0004766: Incorrect type inference with objects

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0004766

OCaml

OCaml general

public

2009-04-09 16:12

2009-04-10 08:33

Reporter

pveber

Assigned To

Priority

normal

Severity

major

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

Target Version

Fixed in Version

3.11.1+dev

Summary

0004766: Incorrect type inference with objects

Description

Consider the following session with ocaml 3.11 interpreter :

        Objective Caml version 3.11.0

# class virtual ['a] c =
object (s : 'a)
  method virtual m : 'b
end
;;
class virtual ['a] c :
  object ('a) constraint 'a = < m : 'b; .. > method virtual m : 'b end
# let o =
    object (s :'a)
      inherit ['a] c
      method m = 42
    end;;
val o : 'a c as 'a = ...
# o#m;;
- : 'a = <poly>

It seems that the typing of instance o is incorrect, and should rather be something like 'a c as 'a constraint 'a = < m : int; .. >. I did not find any previous report of this problem. The behaviour is the same on ocaml 3.10.2.

BTW: thanks for your excellent work on ocaml, and all the very instructive messages sent by the caml dev team on caml-list.

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Notes
(0004920) garrigue (manager) 2009-04-10 08:33	The real problem was in the way abbreviations were simplified in Ctype.normalize_type. Concretely, ('a c as 'a) does not accurately define a type, since it can describe any instance of itself too...

Issue History
Date Modified	Username	Field	Change
2009-04-09 16:12	pveber	New Issue
2009-04-10 08:33	garrigue	Note Added: 0004920
2009-04-10 08:33	garrigue	Status	new => closed
2009-04-10 08:33	garrigue	Resolution	open => fixed
2009-04-10 08:33	garrigue	Fixed in Version	=> 3.11.1+dev