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iOS Object-Oriented Swift Properties Computed Properties

Cannot complete Object-Oriented Swift code challenge

The Challenge Task says, Assume you are creating a Weather app and are provided the temperature in Celsius. We need to create a computed property called Fahrenheit which will return a computed value. (Note: Fahrenheit = (Celsius * 1.8) + 32)

Here is my code. In Xcode I get no errors, is there something I'm missing?

Temperature.swift
class Temperature {
    var celsius: Float = 0.0
    var fahrenheit: Float {
       return (celsius * 1.8) + 32
       }

       init(celsius: Float) {
       self.celsius = celsius
       }
}
let celsiusConverstionTo = Temperature(celsius: 37.0)
celsiusConversionTo.fahrenheit

The Code Challenge after that

We need to add getter and setter methods to the fahrenheit property of the Temperature class. Add a getter method to the access the value of the fahrenheit property. Then add a setter method. When the user assigns a value to the fahrenheit property, the setter method will calculate and assign a value to the celsius property. (Note: Celsius = (Fahrenheit-32)/1.8))

Here's my code:

class Temperature {
    var celsius: Float = 0.0
    var fahrenheit: Float {
       get{
       return (celsius * 1.8) + 32
       }
       set {
       celsius = (fahrenheit-32)/1.8
       }
    }    
}

Which gives the error:

Bummer! The setter method for fahrenheit did not assign the right value to the celsius property. (Note: Celsius = (Fahrenheit-32)/1.8)

6 Answers

Chris Shaw
Chris Shaw
26,650 Points

Hi Leviticus,

This task has caught a few people off guard mainly because of the random fahrenheit occurrence which doesn't actually belong there, if you remember back in the previous video Amit shows us a variable that's scoped to the set method on the computed variable called newValue.

Instead of fahrenheit we want to use newValue instead.

class Temperature {
  var celsius: Float = 0.0
  var fahrenheit: Float {
    get{
      return (celsius * 1.8) + 32
    }
    set {
      celsius = (newValue - 32) / 1.8
    }
  }    
}

Happy coding!

How does the program know the newValue will be the fahrenheit?

I had code like this

class Temperature {
    var celsius: Float = 0.0
    var fahrenheit: Float {
        get {
            return (celsius * 1.8) + 32.0
        }

        set {
            self.fahrenheit = newValue
            celsius = ((fahrenheit - 32) / 1.8)
        }

    }
}

Can you explain why my code wouldn't work (i guess the exercise is checking for only that answer) and how the 'newValue' knows that it belongs to fahrenheit?

Srinivasan Senthil
Srinivasan Senthil
2,266 Points

We have to use the newValue. The newValue holds the value of fahrenheit now. i.e. Once the get method is completed executing.

After the get method is completed, the code moves to the set method. Under the set method, it needs the value of fahrenheit to be subtracted from 32. The variable that holds the fahrenheit is newValue.

Consider the get method as computed property under video Transcript.

Read these lines on getter and setter methods. "The other thing you'll wanna note is that this is a read only property, 1:15 which means that we cannot assign a value here. 1:18 There is no underlying storage mechanism to store this value.

This is my understanding.

So the only thing that has the Fahrenheit value is newValue.

Yuda Leh
Yuda Leh
7,618 Points

We haven't done the set method, so....

Gahh.. Good Man! Thanks Chris, you don't happen to have the solution to the first Challenge as well do you?

Chris Shaw
Chris Shaw
26,650 Points

The first challenge is the same as above with the minor difference that get and set aren't defined yet.

class Temperature {
  var celsius: Float = 0.0
  var fahrenheit: Float {
    return (celsius * 1.8) + 32
  }    
}
Susanna Remec
Susanna Remec
12,316 Points

Hi, I had the same error. The keyword newValue was the answer that worked for me.

rd. ln.
rd. ln.
7,851 Points

god. i keep getting

There was a communication problem.

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this is SO incredibly frustrating.