stream_select_mod.rs

//! The `select` macro.

use proc_macro_hack::proc_macro_hack;

#[cfg(feature = "std")]
#[doc(hidden)]
#[proc_macro_hack(support_nested, only_hack_old_rustc)]
pub use futures_macro::stream_select_internal;

/// Combines several streams, all producing the same `Item` type, into one stream.a
/// This is similar to `select_all` but does not require the streams to all be the same type.
/// It also keeps the streams inline, and does not require `Box<dyn Stream>`s to be allocated.
/// Streams passed to this macro must be `Unpin` and implement `FusedStream`.
/// 
/// Fairness for this stream is implemented in terms of the futures `select` macro. If multiple
/// streams are ready, one will be pseudo randomly selected at runtime. Streams which are not
/// already fused can be fused by using the `.fuse()` method.
/// 
/// This macro is gated behind the `async-await` feature of this library, which is activated by default.
/// Note that `stream_select!` relies on `proc-macro-hack`, and may require to set the compiler's recursion
/// limit very high, e.g. `#![recursion_limit="1024"]`.
/// 
/// # Examples
/// 
/// ```
/// # futures::executor::block_on(async {
/// use futures::{stream, StreamExt, stream_select};
/// let endless_ints = |i| stream::iter(vec![i].into_iter().cycle()).fuse();
/// 
/// let mut endless_numbers = stream_select!(endless_ints(1i32), endless_ints(2), endless_ints(3));
/// match endless_numbers.next().await {
///     Some(1) => println!("Got a 1"),
///     Some(2) => println!("Got a 2"),
///     Some(3) => println!("Got a 3"),
///     _ => unreachable!(),
/// }
/// # });
/// ```
#[cfg(feature = "std")]
#[macro_export]
macro_rules! stream_select {
    ($($tokens:tt)*) => {{
        use $crate::__private as __futures_crate;
        $crate::stream_select_internal! {
            $( $tokens )*
        }
    }}
}