default arguments in classes

default arguments in classes

[Jacques Le Normand]

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Hello list,
I'm trying to define a method with a default argument, but I keep getting an
error. Here's the code:

class foo  =
  object (self)
    method bar ?(baz="moo") () =
    (new foo)#bar ~baz ()
  end

and the error:

The expression "new foo" has type foo but is used with type
  < bar : baz:string -> unit -> 'a; .. >
Types for method bar are incompatible

how do I fix this?
cheers
--Jacques L.

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Re: [Caml-list] default arguments in classes

[Paolo Donadeo]

This should work:

# class foo =
  object
    method bar =
      let helper a b ?(c = "") () =
        Printf.printf "a = %d; b = %b; c = %s\n" a b c in
        helper
  end;;
class foo : object method bar : int -> bool -> ?c:string -> unit -> unit end

Any undesired side effects?


-- 
Paolo
~
~
:wq

Re: [Caml-list] default arguments in classes

[Martin Jambon]

Jacques Le Normand wrote:
> Hello list,
> I'm trying to define a method with a default argument, but I keep
> getting an error. Here's the code:
> 
> class foo  =
>   object (self)
>     method bar ?(baz="moo") () =
>     (new foo)#bar ~baz ()
>   end
> 
> and the error:
> 
> The expression "new foo" has type foo but is used with type
>   < bar : baz:string -> unit -> 'a; .. >
> Types for method bar are incompatible
> 
> how do I fix this?


Adding type annotations often helps:

class foo =
object (self)
  method bar ?(baz="moo") () : unit =
    ((new foo) # bar : ?baz:_ -> _) ~baz ()
end



Martin

-- 
http://mjambon.com/