add either example

futures-util/src/future/either.rs

@@ -5,8 +5,25 @@ use futures_core::stream::{FusedStream, Stream};
 #[cfg(feature = "sink")]
 use futures_sink::Sink;
 
-/// Combines two different futures, streams, or sinks having the same associated types into a single
-/// type.
+/// Combines two different futures, streams, or sinks having the same associated types into a single type.
+///
+/// This is useful when conditionally choosing between two distinct future types:
+///
+/// ```rust
+/// use futures::future::Either;
+///
+/// # futures::executor::block_on(async {
+/// let cond = true;
+///
+/// let fut = if cond {
+///     Either::Left(async move { 12 })
+/// } else {
+///     Either::Right(async move { 44 })
+/// };
+///
+/// assert_eq!(fut.await, 12);
+/// # })
+/// ```
 #[derive(Debug, Clone)]
 pub enum Either<A, B> {
     /// First branch of the type

futures-util/src/sink/mod.rs

@@ -243,7 +243,7 @@ pub trait SinkExt<Item>: Sink<Item> {
     /// This future will drive the stream to keep producing items until it is
     /// exhausted, sending each item to the sink. It will complete once both the
     /// stream is exhausted, the sink has received all items, and the sink has
-    /// been flushed. Note that the sink is **not** closed. If the stream produces 
+    /// been flushed. Note that the sink is **not** closed. If the stream produces
     /// an error, that error will be returned by this future without flushing the sink.
     ///
     /// Doing `sink.send_all(stream)` is roughly equivalent to