Question

When we are defining getter and setter methods for name in the following code:

class Animal
    attr_accessor :name
    def initialize(name)
        @name = name
    end
end

what is happening internally? How is Ruby able to take a symbol and match it with a variable?

Answer 1

It uses instance_variable_get and instance_variable_set for that.

Update: as Andrew Marshall noted, not exactly. Most ruby core methods are defined in C, but the result is essentially the same.

One could define attr_accessor and friends as follows:

def self.attr_accessor(*names)
  names.each do |name|
    define_method(name) do
      instance_variable_get("@#{name}")
    end

    define_method("#{name}=") do |new_value|
      instance_variable_set("@#{name}", new_value)
    end
  end
end

Note that I’ve also used define_method here to define the accessor methods.

I recommend that you take a look at some introductory texts about ruby metaprogramming, such as “Don’t Know Metaprogramming In Ruby?”.