From eeb549bfc31c27c6cec98eb852409a51f0a8162c Mon Sep 17 00:00:00 2001
From: Clar Fon <them@lightdark.xyz>
Date: Sat, 5 Oct 2019 18:23:37 -0400
Subject: [PATCH] Add Cow::is_borrowed and Cow::is_owned

---
 src/liballoc/borrow.rs | 41 +++++++++++++++++++++++++++++++++++++++++
 src/liballoc/lib.rs    |  1 +
 2 files changed, 42 insertions(+)

diff --git a/src/liballoc/borrow.rs b/src/liballoc/borrow.rs
index a9c5bce4c25fc..d2bdda83fa998 100644
--- a/src/liballoc/borrow.rs
+++ b/src/liballoc/borrow.rs
@@ -207,6 +207,47 @@ impl<B: ?Sized + ToOwned> Clone for Cow<'_, B> {
 }
 
 impl<B: ?Sized + ToOwned> Cow<'_, B> {
+    /// Returns true if the data is borrowed, i.e. if `to_mut` would require additional work.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cow_is_borrowed)]
+    /// use std::borrow::Cow;
+    ///
+    /// let cow = Cow::Borrowed("moo");
+    /// assert!(cow.is_borrowed());
+    ///
+    /// let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string());
+    /// assert!(!bull.is_borrowed());
+    /// ```
+    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
+    pub fn is_borrowed(&self) -> bool {
+        match *self {
+            Borrowed(_) => true,
+            Owned(_) => false,
+        }
+    }
+
+    /// Returns true if the data is owned, i.e. if `to_mut` would be a no-op.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cow_is_borrowed)]
+    /// use std::borrow::Cow;
+    ///
+    /// let cow: Cow<'_, str> = Cow::Owned("moo".to_string());
+    /// assert!(cow.is_owned());
+    ///
+    /// let bull = Cow::Borrowed("...moo?");
+    /// assert!(!bull.is_owned());
+    /// ```
+    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
+    pub fn is_owned(&self) -> bool {
+        !self.is_borrowed()
+    }
+
     /// Acquires a mutable reference to the owned form of the data.
     ///
     /// Clones the data if it is not already owned.
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 3684162d8b187..94379afc2bd45 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -85,6 +85,7 @@
 #![feature(const_generic_impls_guard)]
 #![feature(const_generics)]
 #![feature(const_in_array_repeat_expressions)]
+#![feature(cow_is_borrowed)]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]
 #![feature(container_error_extra)]