1 files changed, 53 insertions, 0 deletions
diff --git a/library/alloc/src/vec/cow.rs b/library/alloc/src/vec/cow.rs
new file mode 100644
index 000000000..64943a273
--- /dev/null
+++ b/library/alloc/src/vec/cow.rs
@@ -0,0 +1,53 @@
+use crate::borrow::Cow;
+use core::iter::FromIterator;
+
+use super::Vec;
+
+#[stable(feature = "cow_from_vec", since = "1.8.0")]
+impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
+    /// Creates a [`Borrowed`] variant of [`Cow`]
+    /// from a slice.
+    ///
+    /// This conversion does not allocate or clone the data.
+    ///
+    /// [`Borrowed`]: crate::borrow::Cow::Borrowed
+    fn from(s: &'a [T]) -> Cow<'a, [T]> {
+        Cow::Borrowed(s)
+    }
+}
+
+#[stable(feature = "cow_from_vec", since = "1.8.0")]
+impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
+    /// Creates an [`Owned`] variant of [`Cow`]
+    /// from an owned instance of [`Vec`].
+    ///
+    /// This conversion does not allocate or clone the data.
+    ///
+    /// [`Owned`]: crate::borrow::Cow::Owned
+    fn from(v: Vec<T>) -> Cow<'a, [T]> {
+        Cow::Owned(v)
+    }
+}
+
+#[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
+impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
+    /// Creates a [`Borrowed`] variant of [`Cow`]
+    /// from a reference to [`Vec`].
+    ///
+    /// This conversion does not allocate or clone the data.
+    ///
+    /// [`Borrowed`]: crate::borrow::Cow::Borrowed
+    fn from(v: &'a Vec<T>) -> Cow<'a, [T]> {
+        Cow::Borrowed(v.as_slice())
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> FromIterator<T> for Cow<'a, [T]>
+where
+    T: Clone,
+{
+    fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
+        Cow::Owned(FromIterator::from_iter(it))
+    }
+}