Delivered-To: lablgtk at yquem.inria.fr
To: lablgtk at math.nagoya-u.ac.jp
From: Dawid Toton <d0 at wp.pl>
Date: Tue, 30 Oct 2007 02:23:30 +0100
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Message-ID: <fg6136$gqt$1 at ger.gmane.org>
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Subject: [Lablgtk] Signals - how to inherit GObj.gobject_signals properly?
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I have stuck trying to understand the following error message:
......
The method connect has type
  'a.
    ([> GtkPrintOperation_types.print_operation ] as 'b, 'a) GtkSignal.t ->
    callback:'a -> GtkSignal.id
but is expected to have type
  'c.
    ([> GtkPrintOperation_types.print_operation ] as 'd, 'c) GtkSignal.t ->
    callback:'c -> GtkSignal.id
Type 'b = [> `printoperation | `printoperationpreview ]
is not compatible with type
  'd = [> `printoperation | `printoperationpreview ]

(the whole message is here: 
http://www.toton.2-0.pl/OCaml/LablGTK/src/GtkPrintOperation/KillerErrorMessage.txt 
)

I'm trying to compile the following:
--- in gPrintOperation.ml ( 
http://www.toton.2-0.pl/OCaml/LablGTK/src/GtkPrintOperation/Output/gPrintOperation.ml 
):
class print_operation_signals obj = object
  inherit [[> GtkPrintOperation_types.print_operation]] 
GObj.gobject_signals obj
  inherit OgtkPrintOperationProps.print_operation_sigs
end

--- 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

(other source files are in 
http://www.toton.2-0.pl/OCaml/LablGTK/src/GtkPrintOperation/Output/ )

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.

I've tried to mimic some existing code, but in gAction.mli there is 
declaration of action_signals that contains only 2 values an 2 methods. 
Should I show (in the interface) the parts inherited from 
gobject_signals ? If (in interface sourcecode) print_operation_signals 
doesn't inherit from gobject_signals, compiler tells me that there is a 
problem with the connect method.
 
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.

Thank you in advance.
I'm still working on GtkPrintOperation, but currently I don't know how 
to overcome the problem.
Dawid Toton

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