diff options
| -rw-r--r-- | src/libcore/future/future_obj.rs | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/src/libcore/future/future_obj.rs b/src/libcore/future/future_obj.rs index 86fe9825ded..173e381ca50 100644 --- a/src/libcore/future/future_obj.rs +++ b/src/libcore/future/future_obj.rs @@ -20,7 +20,15 @@ use task::{Context, Poll}; /// A custom trait object for polling futures, roughly akin to /// `Box<dyn Future<Output = T> + 'a>`. -/// Contrary to `FutureObj`, `LocalFutureObj` does not have a `Send` bound. +/// +/// This custom trait object was introduced for two reasons: +/// - Currently it is not possible to take `dyn Trait` by value and +/// `Box<dyn Trait>` is not available in no_std contexts. +/// - The `Future` trait is currently not object safe: The `Future::poll` +/// method makes uses the arbitrary self types feature and traits in which +/// this feature is used are currently not object safe due to current compiler +/// limitations. (See tracking issue for arbitray self types for more +/// information #44874) pub struct LocalFutureObj<'a, T> { ptr: *mut (), poll_fn: unsafe fn(*mut (), &mut Context) -> Poll<T>, @@ -87,6 +95,15 @@ impl<'a, T> Drop for LocalFutureObj<'a, T> { /// A custom trait object for polling futures, roughly akin to /// `Box<dyn Future<Output = T> + Send + 'a>`. +/// +/// This custom trait object was introduced for two reasons: +/// - Currently it is not possible to take `dyn Trait` by value and +/// `Box<dyn Trait>` is not available in no_std contexts. +/// - The `Future` trait is currently not object safe: The `Future::poll` +/// method makes uses the arbitrary self types feature and traits in which +/// this feature is used are currently not object safe due to current compiler +/// limitations. (See tracking issue for arbitray self types for more +/// information #44874) pub struct FutureObj<'a, T>(LocalFutureObj<'a, T>); unsafe impl<'a, T> Send for FutureObj<'a, T> {} |