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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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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. /// /// # Examples /// /// Basic usage: /// /// ``` /// 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>` /// /// # Examples /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ``` /// 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 /// /// Basic usage: /// /// ```{.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 /// /// Basic usage: /// /// ``` /// 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), } } }