Cannot return a vector slice - ops::Range is not implemented

Question

Why does the following Rust code give an error?

fn getVecSlice(vec: &Vec, start: i32, len: i32) -> &[f64] {
    vec[start..start + len]         


        

Answer 1

Why do we need usize:

usize gives you the guarantee to be always big enough to hold any pointer or any offset in a data structure, while u32 can be too small on some architectures.

As an example, on a 32 bit x86 computer, usize = u32, while on x86_64 computers, usize = u64.

Answer 2

The error messages tells you that you can't index into a vector with values of type u32. Vec indices have to be of type usize, so you have to cast your indices to that type like this:

vec[start as usize..(start + len) as usize]

or just change the type of the start and len arguments to usize.

You also need to take a reference to the result:

&vec[start as usize..(start + len) as usize]