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Rollup merge of rust-lang#79479 - camelid:intersperse, r=m-ou-se
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Add `Iterator::intersperse`

This is a rebase of rust-lang#75784. I'm hoping to push this past the finish line!

cc `@jonas-schievink`
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m-ou-se authored Dec 30, 2020
2 parents 242a252 + 40bbb7f commit 9cf2438
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Showing 8 changed files with 189 additions and 2 deletions.
76 changes: 76 additions & 0 deletions library/core/src/iter/adapters/intersperse.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,76 @@
use super::Peekable;

/// An iterator adapter that places a separator between all elements.
#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
#[derive(Debug, Clone)]
pub struct Intersperse<I: Iterator>
where
I::Item: Clone,
{
separator: I::Item,
iter: Peekable<I>,
needs_sep: bool,
}

impl<I: Iterator> Intersperse<I>
where
I::Item: Clone,
{
pub(in crate::iter) fn new(iter: I, separator: I::Item) -> Self {
Self { iter: iter.peekable(), separator, needs_sep: false }
}
}

#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
impl<I> Iterator for Intersperse<I>
where
I: Iterator,
I::Item: Clone,
{
type Item = I::Item;

#[inline]
fn next(&mut self) -> Option<I::Item> {
if self.needs_sep && self.iter.peek().is_some() {
self.needs_sep = false;
Some(self.separator.clone())
} else {
self.needs_sep = true;
self.iter.next()
}
}

fn fold<B, F>(mut self, init: B, mut f: F) -> B
where
Self: Sized,
F: FnMut(B, Self::Item) -> B,
{
let mut accum = init;

// Use `peek()` first to avoid calling `next()` on an empty iterator.
if !self.needs_sep || self.iter.peek().is_some() {
if let Some(x) = self.iter.next() {
accum = f(accum, x);
}
}

let element = &self.separator;

self.iter.fold(accum, |mut accum, x| {
accum = f(accum, element.clone());
accum = f(accum, x);
accum
})
}

fn size_hint(&self) -> (usize, Option<usize>) {
let (lo, hi) = self.iter.size_hint();
let next_is_elem = !self.needs_sep;
let lo = lo.saturating_sub(next_is_elem as usize).saturating_add(lo);
let hi = match hi {
Some(hi) => hi.saturating_sub(next_is_elem as usize).checked_add(hi),
None => None,
};
(lo, hi)
}
}
4 changes: 4 additions & 0 deletions library/core/src/iter/adapters/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ mod filter_map;
mod flatten;
mod fuse;
mod inspect;
mod intersperse;
mod map;
mod map_while;
mod peekable;
Expand Down Expand Up @@ -41,6 +42,9 @@ pub use self::flatten::Flatten;
#[stable(feature = "iter_copied", since = "1.36.0")]
pub use self::copied::Copied;

#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
pub use self::intersperse::Intersperse;

#[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")]
pub use self::map_while::MapWhile;

Expand Down
2 changes: 2 additions & 0 deletions library/core/src/iter/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -395,6 +395,8 @@ pub use self::adapters::Cloned;
pub use self::adapters::Copied;
#[stable(feature = "iterator_flatten", since = "1.29.0")]
pub use self::adapters::Flatten;
#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
pub use self::adapters::Intersperse;
#[unstable(feature = "iter_map_while", reason = "recently added", issue = "68537")]
pub use self::adapters::MapWhile;
#[unstable(feature = "inplace_iteration", issue = "none")]
Expand Down
24 changes: 23 additions & 1 deletion library/core/src/iter/traits/iterator.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use crate::ops::{Add, ControlFlow, Try};
use super::super::TrustedRandomAccess;
use super::super::{Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse};
use super::super::{FlatMap, Flatten};
use super::super::{FromIterator, Product, Sum, Zip};
use super::super::{FromIterator, Intersperse, Product, Sum, Zip};
use super::super::{
Inspect, Map, MapWhile, Peekable, Rev, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile,
};
Expand Down Expand Up @@ -569,6 +569,28 @@ pub trait Iterator {
Zip::new(self, other.into_iter())
}

/// Places a copy of `separator` between all elements.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(iter_intersperse)]
///
/// let hello = ["Hello", "World"].iter().copied().intersperse(" ").collect::<String>();
/// assert_eq!(hello, "Hello World");
/// ```
#[inline]
#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
fn intersperse(self, separator: Self::Item) -> Intersperse<Self>
where
Self: Sized,
Self::Item: Clone,
{
Intersperse::new(self, separator)
}

/// Takes a closure and creates an iterator which calls that closure on each
/// element.
///
Expand Down
82 changes: 82 additions & 0 deletions library/core/tests/iter.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3505,3 +3505,85 @@ pub fn extend_for_unit() {
}
assert_eq!(x, 5);
}

#[test]
fn test_intersperse() {
let xs = ["a", "", "b", "c"];
let v: Vec<&str> = xs.iter().map(|x| x.clone()).intersperse(", ").collect();
let text: String = v.concat();
assert_eq!(text, "a, , b, c".to_string());

let ys = [0, 1, 2, 3];
let mut it = ys[..0].iter().map(|x| *x).intersperse(1);
assert!(it.next() == None);
}

#[test]
fn test_intersperse_size_hint() {
let xs = ["a", "", "b", "c"];
let mut iter = xs.iter().map(|x| x.clone()).intersperse(", ");
assert_eq!(iter.size_hint(), (7, Some(7)));

assert_eq!(iter.next(), Some("a"));
assert_eq!(iter.size_hint(), (6, Some(6)));
assert_eq!(iter.next(), Some(", "));
assert_eq!(iter.size_hint(), (5, Some(5)));

assert_eq!([].iter().intersperse(&()).size_hint(), (0, Some(0)));
}

#[test]
fn test_fold_specialization_intersperse() {
let mut iter = (1..2).intersperse(0);
iter.clone().for_each(|x| assert_eq!(Some(x), iter.next()));

let mut iter = (1..3).intersperse(0);
iter.clone().for_each(|x| assert_eq!(Some(x), iter.next()));

let mut iter = (1..4).intersperse(0);
iter.clone().for_each(|x| assert_eq!(Some(x), iter.next()));
}

#[test]
fn test_try_fold_specialization_intersperse_ok() {
let mut iter = (1..2).intersperse(0);
iter.clone().try_for_each(|x| {
assert_eq!(Some(x), iter.next());
Some(())
});

let mut iter = (1..3).intersperse(0);
iter.clone().try_for_each(|x| {
assert_eq!(Some(x), iter.next());
Some(())
});

let mut iter = (1..4).intersperse(0);
iter.clone().try_for_each(|x| {
assert_eq!(Some(x), iter.next());
Some(())
});
}

#[test]
fn test_try_fold_specialization_intersperse_err() {
let orig_iter = ["a", "b"].iter().copied().intersperse("-");

// Abort after the first item.
let mut iter = orig_iter.clone();
iter.try_for_each(|_| None::<()>);
assert_eq!(iter.next(), Some("-"));
assert_eq!(iter.next(), Some("b"));
assert_eq!(iter.next(), None);

// Abort after the second item.
let mut iter = orig_iter.clone();
iter.try_for_each(|item| if item == "-" { None } else { Some(()) });
assert_eq!(iter.next(), Some("b"));
assert_eq!(iter.next(), None);

// Abort after the third item.
let mut iter = orig_iter.clone();
iter.try_for_each(|item| if item == "b" { None } else { Some(()) });
assert_eq!(iter.next(), None);
}
1 change: 1 addition & 0 deletions library/core/tests/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,7 @@
#![feature(array_value_iter)]
#![feature(iter_advance_by)]
#![feature(iter_partition_in_place)]
#![feature(iter_intersperse)]
#![feature(iter_is_partitioned)]
#![feature(iter_order_by)]
#![feature(cmp_min_max_by)]
Expand Down
1 change: 0 additions & 1 deletion src/librustdoc/clean/utils.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,6 @@ use crate::clean::{
};
use crate::core::DocContext;

use itertools::Itertools;
use rustc_data_structures::fx::FxHashSet;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
Expand Down
1 change: 1 addition & 0 deletions src/librustdoc/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
#![feature(type_ascription)]
#![feature(split_inclusive)]
#![feature(str_split_once)]
#![feature(iter_intersperse)]
#![recursion_limit = "256"]

#[macro_use]
Expand Down

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