In Ruby, is the attribute of an object an object?

ruby_attributes_objects.md

###In Ruby, is the attribute of an object an object?

To illustrate, let's define a Book class where each book (or each instance of Book) has an author.

class Book
  attr_accessor :author

  def author
    @author
  end
end

We can create a new instance of Book and call it new_book by saying:

new_book = Book.new
=> #<Book:0x007f974c94f238>

We created a new instance of Book called new_book and it is stored as object #<Book:0x007f974c94f238>.

And to make sure that new_book is in fact an object, we can use the method #object_id, which returns an error if passed to anything other than an object.

new_book.object_id
=> 70143900809500

What happens if we ask new_book who its author is?

new_book.author
=> nil

We get nil because we haven't yet told new_book who authored him.

Let's tell it:

new_book.author = "Rudyard Kipling"
=> "Rudyard Kipling"

If we now ask new_book who its author is,

new_book.author
=> nil

It tells us that its author is "Rudyard Kipling".

Perfect! Now we can determine whether an attribute of an object is an object by passing #object_id to the author attribute of new_book. If it returns an object_id, we should conclude that attributes are objects.

new_book.author.object_id
=> 70143900735760

So there you have it. In Ruby the attribute of an object is indeed an object.