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Optional parameters in abstract members.
f#

Hello,

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type Optional() =

  abstract Foo:int * (int option) -> unit
  default x.Foo(a, ?b:int) =
    match b with
      | Some _ -> ()
      | _ -> ()
  member x.Bar (a, ?b:int) =
    match b with
      | Some _ -> ()
      | _ -> ()


[<EntryPoint>]


let main (args: string []) =
  a = Optional()


  let r0 = a.Bar 1


  let r1 = a.Bar (1, 2)


  let r2 = a.Foo (1)


  let r3 = a.Foo (1, 2)


  (0)

In this example Bar working as expected but Foo needs explicit optional parameter.
Is it possible to create virtual member with optional parameter?

.

This appears to work:

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type Optional() =
  abstract Foo:int * [<OptionalArgument>]b : int option -> unit
  default x.Foo(a, ?b:int) =
    match b with
      | Some _ -> ()
      | _ -> ()
  member x.Bar (a, ?b:int) =
    match b with
      | Some _ -> ()
      | _ -> ()
By on 3/16/2010 10:56 AM ()

Ah, I was wrong, kvb's version works, as does the more obvious

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type Optional() =
    abstract Foo:int * ?b : int -> unit
    default x.Foo(a, ?b:int) =
        match b with
        | Some _ -> ()
        | _ -> ()
    member x.Bar (a, ?b:int) =
        match b with
        | Some _ -> ()
        | _ -> ()
By on 3/16/2010 1:59 PM ()

Thanks for both options!

I believe I tried second approach, but probably made some typo during my attempts.

By on 3/18/2010 6:03 AM ()

I don't think so.

(You can always use overloading instead.)

By on 3/16/2010 10:07 AM ()

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