Generic Type Variable Bound
在 rust 中，泛型变量 T 是 &T 和 &mut T 的超集，而 &T 和 &mut T 是不相交集。
| Type Variable | Examples |
|---|---|
T |
i32, &i32, &mut i32, &&i32, &mut &mut i32 |
&T |
&i32, && i32, &&mut i32 |
&mut T |
&mut i32, &mut &mut i32, &mut &i32 |
T does not only contains owned types
T, &T, and &mut T are all infinite sets, since it's possible to borrow a type ad-infinitum. T is a superset of both &T and &mut T. &T and &mut T are disjoint sets.[1]