How to Use fold and reduce in Rust

Use fold to accumulate a value by iterating over a collection and reduce to combine all elements into a single value without an initial accumulator.

let numbers = vec![1, 2, 3, 4];

// fold: starts with 0, adds each number
let sum_fold: i32 = numbers.iter().fold(0, |acc, &x| acc + x);

// reduce: combines elements pairwise, no initial value
let sum_reduce: Option<i32> = numbers.iter().reduce(|acc, &x| acc + x);

println!("Fold: {}, Reduce: {:?}", sum_fold, sum_reduce);

Think of fold as a bucket you start with a specific amount of water and pour more into as you go. reduce is like mixing two ingredients together repeatedly until only one final mixture remains. You use fold when you need a starting point and reduce when you want to combine everything in a list into one result.