Hi, When I write code like this on a setter function, I am getting the following error Type mismatch. "*Required: Unit, Found: Boolean*".

var isRectangle: Boolean
        get() = field
        set(value) = value.not()  // The error is here

How is it possible to return a Unit type when we use a syntax like "set(value) = " . Thanks in Adavance

a setter function is expected to have side effects only, no return value (hence Unit)

So is this type of syntax for setter only used for side effects?. I believe when you say side effect, it means something like throwing an exception on setter?

set(value) = throw Exception("")

or changing state, for example

set(value) { field = value }

Here my aim was to just invert the boolean value using "set(value) = " style of setter

invert which boolean?

isRectangle = true

as in, you want the next

isRectangle get()

to return false? how could that work?

Sounds like it would be better as a constructor parameter

a getter for a computed property makes sense, but a setter… much rarer

Or use a method rather than a property

since `isRectangle`'s observed value is always based on

width

and

height

, do you expect setting it to somehow change

width

and

height

to "correct" the computed value of

isRectangle

?

My aim was to achieve the equivalent of

set(value) {
    field = value.not()
}

using "set(value) = " style.

Personally I've not come across a real world use-case for such a thing. As an aside, rather than throwing an exception in your example, it is possible to simply declare the setter as private.

yes. make it a

val

(only getter) instead of throwing an exception in the setter.

Thank you @ephemient @James Whitehead. I was just trying to understand how and when to use different styles of property setters in kotlin.