From ec98b41c85bb8c2891755fc6b86366fb85413a5e Mon Sep 17 00:00:00 2001
From: k-nasa <htilcs1115@gmail.com>
Date: Thu, 17 Oct 2019 23:56:01 +0900
Subject: [PATCH] feat: Add FlattenCompat struct

---
 src/lib.rs                   |  1 +
 src/stream/stream/flatten.rs | 24 ++++++++++++++++++++++++
 src/stream/stream/mod.rs     |  1 +
 3 files changed, 26 insertions(+)
 create mode 100644 src/stream/stream/flatten.rs

diff --git a/src/lib.rs b/src/lib.rs
index e138c87..afbad31 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -47,6 +47,7 @@
 #![doc(test(attr(allow(unused_extern_crates, unused_variables))))]
 #![doc(html_logo_url = "https://async.rs/images/logo--hero.svg")]
 #![recursion_limit = "1024"]
+#![feature(associated_type_bounds)]
 
 use cfg_if::cfg_if;
 
diff --git a/src/stream/stream/flatten.rs b/src/stream/stream/flatten.rs
new file mode 100644
index 0000000..fffda4d
--- /dev/null
+++ b/src/stream/stream/flatten.rs
@@ -0,0 +1,24 @@
+use std::pin::Pin;
+
+use crate::stream::{IntoStream, Stream};
+use crate::task::{Context, Poll};
+
+/// Real logic of both `Flatten` and `FlatMap` which simply delegate to
+/// this type.
+#[derive(Clone, Debug)]
+struct FlattenCompat<S, U> {
+    stream: S,
+    frontiter: Option<U>,
+}
+impl<S, U> FlattenCompat<S, U> {
+    pin_utils::unsafe_unpinned!(stream: S);
+    pin_utils::unsafe_unpinned!(frontiter: Option<U>);
+
+    /// Adapts an iterator by flattening it, for use in `flatten()` and `flat_map()`.
+    pub fn new(stream: S) -> FlattenCompat<S, U> {
+        FlattenCompat {
+            stream,
+            frontiter: None,
+        }
+    }
+}
diff --git a/src/stream/stream/mod.rs b/src/stream/stream/mod.rs
index 764dc97..7047b03 100644
--- a/src/stream/stream/mod.rs
+++ b/src/stream/stream/mod.rs
@@ -106,6 +106,7 @@ cfg_if! {
 cfg_if! {
     if #[cfg(any(feature = "unstable", feature = "docs"))] {
         mod merge;
+        mod flatten;
 
         use std::pin::Pin;