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How to inherit methods from a class implementing an interface
f#

Yep, that's my (seemingly trivial) question.

Here's a simple version of what I tried without success:
type A =
new () {}

interface I with
member this.a(x) =
// .... some code

type B =
inherit A

interface I with
override this.a(x) =
//... now somehow here I can't find a way to reference method a from A

.

Here's an example using constructed class types that may give you some ideas:

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#light

type IFoo =
    abstract Foo : unit -> unit


type A() =
    abstract Bar : unit -> unit
    default this.Bar() = printfn "from A"


    interface IFoo with
        member this.Foo() = this.Bar()
            

type B() =
    inherit A()
 
    override this.Bar() = base.Bar(); printfn "from B"
            

let a = A() :> IFoo
a.Foo()
// from A
let b = B() :> IFoo
b.Foo()
// from A
// from B
By on 9/2/2008 6:46 AM ()

I was struggling with this question too.

In the older release (1.9.4.19), I was able to do something like this:

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#light

type IFoo =
    abstract Foo : unit -> unit

type A() =
    interface IFoo

    abstract Foo : unit -> unit
    default this.Foo() = printfn "from A"
           
type B() =
    inherit A()
 
    override this.Foo() = base.Foo(); printfn "from B"

That's was closest approximation to the default method implementation in the base class I could get.

But it's not possible to do anymore in the latest 1.9.6 release...
Why?

Is this idiom is not that useful in the F# programming as it was in the OO world?

thanks!
- Sergey

By on 9/3/2008 7:50 AM ()

Hi daniel,

I can see no way of doing this. The FSharp manual Section 14.8 Dispatch Slot Inference describes why this is the case.

regards,
Danny

By on 9/2/2008 5:09 AM ()

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