Defensive programming

Defensive programming follows a somewhat different approach to DbC. Instead of stating all conditions that must be held in a contract, which, if unmet, will raise an exception and make the program fail, this is more about making all parts of the code (objects, functions, or methods) able to protect themselves against invalid inputs.

Defensive programming is a technique that has several aspects, and it is particularly useful if it is combined with other design principles (this means that the fact that it follows a different philosophy to DbC does not mean that it is a case of either one or the other—it could mean that they might complement one another).

The main ideas on the subject of defensive programming are how to handle errors for scenarios that we might expect to occur, and how to deal with errors that should never occur (when impossible conditions happen). The former will fall into error handling procedures, while the latter will be the case...