Created
October 16, 2019 18:03
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| struct Select<A, B>(Option<(A, B)>); | |
| impl<A:Future, B:Future> Future for Select<A, B> { | |
| type Output = Either<(A::Output, B), (A, B::Output)>; | |
| fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> { | |
| // omit | |
| } | |
| } | |
| impl<A, B> Drop for Select<A, B> { | |
| fn drop(&mut self) { | |
| // async context の外にいるときの dtor | |
| // | |
| // poll が一度も呼び出されていないか、Readyを返した後の状態になる？ | |
| if let Some((a, b)) = &mut self.0 { | |
| unsafe { | |
| ptr::drop_in_place(a); | |
| ptr::drop_in_place(b); | |
| } | |
| } | |
| } | |
| fn poll_drop(self: Pin<&mut Self>, cx: &mut Context) -> Poll<()> { | |
| // async context 内にいるときの非同期 dtor | |
| // | |
| // drop とは異なり、タスクの完了・未完了に関わらず任意のタイミングで呼ばれる可能性がある（多分） | |
| let this = unsafe { self.get_unchecked_mut() }; | |
| if let Some((a, b)) = &mut this.0 { | |
| ready!(unsafe { Pin::new_unchecked(a) }.poll_drop(cx)); | |
| ready!(unsafe { Pin::new_unchecked(b) }.poll_drop(cx)); | |
| } | |
| Poll::Ready(()) | |
| } | |
| } |
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