0005388: recursive class type definition via module rec misses some inheritance information - MantisBT

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ID

Project

Category

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Date Submitted

Last Update

0005388

OCaml

OCaml general

public

2011-10-26 20:34

2011-12-21 11:54

Reporter

furuse

Assigned To

garrigue

Priority

normal

Severity

major

Reproducibility

always

Status

resolved

Resolution

not fixable

Platform

OS

OS Version

Product Version

3.12.1

Target Version

Fixed in Version

Summary

0005388: recursive class type definition via module rec misses some inheritance information

Description

The following code is not type-checked:

----------------------------

type 'a t

type _Unicode
type _String
type _Sequence

module rec M_Sequence : sig
  class type o_Sequence = object method _Sequence : _Sequence t end
end = struct
  class type o_Sequence = object method _Sequence : _Sequence t end
end

and M_String : sig
  class type o_String = object inherit M_Sequence.o_Sequence method _String : _String t end
end = struct
  class type o_String = object inherit M_Sequence.o_Sequence method _String : _String t end
end

and M_Unicode : sig
  class type o_Unicode = object inherit M_String.o_String method _Unicode : _Unicode t end
end = struct
  class type o_Unicode = object inherit M_String.o_String method _Unicode : _Unicode t end
end

---------------

Saying:
       class type o_Unicode =
           object method _String : _String t method _Unicode : _Unicode t end
       The public method _Sequence cannot be hidden

So, there is something strange around the conjunction of module rec and class inheritance.

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Notes
(0006187) furuse (reporter) 2011-10-27 02:34	Now I have something simpler and working, but still the above example indicates a bug of computing the fixed point of inheritance... ------------------------------ type 'a t type _Unicode type _String type _Sequence module rec M : sig class type o_Sequence = object method _Sequence : _Sequence t end class type o_String = object inherit M.o_Sequence method _String : _String t end class type o_Unicode = object inherit M.o_String method _Unicode : _Unicode t end end = M

(0006192) garrigue (manager) 2011-10-29 10:45	My understanding is that computation of fixpoints for recursive modules is incomplete, and cannot even be so from a theoretical point of view (impossible to know the number of iterations needed to reach a fixpoint). For classes, the algorithm is bootstrapped by starting from empty classes, which explains why inheritance doesn't work when the number of modules involved is too large. Since I don't see any complete solution coming, the best approach is to avoid inheritance between recursive modules. By the way, I don't know why your workaround using a single interface works, but this seems to scale for an arbitrary number of levels of inheritance. Good.

Issue History
Date Modified	Username	Field	Change
2011-10-26 20:34	furuse	New Issue
2011-10-27 02:34	furuse	Note Added: 0006187
2011-10-29 10:45	garrigue	Note Added: 0006192
2011-12-21 11:54	gasche	Status	new => resolved
2011-12-21 11:54	gasche	Resolution	open => not fixable
2011-12-21 11:54	gasche	Assigned To	=> garrigue

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