120 lines
3.1 KiB
Rust
120 lines
3.1 KiB
Rust
use std::iter::{Fuse, FusedIterator};
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use super::size_hint;
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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 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 I: Iterator,
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{
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element: ElemF,
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iter: Fuse<I>,
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peek: 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 I: Iterator,
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{
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let mut iter = iter.fuse();
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IntersperseWith {
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peek: iter.next(),
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iter,
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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 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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if self.peek.is_some() {
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self.peek.take()
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} else {
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self.peek = self.iter.next();
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if self.peek.is_some() {
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Some(self.element.generate())
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} else {
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None
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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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// 2 * SH + { 1 or 0 }
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let has_peek = self.peek.is_some() as usize;
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let sh = self.iter.size_hint();
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size_hint::add_scalar(size_hint::add(sh, sh), has_peek)
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}
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fn fold<B, F>(mut self, init: B, mut f: F) -> B where
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Self: Sized, F: FnMut(B, Self::Item) -> B,
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{
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let mut accum = init;
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if let Some(x) = self.peek.take() {
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accum = f(accum, x);
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}
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let element = &mut self.element;
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self.iter.fold(accum,
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|accum, x| {
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let accum = f(accum, element.generate());
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let accum = f(accum, x);
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accum
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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 I: Iterator,
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ElemF: IntersperseElement<I::Item>
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{}
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