VDM-10 Language Manual

Chapter 14. Top-level Specification (VDM++ and VDM-RT)
end A
class B is subclass of A
instance variables
v4 : Atype --inherited from A
operations
BInit: () ==> ()
BInit() ==
(AInit(1,true,2.718); --OK: can access protected members
--in superclass
v4 := compare(v1); --OK since v1 is public
v3 := 3.5;
--OK since v3 protected and this
--is a subclass of A
v2 := false
--illegal since v2 is private to A
)
end B
class C
instance variables
a: A := new A();
b: B := new B();
operations
CInit: () ==> A‘Atype--types are class attributes
CInit() ==
(a.AInit(3,false,1.1);
--illegal since AInit is protected
b.BInit();
--illegal since BInit is (by default)
--private
let - = a.compare(b.v3) in skip;
--illegal since C is not subclass
--of A so b.v3 is not available
return b.compare(B‘Avalue)
--OK since compare is a public instance
--attribute and Avalue is public class
--attribute in B
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