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.