Getting Class of list with generic eg: List<Number>::class

Question

I have a generically typed class Builder<T> that takes a constructor argument Class<T> so I can keep the type around. This is a class that I use a lot in java code so I don't want to change the signature. When I try to use the constructor like this:

Builder<List<Number>>(List<Number>::class)

I get an error: "Only classes are allowed on the left hand side of a class literal"

Any way to resolve this? I can't change the constructor for Builder, too many java classes rely upon it.

I understand the whole type erasure issue, I really just want to make the compiler happy.

Answer 1

Due to generic type erasure List class has a single implementation for all its generic instantiations. You can only get a class corresponding to List<*> type, and thus create only Builder<List<*>>.

That builder instance is suitable for building a list of something. And again due to type erasure what that something is you can decide by yourself with the help of unchecked casts:

Builder(List::class.java) as Builder<List<Number>> Builder(List::class.java as Class<List<Number>>) 

Another approach is to create inline reified helper function:

inline fun <reified T : Any> Builder() = Builder(T::class.java) 

and use it the following way:

Builder<List<Number>>()