Extending a class constrained in a signature

Extending a class constrained in a signature

[Jean Balthazar]

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Dear OCamlers (again !),

I tried this time to specify explictly what I expect from a container. This
specification is given by the signature CONTAINER below. Everyhting works
perfectly but I don't understand why it fails if I remove the 'private'
keyword... Why
am I only able to extend an object when the type have the 'private' keyword
in its definition?

Is it possible to achieve the same behaviour using a class type rather a row
type
with private keyword?

All the best,
Jean

***********************************************************************************************
module type CONTAINER =
sig

  type 'elt container = private < hd : 'elt; .. >
end

module Check = functor(Coll : CONTAINER) -> struct end



module Seq =
struct

  class ['elt] container (arg : 'elt list) =
  object(self : 'selftype)

    method hd  = List.hd arg
    method tl  = new container (List.tl arg)

  end

end

module CheckSeq = Check(Seq)

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