Rust: What is the difference between fold and reduce?

fold — accumulate with initial value. reduce — accumulate without initial.

fold:

• Initial value required.
• Always returns.
• More general.

reduce:

• No initial value.
• Returns Option.
• For non-empty.

1let v = vec![1, 2, 3, 4, 5];
2
3// fold: 15
4let sum = v.iter().fold(0, |acc, &x| acc + x);
5
6// reduce: Some(15)
7let sum = v.iter().reduce(|acc, &x| acc + x);

Key: fold with initial, reduce without.