Part of the reason Java hasn't reified generics is because C# did and it was a real big headache that also limited non-C# languages on the C# runtime (CLI?). Everything had to be recompiled to work with newer C# runtimes. While it's pretty easy to run a bunch of language on the JVM (Javascript, python, ruby, clojure) doing the same for C# is somewhat a nightmare, particularly for non-type aware languages.

For example, Imagine you have an api like `void do(List<Foo> foos)`. In the erasure environment of the JVM that looks like `void do(List foos)`. From python it's pretty easy to call with a `foos = [Foo()]`. But not so much if your python implementation needs to figure out how and if it can coarse it's `List` type into a `List<Foo>` type.

The gotcha is the potential boxing of structs onto the heap, but that can be avoided using `ref struct`s.

https://news.ycombinator.com/item?id=48599273

Why would you presume the parent is "just handwaving"? It's odd how people in the .NET community struggle to earnestly engage in conversation with Java folk. The reverse isn't true.