Assertions

Abstract

A distinctive feature of this book is that types are preferably equipped with assertions. Assertions are the topic of Sect. 2.1. The basic notions related to assertions are introduced in Sect. 2.1.1. This section also specifies the basic reasoning rules such as those that apply to assignments, conditional statements, and loops. Methods equipped with preconditions and postconditions are discussed in Sect. 2.2.1. Loop invariants are the topic of Sect. 2.2.2 and a verification technique for proving loop termination in Sect. 2.2.3. Class assertions called object invariants are the topic of Sect. 2.2.4. The implications of the developed apparatus of assertions on parametric types are discussed in Sect. 2.2.5. Finally, in Sect. 2.2.6 we revisit the notion of subtyping in the presence of assertions and explain the all important compatibility requirement for classes called behavioral subtyping.