Ruby Attributes VS Instance variables

I am finally going to clarify the confusion among developers about the use of attributes and instance variables in Ruby classes. In this article, I will show you the similarities and differences between these two concepts and provide best practices for using them.

First things first SIMILARITIES

• Attributes and instance variables are used to store data within a class.
• They can both be accessed and modified within the class.

Now the differences

• Attributes have a wider scope than instance variables.
• Attributes can be accessed and modified outside the class using accessors, while instance variables are only accessible within the class.
• Attributes can be defined with specific data types, ensuring data integrity. Instance variables, on the other hand, can hold any data type.
• Attributes can be initialized during declaration, while instance variables need to be initialized within the class.
• Instance variables consume more memory than attributes since they are not bound to a specific data type.

Best practices

attr_accessor is so versatile, that it lets us to store a value anywhere.

class AttributesInstances
  attr_accessor :my_attribute

  def initialize
    @my_attribute = "Hello" # instance variable used to store the value of the attribute
  end

  def show_me
    puts @my_attribute # instance variable used to access the value of the attribute
    puts self.my_attribute # attribute reader used to access the value of the attribute
  end
end

ai = AttributesInstances.new
ai.show_me
#=> Hello
#=> Hello

As you can see, it is possible to access the attribute value by the instance variable used to store it during the initialization.

class AttributesInstances
  attr_accessor :my_attribute

  def initialize
    self.my_attribute = "Hello" # attribute writer used to set the value of the attribute
  end

  def show_me
    puts @my_attribute # instance variable used to access the value of the attribute
    puts self.my_attribute # attribute reader used to access the value of the attribute
  end
end

ai = AttributesInstances.new
ai.show_me
#=> Hello
#=> Hello

In this case, the value can be stored with self which is the attribute writer method.

attr_reader and attr_writer It has their special treatment.

class AttributesInstances
  attr_reader :my_attribute_reader

  def initialize
    # self.my_attribute_reader = 'Hello' # RISES NoMethodError: undefined method `my_attribute_reader=' for #<AttributesInstances:0x00007f8f3b8b3e40>
    @my_attribute_reader = 'Hello' # instance variable used to set the value of the attribute
  end

  def show_me
    puts @my_attribute_reader # instance variable used to access the value of the attribute
    puts self.my_attribute_reader # attribute reader used to access the value of the attribute
  end
end

ai = AttributesInstances.new
ai.show_me
#=> Hello
#=> Hello

Here, the value can only be stored by an instance variable, when self is used, it raises the undefined method exception.

I hope this is useful for getting your code cleaner and better organized.

Any comments are fully welcomed.