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Date: Wed, 21 Aug 2002 23:49:38 +0200
From: nadji@noos.fr
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To: caml-list@inria.fr
Subject: [Caml-list] polymorphic method question
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Hi,

I am puzzled by this behaviour, can a guru explain me ?
I have two classes
class type ['a] basic = object
  method foo : 'a
end;;

 class ['a] toto (a:'a) = object
  method foo = a
  method bar = ()
end;;

I want to do a class gentoto :
class gentoto = object
  method gen : 'a . 'a -> 'a basic =
    fun x -> (new toto x :> 'a basic )
end;;
But the compiler complains that :
      Characters 64-98:
      fun x -> (new toto x :> 'a basic )
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This method has type 'a -> 'a basic which is less general than
  'b. 'b -> 'b basic

... but if I do :
let newtotoasbasic x = (new toto x :> 'a basic );;

class gentoto =
object
  method gen : 'a . 'a -> 'a basic =
(*     fun x -> (new toto x :> 'a basic ) *)
    newtotoasbasic
end;;

The compiler agrees with me ...
What is wrong with the first declaration ?

Thanks,
Nadji

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