CODEWITHSUNDEEP
javakotlinconstructor
Pau Garcia Gozàlvez
Pau Garcia Gozàlvez

Reputation: 381

Is there a way to inherit constructors in Kotlin?

I have a Parent class which is extended by a lot of childs and I want to avoid to copy the long constructor in each of them because it is always the same.

open class Parent(arg1: Any, arg2: Any, arg3: Any...)

class ChildA(arg1: Any, arg2: Any, arg3: Any...): Parent(arg1, arg2, arg3...)
class ChildB(arg1: Any, arg2: Any, arg3: Any...): Parent(arg1, arg2, arg3...)
[...]

Is there a way to inherit the constructor or maybe a function implemented on the Parent that instantiates a Child class?

Edit

My expectation is to implement the Child classes without having to define its constructor. The reason is that I have about 15 childs and each parameter have an optional value, so the resulting code is not so pretty.

Upvotes: 16

Views: 8446

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170723

If it's always the same (or only extended), you can create a class for holding the parameters:

data class ConstructorParams(arg1: Any, arg2: Any, arg3: Any...)

open class Parent(params: ConstructorParams)

class ChildA(params: ConstructorParams) : Parent(params)

class ChildB(params: ConstructorParams, extraParam: Int) : Parent(params)

You could add to it a helper function to avoid explicit ConstructorParams when instantiating the classes, but it has a performance trade-off (though this version won't work for Child2):

inline fun <reified T : Parent> create(arg1: Any, arg2: Any, arg3: Any...) = 
    T::class.primaryConstructor.call(ConstructorParams(arg1, arg2, ...))

create<Parent>(1, 2, "")

Upvotes: 10

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