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Narrowing the type of class parameters with module specification #4824

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vicuna opened this Issue Jun 15, 2009 · 3 comments

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vicuna commented Jun 15, 2009

Original bug ID: 4824
Reporter: pveber
Assigned to: @garrigue
Status: closed (set by @garrigue on 2010-06-08T08:46:06Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.11.0
Fixed in version: 3.12.0+dev
Category: ~DO NOT USE (was: OCaml general)

Bug 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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vicuna commented Jun 16, 2009

Comment author: pveber

Sorry, I wrongly labeled this report's category, which should be "Ocaml general".
Maybe it should also be labeled as feature, rather than bug ...

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vicuna commented Jun 8, 2010

Comment author: @garrigue

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;;

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vicuna commented Jun 8, 2010

Comment author: @garrigue

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.

@vicuna vicuna closed this Jun 8, 2010

@vicuna vicuna added the bug label Mar 20, 2019

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