How to sum the values in an array, slice, or Vec in Rust?

问题

Editor's note: This question's example is from a version of Rust prior to 1.0 and references types and methods no longer found in Rust. The answers still contain valuable information.

The following code

let mut numbers = new_serial.as_bytes().iter().map(|&x| (x - 48));
let sum = numbers.sum(); 

results in the following error:

std::iter::Map<,&u8,u8,std::slice::Items<,u8>>` does not implement any method in scope named `sum`

What must I do to sum an array of bytes?

The following works:

for byte in new_serial.as_bytes().iter() {
    sum = sum + (byte - 48);
}

回答1:

Iterator::sum was stabilized in Rust 1.11.0. You can get an iterator from your array/slice/Vec and then use sum:

fn main() {
    let a = [1, 2, 3, 4, 5];
    let sum: u8 = a.iter().sum();
    println!("the total sum is: {}", sum);
}

Of special note is that you need to specify the type to sum into (sum: u8) as the method allows for multiple implementations. See Why can't Rust infer the resulting type of Iterator::sum? for more information.

---

Applied to your original example:

let new_serial = "01234";
let sum: u8 = new_serial.as_bytes().iter().map(|&x| x - 48).sum();
println!("{}", sum);

As an aside, it's likely more clear if you use b'0' instead of 48.

来源：https://stackoverflow.com/questions/23100534/how-to-sum-the-values-in-an-array-slice-or-vec-in-rust