SOLID Class Principles

gistfile1.txt

- Single Responsability - classes and methods should handle/do only one thing. Methods max 5 lines long, classes max 100 lines long.
- Open Closed - classes should be open for extension and closed for change
- Liskov Substitution - Having a main class and a subclass. Anywhere we use the main we should get same result by using the subclass.
- Interface Segragation - no client should be forced to depend on methods it does not use. Maybe class does not do only one thing? Split the class in more classes (and maybe add a facade).
- Dependency Inversion - Dont tight couple the classes by creating one instance inside another class. Inject them as dependencies when calling the method outside the class.  
                         Use `A.new(b: B.new(5))` instead of `A.new(5)` where `class A; def initialize(i); @b= B.new(i); end`

- Law of Demeter - don't chain methods that could be changed in future. (except when methods returns self)
- Don't repeat yourself - reuse code


- public - what?
- private - how?
- protected - 

- abstract class - class that should not be instanciated. Mostly used as parent class or for static methods.