1 files changed, 35 insertions, 0 deletions
diff --git a/library/alloc/src/collections/btree/mem.rs b/library/alloc/src/collections/btree/mem.rs
new file mode 100644
index 000000000..e1363d1ae
--- /dev/null
+++ b/library/alloc/src/collections/btree/mem.rs
@@ -0,0 +1,35 @@
+use core::intrinsics;
+use core::mem;
+use core::ptr;
+
+/// This replaces the value behind the `v` unique reference by calling the
+/// relevant function.
+///
+/// If a panic occurs in the `change` closure, the entire process will be aborted.
+#[allow(dead_code)] // keep as illustration and for future use
+#[inline]
+pub fn take_mut<T>(v: &mut T, change: impl FnOnce(T) -> T) {
+    replace(v, |value| (change(value), ()))
+}
+
+/// This replaces the value behind the `v` unique reference by calling the
+/// relevant function, and returns a result obtained along the way.
+///
+/// If a panic occurs in the `change` closure, the entire process will be aborted.
+#[inline]
+pub fn replace<T, R>(v: &mut T, change: impl FnOnce(T) -> (T, R)) -> R {
+    struct PanicGuard;
+    impl Drop for PanicGuard {
+        fn drop(&mut self) {
+            intrinsics::abort()
+        }
+    }
+    let guard = PanicGuard;
+    let value = unsafe { ptr::read(v) };
+    let (new_value, ret) = change(value);
+    unsafe {
+        ptr::write(v, new_value);
+    }
+    mem::forget(guard);
+    ret
+}