Implement `iter::Sum` and `iter::Product` for `Option`
This is similar to the existing implementation for `Result`. It will take each item into the accumulator unless a `None` is returned.
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@ -223,3 +223,116 @@ impl<T, U, E> Product<Result<U, E>> for Result<T, E>
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ResultShunt::process(iter, |i| i.product())
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}
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}
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/// An iterator adapter that produces output as long as the underlying
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/// iterator produces `Option::Some` values.
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struct OptionShunt<I> {
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iter: I,
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exited_early: bool,
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}
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impl<I, T> OptionShunt<I>
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where
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I: Iterator<Item = Option<T>>,
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{
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/// Process the given iterator as if it yielded a `T` instead of a
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/// `Option<T>`. Any `None` value will stop the inner iterator and
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/// the overall result will be a `None`.
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pub fn process<F, U>(iter: I, mut f: F) -> Option<U>
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where
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F: FnMut(&mut Self) -> U,
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{
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let mut shunt = OptionShunt::new(iter);
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let value = f(shunt.by_ref());
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shunt.reconstruct(value)
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}
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fn new(iter: I) -> Self {
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OptionShunt {
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iter,
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exited_early: false,
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}
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}
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/// Consume the adapter and rebuild a `Option` value.
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fn reconstruct<U>(self, val: U) -> Option<U> {
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if self.exited_early {
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None
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} else {
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Some(val)
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}
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}
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}
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impl<I, T> Iterator for OptionShunt<I>
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where
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I: Iterator<Item = Option<T>>,
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{
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type Item = T;
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fn next(&mut self) -> Option<Self::Item> {
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match self.iter.next() {
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Some(Some(v)) => Some(v),
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Some(None) => {
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self.exited_early = true;
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None
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}
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None => None,
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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if self.exited_early {
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(0, Some(0))
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} else {
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let (_, upper) = self.iter.size_hint();
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(0, upper)
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}
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}
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}
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#[stable(feature = "iter_arith_traits_option", since = "1.34.0")]
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impl<T, U> Sum<Option<U>> for Option<T>
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where
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T: Sum<U>,
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{
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/// Takes each element in the `Iterator`: if it is a `None`, no further
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/// elements are taken, and the `None` is returned. Should no `None` occur,
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/// the sum of all elements is returned.
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///
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/// # Examples
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///
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/// This sums up every integer in a vector, rejecting the sum if a negative
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/// element is encountered:
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///
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/// ```
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/// let v = vec![1, 2];
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/// let res: Option<i32> = v.iter().map(|&x: &i32|
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/// if x < 0 { None }
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/// else { Some(x) }
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/// ).sum();
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/// assert_eq!(res, Some(3));
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/// ```
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fn sum<I>(iter: I) -> Option<T>
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where
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I: Iterator<Item = Option<U>>,
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{
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OptionShunt::process(iter, |i| i.sum())
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}
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}
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#[stable(feature = "iter_arith_traits_option", since = "1.34.0")]
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impl<T, U> Product<Option<U>> for Option<T>
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where
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T: Product<U>,
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{
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/// Takes each element in the `Iterator`: if it is a `None`, no further
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/// elements are taken, and the `None` is returned. Should no `None` occur,
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/// the product of all elements is returned.
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fn product<I>(iter: I) -> Option<T>
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where
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I: Iterator<Item = Option<U>>,
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{
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OptionShunt::process(iter, |i| i.product())
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}
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}
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@ -1066,6 +1066,14 @@ fn test_iterator_sum_result() {
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assert_eq!(v.iter().cloned().sum::<Result<i32, _>>(), Err(()));
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}
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#[test]
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fn test_iterator_sum_option() {
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let v: &[Option<i32>] = &[Some(1), Some(2), Some(3), Some(4)];
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assert_eq!(v.iter().cloned().sum::<Option<i32>>(), Some(10));
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let v: &[Option<i32>] = &[Some(1), None, Some(3), Some(4)];
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assert_eq!(v.iter().cloned().sum::<Option<i32>>(), None);
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}
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#[test]
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fn test_iterator_product() {
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let v: &[i32] = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
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@ -1082,6 +1090,14 @@ fn test_iterator_product_result() {
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assert_eq!(v.iter().cloned().product::<Result<i32, _>>(), Err(()));
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}
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#[test]
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fn test_iterator_product_option() {
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let v: &[Option<i32>] = &[Some(1), Some(2), Some(3), Some(4)];
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assert_eq!(v.iter().cloned().product::<Option<i32>>(), Some(24));
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let v: &[Option<i32>] = &[Some(1), None, Some(3), Some(4)];
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assert_eq!(v.iter().cloned().product::<Option<i32>>(), None);
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}
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#[test]
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fn test_iterator_max() {
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let v: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
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