Ruby Interview Questions

// What is a class?
- They hold data
- They have methods that interact with that data
- They instantiate objects

// What is an object?
- An instance of a class
- Classes descend from the Object root class

// What is a module?
- Modules serve as a mechanism for namespaces
- Modules provide a way for multi inheritance via mixins, but can't be instantiated

// Ways to invoke a method in ruby?
1. obj = Object.new
2. obj.send :method
3. obj.method(:method).call
  
// ?? a ||= b
or equals
if a is false or nil it gets the value of b

// What does self mean?
class level = self refers to current object 
instance level = self is the memory location

// What is unit testing?
testing methods
assert the actual expected result


// How to prevent an object from being changed

.freeze

// Advantages of Ruby
1. Pure OOL - methods, classes, and booleans are Objects
2. Open Source
3. Metaprogramming - code that acts on other code, not data.
4. Clean and Simple Syntax

//4 types of variables
1. Global - begin with $
2. Local variables - begin with lowercase letter or underscore
3. Class variables - begin with @@ shared by all instances of the class
4. Instance variables - begin with @ local, singe instance of class

//Three levels of access control
1. Public - called by anyone
2. Protected - accessible within their defining class and subclasses
3. Private - only viewed within defining class except with Object.new.send(:method) is called

//Thread lifecycle and pooling
Lifecycle - begins as soon as CPU resources are available, use up resources, but running multiple at a time can improve performance
Pooling - threads in standby, best for large number of short tasks

//Modules uses

--Modules as mixins - share methods / code among different classes

//Stabby Proc

-> (s) (p s) [“I’m a Proc”]

Create a lambda (nameless function). Takes s preforms (p s) and feeds [ ] as s.


// Fun Ruby Facts

and / or are lower than =
&& / || are higher than =

== - value
=== - used in a when clause of a case statement
eql? - value and type
equal? - identity of two objects based on object id


false and nil are the only things that are falsy

// &:
[1, 2, 3].map(&:to_s)

It takes the array of numbers, calls to_s on each item, and returns an array of the return values.

But what if you want to do the opposite? Rather than calling a method on the object, what if you want to call a method with the object as a parameter? Simple!

["1", "2", "3"].map(&method(:Integer))