macros: add assignment form to pin! (#2274)

Allows combining assignment to a binding and pinning it.

1 files changed, 33 insertions, 1 deletions

diff --git a/tokio/src/macros/pin.rs b/tokio/src/macros/pin.rs
index e8511d3f..5b677610 100644
--- a/tokio/src/macros/pin.rs
+++ b/tokio/src/macros/pin.rs
@@ -97,6 +97,30 @@
 ///     }
 /// }
 /// ```
+///
+/// Because assigning to a variable followed by pinning is common, there is also
+/// a variant of the macro that supports doing both in one go.
+///
+/// ```
+/// use tokio::{pin, select};
+///
+/// async fn my_async_fn() {
+///     // async logic here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     pin! {
+///         let future1 = my_async_fn();
+///         let future2 = my_async_fn();
+///     }
+///
+///     select! {
+///         _ = &mut future1 => {}
+///         _ = &mut future2 => {}
+///     }
+/// }
+/// ```
 #[macro_export]
 macro_rules! pin {
     ($($x:ident),*) => { $(
@@ -108,5 +132,13 @@ macro_rules! pin {
         let mut $x = unsafe {
             $crate::macros::support::Pin::new_unchecked(&mut $x)
         };
-    )* }
+    )* };
+    ($(
+            let $x:ident = $init:expr;
+    )*) => {
+        $(
+            let $x = $init;
+            crate::pin!($x);
+        )*
+    };
 }