diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs index 78bf28c843c..3065169e5e2 100644 --- a/library/alloc/src/rc.rs +++ b/library/alloc/src/rc.rs @@ -1203,6 +1203,41 @@ impl Rc { // reference to the allocation. unsafe { &mut this.ptr.as_mut().value } } + + /// If we have the only reference to `T` then unwrap it. Otherwise, clone `T` and return the + /// clone. + /// + /// Assuming `rc_t` is of type `Rc`, this function is functionally equivalent to + /// `(*rc_t).clone()`, but will avoid cloning the inner value where possible. + /// + /// # Examples + /// + /// ``` + /// #![feature(arc_unwrap_or_clone)] + /// # use std::{ptr, rc::Rc}; + /// let inner = String::from("test"); + /// let ptr = inner.as_ptr(); + /// + /// let rc = Rc::new(inner); + /// let inner = Rc::unwrap_or_clone(rc); + /// // The inner value was not cloned + /// assert!(ptr::eq(ptr, inner.as_ptr())); + /// + /// let rc = Rc::new(inner); + /// let rc2 = rc.clone(); + /// let inner = Rc::unwrap_or_clone(rc); + /// // Because there were 2 references, we had to clone the inner value. + /// assert!(!ptr::eq(ptr, inner.as_ptr())); + /// // `rc2` is the last reference, so when we unwrap it we get back + /// // the original `String`. + /// let inner = Rc::unwrap_or_clone(rc2); + /// assert!(ptr::eq(ptr, inner.as_ptr())); + /// ``` + #[inline] + #[unstable(feature = "arc_unwrap_or_clone", issue = "93610")] + pub fn unwrap_or_clone(this: Self) -> T { + Rc::try_unwrap(this).unwrap_or_else(|rc| (*rc).clone()) + } } impl Rc { diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs index 3d132484b2f..7e7670aad64 100644 --- a/library/alloc/src/sync.rs +++ b/library/alloc/src/sync.rs @@ -1508,7 +1508,7 @@ impl Arc { /// assert!(ptr::eq(ptr, inner.as_ptr())); /// ``` #[inline] - #[unstable(feature = "arc_unwrap_or_clone", issue = "none")] + #[unstable(feature = "arc_unwrap_or_clone", issue = "93610")] pub fn unwrap_or_clone(this: Self) -> T { Arc::try_unwrap(this).unwrap_or_else(|arc| (*arc).clone()) }