pub trait CloneToAny {
/// Clone `self` into a new `Box<dyn CloneAny>` object.
fn clone_to_any(&self) -> Box<dyn CloneAny>;
-
- /// Clone `self` into a new `Box<dyn CloneAny + Send>` object.
- fn clone_to_any_send(&self) -> Box<dyn CloneAny + Send> where Self: Send;
-
- /// Clone `self` into a new `Box<dyn CloneAny + Sync>` object.
- fn clone_to_any_sync(&self) -> Box<dyn CloneAny + Sync> where Self: Sync;
-
- /// Clone `self` into a new `Box<dyn CloneAny + Send + Sync>` object.
- fn clone_to_any_send_sync(&self) -> Box<dyn CloneAny + Send + Sync> where Self: Send + Sync;
}
impl<T: Any + Clone> CloneToAny for T {
fn clone_to_any(&self) -> Box<dyn CloneAny> {
Box::new(self.clone())
}
-
- #[inline]
- fn clone_to_any_send(&self) -> Box<dyn CloneAny + Send> where Self: Send {
- Box::new(self.clone())
- }
-
- #[inline]
- fn clone_to_any_sync(&self) -> Box<dyn CloneAny + Sync> where Self: Sync {
- Box::new(self.clone())
- }
-
- #[inline]
- fn clone_to_any_send_sync(&self) -> Box<dyn CloneAny + Send + Sync> where Self: Send + Sync {
- Box::new(self.clone())
- }
}
macro_rules! impl_clone {
- ($t:ty, $method:ident) => {
+ ($t:ty) => {
impl Clone for Box<$t> {
#[inline]
fn clone(&self) -> Box<$t> {
- (**self).$method()
+ // SAFETY: this dance is to reapply any Send/Sync marker. I’m not happy about this
+ // approach, given that I used to do it in safe code, but then came a dodgy
+ // future-compatibility warning where_clauses_object_safety, which is spurious for
+ // auto traits but still super annoying (future-compatibility lints seem to mean
+ // your bin crate needs a corresponding allow!). Although I explained my plight¹
+ // and it was all explained and agreed upon, no action has been taken. So I finally
+ // caved and worked around it by doing it this way, which matches what’s done for
+ // std::any², so it’s probably not *too* bad.
+ //
+ // ¹ https://github.com/rust-lang/rust/issues/51443#issuecomment-421988013
+ // ² https://github.com/rust-lang/rust/blob/e7825f2b690c9a0d21b6f6d84c404bb53b151b38/library/alloc/src/boxed.rs#L1613-L1616
+ let clone: Box<dyn CloneAny> = (**self).clone_to_any();
+ let raw: *mut dyn CloneAny = Box::into_raw(clone);
+ unsafe { Box::from_raw(raw as *mut $t) }
}
}
}
implement!(CloneAny, + Send);
implement!(CloneAny, + Sync);
implement!(CloneAny, + Send + Sync);
-impl_clone!(dyn CloneAny, clone_to_any);
-impl_clone!(dyn CloneAny + Send, clone_to_any_send);
-impl_clone!(dyn CloneAny + Sync, clone_to_any_sync);
-impl_clone!(dyn CloneAny + Send + Sync, clone_to_any_send_sync);
+impl_clone!(dyn CloneAny);
+impl_clone!(dyn CloneAny + Send);
+impl_clone!(dyn CloneAny + Sync);
+impl_clone!(dyn CloneAny + Send + Sync);