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core: Add unwrap()/unwrap_err() methods to Result

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These implementations must live in libstd right now because the fmt module has
not been migrated yet. This will occur in a later PR.

Just to be clear, there are new extension traits, but they are not necessary
once the std::fmt module has migrated to libcore, which is a planned migration
in the future.
This commit is contained in:
Alex Crichton 2014-05-01 11:12:16 -07:00
parent a156534a96
commit d4b5d82a33
12 changed files with 327 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/libstd/fmt/num.rs
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@ -400,6 +400,7 @@ mod bench {
use super::test::Bencher;
use fmt::radix;
use rand::{XorShiftRng, Rng};
use realstd::result::ResultUnwrap;
#[bench]
fn format_bin(b: &mut Bencher) {
@ -436,6 +437,7 @@ mod bench {
use super::test::Bencher;
use fmt::radix;
use rand::{XorShiftRng, Rng};
use realstd::result::ResultUnwrap;
#[bench]
fn format_bin(b: &mut Bencher) {

2
src/libstd/io/buffered.rs
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@ -16,7 +16,7 @@ use io::{Reader, Writer, Stream, Buffer, DEFAULT_BUF_SIZE, IoResult};
use iter::ExactSize;
use ops::Drop;
use option::{Some, None, Option};
use result::{Ok, Err};
use result::{Ok, Err, ResultUnwrap};
use slice::{ImmutableVector, MutableVector};
use slice;
use vec::Vec;

2
src/libstd/io/fs.rs
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@ -1335,7 +1335,7 @@ mod test {
use rand::{StdRng, Rng};
let mut bytes = [0, ..1024];
StdRng::new().unwrap().fill_bytes(bytes);
StdRng::new().ok().unwrap().fill_bytes(bytes);
let tmpdir = tmpdir();

2
src/libstd/io/net/udp.rs
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@ -358,6 +358,8 @@ mod test {
})
pub fn socket_name(addr: SocketAddr) {
use result::ResultUnwrap;
let server = UdpSocket::bind(addr);
assert!(server.is_ok());

2
src/libstd/io/stdio.rs
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@ -36,7 +36,7 @@ use mem::replace;
use option::{Option, Some, None};
use owned::Box;
use prelude::drop;
use result::{Ok, Err};
use result::{Ok, Err, ResultUnwrap};
use rt;
use rt::local::Local;
use rt::rtio::{DontClose, IoFactory, LocalIo, RtioFileStream, RtioTTY};

2
src/libstd/io/tempfile.rs
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@ -18,7 +18,7 @@ use ops::Drop;
use option::{Option, None, Some};
use os;
use path::{Path, GenericPath};
use result::{Ok, Err};
use result::{Ok, Err, ResultUnwrap};
use sync::atomics;
/// A wrapper for a path to temporary directory implementing automatic

3
src/libstd/num/strconv.rs
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@ -820,6 +820,7 @@ mod bench {
use super::test::Bencher;
use rand::{XorShiftRng, Rng};
use num::ToStrRadix;
use realstd::result::ResultUnwrap;
#[bench]
fn to_str_bin(b: &mut Bencher) {
@ -856,6 +857,7 @@ mod bench {
use super::test::Bencher;
use rand::{XorShiftRng, Rng};
use num::ToStrRadix;
use realstd::result::ResultUnwrap;
#[bench]
fn to_str_bin(b: &mut Bencher) {
@ -892,6 +894,7 @@ mod bench {
use super::test::Bencher;
use rand::{XorShiftRng, Rng};
use f64;
use realstd::result::ResultUnwrap;
#[bench]
fn float_to_str(b: &mut Bencher) {

1
src/libstd/prelude.rs
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@ -69,6 +69,7 @@ pub use owned::Box;
pub use path::{GenericPath, Path, PosixPath, WindowsPath};
pub use ptr::RawPtr;
pub use io::{Buffer, Writer, Reader, Seek};
pub use result::{ResultUnwrap, ResultUnwrapErr};
pub use str::{Str, StrVector, StrSlice, OwnedStr, IntoMaybeOwned};
pub use str::{StrAllocating};
pub use to_str::{ToStr, IntoStr};

2
src/libstd/repr.rs
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@ -25,7 +25,7 @@ use option::{Some, None, Option};
use ptr::RawPtr;
use reflect;
use reflect::{MovePtr, align};
use result::{Ok, Err};
use result::{Ok, Err, ResultUnwrap};
use str::StrSlice;
use to_str::ToStr;
use slice::Vector;

312
src/libstd/result.rs Normal file
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@ -0,0 +1,312 @@
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Error handling with the `Result` type
//!
//! `Result<T>` is the type used for returning and propagating
//! errors. It is an enum with the variants, `Ok(T)`, representing
//! success and containing a value, and `Err(E)`, representing error
//! and containing an error value.
//!
//! ~~~
//! enum Result<T, E> {
//! Ok(T),
//! Err(E)
//! }
//! ~~~
//!
//! Functions return `Result` whenever errors are expected and
//! recoverable. In the `std` crate `Result` is most prominently used
//! for [I/O](../io/index.html).
//!
//! A simple function returning `Result` might be
//! defined and used like so:
//!
//! ~~~
//! #[deriving(Show)]
//! enum Version { Version1, Version2 }
//!
//! fn parse_version(header: &[u8]) -> Result<Version, &'static str> {
//! if header.len() < 1 {
//! return Err("invalid header length");
//! }
//! match header[0] {
//! 1 => Ok(Version1),
//! 2 => Ok(Version2),
//! _ => Err("invalid version")
//! }
//! }
//!
//! let version = parse_version(&[1, 2, 3, 4]);
//! match version {
//! Ok(v) => {
//! println!("working with version: {}", v);
//! }
//! Err(e) => {
//! println!("error parsing header: {}", e);
//! }
//! }
//! ~~~
//!
//! Pattern matching on `Result`s is clear and straightforward for
//! simple cases, but `Result` comes with some convenience methods
//! that make working it more succinct.
//!
//! ~~~
//! let good_result: Result<int, int> = Ok(10);
//! let bad_result: Result<int, int> = Err(10);
//!
//! // The `is_ok` and `is_err` methods do what they say.
//! assert!(good_result.is_ok() && !good_result.is_err());
//! assert!(bad_result.is_err() && !bad_result.is_ok());
//!
//! // `map` consumes the `Result` and produces another.
//! let good_result: Result<int, int> = good_result.map(|i| i + 1);
//! let bad_result: Result<int, int> = bad_result.map(|i| i - 1);
//!
//! // Use `and_then` to continue the computation.
//! let good_result: Result<bool, int> = good_result.and_then(|i| Ok(i == 11));
//!
//! // Use `or_else` to handle the error.
//! let bad_result: Result<int, int> = bad_result.or_else(|i| Ok(11));
//!
//! // Consume the result and return the contents with `unwrap`.
//! let final_awesome_result = good_result.ok().unwrap();
//! ~~~
//!
//! # Results must be used
//!
//! A common problem with using return values to indicate errors is
//! that it is easy to ignore the return value, thus failing to handle
//! the error. Result is annotated with the #[must_use] attribute,
//! which will cause the compiler to issue a warning when a Result
//! value is ignored. This makes `Result` especially useful with
//! functions that may encounter errors but don't otherwise return a
//! useful value.
//!
//! Consider the `write_line` method defined for I/O types
//! by the [`Writer`](../io/trait.Writer.html) trait:
//!
//! ~~~
//! use std::io::IoError;
//!
//! trait Writer {
//! fn write_line(&mut self, s: &str) -> Result<(), IoError>;
//! }
//! ~~~
//!
//! *Note: The actual definition of `Writer` uses `IoResult`, which
//! is just a synonym for `Result<T, IoError>`.*
//!
//! This method doesn`t produce a value, but the write may
//! fail. It's crucial to handle the error case, and *not* write
//! something like this:
//!
//! ~~~ignore
//! use std::io::{File, Open, Write};
//!
//! let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
//! // If `write_line` errors, then we'll never know, because the return
//! // value is ignored.
//! file.write_line("important message");
//! drop(file);
//! ~~~
//!
//! If you *do* write that in Rust, the compiler will by give you a
//! warning (by default, controlled by the `unused_must_use` lint).
//!
//! You might instead, if you don't want to handle the error, simply
//! fail, by converting to an `Option` with `ok`, then asserting
//! success with `expect`. This will fail if the write fails, proving
//! a marginally useful message indicating why:
//!
//! ~~~no_run
//! use std::io::{File, Open, Write};
//!
//! let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
//! file.write_line("important message").ok().expect("failed to write message");
//! drop(file);
//! ~~~
//!
//! You might also simply assert success:
//!
//! ~~~no_run
//! # use std::io::{File, Open, Write};
//!
//! # let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
//! assert!(file.write_line("important message").is_ok());
//! # drop(file);
//! ~~~
//!
//! Or propagate the error up the call stack with `try!`:
//!
//! ~~~
//! # use std::io::{File, Open, Write, IoError};
//! fn write_message() -> Result<(), IoError> {
//! let mut file = File::open_mode(&Path::new("valuable_data.txt"), Open, Write);
//! try!(file.write_line("important message"));
//! drop(file);
//! return Ok(());
//! }
//! ~~~
//!
//! # The `try!` macro
//!
//! When writing code that calls many functions that return the
//! `Result` type, the error handling can be tedious. The `try!`
//! macro hides some of the boilerplate of propagating errors up the
//! call stack.
//!
//! It replaces this:
//!
//! ~~~
//! use std::io::{File, Open, Write, IoError};
//!
//! struct Info { name: ~str, age: int, rating: int }
//!
//! fn write_info(info: &Info) -> Result<(), IoError> {
//! let mut file = File::open_mode(&Path::new("my_best_friends.txt"), Open, Write);
//! // Early return on error
//! match file.write_line(format!("name: {}", info.name)) {
//! Ok(_) => (),
//! Err(e) => return Err(e)
//! }
//! match file.write_line(format!("age: {}", info.age)) {
//! Ok(_) => (),
//! Err(e) => return Err(e)
//! }
//! return file.write_line(format!("rating: {}", info.rating));
//! }
//! ~~~
//!
//! With this:
//!
//! ~~~
//! use std::io::{File, Open, Write, IoError};
//!
//! struct Info { name: ~str, age: int, rating: int }
//!
//! fn write_info(info: &Info) -> Result<(), IoError> {
//! let mut file = File::open_mode(&Path::new("my_best_friends.txt"), Open, Write);
//! // Early return on error
//! try!(file.write_line(format!("name: {}", info.name)));
//! try!(file.write_line(format!("age: {}", info.age)));
//! try!(file.write_line(format!("rating: {}", info.rating)));
//! return Ok(());
//! }
//! ~~~
//!
//! *It's much nicer!*
//!
//! Wrapping an expression in `try!` will result in the unwrapped
//! success (`Ok`) value, unless the result is `Err`, in which case
//! `Err` is returned early from the enclosing function. Its simple definition
//! makes it clear:
//!
//! ~~~
//! # #![feature(macro_rules)]
//! macro_rules! try(
//! ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
//! )
//! # fn main() { }
//! ~~~
//!
//! `try!` is imported by the prelude, and is available everywhere.
//!
//! # `Result` and `Option`
//!
//! The `Result` and [`Option`](../option/index.html) types are
//! similar and complementary: they are often employed to indicate a
//! lack of a return value; and they are trivially converted between
//! each other, so `Result`s are often handled by first converting to
//! `Option` with the [`ok`](enum.Result.html#method.ok) and
//! [`err`](enum.Result.html#method.ok) methods.
//!
//! Whereas `Option` only indicates the lack of a value, `Result` is
//! specifically for error reporting, and carries with it an error
//! value. Sometimes `Option` is used for indicating errors, but this
//! is only for simple cases and is generally discouraged. Even when
//! there is no useful error value to return, prefer `Result<T, ()>`.
//!
//! Converting to an `Option` with `ok()` to handle an error:
//!
//! ~~~
//! use std::io::Timer;
//! let mut t = Timer::new().ok().expect("failed to create timer!");
//! ~~~
//!
//! # `Result` vs. `fail!`
//!
//! `Result` is for recoverable errors; `fail!` is for unrecoverable
//! errors. Callers should always be able to avoid failure if they
//! take the proper precautions, for example, calling `is_some()`
//! on an `Option` type before calling `unwrap`.
//!
//! The suitability of `fail!` as an error handling mechanism is
//! limited by Rust's lack of any way to "catch" and resume execution
//! from a thrown exception. Therefore using failure for error
//! handling requires encapsulating fallable code in a task. Calling
//! the `fail!` macro, or invoking `fail!` indirectly should be
//! avoided as an error reporting strategy. Failure is only for
//! unrecoverable errors and a failing task is typically the sign of
//! a bug.
//!
//! A module that instead returns `Results` is alerting the caller
//! that failure is possible, and providing precise control over how
//! it is handled.
//!
//! Furthermore, failure may not be recoverable at all, depending on
//! the context. The caller of `fail!` should assume that execution
//! will not resume after failure, that failure is catastrophic.
use fmt::Show;
pub use core::result::{Result, Ok, Err, collect, fold, fold_};
// FIXME: These traits should not exist. Once std::fmt is moved to libcore,
// these can once again become inherent methods on Result.
/// Temporary trait for unwrapping a result
pub trait ResultUnwrap<T, E> {
/// Unwraps a result, yielding the content of an `Ok`.
///
/// Fails if the value is an `Err`.
fn unwrap(self) -> T;
}
/// Temporary trait for unwrapping the error of a result
pub trait ResultUnwrapErr<T, E> {
/// Unwraps a result, yielding the content of an `Err`.
///
/// Fails if the value is an `Ok`.
fn unwrap_err(self) -> E;
}
impl<T, E: Show> ResultUnwrap<T, E> for Result<T, E> {
#[inline]
fn unwrap(self) -> T {
match self {
Ok(t) => t,
Err(e) =>
fail!("called `Result::unwrap()` on an `Err` value: {}", e)
}
}
}
impl<T: Show, E> ResultUnwrapErr<T, E> for Result<T, E> {
#[inline]
fn unwrap_err(self) -> E {
match self {
Ok(t) =>
fail!("called `Result::unwrap_err()` on an `Ok` value: {}", t),
Err(e) => e
}
}
}

2
src/libstd/rt/task.rs
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@ -436,7 +436,7 @@ mod test {
#[test]
fn rng() {
use rand::{StdRng, Rng};
let mut r = StdRng::new().unwrap();
let mut r = StdRng::new().ok().unwrap();
let _ = r.next_u32();
}

1
src/libstd/task.rs
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@ -50,6 +50,7 @@ use str::{Str, SendStr, IntoMaybeOwned};
#[cfg(test)] use any::{AnyOwnExt, AnyRefExt};
#[cfg(test)] use result;
#[cfg(test)] use str::StrAllocating;
#[cfg(test)] use realstd::result::ResultUnwrap;
/// Indicates the manner in which a task exited.
///