如何实现采用带有生命周期注释的通用向量的结构？

Question

The following compiles fine:

pub struct Reader<'a> {
    position: uint,
    data: &'a [u8]
}

It's a reader that takes a vector (actually a slice) of type u8 as a reference, and I specify the lifetime.

However this is not exactly what I want. I want to be able to make the struct generic, and to be even more precise, I want to denote that the type should be a slice of anything. I tried this for starters:

pub struct Reader<'a, T> {
    position: uint,
    data: &'a T
}

It does not denote T to be a slice, but this is already failing with a message:

the parameter type T may not live long enough; consider adding an explicit lifetime bound T:'a ...

Ok so I just had to specify the lifetime.

But now my problem is that how do I make it generic of type slice and have the lifetime? I tried things like Reader<'a, T: 'a Vec> and T: 'a [T] but I have no idea how I am supposed to denote this and the official guide does not seem to deal with a case like this.

I simply want to construct a Reader that takes in any type of slice by borrowing it, and provides methods to operate on the data (in read-only ways).

Answer 1

After trying a bit more, I finally figured it out:

pub struct Reader<'a, T: 'a> {
    position: uint,
    data: &'a [T]
}

This defines the reader's data to be of type Slice<T> ( [] denotes the slice) and &'a specifies the lifetime for the borrowed data.

Now I can implement stuff like this:

impl<'a, T> Reader<'a, T> {
    pub fn from_data(bytes: &'a[T]) -> Reader<'a, T> {
        Reader {
            position: 0,
            data: bytes
        }
    }
}

Answer 2

Not intending to answer directly, it's just that I came across this SO answer when I was looking for an answer to my own problem: How to apply a generic type constraint and a lifetime constraint to a struct's field.

(Here's the working solution I came up with.)

use std::io::Writer;

// This specifies lifetime constraint of 'a
// Type W must implement the Writer trait
// Type W has the lifetime 'a (the same as the related struct instance)
pub struct Foo<'a, W: 'a + Writer> {
    writer: &'a mut W
}