variables.md

Variables in Ruby

• $DATA_DIR = "/data/set1"

  • global variable
  • global scope
  • starts with $
  • snake_case

• my_fav_color = "red"

  • local variable
  • local scope (only valid in the current method)
  • lower_snake_case

• PI = 3.14

  • constant
  • local scope
  • can't be changed
  • ALL_CAPS_SNAKE_CASE

• @name = "Adam"

  • instance variable
  • scoped to the class definition
  • starts with @
  • lower_snake_case
  • each instance gets its own unique copy of the variable

• @@person_count

  • class variable
  • scope: anywhere in the class
  • two @s
  • one copy shared within the class and it's instance

Instance Methods:

• defined without self in the name
• called on instances
• can reference instance vars
• can reference class vars

Class Methods:

• define with like: def self.method_name
• called on the Class: e.g. Person.person_count
• can reference class vars
• can't reference instance methods/vars