Object Expressions Sample Clauses

Object Expressions. ‌ ∈ T ∪ UTP expressions do not, by default, contain explicit type information. For object oriented programming it is necessary that we carry type data about the class to which an object belongs. We thus define a derived form of expression and functions for querying this type data. An object expression e is represented by a pair: (eτ , ev), where the first element eτ cls is the type of e and the second element ev is its value. We can then define the construct null that stands for a family of values, one for each class. The type held by eτ in this case is inferred from the context. For instance, in an assignment x := null, we have that eτ = xτ ; this means that the runtime type of null is the declared type of variable x. For our implementation of the UTP in Isabelle all variables and expressions carry such data from the type system, thus this is a valid assumption (Isabelle/UTP is inherently strongly typed in nature).