diff --git a/library/core/src/iter/adapters/intersperse.rs b/library/core/src/iter/adapters/intersperse.rs new file mode 100644 index 0000000000000..362326725490f --- /dev/null +++ b/library/core/src/iter/adapters/intersperse.rs @@ -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 +where + I::Item: Clone, +{ + separator: I::Item, + iter: Peekable, + needs_sep: bool, +} + +impl Intersperse +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 Iterator for Intersperse +where + I: Iterator, + I::Item: Clone, +{ + type Item = I::Item; + + #[inline] + fn next(&mut self) -> Option { + 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(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) { + 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) + } +} diff --git a/library/core/src/iter/adapters/mod.rs b/library/core/src/iter/adapters/mod.rs index b8d3430f91099..7dfbf32cea7b8 100644 --- a/library/core/src/iter/adapters/mod.rs +++ b/library/core/src/iter/adapters/mod.rs @@ -11,6 +11,7 @@ mod filter_map; mod flatten; mod fuse; mod inspect; +mod intersperse; mod map; mod map_while; mod peekable; @@ -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; diff --git a/library/core/src/iter/mod.rs b/library/core/src/iter/mod.rs index 3e74637b49f1c..569de719d03d6 100644 --- a/library/core/src/iter/mod.rs +++ b/library/core/src/iter/mod.rs @@ -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")] diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs index 7ba16f89284e1..633175702d870 100644 --- a/library/core/src/iter/traits/iterator.rs +++ b/library/core/src/iter/traits/iterator.rs @@ -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, }; @@ -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::(); + /// assert_eq!(hello, "Hello World"); + /// ``` + #[inline] + #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")] + fn intersperse(self, separator: Self::Item) -> Intersperse + where + Self: Sized, + Self::Item: Clone, + { + Intersperse::new(self, separator) + } + /// Takes a closure and creates an iterator which calls that closure on each /// element. /// diff --git a/library/core/tests/iter.rs b/library/core/tests/iter.rs index ec4b49da384c3..7376e7848eff5 100644 --- a/library/core/tests/iter.rs +++ b/library/core/tests/iter.rs @@ -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); +} diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs index 9e8ec7060216b..fba3294e0bbdb 100644 --- a/library/core/tests/lib.rs +++ b/library/core/tests/lib.rs @@ -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)] diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs index 2cde0c209ee9b..a6c090c6576ef 100644 --- a/src/librustdoc/clean/utils.rs +++ b/src/librustdoc/clean/utils.rs @@ -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}; diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs index e8bf664d45c4d..7ed64c5813fcd 100644 --- a/src/librustdoc/lib.rs +++ b/src/librustdoc/lib.rs @@ -17,6 +17,7 @@ #![feature(type_ascription)] #![feature(split_inclusive)] #![feature(str_split_once)] +#![feature(iter_intersperse)] #![recursion_limit = "256"] #[macro_use]