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Make iter::Empty<T> Send and Sync for any T #57682

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Make iter::Empty<T> Send and Sync for any T #57682

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e19fc28
Make iter::Empty<T> Send, Sync and Unpin for any T
LunaBorowska Jan 17, 2019
313c628
Add a test for iter::empty::<*mut i32> being Sync and Send
LunaBorowska Jan 16, 2019
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5 changes: 4 additions & 1 deletion src/libcore/iter/sources.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -198,7 +198,10 @@ pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F> {
///
/// [`empty`]: fn.empty.html
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
pub struct Empty<T>(marker::PhantomData<PhantomFnWorkaround<T>>);

// Workaround for PhantomData<fn() -> T> not being allowed in const fn.
struct PhantomFnWorkaround<T>(fn() -> T);

#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T> fmt::Debug for Empty<T> {
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1 change: 1 addition & 0 deletions src/test/run-pass/threads-sendsync/sync-send-iterators-in-libcore.rs
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Expand Up @@ -91,6 +91,7 @@ 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
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