```rust
struct MyError<U> {
    Foo,
    Bar,
    Uart(U),
}

struct MyDriver<U: Read+Write> {
    uart: U
}

impl<U: Read+Write> MyDriver<U> {
    fn foo(&mut self) -> Result<(), MyError<U::Error>> {
        self.uart.read(..).map_err(MyError::Uart)?;
        Ok(())
    }
}