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Ruby Objects and Classes

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The to_s method

2:16 with Jason Seifer

A common idiom that Ruby programmers use when writing classes is to define a `to_s` method, which tells Ruby how to print out a class.

Code Samples

class Name
  attr_accessor :title, :first_name, :middle_name, :last_name

  def initialize(title, first_name, middle_name, last_name)
    @title = title
    @first_name = first_name
    @middle_name = middle_name
    @last_name = last_name
  end

  def full_name
    @first_name + " " + @middle_name + " " + @last_name
  end

  def full_name_with_title
    @title + " " + full_name()
  end

  def to_s
    full_name_with_title
  end

end

name = Name.new("Mr.", "Jason", "", "Seifer")
puts name.full_name_with_title
puts name
puts name.inspect

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    A common idiom that Ruby programmers use when writing classes and 0:00
    instances is to use the to_s method. 0:04
    This method is a convention, and 0:08
    is called by Ruby when an object wants to be formatted as a string. 0:10
    Let's see how that works now with the name class using workspaces. 0:16
    Okay, so here's our name class and 0:21
    it's just like before except I took out the attribute reader for 0:24
    first and middle name and put it back to what we have before with full name. 0:29
    Now let's take a look at what happens when we print out just the name so 0:33
    I'm gonna write ruby name.rb. 0:38
    And we see that we get this funny little format right here, 0:43
    which is the name of the class and its address in memory. 0:48
    Whenever we print something out to the screen using the puts method, 0:53
    internally Ruby is calling to string on it or to_s. 0:59
    And we can override that in our classes if we want to. 1:04
    [BLANK_AUDIO] 1:07
    So if we look here, we've got this to_s method. 1:15
    And let's just have this print out the full name with the title. 1:19
    [BLANK_AUDIO] 1:23
    Now when to_s is called is should print out the full name. 1:28
    And there we go. 1:34
    It can be very useful when you're working with your own classes to 1:36
    define a to_s method. 1:40
    Another method that we could use if we wanna find out 1:44
    a little bit more about the object we're working with is the inspect method. 1:46
    Inspect will tell you the internal state of the object that you’re working with. 1:53
    So here we can see the same thing as before, it’s the name class. 1:59
    And the place in memory or the object ID. 2:04
    And we also have a listing of all of the internal instance variables 2:07
    of the class as well as their values. 2:13

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