Rollup merge of #50170 - burtonageo:more_cow_from, r=alexcrichton

Implement From for more types on Cow

This is basically https://github.com/rust-lang/rust/pull/48191, except that it should be implemented in a way that doesn't break third party crates.

2 files changed, 15 insertions, 0 deletions

diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index da9afdd2ca3..449e3152d8f 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -2240,6 +2240,14 @@ impl<'a> From<String> for Cow<'a, str> {
     }
 }
 
+#[stable(feature = "cow_from_string_ref", since = "1.28.0")]
+impl<'a> From<&'a String> for Cow<'a, str> {
+    #[inline]
+    fn from(s: &'a String) -> Cow<'a, str> {
+        Cow::Borrowed(s.as_str())
+    }
+}
+
 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
 impl<'a> FromIterator<char> for Cow<'a, str> {
     fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index 690cbcb559b..d30f8cd0fca 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -2286,6 +2286,13 @@ impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
     }
 }
 
+#[stable(feature = "cow_from_vec_ref", since = "1.28.0")]
+impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]> {
+    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]> {