Trying to learn / understand Ruby setter and getter methods

Question

I'm just learning to program and have decided to try Ruby. I'm sure this is a stupid question, but the instructor is talking about setter and getter methods, and I'm confused. Here is the example:

class Human   def noise=(noise)     @noise = noise   end    def noise     @noise   end end 

From this, the class is instantiated, and I can puts this out:

man = Human.new man.noise=("Howdie!") puts man.noise 

This results in Howdie!

Now what confuses me is that the instructor is saying without the getter method (the 2nd of the two methods), there is no way to interact with the instance variable @noise.

But when I remove the getter method, I'm able to still access @noise, see example:

class Human   def noise=(noise)     @noise = noise   end end  man = Human.new puts man.noise=("Howdie!") 

This works the same as when the getter method it used.

So now I'm confused. Why is the getter needed? What does the instructor mean by not being able to access the instance variable without it? Is it possible he's using an older version of Ruby?

Thanks in advance for your help.

Answer 1

You can interact with that instance variable from other methods belonging to that instance, even if there is no getter:

def noise=(noise)   @noise = noise end  def last_noise   @noise end 

There doesn't need to be a getter defined with the same name as the method; the two are not linked at all. The getter is needed to "get" the value of the instance variable, but only in a short syntax.

What's happening in your example is that you're initializing a new object (Human.new), and then using a method (noise=, yes the method name contains the = symbol) that just-so-happens to define an instance variable (that is, a variable just for that instance), and then finally retrieving that instance variable with another method call.

You can actually use instance_variable_get to get the instance variable without defining any getter at all:

man = Human.new man.noise = "Howdie" man.instance_variable_get("@noise") 

This will return "Howdie", even though there is no getter defined.

And no, I don't think he's using an older version of Ruby.