143 lines
3.6 KiB
Rust
143 lines
3.6 KiB
Rust
use super::size_hint;
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use std::iter::{Fuse, FusedIterator};
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pub trait IntersperseElement<Item> {
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fn generate(&mut self) -> Item;
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}
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#[derive(Debug, Clone)]
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pub struct IntersperseElementSimple<Item>(Item);
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impl<Item: Clone> IntersperseElement<Item> for IntersperseElementSimple<Item> {
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fn generate(&mut self) -> Item {
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self.0.clone()
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}
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}
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/// An iterator adaptor to insert a particular value
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/// between each element of the adapted iterator.
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///
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/// Iterator element type is `I::Item`
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///
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/// This iterator is *fused*.
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///
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/// See [`.intersperse()`](crate::Itertools::intersperse) for more information.
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pub type Intersperse<I> = IntersperseWith<I, IntersperseElementSimple<<I as Iterator>::Item>>;
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/// Create a new Intersperse iterator
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pub fn intersperse<I>(iter: I, elt: I::Item) -> Intersperse<I>
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where
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I: Iterator,
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{
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intersperse_with(iter, IntersperseElementSimple(elt))
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}
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impl<Item, F: FnMut() -> Item> IntersperseElement<Item> for F {
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fn generate(&mut self) -> Item {
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self()
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}
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}
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/// An iterator adaptor to insert a particular value created by a function
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/// between each element of the adapted iterator.
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///
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/// Iterator element type is `I::Item`
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///
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/// This iterator is *fused*.
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///
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/// See [`.intersperse_with()`](crate::Itertools::intersperse_with) for more information.
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#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
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#[derive(Clone, Debug)]
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pub struct IntersperseWith<I, ElemF>
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where
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I: Iterator,
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{
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element: ElemF,
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iter: Fuse<I>,
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/// `peek` is None while no item have been taken out of `iter` (at definition).
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/// Then `peek` will alternatively be `Some(None)` and `Some(Some(item))`,
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/// where `None` indicates it's time to generate from `element` (unless `iter` is empty).
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peek: Option<Option<I::Item>>,
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}
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/// Create a new `IntersperseWith` iterator
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pub fn intersperse_with<I, ElemF>(iter: I, elt: ElemF) -> IntersperseWith<I, ElemF>
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where
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I: Iterator,
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{
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IntersperseWith {
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peek: None,
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iter: iter.fuse(),
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element: elt,
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}
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}
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impl<I, ElemF> Iterator for IntersperseWith<I, ElemF>
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where
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I: Iterator,
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ElemF: IntersperseElement<I::Item>,
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{
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type Item = I::Item;
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#[inline]
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fn next(&mut self) -> Option<Self::Item> {
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let Self {
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element,
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iter,
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peek,
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} = self;
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match peek {
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Some(item @ Some(_)) => item.take(),
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Some(None) => match iter.next() {
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new @ Some(_) => {
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*peek = Some(new);
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Some(element.generate())
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}
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None => None,
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},
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None => {
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*peek = Some(None);
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iter.next()
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}
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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let mut sh = self.iter.size_hint();
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sh = size_hint::add(sh, sh);
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match self.peek {
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Some(Some(_)) => size_hint::add_scalar(sh, 1),
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Some(None) => sh,
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None => size_hint::sub_scalar(sh, 1),
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}
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}
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fn fold<B, F>(self, init: B, mut f: F) -> B
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where
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Self: Sized,
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F: FnMut(B, Self::Item) -> B,
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{
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let Self {
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mut element,
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mut iter,
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peek,
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} = self;
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let mut accum = init;
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if let Some(x) = peek.unwrap_or_else(|| iter.next()) {
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accum = f(accum, x);
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}
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iter.fold(accum, |accum, x| {
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let accum = f(accum, element.generate());
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f(accum, x)
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})
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}
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}
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impl<I, ElemF> FusedIterator for IntersperseWith<I, ElemF>
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where
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I: Iterator,
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ElemF: IntersperseElement<I::Item>,
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{
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}
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