]> From: Brian Smith <brian-l-smith@uiowa.edu> > Please consider the following: > > # class virtual x = object method virtual foo : int end > class virtual y = object method virtual bar : string end > class z = > object > method foo = 2 > method bar = "there" > end;; > > How can I assert that class "z" is supposed to be a subtype of class x > and class y? In other words, how can I assert that (some_z : z :> x) and > (some_z : z :> y) will always be valid? You have many ways to force (self : #x) and (self : #y). class z = object ((self : #x) : #y) method foo = 2 method bar = "there" end class z = object (self : 'a) constraint 'a = #x constraint 'a = #y method foo = 2 method bar = "there" end class z = object inherit x inherit y method foo = 2 method bar = "there" end The last one uses the fact x and y are virtual classes, rather than class types. Note that none of these guarantee a subtyping relation, only a matching one. Fortunately, as long as the type of self does not appear in a contravariant position in x or y, this relation is included in subtyping. Jacques Garrigue ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners