JuzerShakir

# Date Created: 17 June 2021
# Ruby Version 3.0.0p

def object_id_of_str obj_1, obj_2
  # The argument has same object_id as original object because..
  # ..it refers to same object, it doesn't copy objects' value but it points..
  # ..to original objects' memory, hence holding objects' reference ID in the memory
  puts "Before modification, object 1 ID: #{obj_1.object_id}" # => 60
  puts "Before modification, object 2 ID: #{obj_2.object_id}" # => 80

JuzerShakir

# Date Created: 16 June 2021
# Ruby Version 3.0.0p

class Abcd;end

# ------------------ Superclass ---------------
Abcd.superclass # => Object
Abcd.superclass.superclass # => BasicObject
Abcd.superclass.superclass.superclass # => nil
# as BasicObject is top level class that doesn't have any parent class

JuzerShakir

# Date Created: 20 June 2021
# Ruby Version 3.0.0p

# initiated constant
FRUIT = 'Apple' # => Apple
# can be modified
FRUIT << 's'  # => Apples
# and can also give totally different value, but with a warning raised by ruby
FRUIT = 'Orange'  # =>  warning: already initialized constant FRUIT
                  # =>  Orange

JuzerShakir

local_var = "I am local var defined in root."
puts local_var  # => "I am local var defined in root."

# accessing local var which is defined in root 
def access
   puts local_var   # => NameError
end

# accessing variable in nested method
def parent_method

JuzerShakir

string = "I am a string."   # => String
int = 123                   # => Integer
float = 34.5                # => Float
complex = 1i                # => Complex
boolean = true              # => Boolean
array = [a,b,c]             # => Array
hash = {ruby: 3.0}          # => Hash

total = int + float         # => 157.5

JuzerShakir

class Inst_var
  # will initialize instance variable when class is initiated
  def initialize
    @count = 0
  end

  # add up
  def add_count
    @count += 1
  end

JuzerShakir

# accessing through instance of a class
object.instance_variables         # => @var

# accessing through class after initilize
Inst_var.new.instance_variables   # => @var

# accessing directly through class
Inst_var.instance_variables   # => NoMethodError

JuzerShakir

class Class_var
  # class variable
  @@count = 0
  # will increase class variable count as soon as class is initiated
  def initialize
    @@count += 1
  end

  def output
    @@count

JuzerShakir

object.class_variables      # => NoMethodError
Class_var.class_variables   # => [:@@count]

JuzerShakir

# global variable
$count = 0

class Class_var
  # will increase class variable count as soon as class is initiated
  def initialize
    $count += 1
  end
  
  # we dont need this for global var