Rollup of 10 pull requests

CONTRIBUTING.md

@@ -301,12 +301,12 @@ It's absolutely fine to have multiple build directories with different
 [pull-requests]: #pull-requests
 
 Pull requests are the primary mechanism we use to change Rust. GitHub itself
-has some [great documentation][pull-requests] on using the Pull Request feature.
+has some [great documentation][about-pull-requests] on using the Pull Request feature.
 We use the "fork and pull" model [described here][development-models], where
 contributors push changes to their personal fork and create pull requests to
 bring those changes into the source repository.
 
-[pull-requests]: https://help.github.com/articles/about-pull-requests/
+[about-pull-requests]: https://help.github.com/articles/about-pull-requests/
 [development-models]: https://help.github.com/articles/about-collaborative-development-models/
 
 Please make pull requests against the `master` branch.

src/doc/index.md

@@ -28,6 +28,7 @@ Rust provides a number of book-length sets of documentation, collectively
 nicknamed 'The Rust Bookshelf.'
 
 * [The Rust Programming Language][book] teaches you how to program in Rust.
+* [Rust By Example][rbe] teaches you how to program in Rust using editable examples.
 * [The Cargo Book][cargo-book] is a guide to Cargo, Rust's build tool and dependency manager.
 * [The Unstable Book][unstable-book] has documentation for unstable features.
 * [The Rustonomicon][nomicon] is your guidebook to the dark arts of unsafe Rust.
@@ -51,6 +52,7 @@ before this policy was put into place. That work is being tracked
 [refchecklist]: https://github.com/rust-lang-nursery/reference/issues/9
 [err]: error-index.html
 [book]: book/index.html
+[rbe]: rust-by-example/index.html
 [nomicon]: nomicon/index.html
 [unstable-book]: unstable-book/index.html
 [rustdoc-book]: rustdoc/index.html

src/libcore/option.rs

@@ -881,6 +881,35 @@ impl<T: Default> Option<T> {
     }
 }
 
+impl<T, E> Option<Result<T, E>> {
+    /// Transposes an `Option` of a `Result` into a `Result` of an `Option`.
+    ///
+    /// `None` will be mapped to `Ok(None)`.
+    /// `Some(Ok(_))` and `Some(Err(_))` will be mapped to `Ok(Some(_))` and `Err(_)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(transpose_result)]
+    ///
+    /// #[derive(Debug, Eq, PartialEq)]
+    /// struct SomeErr;
+    ///
+    /// let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
+    /// let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
+    /// assert_eq!(x, y.transpose());
+    /// ```
+    #[inline]
+    #[unstable(feature = "transpose_result", issue = "47338")]
+    pub fn transpose(self) -> Result<Option<T>, E> {
+        match self {
+            Some(Ok(x)) => Ok(Some(x)),
+            Some(Err(e)) => Err(e),
+            None => Ok(None),
+        }
+    }
+}
+
 // This is a separate function to reduce the code size of .expect() itself.
 #[inline(never)]
 #[cold]

src/libcore/result.rs

@@ -909,6 +909,35 @@ impl<T: Default, E> Result<T, E> {
     }
 }
 
+impl<T, E> Result<Option<T>, E> {
+    /// Transposes a `Result` of an `Option` into an `Option` of a `Result`.
+    ///
+    /// `Ok(None)` will be mapped to `None`.
+    /// `Ok(Some(_))` and `Err(_)` will be mapped to `Some(Ok(_))` and `Some(Err(_))`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(transpose_result)]
+    ///
+    /// #[derive(Debug, Eq, PartialEq)]
+    /// struct SomeErr;
+    ///
+    /// let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
+    /// let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
+    /// assert_eq!(x.transpose(), y);
+    /// ```
+    #[inline]
+    #[unstable(feature = "transpose_result", issue = "47338")]
+    pub fn transpose(self) -> Option<Result<T, E>> {
+        match self {
+            Ok(Some(x)) => Some(Ok(x)),
+            Ok(None) => None,
+            Err(e) => Some(Err(e)),
+        }
+    }
+}
+
 // This is a separate function to reduce the code size of the methods
 #[inline(never)]
 #[cold]