Repository: rust-itertools/itertools (rust)

Issue:
impl PeekingNext for RepeatN
I can write a quick PR.

Pull request description:
`RepeatN`: implement `PeekingNext`
Fixes #589

Patch:
diff --git a/src/peeking_take_while.rs b/src/peeking_take_while.rs
index b4852c1..b224907 100644
--- a/src/peeking_take_while.rs
+++ b/src/peeking_take_while.rs
@@ -1,6 +1,7 @@
 use crate::PutBack;
 #[cfg(feature = "use_alloc")]
 use crate::PutBackN;
+use crate::RepeatN;
 use std::iter::Peekable;
 
 /// An iterator that allows peeking at an element before deciding to accept it.
@@ -91,6 +92,19 @@ where
     }
 }
 
+impl<T: Clone> PeekingNext for RepeatN<T> {
+    fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item>
+    where
+        F: FnOnce(&Self::Item) -> bool,
+    {
+        let r = self.elt.as_ref()?;
+        if !accept(r) {
+            return None;
+        }
+        self.next()
+    }
+}
+
 /// An iterator adaptor that takes items while a closure returns `true`.
 ///
 /// See [`.peeking_take_while()`](crate::Itertools::peeking_take_while)
diff --git a/src/repeatn.rs b/src/repeatn.rs
index 539c426..d86ad9f 100644
--- a/src/repeatn.rs
+++ b/src/repeatn.rs
@@ -6,7 +6,7 @@ use std::iter::FusedIterator;
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 #[derive(Clone, Debug)]
 pub struct RepeatN<A> {
-    elt: Option<A>,
+    pub(crate) elt: Option<A>,
     n: usize,
 }
 


Test patch:
diff --git a/tests/test_std.rs b/tests/test_std.rs
index be163e9..5d28645 100644
--- a/tests/test_std.rs
+++ b/tests/test_std.rs
@@ -8,6 +8,7 @@ use crate::it::izip;
 use crate::it::multipeek;
 use crate::it::multizip;
 use crate::it::peek_nth;
+use crate::it::repeat_n;
 use crate::it::ExactlyOneError;
 use crate::it::FoldWhile;
 use crate::it::Itertools;
@@ -674,6 +675,21 @@ fn test_multipeek_peeking_next() {
     assert_eq!(mp.peek(), None);
 }
 
+#[test]
+fn test_repeat_n_peeking_next() {
+    use crate::it::PeekingNext;
+    let mut rn = repeat_n(0, 5);
+    assert_eq!(rn.peeking_next(|&x| x != 0), None);
+    assert_eq!(rn.peeking_next(|&x| x <= 0), Some(0));
+    assert_eq!(rn.next(), Some(0));
+    assert_eq!(rn.peeking_next(|&x| x <= 0), Some(0));
+    assert_eq!(rn.peeking_next(|&x| x != 0), None);
+    assert_eq!(rn.peeking_next(|&x| x >= 0), Some(0));
+    assert_eq!(rn.next(), Some(0));
+    assert_eq!(rn.peeking_next(|&x| x <= 0), None);
+    assert_eq!(rn.next(), None);
+}
+
 #[test]
 fn test_peek_nth() {
     let nums = vec![1u8, 2, 3, 4, 5];