Hi, When I write code like this on a setter function, I am getting the following error Type mismatch...

# announcements

[Sonu Sanjeev]

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

[ephemient]

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

[ephemient]

what do you expect to happen when you evaluate isRectangle = true or isRectangle = false?

[Sonu Sanjeev]

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("")

[ephemient]

or changing state, for example set(value) { field = value }

[Sonu Sanjeev]

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

[ephemient]

invert which boolean?

[Sonu Sanjeev]

isRectangle = true

[ephemient]

as in, you want the next isRectangle get() to return false? how could that work?

[James Whitehead]

Sounds like it would be better as a constructor parameter

[ephemient]

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

[James Whitehead]

Or use a method rather than a property

[ephemient]

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?

[Sonu Sanjeev]

My aim was to achieve the equivalent of

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

using "set(value) = " style.

[Sonu Sanjeev]

I have updated the get method to just return the field

[Sonu Sanjeev]

@ephemient @James Whitehead my aim here is to simply understand when to use "set(value) = " style of setter functions.

[Sonu Sanjeev]

The only usecase I can think for this style of assignment is this.

set(value) = throw Exception("Cannot set value")

[James Whitehead]

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.

[James Whitehead]

If the variable shouldn't be mutated at all, hence the need to throw an exception, you should just use val instead

[ephemient]

yes. make it a val (only getter) instead of throwing an exception in the setter.

[Sonu Sanjeev]

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