From ba3da1604ff1d84c8ac90aa6b70d59aae710df7e Mon Sep 17 00:00:00 2001
From: equas <153013428+equas@users.noreply.github.com>
Date: Tue, 5 Dec 2023 23:11:26 +0100
Subject: [PATCH] Implement take_while

---
 src/adapters/mod.rs            |  2 ++
 src/adapters/take_while.rs     | 51 ++++++++++++++++++++++++++++++++++
 src/traits/lending_iterator.rs | 16 ++++++++++-
 3 files changed, 68 insertions(+), 1 deletion(-)
 create mode 100644 src/adapters/take_while.rs

diff --git a/src/adapters/mod.rs b/src/adapters/mod.rs
index f1f965a..6d7d587 100644
--- a/src/adapters/mod.rs
+++ b/src/adapters/mod.rs
@@ -6,6 +6,7 @@ mod filter_map;
 mod map;
 mod step_by;
 mod take;
+mod take_while;
 mod zip;
 pub use self::chain::Chain;
 pub use self::cloned::Cloned;
@@ -15,4 +16,5 @@ pub use self::filter_map::FilterMap;
 pub use self::map::{IntoIter, Map};
 pub use self::step_by::StepBy;
 pub use self::take::Take;
+pub use self::take_while::TakeWhile;
 pub use self::zip::Zip;
diff --git a/src/adapters/take_while.rs b/src/adapters/take_while.rs
new file mode 100644
index 0000000..d160504
--- /dev/null
+++ b/src/adapters/take_while.rs
@@ -0,0 +1,51 @@
+use crate::LendingIterator;
+
+/// A lending iterator that yields items based on a predicate.
+///
+/// This iterator is fused.
+#[derive(Clone)]
+pub struct TakeWhile<I, P> {
+    iter: I,
+    predicate: P,
+    done: bool,
+}
+
+impl<I, P> TakeWhile<I, P> {
+    pub(crate) fn new(iter: I, predicate: P) -> Self {
+        Self {
+            iter,
+            predicate,
+            done: false,
+        }
+    }
+}
+
+impl<I, P> LendingIterator for TakeWhile<I, P>
+where
+    I: LendingIterator,
+    P: for<'a> FnMut(&I::Item<'a>) -> bool
+{
+    type Item<'a> = I::Item<'a> where I: 'a, P: 'a;
+
+    fn next(&mut self) -> Option<Self::Item<'_>> {
+        if self.done {
+            None
+        } else {
+            let item = self.iter.next()?;
+            if (self.predicate)(&item) {
+                Some(item)
+            } else {
+                self.done = true;
+                None
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.done {
+            (0, Some(0))
+        } else {
+            (0, self.iter.size_hint().1)
+        }
+    }
+}
diff --git a/src/traits/lending_iterator.rs b/src/traits/lending_iterator.rs
index 1b5ad88..80e46cc 100644
--- a/src/traits/lending_iterator.rs
+++ b/src/traits/lending_iterator.rs
@@ -2,7 +2,7 @@ use std::{num::NonZeroUsize, ops::Deref};
 
 use crate::{
     Chain, Cloned, Enumerate, Filter, FilterMap, Map, OptionTrait, SingleArgFnMut, SingleArgFnOnce,
-    StepBy, Take, Zip,
+    StepBy, Take, Zip, TakeWhile,
 };
 
 /// Like [`Iterator`], but items may borrow from `&mut self`.
@@ -82,6 +82,20 @@ pub trait LendingIterator {
         Take::new(self, n)
     }
 
+    /// Creates a lending iterator that lends items matching a predicate.
+    ///
+    /// The predicate is called once for every item.
+    /// Once it returns false once, `None` is returned for all subsequent calls to [`next`].
+    ///
+    /// [`next`]: Self::next
+    fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
+    where
+        Self: Sized,
+        P: for <'a> FnMut(&Self::Item<'a>) -> bool
+    {
+        TakeWhile::new(self, predicate)
+    }
+
     /// Takes two lending iterators and creates a new lending iterator over both in sequence.
     ///
     /// See [`Iterator::chain`].