Liskov Substitution Principle

If S is a subtype of T then objects of type T may be replaced with objects with type S, without breaking the problem.

The liskov Substitution states that [[Subtype]]s must be [[substitutable]] for their base types.

Example: - Class called Client uses an interface B. Classes A and C inherit this interface. Class doesn't care if you pass in the class A or C since all it sees is interface B.

Duck typing in dynamic languages: - If a bird swims like a duck, it quacks like a duck then I call that bird a duck.

Ways of breaking substitutability: - Violating a Contract - Violating Covariance/[[Contravariance]]

Contract Liskov Substitution Principle Demo Liskov Substitution Principle Violations Liskov Substitution Princple Common Smells