2 use crate::num::Wrapping;
3 use crate::ops::{Add, Mul};
5 /// Trait to represent types that can be created by summing up an iterator.
7 /// This trait is used to implement the [`sum`] method on iterators. Types which
8 /// implement the trait can be generated by the [`sum`] method. Like
9 /// [`FromIterator`] this trait should rarely be called directly and instead
10 /// interacted with through [`Iterator::sum`].
12 /// [`sum`]: #tymethod.sum
13 /// [`FromIterator`]: crate::iter::FromIterator
14 /// [`Iterator::sum`]: crate::iter::Iterator::sum
15 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
16 pub trait Sum<A = Self>: Sized {
17 /// Method which takes an iterator and generates `Self` from the elements by
18 /// "summing up" the items.
19 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
20 fn sum<I: Iterator<Item = A>>(iter: I) -> Self;
23 /// Trait to represent types that can be created by multiplying elements of an
26 /// This trait is used to implement the [`product`] method on iterators. Types
27 /// which implement the trait can be generated by the [`product`] method. Like
28 /// [`FromIterator`] this trait should rarely be called directly and instead
29 /// interacted with through [`Iterator::product`].
31 /// [`product`]: #tymethod.product
32 /// [`FromIterator`]: crate::iter::FromIterator
33 /// [`Iterator::product`]: crate::iter::Iterator::product
34 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
35 pub trait Product<A = Self>: Sized {
36 /// Method which takes an iterator and generates `Self` from the elements by
37 /// multiplying the items.
38 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
39 fn product<I: Iterator<Item = A>>(iter: I) -> Self;
42 // N.B., explicitly use Add and Mul here to inherit overflow checks
43 macro_rules! integer_sum_product {
44 (@impls $zero:expr, $one:expr, #[$attr:meta], $($a:ty)*) => ($(
47 fn sum<I: Iterator<Item=Self>>(iter: I) -> Self {
48 iter.fold($zero, Add::add)
54 fn product<I: Iterator<Item=Self>>(iter: I) -> Self {
55 iter.fold($one, Mul::mul)
60 impl<'a> Sum<&'a $a> for $a {
61 fn sum<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
62 iter.fold($zero, Add::add)
67 impl<'a> Product<&'a $a> for $a {
68 fn product<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
69 iter.fold($one, Mul::mul)
74 integer_sum_product!(@impls 0, 1,
75 #[stable(feature = "iter_arith_traits", since = "1.12.0")],
77 integer_sum_product!(@impls Wrapping(0), Wrapping(1),
78 #[stable(feature = "wrapping_iter_arith", since = "1.14.0")],
83 macro_rules! float_sum_product {
85 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
87 fn sum<I: Iterator<Item=Self>>(iter: I) -> Self {
88 iter.fold(0.0, Add::add)
92 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
94 fn product<I: Iterator<Item=Self>>(iter: I) -> Self {
95 iter.fold(1.0, Mul::mul)
99 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
100 impl<'a> Sum<&'a $a> for $a {
101 fn sum<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
102 iter.fold(0.0, Add::add)
106 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
107 impl<'a> Product<&'a $a> for $a {
108 fn product<I: Iterator<Item=&'a Self>>(iter: I) -> Self {
109 iter.fold(1.0, Mul::mul)
115 integer_sum_product! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }
116 float_sum_product! { f32 f64 }
118 #[stable(feature = "iter_arith_traits_result", since = "1.16.0")]
119 impl<T, U, E> Sum<Result<U, E>> for Result<T, E>
123 /// Takes each element in the `Iterator`: if it is an `Err`, no further
124 /// elements are taken, and the `Err` is returned. Should no `Err` occur,
125 /// the sum of all elements is returned.
129 /// This sums up every integer in a vector, rejecting the sum if a negative
130 /// element is encountered:
133 /// let v = vec![1, 2];
134 /// let res: Result<i32, &'static str> = v.iter().map(|&x: &i32|
135 /// if x < 0 { Err("Negative element found") }
138 /// assert_eq!(res, Ok(3));
140 fn sum<I>(iter: I) -> Result<T, E>
142 I: Iterator<Item = Result<U, E>>,
144 iter::process_results(iter, |i| i.sum())
148 #[stable(feature = "iter_arith_traits_result", since = "1.16.0")]
149 impl<T, U, E> Product<Result<U, E>> for Result<T, E>
153 /// Takes each element in the `Iterator`: if it is an `Err`, no further
154 /// elements are taken, and the `Err` is returned. Should no `Err` occur,
155 /// the product of all elements is returned.
156 fn product<I>(iter: I) -> Result<T, E>
158 I: Iterator<Item = Result<U, E>>,
160 iter::process_results(iter, |i| i.product())
164 #[stable(feature = "iter_arith_traits_option", since = "1.37.0")]
165 impl<T, U> Sum<Option<U>> for Option<T>
169 /// Takes each element in the `Iterator`: if it is a `None`, no further
170 /// elements are taken, and the `None` is returned. Should no `None` occur,
171 /// the sum of all elements is returned.
175 /// This sums up the position of the character 'a' in a vector of strings,
176 /// if a word did not have the character 'a' the operation returns `None`:
179 /// let words = vec!["have", "a", "great", "day"];
180 /// let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
181 /// assert_eq!(total, Some(5));
183 fn sum<I>(iter: I) -> Option<T>
185 I: Iterator<Item = Option<U>>,
187 iter.map(|x| x.ok_or(())).sum::<Result<_, _>>().ok()
191 #[stable(feature = "iter_arith_traits_option", since = "1.37.0")]
192 impl<T, U> Product<Option<U>> for Option<T>
196 /// Takes each element in the `Iterator`: if it is a `None`, no further
197 /// elements are taken, and the `None` is returned. Should no `None` occur,
198 /// the product of all elements is returned.
199 fn product<I>(iter: I) -> Option<T>
201 I: Iterator<Item = Option<U>>,
203 iter.map(|x| x.ok_or(())).product::<Result<_, _>>().ok()