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genericsf#nested-generics

Nested generic types of interfaces

Given the following interface:

type A<'t> =
    abstract Scratch: 't

How to simply create an interface like this:

type X<A<'t>> =
    abstract f: A<'t>

I also tried this one:

type X<'t,'y when 'y:A<'t>> =
    abstract f: 'y

and this:

type X<'t,A<'t>> =
    abstract f: A<'t>

but none work for me.

Solution

  • If you want to do it as interface try this:

    type IA<'a> =
    abstract Scratch: 'a

type IX<'a, 'b when 'a :> IA<'b>> = 
    abstract F: 'a

type RealA() = 
    interface IA<int> with
        member __.Scratch = 1

type RealX = 
    interface IX<RealA, int> with
        member __.F = RealA()

    If you want abstract classes:

    [<AbstractClass>]
type A<'a>() = 
    abstract member Scratch: 'a

[<AbstractClass>]
type X<'a, 'b when 'a :> A<'b>>() = 
    abstract F: 'a

type RealA'() = 
    inherit A<int>()
    override __.Scratch = 1

type RealX'() = 
    inherit X<RealA', int>()
    override __.F = RealA'()