Delivered-To: lablgtk at yquem.inria.fr
Date: Tue, 30 Oct 2007 11:22:46 +0900 (JST)
Message-Id: <20071030.112246.94981046.garrigue at math.nagoya-u.ac.jp>
To: d0 at wp.pl
Subject: Re: [Lablgtk] Signals - how to inherit GObj.gobject_signals properly?
From: Jacques Garrigue <garrigue at math.nagoya-u.ac.jp>
In-Reply-To: <fg6136$gqt$1 at ger.gmane.org>
References: <fg6136$gqt$1 at ger.gmane.org>
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From: Dawid Toton <d0 at wp.pl>

> --- in gPrintOperation.mli ( 
> http://www.toton.2-0.pl/OCaml/LablGTK/src/GtkPrintOperation/Output/gPrintOperation.mli 
> ):
> class print_operation_signals : 
> [>GtkPrintOperation_types.print_operation] Gobject.obj -> object
>   inherit [[> GtkPrintOperation_types.print_operation]] GObj.gobject_signals
>   inherit OgtkPrintOperationProps.print_operation_sigs
> end
> 
> I believe there is something wrong with my interface part, but I don't 
> know what's going on at all. I thought that the compiler should know 
> that 'b and 'd types (as in the error message) should be the same type. 
> I don't know any way to force it to think so.

Indeed, your interface is wrong. This should be

class print_operation_signals : 
  ([>GtkPrintOperation_types.print_operation] as 'a) Gobject.obj ->
  object
    inherit ['a] GObj.gobject_signals
    inherit OgtkPrintOperationProps.print_operation_sigs
  end

That is, you have to share the type of the argument with the parameter
of GObj.gobject_signals.

> One thing more I don't understand worries me:  why it is legal to write
>   inherit [[> GtkPrintOperation_types.print_operation]] GObj.gobject_signals
> 
> when "[[> GtkPrintOperation_types.print_operation]] 
> GObj.gobject_signals" is sort of Gobject.obj->object and needs to be 
> feeded with some obj to become an OCaml object (that surely can be 
> inherited).
> Now it looks as if it inherits "Gobject.obj->object" function.

The keyword inherit is confusing. Personally, I would have preferred
something like "include", because this is just about including the class
type associated to GObj.gobject_signals, not inheriting from the class
itself. And a class type has no arguments (there is no concept of
"functor type" for classes), so you can include it directly.

Jacques

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