Attribute Readers

This lesson explains attribute readers and how they’re related to instance variables.

We'll cover the following

Asking an object for information

Remember that people have the ability to remember their name, and tell it, when asked.

We’ve already implemented the first part of this. Our Person instance now knows her name, “Ada”.

Let’s look at the second part. Remember also that methods are either questions or commands. We want to add a method that answers the question, What’s your name?

It’s as simple as this:

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class Person
  def initialize(name)
    @name = name
  end
  def name
    @name
  end
end

Before we discuss what this does, let’s look at how we can use our new method. We can now call the method on the person object, like this:

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person = Person.new("Ada")
puts person.name

This prints the name, Ada, and that’s what we want. We can create a new person object, passing a name to it. Once that person is created, we’re able to ask for its name, and we’ll get the name back.

Explanation

Let’s look at how this works internally:

  • In the first line, the object assigned to the person variable is an initialized new instance of the Person class. Initialized means that the initialize method has already been called and has already assigned the "Ada" string to the @name instance variable.

  • Now, this person object has the name method, as defined in the class definition of Person above. In the second line, we call this method, person.name.

  • When the name method is called, it does nothing else but evaluate the @name instance variable from the object scope. Because this has previously been set to "Ada", it returns this string. Because this is the last line in the name method, the method also returns this string.

  • For that reason, the person.name method call returns the "Ada" string, which is then passed to puts, which prints it out.

What are attribute readers?

Methods that do nothing else but return a value assigned to an instance variable with the same name, called attribute readers, are very common.

By attribute, the Ruby community means an instance variable, so an attribute reader is a method that reads an instance variable.

Remember: An attribute reader returns the value of an instance variable.

Another way of looking at this is that an attribute reader is a method that exposes an instance variable. That is, it makes it accessible for others. It allows us to ask for the value of an instance variable with the same name and does nothing but return its value. Once defined, others can ask this object for knowledge that otherwise would be private and inaccessible.

In our case, the name attribute reader exposes the @name instance variable so others can ask for it.

Remember: An attribute reader exposes an instance variable.

It’s unclear why “attribute” was the chosen term. It would be much less confusing to use the term “instance variable reader” instead. Maybe the simple reason is that programmers don’t like to type more than necessary, and this saves eight characters. Who knows?