bjoernager/rust
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Rollup merge of #68348 - xfix:patch-14, r=nagisa

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Make iter::Empty<T> Send and Sync for any T

Continuing from #57682

It's quite funny, when I initially submitted this pull request, I said "Likely nobody will be using that property of `iter::empty`", but then a year later I got a compilation error because it wasn't `Send` and `Sync`.

Unfortunately, `PhantomData<fn() -> T>` still errors out. Oh well. I proposed `
struct PhantomFnWorkaround<T>(fn() -> T);`, but dtolnay did not like it, so using explicit implementations.
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Dylan DPC 2020-01-19 17:22:09 +05:30 • committed by GitHub
commit d276e6942e
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5
src/libcore/iter/sources.rs
View file

@ -208,6 +208,11 @@ pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F> {
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
unsafe impl<T> Send for Empty<T> {}
#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
unsafe impl<T> Sync for Empty<T> {}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T> fmt::Debug for Empty<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

1
src/test/ui/threads-sendsync/sync-send-iterators-in-libcore.rs
View file

@ -88,6 +88,7 @@ fn main() {
is_sync_send!((1..));
is_sync_send!(repeat(1));
is_sync_send!(empty::<usize>());
is_sync_send!(empty::<*mut i32>());
is_sync_send!(once(1));
// for option.rs