The Objective Caml system release 3.06 - The Caml language - Inria

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3.6 Class interfaces
Class interfaces are inferred from class definitions. They may also be defined directly and used to
restrict the type of a class. Like class declarations, they also define a new type abbreviation.
# class type restricted_point_type =
# object
# method get_x : int
# method bump : unit
# end;;
class type restricted_point_type =
object method bump : unit method get_x : int end
# fun (x : restricted_point_type) -> x;;
- : restricted_point_type -> restricted_point_type =
In addition to program documentation, class interfaces can be used to constrain the type of a class.
Both instance variables and concrete private methods can be hidden by a class type constraint.
Public and virtual methods, however, cannot.
# class restricted_point’ x = (restricted_point x : restricted_point_type);;
class restricted_point’ : int -> restricted_point_type
Or, equivalently:
# class restricted_point’ = (restricted_point : int -> restricted_point_type);;
class restricted_point’ : int -> restricted_point_type
The interface of a class can also be specified in a module signature, and used to restrict the inferred
signature of a module.
# module type POINT = sig
# class restricted_point’ : int ->
# object
# method get_x : int
# method bump : unit
# end
# end;;
module type POINT =
sig
class restricted_point’ :
int -> object method bump : unit method get_x : int end
end
# module Point : POINT = struct
# class restricted_point’ = restricted_point
# end;;
module Point : POINT