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Ruby Build an Address Book in Ruby Class Design Phone Number Class

Posted by Muhammad Saif
Muhammad Saif
11,565 Points

What is the purpose of these line written in add_phone_number(kind, number) method?

In the add_phone_number method Jason write these lines.

  def add_phone_number(kind, number)
    phone_number = PhoneNumber.new
    phone_number.kind = kind
    phone_number.number = number
    phone_numbers.push(phone_number)
  end

What is the meaning and purpose of adding these two lines?

    phone_number.kind = kind
    phone_number.number = number

And by adding 

    phone_numbers.push(phone_number)

How does ruby know to interpret it as an array (phone_numbers.inspect shows that phone_numbers is an instance object which is not an array) as Jason uses the each method as below 

  def print_phone_numbers
    puts "Phone Numbers: "
    phone_numbers.each {|phone_number| puts phone_number}
  end

1 Answer

Jay McGavren
STAFF
Jay McGavren
Treehouse Teacher
Jay McGavren
Jay McGavren
Treehouse Teacher

What is the meaning and purpose of adding these two lines? phone_number.kind = kind; phone_number.number = number

In this code:

  def add_phone_number(kind, number)
    phone_number = PhoneNumber.new
    phone_number.kind = kind
    phone_number.number = number
    phone_numbers.push(phone_number)
  end

Basically, you're setting the kind and number attributes on a PhoneNumber object. In detail:

  • kind and number are parameters to the add_phone_number method.
  • phone_number.kind = calls the kind= method (yes, it's a method, I know that's weird) on the PhoneNumber instance (object) stored in the phone_number variable.
  • phone_number.number = calls the number= method on the PhoneNumber instance (object) stored in the phone_number variable.
  • The kind= and number= methods are attribute writer methods. When you call them, you set the @kind and @number instance variables on the PhoneNumber object.

So if I call add_phone_number("Home", "480-555-1212"), it first creates a PhoneNumber object with a kind of "Home" and a number of "480-555-1212".

And by adding phone_numbers.push(phone_number) How does ruby know to interpret it as an array (phone_numbers.inspect shows that phone_numbers is an instance object which is not an array)

Hmm, I'm a little surprised to hear that it doesn't show up as an array. Are you sure phone_numbers.class doesn't return Array? About the only way the push method would work is if it was an Array. Again, in detail, what I think is happening is this:

  • phone_numbers is an attribute reader method that should return an array.
  • Calling push(phone_number) on that array should add the PhoneNumber object to that array.
Muhammad Saif
Muhammad Saif
11,565 Points

Thank you! Your answer help me to understand more! And now I know that Jason is adding the PhoneNumber object to the array list!