Auto merge of #28602 - apasel422:clone_from, r=bluss

r? @bluss

src/libcollections/binary_heap.rs

@@ -167,12 +167,22 @@ use vec::{self, Vec};
 /// item's ordering relative to any other item, as determined by the `Ord`
 /// trait, changes while it is in the heap. This is normally only possible
 /// through `Cell`, `RefCell`, global state, I/O, or unsafe code.
-#[derive(Clone)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct BinaryHeap<T> {
     data: Vec<T>,
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone> Clone for BinaryHeap<T> {
+    fn clone(&self) -> Self {
+        BinaryHeap { data: self.data.clone() }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        self.data.clone_from(&source.data);
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord> Default for BinaryHeap<T> {
     #[inline]

src/libcollections/lib.rs

@@ -62,7 +62,7 @@
 #![feature(unsafe_no_drop_flag, filling_drop)]
 #![feature(decode_utf16)]
 #![feature(utf8_error)]
-#![cfg_attr(test, feature(rand, test))]
+#![cfg_attr(test, feature(clone_from_slice, rand, test))]
 
 #![feature(no_std)]
 #![no_std]

src/libcollections/string.rs

@@ -30,7 +30,7 @@ use vec::Vec;
 use boxed::Box;
 
 /// A growable string stored as a UTF-8 encoded buffer.
-#[derive(Clone, PartialOrd, Eq, Ord)]
+#[derive(PartialOrd, Eq, Ord)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct String {
     vec: Vec<u8>,
@@ -765,6 +765,17 @@ impl fmt::Display for FromUtf16Error {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Clone for String {
+    fn clone(&self) -> Self {
+        String { vec: self.vec.clone() }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        self.vec.clone_from(&source.vec);
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl FromIterator<char> for String {
     fn from_iter<I: IntoIterator<Item=char>>(iterable: I) -> String {

src/libcollections/vec.rs

@@ -1007,19 +1007,15 @@ impl<T:Clone> Clone for Vec<T> {
 
     fn clone_from(&mut self, other: &Vec<T>) {
         // drop anything in self that will not be overwritten
-        if self.len() > other.len() {
-            self.truncate(other.len())
-        }
+        self.truncate(other.len());
+        let len = self.len();
 
         // reuse the contained values' allocations/resources.
-        for (place, thing) in self.iter_mut().zip(other) {
-            place.clone_from(thing)
-        }
+        self.clone_from_slice(&other[..len]);
 
         // self.len <= other.len due to the truncate above, so the
         // slice here is always in-bounds.
-        let slice = &other[self.len()..];
-        self.push_all(slice);
+        self.push_all(&other[len..]);
     }
 }