Why I Avoid Instance Variables in Ruby

1 - why.md

In general, I try to avoid using instance variables directly in Ruby. Using private accessor methods wherever possible accomplishes two things:

1. It makes it much easier to refactor down the line if you end up needing to add some additional behavior whenever a value is set (validation, callbacks, etc), because you need only add the #my_attr= method definition and need not find all the places where you used @my_attr = ... and change them as well.

2. It better guards against the kind of typo-induced bugs that leave one staring at their computer for half an hour cursing the day they decided to earn a living as a programmer. For example:

2 - bad.rb

class Foo
  attr_reader :bar1

  def initialize(bar)
    @barl = bar
  end
end

f = Foo.new('baz')
# ...
# Some significant separation of both space and time in the execution of code...
# ...
f.bar1
#=> nil
# developer chucks laptop at wall

3 - good.rb

class Foo
  attr_accessor :bar1
  private :bar1=

  def initialize(bar)
    self.barl = bar
  end
end

f = Foo.new('baz')
# NoMethodError exception raised that clearly points out
# the source of the error right away