Rollup merge of #59740 - cuviper:folded-extend, r=scottmcm

Use for_each to extend collections

This updates the `Extend` implementations to use `for_each` for many
collections: `BinaryHeap`, `BTreeMap`, `BTreeSet`, `LinkedList`, `Path`,
`TokenStream`, `VecDeque`, and `Wtf8Buf`.

Folding with `for_each` enables better performance than a `for`-loop for
some iterators, especially if they can just forward to internal
iterators, like `Chain` and `FlatMap` do.

2 files changed, 2 insertions, 6 deletions

diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index 71e82f0a9b0..1bbda9b5bcb 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1551,9 +1551,7 @@ impl<P: AsRef<Path>> iter::FromIterator<P> for PathBuf {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<P: AsRef<Path>> iter::Extend<P> for PathBuf {
     fn extend<I: IntoIterator<Item = P>>(&mut self, iter: I) {
-        for p in iter {
-            self.push(p.as_ref())
-        }
+        iter.into_iter().for_each(move |p| self.push(p.as_ref()));
     }
 }
 
diff --git a/src/libstd/sys_common/wtf8.rs b/src/libstd/sys_common/wtf8.rs
index 7fe1818291e..f17020de44e 100644
--- a/src/libstd/sys_common/wtf8.rs
+++ b/src/libstd/sys_common/wtf8.rs
@@ -388,9 +388,7 @@ impl Extend<CodePoint> for Wtf8Buf {
         let (low, _high) = iterator.size_hint();
         // Lower bound of one byte per code point (ASCII only)
         self.bytes.reserve(low);
-        for code_point in iterator {
-            self.push(code_point);
-        }
+        iterator.for_each(move |code_point| self.push(code_point));
     }
 }