How does Kotlin support reification if it is not supported by JVM

# announcements

[kartikpatodi]

How does Kotlin support reification if it is not supported by JVM

[kartikpatodi]

Is clazz.newInstance() expensive?

[Czar]

What happens is the function is removed at compile time and code is inlined.
So if you had

inline fun <reified T> test(): Any {
    return T::class.java
}

println(test<String>())

in the compiled code you'll see something like

Class var1 = String.class;
System.out.println(var1);

[Czar]

This is why Kotlin can only reify params of inline functions.

[Czar]

as for the newInstance, yes it is more expensive than new Clazz()

[kartikpatodi]

Actually i have a custom list impl which requires to create instance in a fun call but I can't do a new T() is there any way ither than reflection?

PS it is a java+Kt proj

[Czar]

it's a bit hard for me to understand the requirements without seeing an example. Can you provide one?

[marstran]

@kartikpatodi Let your function or class know how to create the object by taking a lambda as a parameter. That will let you avoid reified generics. Something like this:

class SomeClass<T>(
  private val createT: () -> T
) {
    fun create(): T = createT()
}

[marstran]

Then you can instantiate your class like this: SomeClass<MyClass> { MyClass() }

[kartikpatodi]

Actually i have a use case where I have to create n instances inside the function but and i tried with reified but it is eventually creating Class object in the bytecode

[marstran]

But you can call that lambda as many times as you want.

[kartikpatodi]

But will it work with java code?

[marstran]

Yes. There's no magic involved 🙂

[marstran]

Instantiation in Java would be like this: new SomeClass<MyClass>(MyClass::new);

[kartikpatodi]

Ok I'll try with that

[kartikpatodi]

@Czar @marstran
Something like this
https://pl.kotl.in/Hy7UVZKYV
But better 😅

[marstran]

@kartikpatodi No, don't use the class object. No reflection is needed. Just do this instead: https://pl.kotl.in/HkEaqZYt4

[kartikpatodi]

Cool thanks @marstran

[kartikpatodi]

Only if java supported reified types like C#

[marstran]

I don't really get what you need the reified type for. 😉