
type Kingdom private () =
    static member Rule (?years : int) = ()