VDM-10 Language Manual

VDM-10 Language Manual
Within the class
In a subclass
In an arbitrary external class
public protected private
√ √ √
√ √
√
×
× ×
Table 14.1: Summary of Access Specifier Semantics
Example In the example below use of the different access specifiers is demonstrated, as well
as the default access to class members. Explanation is given in the comments within the
definitions.
✞
class A
types
public Atype = | |
values
public Avalue = 10;
functions
public compare : nat -> Atype
compare(x) ==
if x < Avalue
then
elseif x = Avalue
then
else
instance variables
public v1: nat;
private v2: bool := false;
protected v3: real := 3.14;
operations
protected AInit : nat * bool * real ==> ()
AInit(n,b,r) ==
(v1 := n;
v2 := b;
v3 := r)
2 In practice, constants will generally be static – a non-static constant would represent a constant whose value may vary
from one instance of the class to another which would be more naturally represented by an instance variable.
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