From dc3a39d807512c626495c16680df2fffc16e8722 Mon Sep 17 00:00:00 2001
From: Steve Klabnik <steve@steveklabnik.com>
Date: Mon, 1 Feb 2016 18:49:47 -0500
Subject: [PATCH 1/2] Explain behavior of _

Fixes #31154
---
 src/doc/book/patterns.md | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/doc/book/patterns.md b/src/doc/book/patterns.md
index 8e9e7246e56f0..39a9cb1885e84 100644
--- a/src/doc/book/patterns.md
+++ b/src/doc/book/patterns.md
@@ -173,7 +173,31 @@ let (x, _, z) = coordinate();
 Here, we bind the first and last element of the tuple to `x` and `z`, but
 ignore the middle element.
 
-Similarly, you can use `..` in a pattern to disregard multiple values.
+It’s worth noting that using `_` never binds the value in the first place,
+which means a value may not move:
+
+```rust
+let tuple: (u32, String) = (5, String::from("five"));
+
+// Here, tuple is moved, because the String moved:
+let (x, _s) = tuple;
+
+// The next line would give "error: use of partially moved value: `tuple`"
+// println!("Tuple is: {:?}", tuple);
+
+// However,
+
+let tuple = (5, String::from("five"));
+
+// Here, tuple is _not_ moved, as the String was never moved, and u32 is Copy:
+let (x, _) = tuple;
+
+// That means this works:
+println!("Tuple is: {:?}", tuple);
+```
+
+In a similar fashion to `_`, you can use `..` in a pattern to disregard
+multiple values:
 
 ```rust
 enum OptionalTuple {

From 6c907212b446e1c39ddb6db621bb72c6d07255f6 Mon Sep 17 00:00:00 2001
From: Steve Klabnik <steve@steveklabnik.com>
Date: Tue, 2 Feb 2016 11:15:45 -0500
Subject: [PATCH 2/2] Add note about temporaries

---
 src/doc/book/patterns.md | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/doc/book/patterns.md b/src/doc/book/patterns.md
index 39a9cb1885e84..6fd7f4cd4755a 100644
--- a/src/doc/book/patterns.md
+++ b/src/doc/book/patterns.md
@@ -196,8 +196,16 @@ let (x, _) = tuple;
 println!("Tuple is: {:?}", tuple);
 ```
 
-In a similar fashion to `_`, you can use `..` in a pattern to disregard
-multiple values:
+This also means that any temporary variables will be dropped at the end of the
+statement:
+
+```rust
+// Here, the String created will be dropped immediately, as it’s not bound:
+
+let _ = String::from("  hello  ").trim();
+```
+
+You can also use `..` in a pattern to disregard multiple values:
 
 ```rust
 enum OptionalTuple {