Trait std::iter::Sum1.12.0[][src]

pub trait Sum<A = Self> {
    fn sum<I>(iter: I) -> Self
    where
        I: Iterator<Item = A>
; }
Expand description

Trait to represent types that can be created by summing up an iterator.

This trait is used to implement the sum() method on iterators. Types which implement the trait can be generated by the sum() method. Like FromIterator this trait should rarely be called directly and instead interacted with through Iterator::sum().

Required methods

Method which takes an iterator and generates Self from the elements by “summing up” the items.

Implementors

Takes each element in the Iterator: if it is a None, no further elements are taken, and the None is returned. Should no None occur, the sum of all elements is returned.

Examples

This sums up the position of the character ‘a’ in a vector of strings, if a word did not have the character ‘a’ the operation returns None:

let words = vec!["have", "a", "great", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, Some(5));
Run

Takes each element in the Iterator: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, the sum of all elements is returned.

Examples

This sums up every integer in a vector, rejecting the sum if a negative element is encountered:

let v = vec![1, 2];
let res: Result<i32, &'static str> = v.iter().map(|&x: &i32|
    if x < 0 { Err("Negative element found") }
    else { Ok(x) }
).sum();
assert_eq!(res, Ok(3));
Run