That definition,

override fun <List<String>> foo(t: List<String>) {}

, is trying to say the following:

foo

is a method that - given some type named

X

- performs an operation on a value of given type

X

.

All you're doing is replacing the name

X

with the name

List<String>

. But that name is invalid for type identifiers in Kotlin. That's the key, here. That's just a name, and it doesn't constrain the actual type of the function.