The type of every attribute must be filled in the environment O before type checking can happen, because otherwise it may refer to an attribute defined later best practice: store object and method tables separately lub the function lub\left(X,Y\right), the least upper bound of X and Y, is Z if:

X is the lub.

both if statements and case statements uses the lub. static type The static type given by the type system/complier maybe a super type of the actual type. In modern type systems, the dynamic type of an object may differ from the static type to enable polymorphism. soundness \begin{equation} \forall E.\ \text{dynamic_type}\left(E\right) \leq \text{static_type}\left(E\right) \end{equation} SELF-TYPE SELF-TYPE is a static type: its not rendered until