Cursor<SmallVec<[u8; N]>> does not implement Write

[rivertam]

I'd be pretty surprised if this weren't implemented for no good reason, but why is SmallVec not a Read? I'd like to be able to use it with the byteorder create like this:

    let mut cursor = std::io::Cursor::new(SmallVec::<[u8; 8]>::new());
    cursor.write_u16::<LittleEndian>(rand::random()).unwrap();
    cursor.write_u16::<LittleEndian>(rand::random()).unwrap();
    cursor.write_u16::<LittleEndian>(rand::random()).unwrap();
    cursor.write_u16::<LittleEndian>(rand::random()).unwrap();

    cursor.set_position(0);

    cursor.read_f64::<LittleEndian>().unwrap()

but this requires that SmallVec implement the Read trait.

[mbrubeck]

Cursor<SmallVec<[u8; 8]>> already implements the Read trait, thanks to this generic implementation in libstd:

impl<T> Read for Cursor<T> where T: AsRef<[u8]>

However, Cursor<SmallVec> does not implement the Write trait, since there's no similar generic implementation. Fortunately you don't need a Cursor to write to a SmallVec. You can do this:

    let mut v = SmallVec::<[u8; 8]>::new();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();

    let mut cursor = Cursor::new(v);
    cursor.read_f64::<LittleEndian>().unwrap()

or even this, since &[u8] implements Read without needing a Cursor:

    let mut v = SmallVec::<[u8; 8]>::new();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();
    v.write_u16::<LittleEndian>(rand::random()).unwrap();

    v.as_slice().read_f64::<LittleEndian>().unwrap()

[rivertam]

@mbrubeck Thanks! The error messages I got here were a little confusing because they seemed to imply it was a read problem, not a write problem.