I tried something like this today, and it failed to compile:

fn ret_ref<'a>(x:&'a mut Vec<u8>)->&'a[u8]{
    x.as_ref()
}

error[E0515]: cannot return value referencing function parameter `x`
 --> src/lib.rs:2:5
  |
2 |     x.as_ref()
  |     -^^^^^^^^^
  |     |
  |     returns a value referencing data owned by the current function
  |     `x` is borrowed here

This however works fine:

fn ret_ref<'a>(x:&'a mut Vec<u8>)->&'a[u8]{
    (&*x).as_ref()
}

I am guessing that one refers to <&Vec<u8> as AsRef> and the other to <&mut Vec<u8> as AsRef>.

Indeed, this also fails:

fn ret_ref<'a>(x:&'a mut Vec<u8>)->&'a[u8]{
    (&mut *x).as_ref()
}

Why are they different?

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