'reified' constructor type parameters ? Possible ? I have a set of classes that use reflection and r...

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[DALDEI]

'reified' constructor type parameters ? Possible ?
I have a set of classes that use reflection and require the KClass object for the 'type' of the class - this is a GUI class that shows a list or edit form for a type.
Rougly:

class BaseView<T>( val kclass : KClass<T> ) {
}

class FormView : BaseView<AFormType>( AFormType::class ) { ... }

I'd like to get rid of either the need for the constructor parameter and/or the need to explicitly pass it
e.g. this would be nice

class BaseView<T>( val kclass : KClasss<T> = T::class ) // inline constructor<reified T> ???

Is this possible ?

I can make a function that does this but I cant derive from it -- (?)

fun <reified T> BaseView() = BaseView<T>(T::class)

--> but how to derive ?

Any suggestions ?

[Andrea Giuliano]

reified is not supported in constructors (yet)

[DALDEI]

Yes. Is there an alternative way to achive something similar ?

[Andrea Giuliano]

what you can do is, you can accept KClass (or java class) in the constructor

[DALDEI]

Yes. Thats what Im doing. Would like to avoid that.
A class delegate by function might work but its not the same and would require interfaces --

class View<T>: BaseView<T> by reifiedFunction<T>() {

}

[DALDEI]

If that worked then so would a constructor default value by reified function

[Andrea Giuliano]

the only thing you can do is create an extension function to achieve this. Something like

reified fun View()...

[DALDEI]

This see3ms to work --



abstract class X<T:Any>() {
val x : Int = 1
abstract fun getView() : KClass<T>
}

inline fun <reified T:Any> X<T>.view() = T::class

class Y : X<StatementJob>() {
override fun getView() = view()
}

[DALDEI]

Not exactly simplier -- but maybe a way to morph it into something

[streetsofboston]

You can use smart-constructors:

class MyClass private constructor(...) {

    companion object {
        inline operator fun <reified T> invoke(...): MyClass {
        }
    }
}

Then you can construct it still like this
val mc = MyClass(…), because it is the same as val mc = MyClass.invoke(…)

[DALDEI]

Yes. But that only works when the call is not the constructor itself.
I.e. you cant derive from a class that requires the type parameter and a class instance in the constructor,
So like my method, one has replace a bit of clumbsy boilerplate with a LOT of clumbsy boilerplate -- it didnt go away.

[DALDEI]

easier to make a global reified function of the same name -- for cases that you dont need it to be a 'constructor' literlly - just look like one in some cases.