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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
  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 to_s
    full_name
  end      
end
  • 0:00

    A common idiom that Ruby programmers use when writing classes and

  • 0:04

    instances is to use the to_s method.

  • 0:08

    This method is a convention, and

  • 0:10

    is called by Ruby when an object wants to be formatted as a string.

  • 0:16

    Let's see how that works now with the name class using workspaces.

  • 0:21

    Okay, so here's our name class and

  • 0:24

    it's just like before except I took out the attribute reader for

  • 0:29

    first and middle name and put it back to what we have before with full name.

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    Now let's take a look at what happens when we print out just the name so

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    I'm gonna write ruby name.rb.

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    And we see that we get this funny little format right here,

  • 0:48

    which is the name of the class and its address in memory.

  • 0:53

    Whenever we print something out to the screen using the puts method,

  • 0:59

    internally Ruby is calling to string on it or to_s.

  • 1:04

    And we can override that in our classes if we want to.

  • 1:07

    [BLANK_AUDIO]

  • 1:15

    So if we look here, we've got this to_s method.

  • 1:19

    And let's just have this print out the full name with the title.

  • 1:23

    [BLANK_AUDIO]

  • 1:28

    Now when to_s is called is should print out the full name.

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    And there we go.

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    It can be very useful when you're working with your own classes to

  • 1:40

    define a to_s method.

  • 1:44

    Another method that we could use if we wanna find out

  • 1:46

    a little bit more about the object we're working with is the inspect method.

  • 1:53

    Inspect will tell you the internal state of the object that you’re working with.

  • 1:59

    So here we can see the same thing as before, it’s the name class.

  • 2:04

    And the place in memory or the object ID.

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    And we also have a listing of all of the internal instance variables

  • 2:13

    of the class as well as their values.

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