Question

Being new to Ruby, I’m having trouble explaining to myself the behavior around method definitions within Ruby.

The example is noted below…

class Foo
  def do_something(action)
    action.inspect
  end
  def do_something_else=action 
    action.inspect
  end
end

?> f.do_something("drive")
=> "\"drive\""

?> f.do_something_else=("drive")
=> "drive"

The first example is self explanatory. What Im trying to understand is the behavior of the second example. Other than what looks to be one producing a string literal and the other is not, what is actually happening? Why would I use one over the other?

Answer 1

Generally, do_something is a getter, and do_something= is a setter.

class Foo
  attr_accessor :bar
end

is equivalent to

class Foo
  def bar
    @bar
  end

  def bar=(value)
    @bar = value
  end
end

To answer your question about the difference in behavior, methods that end in = always return the right hand side of the expression. In this case returning action, not action.inspect.

class Foo
  def do_something=(action)
    "stop"
  end
end

?> f = Foo.new
?> f.do_something=("drive")
=> "drive"