/// A trait that adds `Send` requirement if `send` feature is enabled.
#[cfg(feature = "send")]
pub trait MaybeSend: Send {}
#[cfg(feature = "send")]
impl<T: Send> MaybeSend for T {}
#[cfg(not(feature = "send"))]
pub trait MaybeSend {}
#[cfg(not(feature = "send"))]
impl<T> MaybeSend for T {}