Internal type variables don't work

[vigna]

The derive macros currently don't work with

struct Data<A> {
    a: Vec<A>,
    test: isize,
}

You need at least

struct Data<A: DeepCopy> {
    a: Vec<A>,
    test: isize,
}

to explain how to behave with Vec, but then there's a lifetime problem and if you try

struct Data<A> {
    a: Vec<A>,
    test: isize,
}

You get "higher-ranked lifetime error".