Contents

• Contents
• List of Figures
• Introduction
  • Why type checking?
  • Plan of the paper
• Types and Subtypes, Classes and Subclasses
  • Types and subtypes
    • Record types
    • Function types
    • Types of variables
  • Classes and Subclasses
  • Differences between subtypes and subclasses
• Simple type systems are lacking in flexibility
  • The need to change return types in subclasses
  • The need to change parameter and instance variable types in subclasses
  • Other typing problems
• Toward more flexible type systems
  • Subtyping of method types in subclasses
  • Examples using flexible types
• Introducing MyType
• The matching relation between types
  • Type checking classes using matching
  • Matching is necessary in type checking classes
• Binary methods complicate subtyping
  • Subclasses do not generate subtypes
  • A new definition of subtyping for object types
• Evaluating the use of MyType
• Combining parametric polymorphism with matching
• Solutions to Eiffel's covariant type problems
  • Eiffel's system validity check
  • Solving covariance problems with match-bounded polymorphism
  • Meyer's solution: Banning polymorphic catcalls
• Replacing subtyping with matching
• Conclusions and related work
• References
• Example linked list program using matching