VDM-10 Language Manual

Chapter 6. Expressions
Examples: Assuming the classes Tree, BinarySearchTree, Queue, and identifiers t, b, q
as in the previous example, we have:
isofclass(Tree,t) ≡ true
isofclass(Tree,b) ≡ true
isofclass(Tree,q) ≡ false
isofclass(Queue,q) ≡ true
isofclass(BinarySearchTree,t) ≡ false
isofclass(BinarySearchTree,b) ≡ true
6.20 Same Base Class Membership (VDM++ and VDM-RT)
Syntax: expression = . . .
| samebaseclass expression
| . . . ;
samebaseclass expression =
‘samebaseclass’,
‘(’, expression, expression, ‘)’ ;
Semantics: The function samebaseclass when applied to object references expression1
and expression2 yields the boolean value true if and only if the objects denoted by
expression1 and expression2 are instances of classes that can be derived from the
same root superclass, and false otherwise.
Examples: Assuming the classes Tree, BinarySearchTree, Queue, and identifiers t, b, q
as in the previous example, suppose that AVLTree is another subclass of Tree, BalancedBST
is a subclass of BinarySearchTree, a is an instance of AVLTree and bb is an instance
of BalancedBST :
samebaseclass(a,b) ≡ true
samebaseclass(a,bb) ≡ true
samebaseclass(b,bb) ≡ true
samebaseclass(t,bb) ≡ false
samebaseclass(q,a) ≡ false
6.21 Same Class Membership (VDM++ and VDM-RT)
Syntax: expression = . . .
| sameclass expression
| . . . ;
sameclass expression = ‘sameclass’,
‘(’, expression, expression, ‘)’ ;
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