Default values through inheritance

Language Design
1

Hey there, default values are easy to use with functions,… I tried using them with Classes instead through inheritance and its not working… Is it a feature that only works for functions?

packagesomething.objectorientedprograming

open class Shape(open val name:String)
{
open fun area() = 0.0
}

class Circle(override val name : String = "Big circle" , val radius : Double) : Shape(name) 
{
override fun area(): Double  = Math.PI * Math.pow(radius, 2.0)
}
fun main(args: Array<String>) {
// Use inheritance...
val smallCircle = Circle(7.0)  // TRIED TO USE DEFALUT VALUE HERE...

// properties from object
println(smallCircle.name)
println(smallCircle.radius)

// get area
println("The area is: ${smallCircle.area()}")
}

Is there a specific reason this feature does not work with classes?

2

Default parameters must be last in the function (or constructor) invocation. If you swap the order of name and radius in the Circle constructor it should all work.

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3

That worked : yes, true true, so many rules to look into but al get it… Thanks alot @al3c :face_with_hand_over_mouth: :innocent: :face_with_hand_over_mouth: :innocent:

1 Like
4

al3c is correct, I would like to add a sugar to the story.

If, for some reason, the swapping of arguments is not an option (for example, this is a API already used), you can use named arguments for calling:

val smallCircle = Circle(radius = 7.0)

It’s my preference, but I often use named arguments in function calls even when it is not strictly required, when.

  • There are more than 4-5 arguments:
  • There are arguments of the same type
  • When I pass constant values instead of variables (I know IDEA helps here.)

These make reading the code much easier.

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