Version française
Home     About     Download     Resources     Contact us    
Browse thread
[Caml-list] Syntax for multiple subtyping constraints?
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: -- (:)
From: Brian Smith <brian-l-smith@u...>
Subject: [Caml-list] Syntax for multiple subtyping constraints?
Hello everbody,

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? I tried:

# class z =
     object (self : #x, self : #y)
      method foo = 2
      method bar = "there"
     end;;
Characters 29-30:
     object (self : #x, self : #y)
                      ^
Syntax error

But, it only works for one supertype, e.g.:

class z =
   object (self : #x) (* or (self : #y) *)
    method foo = 2
    method bar = "there"
   end;;

I know that I could just leave it out and everything would work, but I 
want to specify that z is supposed to be a subtype of both x and y so 
that, if I screw up the definition of class z, the compiler will give me 
an error. For example, if I didn't define the method "bar" in class "z", 
I want to get the error:

   This class  type should be virtual
   The following methods are undefined : bar

Thanks,
Brian

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