Ruby - how different are modules from classes?
97804
Difference between a class and a module
153216
How to return different classes from one function?
74854
Are strings mutable in Ruby?
103294
How to implement an abstract class in ruby?
114773
counterexamples on modules
150533
What's the difference between a header file and a library?
17633
class << self vs self.method with Ruby: what's better?
9988
What is the difference between  in ERB in Rails?
139373
Class vs Struct for data only?
16831
What's the difference between importing and extending a class?
104815
Redefine Class Methods or Class
24052
Use 'import module' or 'from module import'?
112854
Does Python have class prototypes (or forward declarations)?
18262
how does this Ruby class method get invoked?
70328
@class vs. #import
40600
How to access a standard-library module in Python when there is a local module with the same name?
121064
How to get class instances in Ruby?