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How to create a class setter and why you should.

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Class Setters.docx
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Quick reference

Class Setters

To set things in a class, use a setter.

When to use

Use a setter whenever you create a getter in a class.

Instructions

To create a setter in a class:

class Square
    def initialize(side_length)
        @side_length = side_length
    end
    
    # Create Getter
    def side_length
        return @side_length
    end

    # Create Setter
    def side_length=(side_length)
        @side_lenght = side_length
    end
end

 

Hints & tips

  • Setters let you set things in a class.
  • To name your setter method, use your same instance variable name, but put an equal sign on it.
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  • 00:04 In the last video, we looked at getters, in this video, I want to look at setters,
  • 00:09 and that's just S-E-T-T-E-R-S.
  • 00:11 So you can imagine what a setter does if a getter gets something,
  • 00:14 a setter sets something.
  • 00:16 So in our little class here, all we have here is this side length.
  • 00:20 And when we create our instance, when we instantiate
  • 00:24 our class at the beginning here with the mysquare = square.new with a 20,
  • 00:28 we're telling it right now, pass in 20 as the side length.
  • 00:32 And that's fine, later on we can use our getter to return that value if we want.
  • 00:37 But what if later on, we change our mind and we want to set it to something else?
  • 00:41 Well, you need to use a setter for that, so
  • 00:43 you need to define a setter as one of your methods inside your class.
  • 00:47 So it's pretty simple, it's just like all the other methods we've created.
  • 00:51 You start with define and then you name it.
  • 00:54 So again, you want to use the same name that you used as your parameter up there.
  • 00:59 So side_length,
  • 01:01 the difference is because we've already used side_length as a getter right here.
  • 01:05 We've already named this method, you can't have two methods with the same names, but
  • 01:09 you put an equal to sign because we are assigning something new to side_length.
  • 01:14 Remember, our assignment operator from way back at the beginning of the course,
  • 01:17 same thing here we're assigning something new, but
  • 01:19 we add it right to the name of the method.
  • 01:22 Don't do that with the space that won't work,
  • 01:25 it has to actually be touching, right?
  • 01:26 So then we pass in the parameter, it's the same thing,
  • 01:30 we want to do side length.
  • 01:32 Keep the parameter name the same throughout.
  • 01:34 And now we can end our method, and inside of here
  • 01:39 we just set @side_length = side_length.
  • 01:45 So this side_length is this
  • 01:49 side_length's parameter that we're passing into our setter.
  • 01:53 And our setter is called side_length=, you could probably do that,
  • 01:58 that would work too.
  • 01:59 I tend to them together just to remind myself that this is a setter, and
  • 02:02 in fact, I might
  • 02:06 use a comment here, because we're starting to get a little complicated here,
  • 02:09 things are starting to run together.
  • 02:13 All right?
  • 02:15 So okay, so we've got our setter created, how do we use it?
  • 02:18 Well, we come down here and we've instantiated our class.
  • 02:22 And if I comment that out, all we have to do is go
  • 02:25 my_square.side_length =, let's say, 5.
  • 02:32 So actually, let's go puts my_square and that's puts it again beneath it.
  • 02:39 So we're going to start out with our class, and our sides are going to
  • 02:43 be 20 each, and then we're going to put that out, we'll see if that's true.
  • 02:47 And then we're going to change it, we're going to set it to 5.
  • 02:50 Save this and see if it works correctly.
  • 02:52 So your square has a side length of 20.
  • 02:55 And then we set it to 5, and output it, your square now has a side length of 5, so
  • 02:59 we can change these things on the fly in the future.
  • 03:02 We can do it from outside of our class, but we do it with this setter.
  • 03:06 So those are setters, those are getters, in the next video,
  • 03:09 we're going to talk about the attr_accessor.

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