# Sandi Metz - Nothing is Something

:::: tags
- OOP
- Ruby
::::

Some insightful thoughts on OOP.

Clever examples of message-passing to get rid of conditionals.

Prefer composition with dependency injection to inheritance:
inheriting to override a method really means that the parent class had
a default "null" behaviour that can be injected explicitly.

Name the role, make an interface for it, and make classes that
implement each behaviour (the null one and the specialiazed one).
This will make it easier to compose specializations (i.e. save you
from multiple inheritance).


# Sandi Metz - Rules

:::: tags
- OOP
- Ruby
::::

Some theory-crafting on rule-following, then the actual rules, which
amount to

- small classes,
- tiny methods,
- few parameters.

At the 16-minute mark, an interesting interaction between Metz and a
programmer starting to apply these rules: the programmer wonders when
they will be able to understand the new application "the same way"
they understood the old one.  I.e. will they ever reach a point where
they have a complete mental map of every interaction between every
object, the same way the used to have a complete mental map of the old
monolithic, sequential application?

Metz's response is that nope, this will never happen; they will "cease
to care" instead.  In exchange, they will be able to make localized
changes without worrying about breaking the whole application.