VDM-10 Language Manual

VDM-10 Language Manual
The overall invariant expression of a class is all the invariant definitions of the class and its
superclasses combined by logical and in the order that they are defined in 1) the superclasses
and 2) the class itself.
This operation is private, has no parameters and returns a boolean corresponding to the
execution of the invariant expression.
Example: The following examples show instance variable definitions. The first class specifies one
instance variable:
✞
class GroupPhase
types
GroupName = | | | | | | | ;
Team = ... -- as on page 24
Score::team : Team
won : nat
drawn : nat
lost : nat
points : nat;
instance variables
gps : map GroupName to set of Score;
inv forall gp in set rng gps &
(card gp = 4 and
forall sc in set gp & sc.won + sc.lost + sc.drawn