From 68d05b2a073d2679ec1621ea1ebc49b7814cf250 Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Wed, 18 Oct 2017 23:12:37 -0700
Subject: [PATCH] impl FromIterator<()> for ()

This just collapses all unit items from an iterator into one.  This is
more useful when combined with higher-level abstractions, like
collecting to a `Result<(), E>` where you only care about errors:

```rust
use std::io::*;
data = vec![1, 2, 3, 4, 5];
let res: Result<()> = data.iter()
    .map(|x| writeln!(stdout(), "{}", x))
    .collect();
assert!(res.is_ok());
```
---
 src/libcore/lib.rs  |  1 +
 src/libcore/unit.rs | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 src/libcore/unit.rs

diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 69612bd2a32a4..dc7ec29ce4527 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -190,3 +190,4 @@ pub mod fmt;
 mod char_private;
 mod iter_private;
 mod tuple;
+mod unit;
diff --git a/src/libcore/unit.rs b/src/libcore/unit.rs
new file mode 100644
index 0000000000000..087ddf9688ab7
--- /dev/null
+++ b/src/libcore/unit.rs
@@ -0,0 +1,31 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use iter::FromIterator;
+
+/// Collapses all unit items from an iterator into one.
+///
+/// This is more useful when combined with higher-level abstractions, like
+/// collecting to a `Result<(), E>` where you only care about errors:
+///
+/// ```
+/// use std::io::*;
+/// let data = vec![1, 2, 3, 4, 5];
+/// let res: Result<()> = data.iter()
+///     .map(|x| writeln!(stdout(), "{}", x))
+///     .collect();
+/// assert!(res.is_ok());
+/// ```
+#[stable(feature = "unit_from_iter", since = "1.23.0")]
+impl FromIterator<()> for () {
+    fn from_iter<I: IntoIterator<Item=()>>(iter: I) -> Self {
+        iter.into_iter().for_each(|()| {})
+    }
+}