add libcore from 2016-04-11 nightly

1 files changed, 944 insertions, 0 deletions

diff --git a/libcore/result.rs b/libcore/result.rs
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--- /dev/null
+++ b/libcore/result.rs
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+// Copyright 2012-2014 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.
+
+//! Error handling with the `Result` type.
+//!
+//! `Result<T, E>` is the type used for returning and propagating
+//! errors. It is an enum with the variants, `Ok(T)`, representing
+//! success and containing a value, and `Err(E)`, representing error
+//! and containing an error value.
+//!
+//! ```
+//! # #[allow(dead_code)]
+//! enum Result<T, E> {
+//!    Ok(T),
+//!    Err(E)
+//! }
+//! ```
+//!
+//! Functions return `Result` whenever errors are expected and
+//! recoverable. In the `std` crate `Result` is most prominently used
+//! for [I/O](../../std/io/index.html).
+//!
+//! A simple function returning `Result` might be
+//! defined and used like so:
+//!
+//! ```
+//! #[derive(Debug)]
+//! enum Version { Version1, Version2 }
+//!
+//! fn parse_version(header: &[u8]) -> Result<Version, &'static str> {
+//!     match header.get(0) {
+//!         None => Err("invalid header length"),
+//!         Some(&1) => Ok(Version::Version1),
+//!         Some(&2) => Ok(Version::Version2),
+//!         Some(_) => Err("invalid version")
+//!     }
+//! }
+//!
+//! let version = parse_version(&[1, 2, 3, 4]);
+//! match version {
+//!     Ok(v) => println!("working with version: {:?}", v),
+//!     Err(e) => println!("error parsing header: {:?}", e),
+//! }
+//! ```
+//!
+//! Pattern matching on `Result`s is clear and straightforward for
+//! simple cases, but `Result` comes with some convenience methods
+//! that make working with it more succinct.
+//!
+//! ```
+//! let good_result: Result<i32, i32> = Ok(10);
+//! let bad_result: Result<i32, i32> = Err(10);
+//!
+//! // The `is_ok` and `is_err` methods do what they say.
+//! assert!(good_result.is_ok() && !good_result.is_err());
+//! assert!(bad_result.is_err() && !bad_result.is_ok());
+//!
+//! // `map` consumes the `Result` and produces another.
+//! let good_result: Result<i32, i32> = good_result.map(|i| i + 1);
+//! let bad_result: Result<i32, i32> = bad_result.map(|i| i - 1);
+//!
+//! // Use `and_then` to continue the computation.
+//! let good_result: Result<bool, i32> = good_result.and_then(|i| Ok(i == 11));
+//!
+//! // Use `or_else` to handle the error.
+//! let bad_result: Result<i32, i32> = bad_result.or_else(|i| Ok(i + 20));
+//!
+//! // Consume the result and return the contents with `unwrap`.
+//! let final_awesome_result = good_result.unwrap();
+//! ```
+//!
+//! # Results must be used
+//!
+//! A common problem with using return values to indicate errors is
+//! that it is easy to ignore the return value, thus failing to handle
+//! the error. Result is annotated with the #[must_use] attribute,
+//! which will cause the compiler to issue a warning when a Result
+//! value is ignored. This makes `Result` especially useful with
+//! functions that may encounter errors but don't otherwise return a
+//! useful value.
+//!
+//! Consider the `write_all` method defined for I/O types
+//! by the [`Write`](../../std/io/trait.Write.html) trait:
+//!
+//! ```
+//! use std::io;
+//!
+//! trait Write {
+//!     fn write_all(&mut self, bytes: &[u8]) -> Result<(), io::Error>;
+//! }
+//! ```
+//!
+//! *Note: The actual definition of `Write` uses `io::Result`, which
+//! is just a synonym for `Result<T, io::Error>`.*
+//!
+//! This method doesn't produce a value, but the write may
+//! fail. It's crucial to handle the error case, and *not* write
+//! something like this:
+//!
+//! ```no_run
+//! # #![allow(unused_must_use)] // \o/
+//! use std::fs::File;
+//! use std::io::prelude::*;
+//!
+//! let mut file = File::create("valuable_data.txt").unwrap();
+//! // If `write_all` errors, then we'll never know, because the return
+//! // value is ignored.
+//! file.write_all(b"important message");
+//! ```
+//!
+//! If you *do* write that in Rust, the compiler will give you a
+//! warning (by default, controlled by the `unused_must_use` lint).
+//!
+//! You might instead, if you don't want to handle the error, simply
+//! assert success with `expect`. This will panic if the
+//! write fails, providing a marginally useful message indicating why:
+//!
+//! ```{.no_run}
+//! use std::fs::File;
+//! use std::io::prelude::*;
+//!
+//! let mut file = File::create("valuable_data.txt").unwrap();
+//! file.write_all(b"important message").expect("failed to write message");
+//! ```
+//!
+//! You might also simply assert success:
+//!
+//! ```{.no_run}
+//! # use std::fs::File;
+//! # use std::io::prelude::*;
+//! # let mut file = File::create("valuable_data.txt").unwrap();
+//! assert!(file.write_all(b"important message").is_ok());
+//! ```
+//!
+//! Or propagate the error up the call stack with `try!`:
+//!
+//! ```
+//! # use std::fs::File;
+//! # use std::io::prelude::*;
+//! # use std::io;
+//! # #[allow(dead_code)]
+//! fn write_message() -> io::Result<()> {
+//!     let mut file = try!(File::create("valuable_data.txt"));
+//!     try!(file.write_all(b"important message"));
+//!     Ok(())
+//! }
+//! ```
+//!
+//! # The `try!` macro
+//!
+//! When writing code that calls many functions that return the
+//! `Result` type, the error handling can be tedious.  The `try!`
+//! macro hides some of the boilerplate of propagating errors up the
+//! call stack.
+//!
+//! It replaces this:
+//!
+//! ```
+//! # #![allow(dead_code)]
+//! use std::fs::File;
+//! use std::io::prelude::*;
+//! use std::io;
+//!
+//! struct Info {
+//!     name: String,
+//!     age: i32,
+//!     rating: i32,
+//! }
+//!
+//! fn write_info(info: &Info) -> io::Result<()> {
+//!     let mut file = try!(File::create("my_best_friends.txt"));
+//!     // Early return on error
+//!     if let Err(e) = file.write_all(format!("name: {}\n", info.name).as_bytes()) {
+//!         return Err(e)
+//!     }
+//!     if let Err(e) = file.write_all(format!("age: {}\n", info.age).as_bytes()) {
+//!         return Err(e)
+//!     }
+//!     if let Err(e) = file.write_all(format!("rating: {}\n", info.rating).as_bytes()) {
+//!         return Err(e)
+//!     }
+//!     Ok(())
+//! }
+//! ```
+//!
+//! With this:
+//!
+//! ```
+//! # #![allow(dead_code)]
+//! use std::fs::File;
+//! use std::io::prelude::*;
+//! use std::io;
+//!
+//! struct Info {
+//!     name: String,
+//!     age: i32,
+//!     rating: i32,
+//! }
+//!
+//! fn write_info(info: &Info) -> io::Result<()> {
+//!     let mut file = try!(File::create("my_best_friends.txt"));
+//!     // Early return on error
+//!     try!(file.write_all(format!("name: {}\n", info.name).as_bytes()));
+//!     try!(file.write_all(format!("age: {}\n", info.age).as_bytes()));
+//!     try!(file.write_all(format!("rating: {}\n", info.rating).as_bytes()));
+//!     Ok(())
+//! }
+//! ```
+//!
+//! *It's much nicer!*
+//!
+//! Wrapping an expression in `try!` will result in the unwrapped
+//! success (`Ok`) value, unless the result is `Err`, in which case
+//! `Err` is returned early from the enclosing function. Its simple definition
+//! makes it clear:
+//!
+//! ```
+//! macro_rules! try {
+//!     ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
+//! }
+//! ```
+//!
+//! `try!` is imported by the prelude and is available everywhere, but it can only
+//! be used in functions that return `Result` because of the early return of
+//! `Err` that it provides.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use self::Result::{Ok, Err};
+
+use clone::Clone;
+use fmt;
+use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSizeIterator, IntoIterator};
+use ops::FnOnce;
+use option::Option::{self, None, Some};
+
+/// `Result` is a type that represents either success (`Ok`) or failure (`Err`).
+///
+/// See the [`std::result`](index.html) module documentation for details.
+#[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub enum Result<T, E> {
+    /// Contains the success value
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Ok(#[stable(feature = "rust1", since = "1.0.0")] T),
+
+    /// Contains the error value
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Err(#[stable(feature = "rust1", since = "1.0.0")] E)
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Type implementation
+/////////////////////////////////////////////////////////////////////////////
+
+impl<T, E> Result<T, E> {
+    /////////////////////////////////////////////////////////////////////////
+    // Querying the contained values
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Returns true if the result is `Ok`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<i32, &str> = Ok(-3);
+    /// assert_eq!(x.is_ok(), true);
+    ///
+    /// let x: Result<i32, &str> = Err("Some error message");
+    /// assert_eq!(x.is_ok(), false);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_ok(&self) -> bool {
+        match *self {
+            Ok(_) => true,
+            Err(_) => false
+        }
+    }
+
+    /// Returns true if the result is `Err`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<i32, &str> = Ok(-3);
+    /// assert_eq!(x.is_err(), false);
+    ///
+    /// let x: Result<i32, &str> = Err("Some error message");
+    /// assert_eq!(x.is_err(), true);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_err(&self) -> bool {
+        !self.is_ok()
+    }
+
+    /////////////////////////////////////////////////////////////////////////
+    // Adapter for each variant
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Converts from `Result<T, E>` to `Option<T>`
+    ///
+    /// Converts `self` into an `Option<T>`, consuming `self`,
+    /// and discarding the error, if any.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(2);
+    /// assert_eq!(x.ok(), Some(2));
+    ///
+    /// let x: Result<u32, &str> = Err("Nothing here");
+    /// assert_eq!(x.ok(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn ok(self) -> Option<T> {
+        match self {
+            Ok(x)  => Some(x),
+            Err(_) => None,
+        }
+    }
+
+    /// Converts from `Result<T, E>` to `Option<E>`
+    ///
+    /// Converts `self` into an `Option<E>`, consuming `self`,
+    /// and discarding the success value, if any.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(2);
+    /// assert_eq!(x.err(), None);
+    ///
+    /// let x: Result<u32, &str> = Err("Nothing here");
+    /// assert_eq!(x.err(), Some("Nothing here"));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn err(self) -> Option<E> {
+        match self {
+            Ok(_)  => None,
+            Err(x) => Some(x),
+        }
+    }
+
+    /////////////////////////////////////////////////////////////////////////
+    // Adapter for working with references
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Converts from `Result<T, E>` to `Result<&T, &E>`
+    ///
+    /// Produces a new `Result`, containing a reference
+    /// into the original, leaving the original in place.
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(2);
+    /// assert_eq!(x.as_ref(), Ok(&2));
+    ///
+    /// let x: Result<u32, &str> = Err("Error");
+    /// assert_eq!(x.as_ref(), Err(&"Error"));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn as_ref(&self) -> Result<&T, &E> {
+        match *self {
+            Ok(ref x) => Ok(x),
+            Err(ref x) => Err(x),
+        }
+    }
+
+    /// Converts from `Result<T, E>` to `Result<&mut T, &mut E>`
+    ///
+    /// ```
+    /// fn mutate(r: &mut Result<i32, i32>) {
+    ///     match r.as_mut() {
+    ///         Ok(&mut ref mut v) => *v = 42,
+    ///         Err(&mut ref mut e) => *e = 0,
+    ///     }
+    /// }
+    ///
+    /// let mut x: Result<i32, i32> = Ok(2);
+    /// mutate(&mut x);
+    /// assert_eq!(x.unwrap(), 42);
+    ///
+    /// let mut x: Result<i32, i32> = Err(13);
+    /// mutate(&mut x);
+    /// assert_eq!(x.unwrap_err(), 0);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn as_mut(&mut self) -> Result<&mut T, &mut E> {
+        match *self {
+            Ok(ref mut x) => Ok(x),
+            Err(ref mut x) => Err(x),
+        }
+    }
+
+    /////////////////////////////////////////////////////////////////////////
+    // Transforming contained values
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Maps a `Result<T, E>` to `Result<U, E>` by applying a function to a
+    /// contained `Ok` value, leaving an `Err` value untouched.
+    ///
+    /// This function can be used to compose the results of two functions.
+    ///
+    /// # Examples
+    ///
+    /// Print the numbers on each line of a string multiplied by two.
+    ///
+    /// ```
+    /// let line = "1\n2\n3\n4\n";
+    ///
+    /// for num in line.lines() {
+    ///     match num.parse::<i32>().map(|i| i * 2) {
+    ///         Ok(n) => println!("{}", n),
+    ///         Err(..) => {}
+    ///     }
+    /// }
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn map<U, F: FnOnce(T) -> U>(self, op: F) -> Result<U,E> {
+        match self {
+            Ok(t) => Ok(op(t)),
+            Err(e) => Err(e)
+        }
+    }
+
+    /// Maps a `Result<T, E>` to `Result<T, F>` by applying a function to a
+    /// contained `Err` value, leaving an `Ok` value untouched.
+    ///
+    /// This function can be used to pass through a successful result while handling
+    /// an error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// fn stringify(x: u32) -> String { format!("error code: {}", x) }
+    ///
+    /// let x: Result<u32, u32> = Ok(2);
+    /// assert_eq!(x.map_err(stringify), Ok(2));
+    ///
+    /// let x: Result<u32, u32> = Err(13);
+    /// assert_eq!(x.map_err(stringify), Err("error code: 13".to_string()));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn map_err<F, O: FnOnce(E) -> F>(self, op: O) -> Result<T,F> {
+        match self {
+            Ok(t) => Ok(t),
+            Err(e) => Err(op(e))
+        }
+    }
+
+    /////////////////////////////////////////////////////////////////////////
+    // Iterator constructors
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Returns an iterator over the possibly contained value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(7);
+    /// assert_eq!(x.iter().next(), Some(&7));
+    ///
+    /// let x: Result<u32, &str> = Err("nothing!");
+    /// assert_eq!(x.iter().next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter(&self) -> Iter<T> {
+        Iter { inner: self.as_ref().ok() }
+    }
+
+    /// Returns a mutable iterator over the possibly contained value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut x: Result<u32, &str> = Ok(7);
+    /// match x.iter_mut().next() {
+    ///     Some(v) => *v = 40,
+    ///     None => {},
+    /// }
+    /// assert_eq!(x, Ok(40));
+    ///
+    /// let mut x: Result<u32, &str> = Err("nothing!");
+    /// assert_eq!(x.iter_mut().next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter_mut(&mut self) -> IterMut<T> {
+        IterMut { inner: self.as_mut().ok() }
+    }
+
+    ////////////////////////////////////////////////////////////////////////
+    // Boolean operations on the values, eager and lazy
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Returns `res` if the result is `Ok`, otherwise returns the `Err` value of `self`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(2);
+    /// let y: Result<&str, &str> = Err("late error");
+    /// assert_eq!(x.and(y), Err("late error"));
+    ///
+    /// let x: Result<u32, &str> = Err("early error");
+    /// let y: Result<&str, &str> = Ok("foo");
+    /// assert_eq!(x.and(y), Err("early error"));
+    ///
+    /// let x: Result<u32, &str> = Err("not a 2");
+    /// let y: Result<&str, &str> = Err("late error");
+    /// assert_eq!(x.and(y), Err("not a 2"));
+    ///
+    /// let x: Result<u32, &str> = Ok(2);
+    /// let y: Result<&str, &str> = Ok("different result type");
+    /// assert_eq!(x.and(y), Ok("different result type"));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn and<U>(self, res: Result<U, E>) -> Result<U, E> {
+        match self {
+            Ok(_) => res,
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Calls `op` if the result is `Ok`, otherwise returns the `Err` value of `self`.
+    ///
+    /// This function can be used for control flow based on result values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// fn sq(x: u32) -> Result<u32, u32> { Ok(x * x) }
+    /// fn err(x: u32) -> Result<u32, u32> { Err(x) }
+    ///
+    /// assert_eq!(Ok(2).and_then(sq).and_then(sq), Ok(16));
+    /// assert_eq!(Ok(2).and_then(sq).and_then(err), Err(4));
+    /// assert_eq!(Ok(2).and_then(err).and_then(sq), Err(2));
+    /// assert_eq!(Err(3).and_then(sq).and_then(sq), Err(3));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn and_then<U, F: FnOnce(T) -> Result<U, E>>(self, op: F) -> Result<U, E> {
+        match self {
+            Ok(t) => op(t),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Returns `res` if the result is `Err`, otherwise returns the `Ok` value of `self`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(2);
+    /// let y: Result<u32, &str> = Err("late error");
+    /// assert_eq!(x.or(y), Ok(2));
+    ///
+    /// let x: Result<u32, &str> = Err("early error");
+    /// let y: Result<u32, &str> = Ok(2);
+    /// assert_eq!(x.or(y), Ok(2));
+    ///
+    /// let x: Result<u32, &str> = Err("not a 2");
+    /// let y: Result<u32, &str> = Err("late error");
+    /// assert_eq!(x.or(y), Err("late error"));
+    ///
+    /// let x: Result<u32, &str> = Ok(2);
+    /// let y: Result<u32, &str> = Ok(100);
+    /// assert_eq!(x.or(y), Ok(2));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn or<F>(self, res: Result<T, F>) -> Result<T, F> {
+        match self {
+            Ok(v) => Ok(v),
+            Err(_) => res,
+        }
+    }
+
+    /// Calls `op` if the result is `Err`, otherwise returns the `Ok` value of `self`.
+    ///
+    /// This function can be used for control flow based on result values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// fn sq(x: u32) -> Result<u32, u32> { Ok(x * x) }
+    /// fn err(x: u32) -> Result<u32, u32> { Err(x) }
+    ///
+    /// assert_eq!(Ok(2).or_else(sq).or_else(sq), Ok(2));
+    /// assert_eq!(Ok(2).or_else(err).or_else(sq), Ok(2));
+    /// assert_eq!(Err(3).or_else(sq).or_else(err), Ok(9));
+    /// assert_eq!(Err(3).or_else(err).or_else(err), Err(3));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn or_else<F, O: FnOnce(E) -> Result<T, F>>(self, op: O) -> Result<T, F> {
+        match self {
+            Ok(t) => Ok(t),
+            Err(e) => op(e),
+        }
+    }
+
+    /// Unwraps a result, yielding the content of an `Ok`.
+    /// Else it returns `optb`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let optb = 2;
+    /// let x: Result<u32, &str> = Ok(9);
+    /// assert_eq!(x.unwrap_or(optb), 9);
+    ///
+    /// let x: Result<u32, &str> = Err("error");
+    /// assert_eq!(x.unwrap_or(optb), optb);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn unwrap_or(self, optb: T) -> T {
+        match self {
+            Ok(t) => t,
+            Err(_) => optb
+        }
+    }
+
+    /// Unwraps a result, yielding the content of an `Ok`.
+    /// If the value is an `Err` then it calls `op` with its value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// fn count(x: &str) -> usize { x.len() }
+    ///
+    /// assert_eq!(Ok(2).unwrap_or_else(count), 2);
+    /// assert_eq!(Err("foo").unwrap_or_else(count), 3);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn unwrap_or_else<F: FnOnce(E) -> T>(self, op: F) -> T {
+        match self {
+            Ok(t) => t,
+            Err(e) => op(e)
+        }
+    }
+}
+
+impl<T, E: fmt::Debug> Result<T, E> {
+    /// Unwraps a result, yielding the content of an `Ok`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is an `Err`, with a panic message provided by the
+    /// `Err`'s value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(2);
+    /// assert_eq!(x.unwrap(), 2);
+    /// ```
+    ///
+    /// ```{.should_panic}
+    /// let x: Result<u32, &str> = Err("emergency failure");
+    /// x.unwrap(); // panics with `emergency failure`
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn unwrap(self) -> T {
+        match self {
+            Ok(t) => t,
+            Err(e) => unwrap_failed("called `Result::unwrap()` on an `Err` value", e),
+        }
+    }
+
+    /// Unwraps a result, yielding the content of an `Ok`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is an `Err`, with a panic message including the
+    /// passed message, and the content of the `Err`.
+    ///
+    /// # Examples
+    /// ```{.should_panic}
+    /// let x: Result<u32, &str> = Err("emergency failure");
+    /// x.expect("Testing expect"); // panics with `Testing expect: emergency failure`
+    /// ```
+    #[inline]
+    #[stable(feature = "result_expect", since = "1.4.0")]
+    pub fn expect(self, msg: &str) -> T {
+        match self {
+            Ok(t) => t,
+            Err(e) => unwrap_failed(msg, e),
+        }
+    }
+}
+
+impl<T: fmt::Debug, E> Result<T, E> {
+    /// Unwraps a result, yielding the content of an `Err`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is an `Ok`, with a custom panic message provided
+    /// by the `Ok`'s value.
+    ///
+    /// # Examples
+    ///
+    /// ```{.should_panic}
+    /// let x: Result<u32, &str> = Ok(2);
+    /// x.unwrap_err(); // panics with `2`
+    /// ```
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Err("emergency failure");
+    /// assert_eq!(x.unwrap_err(), "emergency failure");
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn unwrap_err(self) -> E {
+        match self {
+            Ok(t) => unwrap_failed("called `Result::unwrap_err()` on an `Ok` value", t),
+            Err(e) => e,
+        }
+    }
+}
+
+// This is a separate function to reduce the code size of the methods
+#[inline(never)]
+#[cold]
+fn unwrap_failed<E: fmt::Debug>(msg: &str, error: E) -> ! {
+    panic!("{}: {:?}", msg, error)
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// Trait implementations
+/////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, E> IntoIterator for Result<T, E> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    /// Returns a consuming iterator over the possibly contained value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x: Result<u32, &str> = Ok(5);
+    /// let v: Vec<u32> = x.into_iter().collect();
+    /// assert_eq!(v, [5]);
+    ///
+    /// let x: Result<u32, &str> = Err("nothing!");
+    /// let v: Vec<u32> = x.into_iter().collect();
+    /// assert_eq!(v, []);
+    /// ```
+    #[inline]
+    fn into_iter(self) -> IntoIter<T> {
+        IntoIter { inner: self.ok() }
+    }
+}
+
+#[stable(since = "1.4.0", feature = "result_iter")]
+impl<'a, T, E> IntoIterator for &'a Result<T, E> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(since = "1.4.0", feature = "result_iter")]
+impl<'a, T, E> IntoIterator for &'a mut Result<T, E> {
+    type Item = &'a mut T;
+    type IntoIter = IterMut<'a, T>;
+
+    fn into_iter(mut self) -> IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// The Result Iterators
+/////////////////////////////////////////////////////////////////////////////
+
+/// An iterator over a reference to the `Ok` variant of a `Result`.
+#[derive(Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Iter<'a, T: 'a> { inner: Option<&'a T> }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a T> { self.inner.take() }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = if self.inner.is_some() {1} else {0};
+        (n, Some(n))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a T> { self.inner.take() }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> ExactSizeIterator for Iter<'a, T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Clone for Iter<'a, T> {
+    fn clone(&self) -> Iter<'a, T> { Iter { inner: self.inner } }
+}
+
+/// An iterator over a mutable reference to the `Ok` variant of a `Result`.
+#[derive(Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IterMut<'a, T: 'a> { inner: Option<&'a mut T> }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for IterMut<'a, T> {
+    type Item = &'a mut T;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a mut T> { self.inner.take() }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = if self.inner.is_some() {1} else {0};
+        (n, Some(n))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a mut T> { self.inner.take() }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> ExactSizeIterator for IterMut<'a, T> {}
+
+/// An iterator over the value in a `Ok` variant of a `Result`.
+#[derive(Debug)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IntoIter<T> { inner: Option<T> }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> { self.inner.take() }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = if self.inner.is_some() {1} else {0};
+        (n, Some(n))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> { self.inner.take() }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for IntoIter<T> {}
+
+/////////////////////////////////////////////////////////////////////////////
+// FromIterator
+/////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E> {
+    /// Takes each element in the `Iterator`: if it is an `Err`, no further
+    /// elements are taken, and the `Err` is returned. Should no `Err` occur, a
+    /// container with the values of each `Result` is returned.
+    ///
+    /// Here is an example which increments every integer in a vector,
+    /// checking for overflow:
+    ///
+    /// ```
+    /// use std::u32;
+    ///
+    /// let v = vec!(1, 2);
+    /// let res: Result<Vec<u32>, &'static str> = v.iter().map(|&x: &u32|
+    ///     if x == u32::MAX { Err("Overflow!") }
+    ///     else { Ok(x + 1) }
+    /// ).collect();
+    /// assert!(res == Ok(vec!(2, 3)));
+    /// ```
+    #[inline]
+    fn from_iter<I: IntoIterator<Item=Result<A, E>>>(iter: I) -> Result<V, E> {
+        // FIXME(#11084): This could be replaced with Iterator::scan when this
+        // performance bug is closed.
+
+        struct Adapter<Iter, E> {
+            iter: Iter,
+            err: Option<E>,
+        }
+
+        impl<T, E, Iter: Iterator<Item=Result<T, E>>> Iterator for Adapter<Iter, E> {
+            type Item = T;
+
+            #[inline]
+            fn next(&mut self) -> Option<T> {
+                match self.iter.next() {
+                    Some(Ok(value)) => Some(value),
+                    Some(Err(err)) => {
+                        self.err = Some(err);
+                        None
+                    }
+                    None => None,
+                }
+            }
+        }
+
+        let mut adapter = Adapter { iter: iter.into_iter(), err: None };
+        let v: V = FromIterator::from_iter(adapter.by_ref());
+
+        match adapter.err {
+            Some(err) => Err(err),
+            None => Ok(v),
+        }
+    }
+}