some elegant solution for allocating a not nullable array as kotlinlang #announcements

some elegant solution for allocating a not-nullable array as buffer for a generic ringBuffer implementation since I cant use inline reified? The only option I see is to pass down as argument the class itself

diesieben07

06/12/2019, 9:26 AM

Why can't you use

inline

reified

exactly?

elect

06/12/2019, 9:27 AM

class SteamVR_RingBuffer<T>(clazz: Class<T>, size: Int) {

    protected val buffer = Array(size) {
        clazz.getDeclaredConstructor().newInstance() }

only functions can be reified

diesieben07

06/12/2019, 9:28 AM

You can extend that class as follows:

companion object {
  inline operator fun <reified T : Any> invoke() = SteamVR_RingBuffer(T::class)
}

😮 1

elect

06/12/2019, 9:28 AM

uh nice

diesieben07

06/12/2019, 9:28 AM

Then you can use both the reified "fake constructor" or the normal one

elect

06/12/2019, 9:29 AM

thanks man

another thing @diesieben07

compiler complains about

here

class SteamVR_RingBuffer<T : Any>(val clazz: Class<T>, size: Int) {

    val default: T
        get() = clazz.getDeclaredConstructor().newInstance()

    protected val buffer = Array(size) { default }

cant use T as reified parameter, use a class instead

but it doesnt look it accepts

clazz

either

diesieben07

06/12/2019, 9:39 AM

Yeah, you probably shouldn't use

Array<T>

. Arrays are weird on the JVM in that

Array<String>

and

Array<Any>

are completely different classes (every element type has it's own class)

You should probably use

Array<Any>

and insert appropriate casts at the appropriate places.

That is what things like

ArrayList

do inside, too.

elect

06/12/2019, 9:40 AM

uhm, ok

cbruegg

06/12/2019, 9:48 AM

Or just use a list as the buffer?

elect

06/12/2019, 9:48 AM

arrays shall be better for performances

cbruegg

06/12/2019, 9:49 AM

Sidenote: The standard naming convention would be

SteamVRRingBuffer

elect

06/12/2019, 9:49 AM

I know, but it's a port

cbruegg

06/12/2019, 9:50 AM

Did you measure whether it actually gives a performance advantage? An

ArrayList

is, as the name implies, backed by an array and should give similar performance.

elect

06/12/2019, 9:50 AM

no, I always read about it around

cbruegg

06/12/2019, 9:50 AM

The JVM is also pretty good at inlining methods in hot code

I'd just use a list and only if that hurts performance use a raw array

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