Invariant Contracts Sample Clauses

Invariant Contracts. ‌ Formally, an invariant is a condition which might be true or false during the execution of a program. From a contract’s perspective, an invariant is some kind of delayed predicate that is checked on every use of a contracted subject value. Invariants are especially useful to enforce a particular property on an object during program execution. To demonstrate this, let’s consider the definition of a binary tree root, as defined by Node and Leaf elements in Listing 4.58. Each Node element consists of a value field, a left child, and a right child, whereas a Leaf element only consists of a value field. Their height property returns the height of the element in the binary tree. 1 let root = new Node(2, new Node(1, new Leaf(0), new Leaf(0)), new Leaf(0));