Objects across languages.
WHAT THE CORE IDEAS ARE
- Encapsulation: data and behaviour together, with internals hidden
- Inheritance: types derived from other types
- Polymorphism: different types used through a common interface
WHAT VARIES BETWEEN LANGUAGES
Whether classes exist, or objects are built from prototypes Whether multiple inheritance is permitted How interfaces are expressed How access is controlled
WHAT INTERFACES PROVIDE
A contract without an implementation.
WHY THAT MATTERS
Code depends on the contract, not on a concrete type, which makes substitution and testing possible.
WHAT COMPOSITION MEANS
Building behaviour by combining objects rather than inheriting.
WHY IT IS GENERALLY PREFERRED
Deep inheritance hierarchies become rigid, and changes propagate unpredictably.
WHAT THE GUIDANCE IS
Inherit to express a genuine is-a relationship; compose otherwise.
WHAT ENCAPSULATION ACTUALLY ACHIEVES
The ability to change internals without breaking callers.
WHAT DEFEATS IT
Exposing internal state directly.
WHAT TO PREFER
Exposing behaviour, not data.
WHAT TO BE CAUTIOUS OF
Applying patterns where simple functions would serve.
