Design by contract

Design by contract (DbC) is a way to architecture a system where components force the use of their methods via interfaces.

Conditions

• Precondition
  • Callers have the responsibility to respect the preconditions
  • If not, an error is raised and the interface is not implemented
  • Example: chose of topping in a pizza order is a precondition
• Postcondition
  • Implementers have the responsibility to respect the postconditions
  • They must be satisfied after an interface method is invoked.
  • Example: delivery time in a pizza order is postcondition
• Invariant
  • Absolute rules
  • Must remain true before and after the execution of the method
  • Example: dough is an invariant condition to cook a pizza