Rollup merge of #72162 - cuviper:extend_one, r=Mark-Simulacrum

Add Extend::{extend_one,extend_reserve}

This adds new optional methods on `Extend`: `extend_one` add a single
element to the collection, and `extend_reserve` pre-allocates space for
the predicted number of incoming elements. These are used in `Iterator`
for `partition` and `unzip` as they shuffle elements one-at-a-time into
their respective collections.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/libstd/sys_common/wtf8.rs b/src/libstd/sys_common/wtf8.rs
index a98407da448..a5ba3daba3e 100644
--- a/src/libstd/sys_common/wtf8.rs
+++ b/src/libstd/sys_common/wtf8.rs
@@ -386,6 +386,17 @@ impl Extend<CodePoint> for Wtf8Buf {
         self.bytes.reserve(low);
         iterator.for_each(move |code_point| self.push(code_point));
     }
+
+    #[inline]
+    fn extend_one(&mut self, code_point: CodePoint) {
+        self.push(code_point);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        // Lower bound of one byte per code point (ASCII only)
+        self.bytes.reserve(additional);
+    }
 }
 
 /// A borrowed slice of well-formed WTF-8 data.