An Introduction to Contract-Based Programming in Ada
One of the most powerful features of Ada 2012* is the ability to specify contracts on your code. Contracts describe conditions that must be satisfied upon entry (preconditions) and upon exit (postconditions) of your subprogram. Preconditions describe the context in which the subprogram must be called, and postconditions describe conditions that will be adhered to by the subprogram’s implementation. If you think about it, contracts are a natural evolution of Ada’s core design principle. To encourage developers to be as explicit as possible with their expressions, putting both the compiler/toolchain and other developers in the best position to help them develop better code.