How do I sum a vector using fold?

Question

This Rust tutorial explains the fold() mechanism well, and this example code:

let sum = (1..4).fold(0, |sum, x| sum + x);

work

Answer 1

So it turned out there was a huge difference in my code, as I wrote

sum += x

instead of

sum + x.

Well, at least I hope this question helps, in case someone gets into similar situation.