Test specialization for AsyncWrite with Vec

futures-io/src/lib.rs

@@ -10,6 +10,8 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
+#![feature(specialization)]
+
 #![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
 #![warn(clippy::all)]
 
@@ -505,7 +507,7 @@ mod if_std {
     }
 
     impl<T: AsMut<[u8]> + Unpin> AsyncWrite for StdIo::Cursor<T> {
-        fn poll_write(
+        default fn poll_write(
             mut self: Pin<&mut Self>,
             _: &mut Context<'_>,
             buf: &[u8],
@@ -537,6 +539,26 @@ mod if_std {
         }
     }
 
+    impl AsyncWrite for StdIo::Cursor<&mut Vec<u8>> {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<Result<usize>> {
+            Poll::Ready(StdIo::Write::write(self.get_mut(), buf))
+        }
+    }
+
+    impl AsyncWrite for StdIo::Cursor<Vec<u8>> {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<Result<usize>> {
+            Poll::Ready(StdIo::Write::write(self.get_mut(), buf))
+        }
+    }
+
     impl AsyncWrite for Vec<u8> {
         delegate_async_write_to_stdio!();
     }

futures/tests/io_buf_writer.rs

@@ -222,9 +222,7 @@ impl AsyncSeek for MaybePendingSeek {
 
 #[test]
 fn maybe_pending_buf_writer_seek() {
-    // FIXME: when https://github.com/rust-lang-nursery/futures-rs/issues/1510 fixed,
-    // use `Vec::new` instead of `vec![0; 8]`.
-    let mut w = BufWriter::with_capacity(3, MaybePendingSeek::new(vec![0; 8]));
+    let mut w = BufWriter::with_capacity(3, MaybePendingSeek::new(Vec::new()));
     run(w.write_all(&[0, 1, 2, 3, 4, 5])).unwrap();
     run(w.write_all(&[6, 7])).unwrap();
     assert_eq!(run(w.seek(SeekFrom::Current(0))).ok(), Some(8));