The Handbook for Ruby Developers/

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Scope of Variables

Scope of Variables

Learn scope of local and instance variables in Ruby.

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You might have noticed that we used @, also known as the “at” sign, before the state variable. This syntax is used to define instance variables. We already covered this a little bit in previous chapters. But in general, we have three types of variables:

Local variables

Local variables are normally defined inside of a method and not accessible from other methods. For example, the following code will produce the error because the aaa variable isn’t defined in method m2:

Ruby
# Error due to 'aaa' variable
class Foo 
  def m1
    aaa = 123
    puts aaa
  end
  def m2 
    puts aaa
  end
end
foo = Foo.new
foo.m1 # works fine, prints 123
foo.m2 # won't work, variable not defined

Instance variables

Instance variables are of the particular class instance, or variables of a particular object. We can access these variables with at sign @:

Ruby
# No error due to '@'
class Foo
  def initialize
    @aaa = 123
  end
  def m1
    puts @aaa
  end
  def m2
    puts @aaa
  end
end
foo = Foo.new
foo.m1
foo.m2

Instance variables define the state of an object. Nothing prevents us from ...