CODEWITHSUNDEEP
classinheritanceocaml
user1971598
user1971598

Reputation:

Establishing inheritance and overriding in OCaml class types

I'm trying to write class types and having an issue expressing what I want.

I have

class type event_emitter = object
   method on : string -> unit
end

and then I want to do this:

class type socket = object
    inherit event_emitter
    method on : int -> unit
end

But I get a compiler error about a type signature mismatch between the two. I've also tried using the virtual keyword, doing class type virtual event_emitter = method virtual on : string -> unit but this also doesn't work as I guess these are class type definitions, not implementations anyway.

I really want this method override to work and this seemed straightforward, not sure why its not allowed.

Upvotes: 1

Views: 686

Answers (2)

Drup
Drup

Reputation: 3739

This doesn't contradict antron's answer, but you can do this:

class type ['a] event_emitter = object
   method on : 'a -> unit
end

class type socket = object
    inherit [int] event_emitter
end

Upvotes: 2

antron
antron

Reputation: 3847

What you are trying to do is overloading, not overriding. You are trying to create a new method in socket with the same name as in event_emitter, but with a different type. Overriding would be creating a new method with the same name and type. This description would hold for other languages like Java and C++, as well. The difference is that I don't believe OCaml allows this kind of overloading – the same as for regular functions.

Note that if you entered the analogous declarations for Java, it would work, but socket would have two on methods, not one. OCaml doesn't allow this.

Upvotes: 2

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