66613e26b9
This breaks all implementors of FromIterator, as they must now accept IntoIterator instead of Iterator. The fix for this is generally trivial (change the bound, and maybe call into_iter() on the argument to get the old argument). Users of FromIterator should be unaffected because Iterators are IntoIterator. [breaking-change]
972 lines
29 KiB
Rust
972 lines
29 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Error handling with the `Result` type
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//!
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//! `Result<T, E>` is the type used for returning and propagating
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//! errors. It is an enum with the variants, `Ok(T)`, representing
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//! success and containing a value, and `Err(E)`, representing error
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//! and containing an error value.
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//!
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//! ```
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//! enum Result<T, E> {
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//! Ok(T),
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//! Err(E)
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//! }
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//! ```
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//!
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//! Functions return `Result` whenever errors are expected and
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//! recoverable. In the `std` crate `Result` is most prominently used
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//! for [I/O](../../std/io/index.html).
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//!
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//! A simple function returning `Result` might be
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//! defined and used like so:
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//!
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//! ```
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//! #[derive(Debug)]
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//! enum Version { Version1, Version2 }
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//!
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//! fn parse_version(header: &[u8]) -> Result<Version, &'static str> {
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//! if header.len() < 1 {
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//! return Err("invalid header length");
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//! }
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//! match header[0] {
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//! 1 => Ok(Version::Version1),
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//! 2 => Ok(Version::Version2),
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//! _ => Err("invalid version")
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//! }
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//! }
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//!
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//! let version = parse_version(&[1, 2, 3, 4]);
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//! match version {
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//! Ok(v) => {
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//! println!("working with version: {:?}", v);
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//! }
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//! Err(e) => {
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//! println!("error parsing header: {:?}", e);
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//! }
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//! }
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//! ```
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//!
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//! Pattern matching on `Result`s is clear and straightforward for
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//! simple cases, but `Result` comes with some convenience methods
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//! that make working with it more succinct.
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//!
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//! ```
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//! let good_result: Result<int, int> = Ok(10);
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//! let bad_result: Result<int, int> = Err(10);
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//!
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//! // The `is_ok` and `is_err` methods do what they say.
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//! assert!(good_result.is_ok() && !good_result.is_err());
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//! assert!(bad_result.is_err() && !bad_result.is_ok());
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//!
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//! // `map` consumes the `Result` and produces another.
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//! let good_result: Result<int, int> = good_result.map(|i| i + 1);
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//! let bad_result: Result<int, int> = bad_result.map(|i| i - 1);
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//!
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//! // Use `and_then` to continue the computation.
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//! let good_result: Result<bool, int> = good_result.and_then(|i| Ok(i == 11));
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//!
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//! // Use `or_else` to handle the error.
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//! let bad_result: Result<int, int> = bad_result.or_else(|i| Ok(11));
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//!
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//! // Consume the result and return the contents with `unwrap`.
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//! let final_awesome_result = good_result.ok().unwrap();
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//! ```
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//!
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//! # Results must be used
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//!
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//! A common problem with using return values to indicate errors is
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//! that it is easy to ignore the return value, thus failing to handle
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//! the error. Result is annotated with the #[must_use] attribute,
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//! which will cause the compiler to issue a warning when a Result
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//! value is ignored. This makes `Result` especially useful with
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//! functions that may encounter errors but don't otherwise return a
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//! useful value.
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//!
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//! Consider the `write_line` method defined for I/O types
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//! by the [`Writer`](../io/trait.Writer.html) trait:
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//!
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//! ```
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//! use std::old_io::IoError;
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//!
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//! trait Writer {
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//! fn write_line(&mut self, s: &str) -> Result<(), IoError>;
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//! }
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//! ```
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//!
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//! *Note: The actual definition of `Writer` uses `IoResult`, which
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//! is just a synonym for `Result<T, IoError>`.*
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//!
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//! This method doesn't produce a value, but the write may
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//! fail. It's crucial to handle the error case, and *not* write
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//! something like this:
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//!
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//! ```{.ignore}
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//! use std::old_io::{File, Open, Write};
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//!
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//! let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
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//! // If `write_line` errors, then we'll never know, because the return
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//! // value is ignored.
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//! file.write_line("important message");
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//! drop(file);
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//! ```
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//!
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//! If you *do* write that in Rust, the compiler will give you a
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//! warning (by default, controlled by the `unused_must_use` lint).
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//!
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//! You might instead, if you don't want to handle the error, simply
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//! panic, by converting to an `Option` with `ok`, then asserting
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//! success with `expect`. This will panic if the write fails, proving
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//! a marginally useful message indicating why:
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//!
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//! ```{.no_run}
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//! use std::old_io::{File, Open, Write};
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//!
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//! let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
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//! file.write_line("important message").ok().expect("failed to write message");
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//! drop(file);
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//! ```
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//!
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//! You might also simply assert success:
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//!
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//! ```{.no_run}
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//! # use std::old_io::{File, Open, Write};
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//!
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//! # let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
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//! assert!(file.write_line("important message").is_ok());
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//! # drop(file);
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//! ```
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//!
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//! Or propagate the error up the call stack with `try!`:
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//!
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//! ```
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//! # use std::old_io::{File, Open, Write, IoError};
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//! fn write_message() -> Result<(), IoError> {
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//! let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
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//! try!(file.write_line("important message"));
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//! drop(file);
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//! return Ok(());
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//! }
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//! ```
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//!
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//! # The `try!` macro
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//!
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//! When writing code that calls many functions that return the
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//! `Result` type, the error handling can be tedious. The `try!`
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//! macro hides some of the boilerplate of propagating errors up the
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//! call stack.
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//!
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//! It replaces this:
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//!
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//! ```
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//! use std::old_io::{File, Open, Write, IoError};
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//!
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//! struct Info {
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//! name: String,
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//! age: int,
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//! rating: int
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//! }
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//!
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//! fn write_info(info: &Info) -> Result<(), IoError> {
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//! let mut file = File::open_mode(&Path::new("my_best_friends.txt"), Open, Write);
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//! // Early return on error
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//! if let Err(e) = file.write_line(format!("name: {}", info.name).as_slice()) {
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//! return Err(e)
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//! }
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//! if let Err(e) = file.write_line(format!("age: {}", info.age).as_slice()) {
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//! return Err(e)
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//! }
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//! return file.write_line(format!("rating: {}", info.rating).as_slice());
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//! }
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//! ```
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//!
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//! With this:
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//!
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//! ```
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//! use std::old_io::{File, Open, Write, IoError};
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//!
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//! struct Info {
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//! name: String,
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//! age: int,
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//! rating: int
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//! }
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//!
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//! fn write_info(info: &Info) -> Result<(), IoError> {
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//! let mut file = File::open_mode(&Path::new("my_best_friends.txt"), Open, Write);
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//! // Early return on error
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//! try!(file.write_line(format!("name: {}", info.name).as_slice()));
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//! try!(file.write_line(format!("age: {}", info.age).as_slice()));
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//! try!(file.write_line(format!("rating: {}", info.rating).as_slice()));
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//! return Ok(());
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//! }
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//! ```
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//!
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//! *It's much nicer!*
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//!
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//! Wrapping an expression in `try!` will result in the unwrapped
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//! success (`Ok`) value, unless the result is `Err`, in which case
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//! `Err` is returned early from the enclosing function. Its simple definition
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//! makes it clear:
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//!
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//! ```
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//! macro_rules! try {
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//! ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
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//! }
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//! ```
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//!
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//! `try!` is imported by the prelude, and is available everywhere.
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#![stable(feature = "rust1", since = "1.0.0")]
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use self::Result::{Ok, Err};
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use clone::Clone;
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use fmt;
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use iter::{Iterator, IteratorExt, DoubleEndedIterator,
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FromIterator, ExactSizeIterator, IntoIterator};
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use ops::{FnMut, FnOnce};
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use option::Option::{self, None, Some};
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use slice::AsSlice;
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use slice;
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/// `Result` is a type that represents either success (`Ok`) or failure (`Err`).
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///
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|
/// See the [`std::result`](index.html) module documentation for details.
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#[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
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#[must_use]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub enum Result<T, E> {
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/// Contains the success value
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#[stable(feature = "rust1", since = "1.0.0")]
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Ok(T),
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/// Contains the error value
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#[stable(feature = "rust1", since = "1.0.0")]
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Err(E)
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}
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/////////////////////////////////////////////////////////////////////////////
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// Type implementation
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/////////////////////////////////////////////////////////////////////////////
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T, E> Result<T, E> {
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/////////////////////////////////////////////////////////////////////////
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// Querying the contained values
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/////////////////////////////////////////////////////////////////////////
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/// Returns true if the result is `Ok`
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///
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/// # Example
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///
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/// ```
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/// let x: Result<int, &str> = Ok(-3);
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/// assert_eq!(x.is_ok(), true);
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///
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/// let x: Result<int, &str> = Err("Some error message");
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/// assert_eq!(x.is_ok(), false);
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn is_ok(&self) -> bool {
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match *self {
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Ok(_) => true,
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Err(_) => false
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}
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}
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|
|
|
/// Returns true if the result is `Err`
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|
///
|
|
/// # Example
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|
///
|
|
/// ```
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|
/// let x: Result<int, &str> = Ok(-3);
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/// assert_eq!(x.is_err(), false);
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///
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|
/// let x: Result<int, &str> = Err("Some error message");
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/// assert_eq!(x.is_err(), true);
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn is_err(&self) -> bool {
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!self.is_ok()
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}
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|
|
/////////////////////////////////////////////////////////////////////////
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|
// Adapter for each variant
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|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Convert from `Result<T, E>` to `Option<T>`
|
|
///
|
|
/// Converts `self` into an `Option<T>`, consuming `self`,
|
|
/// and discarding the error, if any.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// let x: Result<u32, &str> = Ok(2);
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|
/// assert_eq!(x.ok(), Some(2));
|
|
///
|
|
/// let x: Result<u32, &str> = Err("Nothing here");
|
|
/// assert_eq!(x.ok(), None);
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/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
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pub fn ok(self) -> Option<T> {
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match self {
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Ok(x) => Some(x),
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|
Err(_) => None,
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|
}
|
|
}
|
|
|
|
/// Convert from `Result<T, E>` to `Option<E>`
|
|
///
|
|
/// Converts `self` into an `Option<E>`, consuming `self`,
|
|
/// and discarding the value, if any.
|
|
///
|
|
/// # Example
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|
///
|
|
/// ```
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/// let x: Result<u32, &str> = Ok(2);
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/// assert_eq!(x.err(), None);
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|
///
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|
/// let x: Result<u32, &str> = Err("Nothing here");
|
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/// assert_eq!(x.err(), Some("Nothing here"));
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/// ```
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|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
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pub fn err(self) -> Option<E> {
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match self {
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Ok(_) => None,
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Err(x) => Some(x),
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|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Adapter for working with references
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|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Convert from `Result<T, E>` to `Result<&T, &E>`
|
|
///
|
|
/// Produces a new `Result`, containing a reference
|
|
/// into the original, leaving the original in place.
|
|
///
|
|
/// ```
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|
/// 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"));
|
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/// ```
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|
#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn as_ref(&self) -> Result<&T, &E> {
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match *self {
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Ok(ref x) => Ok(x),
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|
Err(ref x) => Err(x),
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|
}
|
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}
|
|
|
|
/// Convert from `Result<T, E>` to `Result<&mut T, &mut E>`
|
|
///
|
|
/// ```
|
|
/// fn mutate(r: &mut Result<int, int>) {
|
|
/// match r.as_mut() {
|
|
/// Ok(&mut ref mut v) => *v = 42,
|
|
/// Err(&mut ref mut e) => *e = 0,
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|
/// }
|
|
/// }
|
|
///
|
|
/// let mut x: Result<int, int> = Ok(2);
|
|
/// mutate(&mut x);
|
|
/// assert_eq!(x.unwrap(), 42);
|
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///
|
|
/// let mut x: Result<int, int> = 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),
|
|
}
|
|
}
|
|
|
|
/// Convert from `Result<T, E>` to `&mut [T]` (without copying)
|
|
///
|
|
/// ```
|
|
/// let mut x: Result<&str, u32> = Ok("Gold");
|
|
/// {
|
|
/// let v = x.as_mut_slice();
|
|
/// assert!(v == ["Gold"]);
|
|
/// v[0] = "Silver";
|
|
/// assert!(v == ["Silver"]);
|
|
/// }
|
|
/// assert_eq!(x, Ok("Silver"));
|
|
///
|
|
/// let mut x: Result<&str, u32> = Err(45);
|
|
/// assert!(x.as_mut_slice().is_empty());
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "core",
|
|
reason = "waiting for mut conventions")]
|
|
pub fn as_mut_slice(&mut self) -> &mut [T] {
|
|
match *self {
|
|
Ok(ref mut x) => slice::mut_ref_slice(x),
|
|
Err(_) => {
|
|
// work around lack of implicit coercion from fixed-size array to slice
|
|
let emp: &mut [_] = &mut [];
|
|
emp
|
|
}
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////
|
|
// Transforming contained values
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Maps a `Result<T, E>` to `Result<U, E>` by applying a function to an
|
|
/// contained `Ok` value, leaving an `Err` value untouched.
|
|
///
|
|
/// This function can be used to compose the results of two functions.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// Sum the lines of a buffer by mapping strings to numbers,
|
|
/// ignoring I/O and parse errors:
|
|
///
|
|
/// ```
|
|
/// use std::old_io::IoResult;
|
|
///
|
|
/// let mut buffer = &mut b"1\n2\n3\n4\n";
|
|
///
|
|
/// let mut sum = 0;
|
|
///
|
|
/// while !buffer.is_empty() {
|
|
/// let line: IoResult<String> = buffer.read_line();
|
|
/// // Convert the string line to a number using `map` and `from_str`
|
|
/// let val: IoResult<int> = line.map(|line| {
|
|
/// line.trim_right().parse::<int>().unwrap_or(0)
|
|
/// });
|
|
/// // Add the value if there were no errors, otherwise add 0
|
|
/// sum += val.ok().unwrap_or(0);
|
|
/// }
|
|
///
|
|
/// assert!(sum == 10);
|
|
/// ```
|
|
#[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 an
|
|
/// contained `Err` value, leaving an `Ok` value untouched.
|
|
///
|
|
/// This function can be used to pass through a successful result while handling
|
|
/// an error.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// let mut x: Result<u32, &str> = Ok(7);
|
|
/// match x.iter_mut().next() {
|
|
/// Some(&mut ref mut x) => *x = 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() }
|
|
}
|
|
|
|
/// Returns a consuming iterator over the possibly contained value.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// let x: Result<u32, &str> = Ok(5);
|
|
/// let v: Vec<u32> = x.into_iter().collect();
|
|
/// assert_eq!(v, vec![5]);
|
|
///
|
|
/// let x: Result<u32, &str> = Err("nothing!");
|
|
/// let v: Vec<u32> = x.into_iter().collect();
|
|
/// assert_eq!(v, vec![]);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub fn into_iter(self) -> IntoIter<T> {
|
|
IntoIter { inner: self.ok() }
|
|
}
|
|
|
|
////////////////////////////////////////////////////////////////////////
|
|
// Boolean operations on the values, eager and lazy
|
|
/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Returns `res` if the result is `Ok`, otherwise returns the `Err` value of `self`.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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`.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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(self, res: Result<T, E>) -> Result<T, E> {
|
|
match self {
|
|
Ok(_) => self,
|
|
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.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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`.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// 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)
|
|
}
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
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 custom panic message provided
|
|
/// by the `Err`'s value.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```
|
|
/// let x: Result<u32, &str> = Ok(2);
|
|
/// assert_eq!(x.unwrap(), 2);
|
|
/// ```
|
|
///
|
|
/// ```{.should_fail}
|
|
/// 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) =>
|
|
panic!("called `Result::unwrap()` on an `Err` value: {:?}", e)
|
|
}
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
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.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```{.should_fail}
|
|
/// 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) =>
|
|
panic!("called `Result::unwrap_err()` on an `Ok` value: {:?}", t),
|
|
Err(e) => e
|
|
}
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Trait implementations
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
impl<T, E> AsSlice<T> for Result<T, E> {
|
|
/// Convert from `Result<T, E>` to `&[T]` (without copying)
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
fn as_slice<'a>(&'a self) -> &'a [T] {
|
|
match *self {
|
|
Ok(ref x) => slice::ref_slice(x),
|
|
Err(_) => {
|
|
// work around lack of implicit coercion from fixed-size array to slice
|
|
let emp: &[_] = &[];
|
|
emp
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// The Result Iterators
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
/// An iterator over a reference to the `Ok` variant of a `Result`.
|
|
#[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> {}
|
|
|
|
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`.
|
|
#[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`.
|
|
#[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:
|
|
///
|
|
/// ```rust
|
|
/// 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),
|
|
}
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// FromIterator
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Perform a fold operation over the result values from an iterator.
|
|
///
|
|
/// If an `Err` is encountered, it is immediately returned.
|
|
/// Otherwise, the folded value is returned.
|
|
#[inline]
|
|
#[unstable(feature = "core")]
|
|
pub fn fold<T,
|
|
V,
|
|
E,
|
|
F: FnMut(V, T) -> V,
|
|
Iter: Iterator<Item=Result<T, E>>>(
|
|
iterator: Iter,
|
|
mut init: V,
|
|
mut f: F)
|
|
-> Result<V, E> {
|
|
for t in iterator {
|
|
match t {
|
|
Ok(v) => init = f(init, v),
|
|
Err(u) => return Err(u)
|
|
}
|
|
}
|
|
Ok(init)
|
|
}
|