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Inheritance of Class Structures

• Extension of classes:
  • class EXTENDED-STACK =
    inherits PERSONAL-STACK with
    begin
       ...
    in record
       ...
    end end
  • EXTENDED-STACK is subclass of PERSONAL-STACK.
• Semantics of class inheritance:

  • pi |- T1: pi1class	pi -U- pi1 |- T2: pi2class
    pi |- inherits T1 with T2: (pi1 -U- pi2)class

  • [[pi |- inherits T₁ with T₂: (pi₁ -U- pi₂)class]]e s
    = (f s)
       where f s' =
          [[pi -U- pi₁ |- T₂: pi₂class]](e -U- e₁) s₁
       and (e₁, s₁) = [[pi |- T₁: pi₁class]]e s'