0004824: Narrowing the type of class parameters with module specification

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Date Submitted

Last Update

0004824

OCaml

OCaml general

public

2009-06-15 17:01

2010-06-08 10:46

Reporter

pveber

Assigned To

garrigue

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

3.11.0

Target Version

Fixed in Version

3.12.0+dev

Summary

0004824: Narrowing the type of class parameters with module specification

Description

The following definition is rejected :

# module M :
   sig
     class x : int -> object method m : int end
  end
=
struct
  class x _ = object
    method m = 42
  end
end;;
Error: Signature mismatch:
       Modules do not match:
         sig class x : 'a -> object method m : int end end
       is not included in
         sig class x : int -> object method m : int end end
       Class declarations do not match:
         class x : 'a -> object method m : int end
       does not match
         class x : int -> object method m : int end
       One parameter has type 'a but is expected to have type int

Is there a good reason for this ?

Philippe.

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Notes
(0004997) pveber (reporter) 2009-06-16 15:31	Sorry, I wrongly labeled this report's category, which should be "Ocaml general". Maybe it should also be labeled as feature, rather than bug ...

(0005549) garrigue (manager) 2010-06-08 10:40	While trying to fix this problem, I discovered a gaping hole in the type system, at least since ocaml 2.00: module M : sig class c : 'a -> object val x : 'b end end = struct class c x = object val x = x end end class c (x : int) = object inherit M.c x method x : bool = x end let r = (new c 2)#x;;

(0005550) garrigue (manager) 2010-06-08 10:46	Allow narrowing of class parameters, and close the unsoundness bug mentioned as note. Fixed in version/3.12 revision 10541. Note that the closing of this unsoundness is going to break many programs, including lablgtk.

Issue History
Date Modified	Username	Field	Change
2009-06-15 17:01	pveber	New Issue
2009-06-16 15:31	pveber	Note Added: 0004997
2009-06-22 17:59	doligez	Category	OCaml documentation => OCaml general
2010-04-30 06:50	garrigue	Status	new => assigned
2010-04-30 06:50	garrigue	Assigned To	=> garrigue
2010-06-08 10:40	garrigue	Note Added: 0005549
2010-06-08 10:46	garrigue	Note Added: 0005550
2010-06-08 10:46	garrigue	Status	assigned => closed
2010-06-08 10:46	garrigue	Resolution	open => fixed
2010-06-08 10:46	garrigue	Fixed in Version	=> 3.12.0+dev