Will using this with the `as`s componentX and type params ge

Question

Will using this with the `as`s componentX and type params get the array boxed ``` JvmInline value class MethodParams1 lt A1 gt val value Array lt Any gt operator fun component1 = value 0 as A1 var arg1 A1 get = value 0 as A1 set value this value 0 = value ```

Joffrey · Answer

In general it s the usage of `MethodParams1` that will decide this not the implementation To check a particular piece of code you can try to decompile it to Java with the IDE For instance you can try with this code ```fun main val params = MethodParams1 lt String gt arrayOf bob fred println params component1 println params arg1 ``` Which is decompiled this way ```public final class ValueClassExampleKt public static final void main Object params = MethodParams1 constructor impl new Object bob fred Object var1 = MethodParams1 component1 impl params System out println var1 var1 = MethodParams1 getArg1 impl params System out println var1 $FF synthetic method public static void main String var0 main ``` As you can see the array is not boxed into a `MethodParams1` instance

Joffrey · Answer

But if you intend to use this approach for other elements in the underlying array why not just use a class with properties instead Are you wrapping an existing array that you get from somewhere else with type safety

dave08 · Answer

Exactly and I m afraid to box it for performance reasons

dave08 · Answer

What s these lines ```Object params = MethodParams1 constructor impl new Object bob fred Object var1 = MethodParams1 component1 impl params ```

dave08 · Answer

That s not being boxed

dave08 · Answer

Oh the ` Object var1 = MethodParams1 component1 impl params ` is the function even though I m really not doing much there

dave08 · Answer

But it seems like a new instance IS still being created but not used `Object params = MethodParams1 constructor impl new `

dave08 · Answer

Yup you re right ``` NotNull public static Object constructor impl $FF was constructor impl NotNull Object value Intrinsics checkNotNullParameter value value return value ```

dave08 · Answer

Doesn t box but calls that method

dave08 · Answer

Seems like this usage with componentX decomposition seems to get boxed but using inline all over doesn t box for direct access and doesn t even call any functions ``` JvmInline value class MethodParamsO lt A1 gt val value Array lt Any gt inline operator fun component1 = value 0 as A1 var arg1 A1 inline get = value 0 as A1 inline set value this value 0 = value fun process paramsO MethodParamsO lt String gt block MethodParamsO lt String gt gt Unit block paramsO fun main val params = MethodParamsO lt String gt arrayOf this 0 process params foo gt println process $foo println params arg1 params arg1 = this2 println params arg1 ```

dave08 · Answer

```public static final void process IC3gMN4 $FF was process IC3gMN4 NotNull Object paramsO NotNull Function1 block Intrinsics checkNotNullParameter paramsO paramsO Intrinsics checkNotNullParameter block block block invoke MethodParamsO box impl paramsO public static final void main Object params = MethodParamsO constructor impl new Object this 0 process IC3gMN4 params Function1 null INSTANCE int $i$f$getArg1 = false Object var1 = params 0 System out println var1 Object value$iv = this2 int $i$f$setArg1 = false params 0 = value$iv $i$f$getArg1 = false var1 = params 0 System out println var1 ```

dave08 · Answer

Even though component1 makes this static method ```public static final Object component1 impl $FF was component1 impl Object $this int $i$f$component1 = 0 return $this 0 ``` Is there any way to avoid that < Joffrey>

Joffrey · Answer

gt MethodParams1 constructor impl gt That s not being boxed gt Doesn t box but calls that method Regarding `constructor impl` this is the body of the `MethodParams1` constructor This is what allows you to write initialization code in `init` blocks in your value class This is really not a concern at all for performance gt it seems like a new instance IS still being created but not used `Object params = MethodParams1 constructor impl new ` Only one instance of the array is created it s the `arrayOf` function that creates the initial array but the body of `constructor impl` does not return a new array it returns the same array

Joffrey · Answer

gt Seems like this usage with componentX decomposition seems to get boxed The reason for boxing in your snippet is not due to decomposition methods it s because you re using `MethodParams0` as a generic type argument in `Function1` because you use it in `block MethodParamsO lt String gt gt Unit` Avoiding boxing is not easy As a rule of thumb boxing will happen each time you use the value class as another type this means each time it s assigned to a variable of a parent type or used in a generic type where a generic type parameter is expected like in `Function1 invoke T `

dave08 · Answer

Is there any way to avoid that in my case

dave08 · Answer

I need to pass MethodParams as the param of a lambda and I need the type safety within the lambda itself for property access

Joffrey · Answer

What exactly are you trying to avoid by keeping this array Depending on your use case I would advise to consider mapping the array into a class with fields It wouldn t box the array because there will be no array so there will not be 2 indirections to access fields However it will create a second object but that really isn t an issue in general hence my question

dave08 · Answer

I m really trying to add compile time type safety to work being done with reflected class access but it could get pretty heavy by creating a new object for each instance I need type safety for

dave08 · Answer

But then maybe your right if anyways there s no way to do this with value classes without them getting boxed what you re proposing is the next best solution

Joffrey · Answer

If you re using reflection in the first place you ve already given up on performance so I don t believe creating an instance out of an array will be a concern here

Joffrey · Answer

gt if anyways there s no way to do this with value classes without them getting boxed I don t see one but maybe I m missing something

dave08 · Answer

Ok thanks

ephemient · Answer

the MethodHandle invokeExact etc added in Java 7 do allow for reflective calls without boxing if you really need to squeeze performance out of it

ephemient · Answer

but yeah if you re just using classic reflection then I don t think there s much point whatever you do is not going to make a major impact on performance