Hello, Le mar 01 jui 2008 17:53:34 CEST, SerP <[EMAIL PROTECTED]> a écrit :
> class type session_t = > object > method id:int; > method location: #location_t; > end; > ... > > Error: This expression has type session = < id : int; location : > location > but is here used with type > #session_t as 'a = < id : int; location : 'b. > #location_t; .. > My guess is that session_t is a bit too polymorphic: location is a polymorphic method (indicated by the 'b. in the error message). Thus, a class implementing session_t should have a location method able to return any subtype of location_t, which might be a bit complicated to say the least. A more sensible class type would require that the location method returns a subtype of location_t, which may differ from one implementation to the other, but is fixed for a given implementation. By the way, this matches more or less your second solution. At the class/class type level, this can be done by adding a type parameter to the class type and using a constraint as shown below (warning, this is the regular ocaml syntax, not the revised one): class type ['a]session_t = object method id:int method location: 'a constraint 'a = #location_t end let check_session (session:'a #session_t) = begin print_int session#id; print_int session#location#a; print_string session#location#b; end -- E tutto per oggi, a la prossima volta. Virgile _______________________________________________ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs