reduce indirection in for_each specialization

library/core/src/iter/adapters/take.rs

@@ -303,13 +303,12 @@ fn spec_fold<B, F>(mut self, init: B, mut f: F) -> B
     }
 
     #[inline]
-    fn spec_for_each<F: FnMut(Self::Item)>(self, f: F) {
-        // Based on the the Iterator trait default impl.
-        #[inline]
-        fn call<T>(mut f: impl FnMut(T)) -> impl FnMut((), T) {
-            move |(), item| f(item)
+    fn spec_for_each<F: FnMut(Self::Item)>(mut self, mut f: F) {
+        let end = self.n.min(self.iter.size());
+        for i in 0..end {
+            // SAFETY: i < end <= self.iter.size() and we discard the iterator at the end
+            let val = unsafe { self.iter.__iterator_get_unchecked(i) };
+            f(val);
         }
-
-        self.spec_fold((), call(f));
     }
 }