snippet.rb

class Foo
  attr_accessor :bar

  def set
    @bar = "set in the set method"
  end
  
  def check
    p bar
    bar = "set locally"
    p bar
  end
  
end

obj = Foo.new
obj.set
p obj.bar
p obj.check

__END__

"set in the set method"
"set in the set method"
"set locally"
nil