Instantiating a generic type in Kotlin

Question

What's the best way to get an instance of a generic type in Kotlin? I am hoping to find the best approximation of the following C# code:

public T GetValue<T>() where T : new() {     return new T(); } 

Answer 1

EDIT: As mentioned in comments, this is probably a bad idea. Accepting a () -> T is probably the most reasonable way of achieving this. That said, the following technique will achieve what you're looking for, if not necessarily in the most idiomatic way.

Unfortunately, you can't achieve that directly: Kotlin is hamstrung by its Java ancestry, so generics are erased at run time, meaning T is no longer available to use directly. Using reflection and inline functions, you can work around this, though:

/* We have no way to guarantee that an empty constructor exists, so must return T? instead of T */ inline fun <reified T : Any> getValue(): T? {     val primaryConstructor = T::class.constructors.find { it.parameters.isEmpty() }     return primaryConstructor?.call() } 

If we add some sample classes, you can see that this will return an instance when an empty constructor exists, or null otherwise:

class Foo() {} class Bar(val label: String) { constructor() : this("bar")} class Baz(val label: String)      fun main(args: Array<String>) {     System.out.println("Foo: ${getValue<Foo>()}") // Foo@...     // No need to specify the type when it can be inferred     val foo : Foo? = getValue()     System.out.println("Foo: ${foo}") // Foo@...     System.out.println("Bar: ${getValue<Bar>()}") // Prints Bar@...     System.out.println("Baz: ${getValue<Baz>()}") // null }