On 3 August 2012 08:50, Alain Frisch�<alain@frisch.fr>�wrote:

Hello,

I don't know if this covers all the case, but you need to keep in mind the following points. �Feel free to add to the list.

Thanks for nice and structured answer!�

I'll try to expand it with my cases, but due to lack of comprehension they will not be so clear =)

So the setup is follows: I have a class with a type explicitly specified in mli file. No inference on it's methods. And a function, that takes some object and type system tries to infer what objects it can accept.�

Starting from a �simple case:

let reset_env_model state v =

��let q = Queue.create () in

��Queue.iter (fun p -> v#expand_row p) q

produces an error:

�� This expression has type GTree.view

�� but an expression was expected of type < expand_row : 'a -> unit; .. >

�� Types for method expand_row are incompatible

because expand_row method of type GTree.view has type:

�� expand_row : Gtk.tree_path -> unit;

I think, that compiler have a reason to refuse this code: function wants a method, that can take an�arbitrary�value of type 'a, but I pass a method that has a covariant type�Gtk.tree_path in position left to arrow. So he complains correctly. I agree =) I think that this case has some�correspondence�with your �case #1.

But, why in the following code:

let reset_env_model state v =

��let q = Queue.create () in

��let m,_,_ = State.env_model state in

��m#foreach (fun p _ -> if v#row_expanded p then Queue.push p q; false);

��set_env_model state v;

��Queue.iter (fun p -> v#expand_row p) q

compiler cannot infer, that object p has type Gtk.tree_path, and with this proposition imply, that the expand_row method has a type "Gtk.tree_path -> unit"?�