CODEWITHSUNDEEP
f#
ozgur
ozgur

Reputation: 2719

How to make an Abstract class that inherits an interface in F#?

I have the following code with an interface and an abstract class.

    type INode<'a> =
    abstract member Parent:INode<'a>
    abstract member Evaluate:unit->'a
    abstract member Clone:INode<'a> -> INode<'a>
    abstract member SelectRandom:int->INode<'a> option

[<AbstractClass>]
type TerminalNode<'a>() =
    interface INode<'a> with
        member this.SelectRandom indexOfCurrentNode = 
            let p = 1.0 / float indexOfCurrentNode
            if Random().NextDouble() < p then Some (this:>INode<'a>) else None

I want to implement the hierarchy in this Node hierarchy class diagram but the compiler complains that all methods of the interface should be implemented.

What is the correct way to create an Abstract class that implements an interface and implements that interface's one method leaving other methods abstract?

Note: If you cannot see the image, your network is blocking imgur.com.

Upvotes: 1

Views: 88

Answers (1)

Chad Gilbert
Chad Gilbert

Reputation: 36375

You can define the abstract members on the type, then provide the implementation which points at those abstract members. For example:

[<AbstractClass>]
type TerminalNode<'a>() as self =
    abstract member Parent : INode<'a>
    abstract member Evaluate : unit->'a
    abstract member Clone:INode<'a> -> INode<'a>
    interface INode<'a> with
        member this.Parent = self.Parent
        member this.Evaluate () = self.Evaluate ()
        member this.Clone a = self.Clone a
        member this.SelectRandom indexOfCurrentNode = 
            ...

(note the as self in the type line, which lets you refer to the abstract type by the variable name self)

Upvotes: 5

Related Questions