1514 lines
45 KiB
Rust
1514 lines
45 KiB
Rust
//! Error handling with the `Result` type.
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//!
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//! [`Result<T, E>`][`Result`] 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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//! # #[allow(dead_code)]
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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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//! match header.get(0) {
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//! None => Err("invalid header length"),
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//! Some(&1) => Ok(Version::Version1),
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//! Some(&2) => Ok(Version::Version2),
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//! Some(_) => 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) => println!("working with version: {:?}", v),
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//! Err(e) => println!("error parsing header: {:?}", e),
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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<i32, i32> = Ok(10);
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//! let bad_result: Result<i32, i32> = 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<i32, i32> = good_result.map(|i| i + 1);
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//! let bad_result: Result<i32, i32> = 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, i32> = 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<i32, i32> = bad_result.or_else(|i| Ok(i + 20));
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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.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_all`] method defined for I/O types
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//! by the [`Write`] trait:
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//!
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//! ```
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//! use std::io;
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//!
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//! trait Write {
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//! fn write_all(&mut self, bytes: &[u8]) -> Result<(), io::Error>;
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//! }
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//! ```
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//!
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//! *Note: The actual definition of [`Write`] uses [`io::Result`], which
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//! is just a synonym for [`Result`]`<T, `[`io::Error`]`>`.*
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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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//! ```no_run
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//! # #![allow(unused_must_use)] // \o/
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//! use std::fs::File;
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//! use std::io::prelude::*;
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//!
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//! let mut file = File::create("valuable_data.txt").unwrap();
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//! // If `write_all` errors, then we'll never know, because the return
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//! // value is ignored.
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//! file.write_all(b"important message");
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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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//! assert success with [`expect`]. This will panic if the
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//! write fails, providing a marginally useful message indicating why:
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//!
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//! ```{.no_run}
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//! use std::fs::File;
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//! use std::io::prelude::*;
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//!
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//! let mut file = File::create("valuable_data.txt").unwrap();
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//! file.write_all(b"important message").expect("failed to write message");
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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::fs::File;
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//! # use std::io::prelude::*;
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//! # let mut file = File::create("valuable_data.txt").unwrap();
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//! assert!(file.write_all(b"important message").is_ok());
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//! ```
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//!
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//! Or propagate the error up the call stack with [`?`]:
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//!
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//! ```
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//! # use std::fs::File;
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//! # use std::io::prelude::*;
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//! # use std::io;
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//! # #[allow(dead_code)]
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//! fn write_message() -> io::Result<()> {
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//! let mut file = File::create("valuable_data.txt")?;
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//! file.write_all(b"important message")?;
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//! Ok(())
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//! }
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//! ```
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//!
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//! # The question mark operator, `?`
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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 question mark
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//! operator, [`?`], hides some of the boilerplate of propagating errors
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//! up the 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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//! # #![allow(dead_code)]
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//! use std::fs::File;
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//! use std::io::prelude::*;
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//! use std::io;
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//!
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//! struct Info {
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//! name: String,
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//! age: i32,
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//! rating: i32,
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//! }
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//!
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//! fn write_info(info: &Info) -> io::Result<()> {
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//! // Early return on error
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//! let mut file = match File::create("my_best_friends.txt") {
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//! Err(e) => return Err(e),
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//! Ok(f) => f,
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//! };
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//! if let Err(e) = file.write_all(format!("name: {}\n", info.name).as_bytes()) {
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//! return Err(e)
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//! }
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//! if let Err(e) = file.write_all(format!("age: {}\n", info.age).as_bytes()) {
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//! return Err(e)
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//! }
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//! if let Err(e) = file.write_all(format!("rating: {}\n", info.rating).as_bytes()) {
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//! return Err(e)
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//! }
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//! Ok(())
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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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//! # #![allow(dead_code)]
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//! use std::fs::File;
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//! use std::io::prelude::*;
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//! use std::io;
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//!
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//! struct Info {
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//! name: String,
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//! age: i32,
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//! rating: i32,
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//! }
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//!
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//! fn write_info(info: &Info) -> io::Result<()> {
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//! let mut file = File::create("my_best_friends.txt")?;
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//! // Early return on error
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//! file.write_all(format!("name: {}\n", info.name).as_bytes())?;
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//! file.write_all(format!("age: {}\n", info.age).as_bytes())?;
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//! file.write_all(format!("rating: {}\n", info.rating).as_bytes())?;
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//! 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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//! Ending the expression with [`?`] 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.
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//!
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//! [`?`] can only be used in functions that return [`Result`] because of the
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//! early return of [`Err`] that it provides.
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//!
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//! [`expect`]: Result::expect
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//! [`Write`]: ../../std/io/trait.Write.html
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//! [`write_all`]: ../../std/io/trait.Write.html#method.write_all
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//! [`io::Result`]: ../../std/io/type.Result.html
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//! [`?`]: crate::ops::Try
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//! [`Ok(T)`]: Ok
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//! [`Err(E)`]: Err
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//! [`io::Error`]: ../../std/io/struct.Error.html
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#![stable(feature = "rust1", since = "1.0.0")]
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use crate::iter::{self, FromIterator, FusedIterator, TrustedLen};
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use crate::ops::{self, Deref, DerefMut};
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use crate::{convert, fmt};
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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(Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
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#[must_use = "this `Result` may be an `Err` variant, which should be handled"]
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#[rustc_diagnostic_item = "result_type"]
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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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#[lang = "Ok"]
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#[stable(feature = "rust1", since = "1.0.0")]
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Ok(#[stable(feature = "rust1", since = "1.0.0")] T),
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/// Contains the error value
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#[lang = "Err"]
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#[stable(feature = "rust1", since = "1.0.0")]
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Err(#[stable(feature = "rust1", since = "1.0.0")] E),
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}
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/////////////////////////////////////////////////////////////////////////////
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// Type implementation
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/////////////////////////////////////////////////////////////////////////////
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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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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let x: Result<i32, &str> = Ok(-3);
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/// assert_eq!(x.is_ok(), true);
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///
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/// let x: Result<i32, &str> = Err("Some error message");
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/// assert_eq!(x.is_ok(), false);
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/// ```
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#[must_use = "if you intended to assert that this is ok, consider `.unwrap()` instead"]
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#[rustc_const_unstable(feature = "const_result", issue = "67520")]
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub const fn is_ok(&self) -> bool {
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matches!(*self, Ok(_))
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}
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/// Returns `true` if the result is [`Err`].
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let x: Result<i32, &str> = Ok(-3);
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/// assert_eq!(x.is_err(), false);
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///
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/// let x: Result<i32, &str> = Err("Some error message");
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/// assert_eq!(x.is_err(), true);
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/// ```
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#[must_use = "if you intended to assert that this is err, consider `.unwrap_err()` instead"]
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|
#[rustc_const_unstable(feature = "const_result", issue = "67520")]
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub const fn is_err(&self) -> bool {
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!self.is_ok()
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}
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/// Returns `true` if the result is an [`Ok`] value containing the given value.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(option_result_contains)]
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///
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/// let x: Result<u32, &str> = Ok(2);
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/// assert_eq!(x.contains(&2), true);
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///
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/// let x: Result<u32, &str> = Ok(3);
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/// assert_eq!(x.contains(&2), false);
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///
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/// let x: Result<u32, &str> = Err("Some error message");
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/// assert_eq!(x.contains(&2), false);
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/// ```
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#[must_use]
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#[inline]
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#[unstable(feature = "option_result_contains", issue = "62358")]
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pub fn contains<U>(&self, x: &U) -> bool
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where
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U: PartialEq<T>,
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{
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match self {
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Ok(y) => x == y,
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Err(_) => false,
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}
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}
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|
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/// Returns `true` if the result is an [`Err`] value containing the given value.
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///
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|
/// # Examples
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|
///
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/// ```
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|
/// #![feature(result_contains_err)]
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///
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/// let x: Result<u32, &str> = Ok(2);
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/// assert_eq!(x.contains_err(&"Some error message"), false);
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///
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/// let x: Result<u32, &str> = Err("Some error message");
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/// assert_eq!(x.contains_err(&"Some error message"), true);
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///
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/// let x: Result<u32, &str> = Err("Some other error message");
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/// assert_eq!(x.contains_err(&"Some error message"), false);
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/// ```
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|
#[must_use]
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|
#[inline]
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#[unstable(feature = "result_contains_err", issue = "62358")]
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pub fn contains_err<F>(&self, f: &F) -> bool
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where
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F: PartialEq<E>,
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{
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match self {
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Ok(_) => false,
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Err(e) => f == e,
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}
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}
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|
/////////////////////////////////////////////////////////////////////////
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|
// Adapter for each variant
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/////////////////////////////////////////////////////////////////////////
|
|
|
|
/// Converts from `Result<T, E>` to [`Option<T>`].
|
|
///
|
|
/// Converts `self` into an [`Option<T>`], consuming `self`,
|
|
/// and discarding the error, if any.
|
|
///
|
|
/// [`Option<T>`]: Option
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
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|
/// ```
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|
/// let x: Result<u32, &str> = Ok(2);
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|
/// assert_eq!(x.ok(), Some(2));
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///
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|
/// 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")]
|
|
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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|
}
|
|
}
|
|
|
|
/// Converts from `Result<T, E>` to [`Option<E>`].
|
|
///
|
|
/// Converts `self` into an [`Option<E>`], consuming `self`,
|
|
/// and discarding the success value, if any.
|
|
///
|
|
/// [`Option<E>`]: Option
|
|
///
|
|
/// # 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]
|
|
#[rustc_const_unstable(feature = "const_result", issue = "67520")]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub const fn as_ref(&self) -> Result<&T, &E> {
|
|
match *self {
|
|
Ok(ref x) => Ok(x),
|
|
Err(ref x) => Err(x),
|
|
}
|
|
}
|
|
|
|
/// Converts from `&mut Result<T, E>` to `Result<&mut T, &mut E>`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// fn mutate(r: &mut Result<i32, i32>) {
|
|
/// match r.as_mut() {
|
|
/// Ok(v) => *v = 42,
|
|
/// Err(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),
|
|
}
|
|
}
|
|
|
|
/// Applies a function to the contained value (if [`Ok`]),
|
|
/// or returns the provided default (if [`Err`]).
|
|
///
|
|
/// Arguments passed to `map_or` are eagerly evaluated; if you are passing
|
|
/// the result of a function call, it is recommended to use [`map_or_else`],
|
|
/// which is lazily evaluated.
|
|
///
|
|
/// [`map_or_else`]: Result::map_or_else
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x: Result<_, &str> = Ok("foo");
|
|
/// assert_eq!(x.map_or(42, |v| v.len()), 3);
|
|
///
|
|
/// let x: Result<&str, _> = Err("bar");
|
|
/// assert_eq!(x.map_or(42, |v| v.len()), 42);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "result_map_or", since = "1.41.0")]
|
|
pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U {
|
|
match self {
|
|
Ok(t) => f(t),
|
|
Err(_) => default,
|
|
}
|
|
}
|
|
|
|
/// Maps a `Result<T, E>` to `U` by applying a function to a
|
|
/// contained [`Ok`] value, or a fallback function to a
|
|
/// contained [`Err`] value.
|
|
///
|
|
/// This function can be used to unpack a successful result
|
|
/// while handling an error.
|
|
///
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// let k = 21;
|
|
///
|
|
/// let x : Result<_, &str> = Ok("foo");
|
|
/// assert_eq!(x.map_or_else(|e| k * 2, |v| v.len()), 3);
|
|
///
|
|
/// let x : Result<&str, _> = Err("bar");
|
|
/// assert_eq!(x.map_or_else(|e| k * 2, |v| v.len()), 42);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "result_map_or_else", since = "1.41.0")]
|
|
pub fn map_or_else<U, D: FnOnce(E) -> U, F: FnOnce(T) -> U>(self, default: D, f: F) -> U {
|
|
match self {
|
|
Ok(t) => f(t),
|
|
Err(e) => default(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.
|
|
///
|
|
/// The iterator yields one value if the result is [`Result::Ok`], otherwise none.
|
|
///
|
|
/// # 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.
|
|
///
|
|
/// The iterator yields one value if the result is [`Result::Ok`], otherwise none.
|
|
///
|
|
/// # 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`.
|
|
///
|
|
/// Arguments passed to `or` are eagerly evaluated; if you are passing the
|
|
/// result of a function call, it is recommended to use [`or_else`], which is
|
|
/// lazily evaluated.
|
|
///
|
|
/// [`or_else`]: Result::or_else
|
|
///
|
|
/// # 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),
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Ok`] value or a provided default.
|
|
///
|
|
/// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing
|
|
/// the result of a function call, it is recommended to use [`unwrap_or_else`],
|
|
/// which is lazily evaluated.
|
|
///
|
|
/// [`unwrap_or_else`]: Result::unwrap_or_else
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// let default = 2;
|
|
/// let x: Result<u32, &str> = Ok(9);
|
|
/// assert_eq!(x.unwrap_or(default), 9);
|
|
///
|
|
/// let x: Result<u32, &str> = Err("error");
|
|
/// assert_eq!(x.unwrap_or(default), default);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub fn unwrap_or(self, default: T) -> T {
|
|
match self {
|
|
Ok(t) => t,
|
|
Err(_) => default,
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Ok`] value or computes it from a closure.
|
|
///
|
|
///
|
|
/// # 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: Copy, E> Result<&T, E> {
|
|
/// Maps a `Result<&T, E>` to a `Result<T, E>` by copying the contents of the
|
|
/// `Ok` part.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(result_copied)]
|
|
/// let val = 12;
|
|
/// let x: Result<&i32, i32> = Ok(&val);
|
|
/// assert_eq!(x, Ok(&12));
|
|
/// let copied = x.copied();
|
|
/// assert_eq!(copied, Ok(12));
|
|
/// ```
|
|
#[unstable(feature = "result_copied", reason = "newly added", issue = "63168")]
|
|
pub fn copied(self) -> Result<T, E> {
|
|
self.map(|&t| t)
|
|
}
|
|
}
|
|
|
|
impl<T: Copy, E> Result<&mut T, E> {
|
|
/// Maps a `Result<&mut T, E>` to a `Result<T, E>` by copying the contents of the
|
|
/// `Ok` part.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(result_copied)]
|
|
/// let mut val = 12;
|
|
/// let x: Result<&mut i32, i32> = Ok(&mut val);
|
|
/// assert_eq!(x, Ok(&mut 12));
|
|
/// let copied = x.copied();
|
|
/// assert_eq!(copied, Ok(12));
|
|
/// ```
|
|
#[unstable(feature = "result_copied", reason = "newly added", issue = "63168")]
|
|
pub fn copied(self) -> Result<T, E> {
|
|
self.map(|&mut t| t)
|
|
}
|
|
}
|
|
|
|
impl<T: Clone, E> Result<&T, E> {
|
|
/// Maps a `Result<&T, E>` to a `Result<T, E>` by cloning the contents of the
|
|
/// `Ok` part.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(result_cloned)]
|
|
/// let val = 12;
|
|
/// let x: Result<&i32, i32> = Ok(&val);
|
|
/// assert_eq!(x, Ok(&12));
|
|
/// let cloned = x.cloned();
|
|
/// assert_eq!(cloned, Ok(12));
|
|
/// ```
|
|
#[unstable(feature = "result_cloned", reason = "newly added", issue = "63168")]
|
|
pub fn cloned(self) -> Result<T, E> {
|
|
self.map(|t| t.clone())
|
|
}
|
|
}
|
|
|
|
impl<T: Clone, E> Result<&mut T, E> {
|
|
/// Maps a `Result<&mut T, E>` to a `Result<T, E>` by cloning the contents of the
|
|
/// `Ok` part.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(result_cloned)]
|
|
/// let mut val = 12;
|
|
/// let x: Result<&mut i32, i32> = Ok(&mut val);
|
|
/// assert_eq!(x, Ok(&mut 12));
|
|
/// let cloned = x.cloned();
|
|
/// assert_eq!(cloned, Ok(12));
|
|
/// ```
|
|
#[unstable(feature = "result_cloned", reason = "newly added", issue = "63168")]
|
|
pub fn cloned(self) -> Result<T, E> {
|
|
self.map(|t| t.clone())
|
|
}
|
|
}
|
|
|
|
impl<T, E: fmt::Debug> Result<T, E> {
|
|
/// Returns the contained [`Ok`] value, consuming the `self` value.
|
|
///
|
|
/// # 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]
|
|
#[track_caller]
|
|
#[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),
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Ok`] value, consuming the `self` value.
|
|
///
|
|
/// Because this function may panic, its use is generally discouraged.
|
|
/// Instead, prefer to use pattern matching and handle the [`Err`]
|
|
/// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
|
|
/// [`unwrap_or_default`].
|
|
///
|
|
/// [`unwrap_or`]: Result::unwrap_or
|
|
/// [`unwrap_or_else`]: Result::unwrap_or_else
|
|
/// [`unwrap_or_default`]: Result::unwrap_or_default
|
|
///
|
|
/// # 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]
|
|
#[track_caller]
|
|
#[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),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: fmt::Debug, E> Result<T, E> {
|
|
/// Returns the contained [`Err`] value, consuming the `self` value.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is an [`Ok`], with a panic message including the
|
|
/// passed message, and the content of the [`Ok`].
|
|
///
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```{.should_panic}
|
|
/// let x: Result<u32, &str> = Ok(10);
|
|
/// x.expect_err("Testing expect_err"); // panics with `Testing expect_err: 10`
|
|
/// ```
|
|
#[inline]
|
|
#[track_caller]
|
|
#[stable(feature = "result_expect_err", since = "1.17.0")]
|
|
pub fn expect_err(self, msg: &str) -> E {
|
|
match self {
|
|
Ok(t) => unwrap_failed(msg, &t),
|
|
Err(e) => e,
|
|
}
|
|
}
|
|
|
|
/// Returns the contained [`Err`] value, consuming the `self` value.
|
|
///
|
|
/// # 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]
|
|
#[track_caller]
|
|
#[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,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: Default, E> Result<T, E> {
|
|
/// Returns the contained [`Ok`] value or a default
|
|
///
|
|
/// Consumes the `self` argument then, if [`Ok`], returns the contained
|
|
/// value, otherwise if [`Err`], returns the default value for that
|
|
/// type.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Converts a string to an integer, turning poorly-formed strings
|
|
/// into 0 (the default value for integers). [`parse`] converts
|
|
/// a string to any other type that implements [`FromStr`], returning an
|
|
/// [`Err`] on error.
|
|
///
|
|
/// ```
|
|
/// let good_year_from_input = "1909";
|
|
/// let bad_year_from_input = "190blarg";
|
|
/// let good_year = good_year_from_input.parse().unwrap_or_default();
|
|
/// let bad_year = bad_year_from_input.parse().unwrap_or_default();
|
|
///
|
|
/// assert_eq!(1909, good_year);
|
|
/// assert_eq!(0, bad_year);
|
|
/// ```
|
|
///
|
|
/// [`parse`]: str::parse
|
|
/// [`FromStr`]: crate::str::FromStr
|
|
#[inline]
|
|
#[stable(feature = "result_unwrap_or_default", since = "1.16.0")]
|
|
pub fn unwrap_or_default(self) -> T {
|
|
match self {
|
|
Ok(x) => x,
|
|
Err(_) => Default::default(),
|
|
}
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "unwrap_infallible", reason = "newly added", issue = "61695")]
|
|
impl<T, E: Into<!>> Result<T, E> {
|
|
/// Returns the contained [`Ok`] value, but never panics.
|
|
///
|
|
/// Unlike [`unwrap`], this method is known to never panic on the
|
|
/// result types it is implemented for. Therefore, it can be used
|
|
/// instead of `unwrap` as a maintainability safeguard that will fail
|
|
/// to compile if the error type of the `Result` is later changed
|
|
/// to an error that can actually occur.
|
|
///
|
|
/// [`unwrap`]: Result::unwrap
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// # #![feature(never_type)]
|
|
/// # #![feature(unwrap_infallible)]
|
|
///
|
|
/// fn only_good_news() -> Result<String, !> {
|
|
/// Ok("this is fine".into())
|
|
/// }
|
|
///
|
|
/// let s: String = only_good_news().into_ok();
|
|
/// println!("{}", s);
|
|
/// ```
|
|
#[inline]
|
|
pub fn into_ok(self) -> T {
|
|
match self {
|
|
Ok(x) => x,
|
|
Err(e) => e.into(),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: Deref, E> Result<T, E> {
|
|
/// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&<T as Deref>::Target, &E>`.
|
|
///
|
|
/// Coerces the [`Ok`] variant of the original [`Result`] via [`Deref`](crate::ops::Deref)
|
|
/// and returns the new [`Result`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let x: Result<String, u32> = Ok("hello".to_string());
|
|
/// let y: Result<&str, &u32> = Ok("hello");
|
|
/// assert_eq!(x.as_deref(), y);
|
|
///
|
|
/// let x: Result<String, u32> = Err(42);
|
|
/// let y: Result<&str, &u32> = Err(&42);
|
|
/// assert_eq!(x.as_deref(), y);
|
|
/// ```
|
|
#[stable(feature = "inner_deref", since = "1.47.0")]
|
|
pub fn as_deref(&self) -> Result<&T::Target, &E> {
|
|
self.as_ref().map(|t| t.deref())
|
|
}
|
|
}
|
|
|
|
impl<T: DerefMut, E> Result<T, E> {
|
|
/// Converts from `Result<T, E>` (or `&mut Result<T, E>`) to `Result<&mut <T as DerefMut>::Target, &mut E>`.
|
|
///
|
|
/// Coerces the [`Ok`] variant of the original [`Result`] via [`DerefMut`](crate::ops::DerefMut)
|
|
/// and returns the new [`Result`].
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// let mut s = "HELLO".to_string();
|
|
/// let mut x: Result<String, u32> = Ok("hello".to_string());
|
|
/// let y: Result<&mut str, &mut u32> = Ok(&mut s);
|
|
/// assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);
|
|
///
|
|
/// let mut i = 42;
|
|
/// let mut x: Result<String, u32> = Err(42);
|
|
/// let y: Result<&mut str, &mut u32> = Err(&mut i);
|
|
/// assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);
|
|
/// ```
|
|
#[stable(feature = "inner_deref", since = "1.47.0")]
|
|
pub fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E> {
|
|
self.as_mut().map(|t| t.deref_mut())
|
|
}
|
|
}
|
|
|
|
impl<T, E> Result<Option<T>, E> {
|
|
/// Transposes a `Result` of an `Option` into an `Option` of a `Result`.
|
|
///
|
|
/// `Ok(None)` will be mapped to `None`.
|
|
/// `Ok(Some(_))` and `Err(_)` will be mapped to `Some(Ok(_))` and `Some(Err(_))`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #[derive(Debug, Eq, PartialEq)]
|
|
/// struct SomeErr;
|
|
///
|
|
/// let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
|
|
/// let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
|
|
/// assert_eq!(x.transpose(), y);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "transpose_result", since = "1.33.0")]
|
|
pub fn transpose(self) -> Option<Result<T, E>> {
|
|
match self {
|
|
Ok(Some(x)) => Some(Ok(x)),
|
|
Ok(None) => None,
|
|
Err(e) => Some(Err(e)),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T, E> Result<Result<T, E>, E> {
|
|
/// Converts from `Result<Result<T, E>, E>` to `Result<T, E>`
|
|
///
|
|
/// # Examples
|
|
/// Basic usage:
|
|
/// ```
|
|
/// #![feature(result_flattening)]
|
|
/// let x: Result<Result<&'static str, u32>, u32> = Ok(Ok("hello"));
|
|
/// assert_eq!(Ok("hello"), x.flatten());
|
|
///
|
|
/// let x: Result<Result<&'static str, u32>, u32> = Ok(Err(6));
|
|
/// assert_eq!(Err(6), x.flatten());
|
|
///
|
|
/// let x: Result<Result<&'static str, u32>, u32> = Err(6);
|
|
/// assert_eq!(Err(6), x.flatten());
|
|
/// ```
|
|
///
|
|
/// Flattening once only removes one level of nesting:
|
|
///
|
|
/// ```
|
|
/// #![feature(result_flattening)]
|
|
/// let x: Result<Result<Result<&'static str, u32>, u32>, u32> = Ok(Ok(Ok("hello")));
|
|
/// assert_eq!(Ok(Ok("hello")), x.flatten());
|
|
/// assert_eq!(Ok("hello"), x.flatten().flatten());
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "result_flattening", issue = "70142")]
|
|
pub fn flatten(self) -> Result<T, E> {
|
|
self.and_then(convert::identity)
|
|
}
|
|
}
|
|
|
|
// This is a separate function to reduce the code size of the methods
|
|
#[inline(never)]
|
|
#[cold]
|
|
#[track_caller]
|
|
fn unwrap_failed(msg: &str, error: &dyn fmt::Debug) -> ! {
|
|
panic!("{}: {:?}", msg, error)
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// Trait implementations
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: Clone, E: Clone> Clone for Result<T, E> {
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
match self {
|
|
Ok(x) => Ok(x.clone()),
|
|
Err(x) => Err(x.clone()),
|
|
}
|
|
}
|
|
|
|
#[inline]
|
|
fn clone_from(&mut self, source: &Self) {
|
|
match (self, source) {
|
|
(Ok(to), Ok(from)) => to.clone_from(from),
|
|
(Err(to), Err(from)) => to.clone_from(from),
|
|
(to, from) => *to = from.clone(),
|
|
}
|
|
}
|
|
}
|
|
|
|
#[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.
|
|
///
|
|
/// The iterator yields one value if the result is [`Result::Ok`], otherwise none.
|
|
///
|
|
/// # 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(self) -> IterMut<'a, T> {
|
|
self.iter_mut()
|
|
}
|
|
}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// The Result Iterators
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
/// An iterator over a reference to the [`Ok`] variant of a [`Result`].
|
|
///
|
|
/// The iterator yields one value if the result is [`Ok`], otherwise none.
|
|
///
|
|
/// Created by [`Result::iter`].
|
|
#[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<T> ExactSizeIterator for Iter<'_, T> {}
|
|
|
|
#[stable(feature = "fused", since = "1.26.0")]
|
|
impl<T> FusedIterator for Iter<'_, T> {}
|
|
|
|
#[unstable(feature = "trusted_len", issue = "37572")]
|
|
unsafe impl<A> TrustedLen for Iter<'_, A> {}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T> Clone for Iter<'_, T> {
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
Iter { inner: self.inner }
|
|
}
|
|
}
|
|
|
|
/// An iterator over a mutable reference to the [`Ok`] variant of a [`Result`].
|
|
///
|
|
/// Created by [`Result::iter_mut`].
|
|
#[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<T> ExactSizeIterator for IterMut<'_, T> {}
|
|
|
|
#[stable(feature = "fused", since = "1.26.0")]
|
|
impl<T> FusedIterator for IterMut<'_, T> {}
|
|
|
|
#[unstable(feature = "trusted_len", issue = "37572")]
|
|
unsafe impl<A> TrustedLen for IterMut<'_, A> {}
|
|
|
|
/// An iterator over the value in a [`Ok`] variant of a [`Result`].
|
|
///
|
|
/// The iterator yields one value if the result is [`Ok`], otherwise none.
|
|
///
|
|
/// This struct is created by the [`into_iter`] method on
|
|
/// [`Result`] (provided by the [`IntoIterator`] trait).
|
|
///
|
|
/// [`into_iter`]: IntoIterator::into_iter
|
|
#[derive(Clone, 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> {}
|
|
|
|
#[stable(feature = "fused", since = "1.26.0")]
|
|
impl<T> FusedIterator for IntoIter<T> {}
|
|
|
|
#[unstable(feature = "trusted_len", issue = "37572")]
|
|
unsafe impl<A> TrustedLen for IntoIter<A> {}
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
// 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:
|
|
///
|
|
/// ```
|
|
/// let v = vec![1, 2];
|
|
/// let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
|
|
/// x.checked_add(1).ok_or("Overflow!")
|
|
/// ).collect();
|
|
/// assert_eq!(res, Ok(vec![2, 3]));
|
|
/// ```
|
|
///
|
|
/// Here is another example that tries to subtract one from another list
|
|
/// of integers, this time checking for underflow:
|
|
///
|
|
/// ```
|
|
/// let v = vec![1, 2, 0];
|
|
/// let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
|
|
/// x.checked_sub(1).ok_or("Underflow!")
|
|
/// ).collect();
|
|
/// assert_eq!(res, Err("Underflow!"));
|
|
/// ```
|
|
///
|
|
/// Here is a variation on the previous example, showing that no
|
|
/// further elements are taken from `iter` after the first `Err`.
|
|
///
|
|
/// ```
|
|
/// let v = vec![3, 2, 1, 10];
|
|
/// let mut shared = 0;
|
|
/// let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32| {
|
|
/// shared += x;
|
|
/// x.checked_sub(2).ok_or("Underflow!")
|
|
/// }).collect();
|
|
/// assert_eq!(res, Err("Underflow!"));
|
|
/// assert_eq!(shared, 6);
|
|
/// ```
|
|
///
|
|
/// Since the third element caused an underflow, no further elements were taken,
|
|
/// so the final value of `shared` is 6 (= `3 + 2 + 1`), not 16.
|
|
#[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.
|
|
|
|
iter::process_results(iter.into_iter(), |i| i.collect())
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "try_trait", issue = "42327")]
|
|
impl<T, E> ops::Try for Result<T, E> {
|
|
type Ok = T;
|
|
type Error = E;
|
|
|
|
#[inline]
|
|
fn into_result(self) -> Self {
|
|
self
|
|
}
|
|
|
|
#[inline]
|
|
fn from_ok(v: T) -> Self {
|
|
Ok(v)
|
|
}
|
|
|
|
#[inline]
|
|
fn from_error(v: E) -> Self {
|
|
Err(v)
|
|
}
|
|
}
|