forked from rust-lang/rust
/
result.rs
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/
result.rs
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// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Signaling success or failure states (`Result` type)
use clone::Clone;
use cmp::Eq;
use fmt;
use iter::{Iterator, FromIterator};
use option::{None, Option, Some};
use str::OwnedStr;
use to_str::ToStr;
/// `Result` is a type that represents either success (`Ok`) or failure (`Err`).
#[deriving(Clone, DeepClone, Eq, Ord, TotalEq, TotalOrd, ToStr)]
#[must_use]
pub enum Result<T, E> {
/// Contains the success value
Ok(T),
/// Contains the error value
Err(E)
}
/////////////////////////////////////////////////////////////////////////////
// Type implementation
/////////////////////////////////////////////////////////////////////////////
impl<T, E> Result<T, E> {
/////////////////////////////////////////////////////////////////////////
// Querying the contained values
/////////////////////////////////////////////////////////////////////////
/// Returns true if the result is `Ok`
#[inline]
pub fn is_ok(&self) -> bool {
match *self {
Ok(_) => true,
Err(_) => false
}
}
/// Returns true if the result is `Err`
#[inline]
pub fn is_err(&self) -> bool {
!self.is_ok()
}
/////////////////////////////////////////////////////////////////////////
// Adapter for each variant
/////////////////////////////////////////////////////////////////////////
/// Convert from `Result<T, E>` to `Option<T>`
#[inline]
pub fn ok(self) -> Option<T> {
match self {
Ok(x) => Some(x),
Err(_) => None,
}
}
/// Convert from `Result<T, E>` to `Option<E>`
#[inline]
pub fn err(self) -> Option<E> {
match self {
Ok(_) => None,
Err(x) => Some(x),
}
}
/////////////////////////////////////////////////////////////////////////
// Adapter for working with references
/////////////////////////////////////////////////////////////////////////
/// Convert from `Result<T, E>` to `Result<&T, &E>`
#[inline]
pub fn as_ref<'r>(&'r self) -> Result<&'r T, &'r E> {
match *self {
Ok(ref x) => Ok(x),
Err(ref x) => Err(x),
}
}
/// Convert from `Result<T, E>` to `Result<&mut T, &mut E>`
#[inline]
pub fn as_mut<'r>(&'r mut self) -> Result<&'r mut T, &'r mut E> {
match *self {
Ok(ref mut x) => Ok(x),
Err(ref mut x) => Err(x),
}
}
/////////////////////////////////////////////////////////////////////////
// Transforming contained values
/////////////////////////////////////////////////////////////////////////
/// Maps an `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:
///
/// let res = read_file(file).map(|buf| {
/// parse_bytes(buf)
/// })
#[inline]
pub fn map<U>(self, op: |T| -> U) -> Result<U,E> {
match self {
Ok(t) => Ok(op(t)),
Err(e) => Err(e)
}
}
/// Maps an `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.
#[inline]
pub fn map_err<F>(self, op: |E| -> F) -> Result<T,F> {
match self {
Ok(t) => Ok(t),
Err(e) => Err(op(e))
}
}
////////////////////////////////////////////////////////////////////////
// Boolean operations on the values, eager and lazy
/////////////////////////////////////////////////////////////////////////
/// Returns `res` if the result is `Ok`, otherwise returns the `Err` value of `self`.
#[inline]
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
#[inline]
pub fn and_then<U>(self, op: |T| -> Result<U, E>) -> 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`.
#[inline]
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
#[inline]
pub fn or_else<F>(self, op: |E| -> Result<T, F>) -> Result<T, F> {
match self {
Ok(t) => Ok(t),
Err(e) => op(e),
}
}
/////////////////////////////////////////////////////////////////////////
// Common special cases
/////////////////////////////////////////////////////////////////////////
/// Unwraps a result, yielding the content of an `Ok`.
/// Fails if the value is an `Err`.
#[inline]
pub fn unwrap(self) -> T {
match self {
Ok(t) => t,
Err(_) => fail!("called `Result::unwrap()` on an `Err` value")
}
}
/// Unwraps a result, yielding the content of an `Err`.
/// Fails if the value is an `Ok`.
#[inline]
pub fn unwrap_err(self) -> E {
match self {
Ok(_) => fail!("called `Result::unwrap_err()` on an `Ok` value"),
Err(e) => e
}
}
}
/////////////////////////////////////////////////////////////////////////////
// Trait implementations
/////////////////////////////////////////////////////////////////////////////
impl<T: fmt::Default, E: fmt::Default> fmt::Default for Result<T, E> {
#[inline]
fn fmt(s: &Result<T, E>, f: &mut fmt::Formatter) {
match *s {
Ok(ref t) => write!(f.buf, "Ok({})", *t),
Err(ref e) => write!(f.buf, "Err({})", *e)
}
}
}
/////////////////////////////////////////////////////////////////////////////
// Free functions
/////////////////////////////////////////////////////////////////////////////
/// 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
/// vector containing the values of each `Result` is returned.
///
/// Here is an example which increments every integer in a vector,
/// checking for overflow:
///
/// fn inc_conditionally(x: uint) -> Result<uint, &'static str> {
/// if x == uint::MAX { return Err("overflow"); }
/// else { return Ok(x+1u); }
/// }
/// let v = [1u, 2, 3];
/// let res = collect(v.iter().map(|&x| inc_conditionally(x)));
/// assert!(res == Ok(~[2u, 3, 4]));
#[inline]
pub fn collect<T, E, Iter: Iterator<Result<T, E>>, V: FromIterator<T>>(iter: Iter) -> Result<V, E> {
// FIXME(#11084): This should be twice as fast once this bug is closed.
let mut iter = iter.scan(None, |state, x| {
match x {
Ok(x) => Some(x),
Err(err) => {
*state = Some(err);
None
}
}
});
let v: V = FromIterator::from_iterator(&mut iter);
match iter.state {
Some(err) => Err(err),
None => Ok(v),
}
}
/// 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]
pub fn fold<T,
V,
E,
Iter: Iterator<Result<T, E>>>(
mut iterator: Iter,
mut init: V,
f: |V, T| -> V)
-> Result<V, E> {
for t in iterator {
match t {
Ok(v) => init = f(init, v),
Err(u) => return Err(u)
}
}
Ok(init)
}
/// Perform a trivial fold operation over the result values
/// from an iterator.
///
/// If an `Err` is encountered, it is immediately returned.
/// Otherwise, a simple `Ok(())` is returned.
#[inline]
pub fn fold_<T,E,Iter:Iterator<Result<T,E>>>(iterator: Iter) -> Result<(),E> {
fold(iterator, (), |_, _| ())
}
/////////////////////////////////////////////////////////////////////////////
// Tests
/////////////////////////////////////////////////////////////////////////////
#[cfg(test)]
mod tests {
use super::*;
use prelude::*;
use iter::range;
pub fn op1() -> Result<int, ~str> { Ok(666) }
pub fn op2() -> Result<int, ~str> { Err(~"sadface") }
#[test]
pub fn test_and() {
assert_eq!(op1().and(Ok(667)).unwrap(), 667);
assert_eq!(op1().and(Err::<(), ~str>(~"bad")).unwrap_err(), ~"bad");
assert_eq!(op2().and(Ok(667)).unwrap_err(), ~"sadface");
assert_eq!(op2().and(Err::<(), ~str>(~"bad")).unwrap_err(), ~"sadface");
}
#[test]
pub fn test_and_then() {
assert_eq!(op1().and_then(|i| Ok::<int, ~str>(i + 1)).unwrap(), 667);
assert_eq!(op1().and_then(|_| Err::<int, ~str>(~"bad")).unwrap_err(), ~"bad");
assert_eq!(op2().and_then(|i| Ok::<int, ~str>(i + 1)).unwrap_err(), ~"sadface");
assert_eq!(op2().and_then(|_| Err::<int, ~str>(~"bad")).unwrap_err(), ~"sadface");
}
#[test]
pub fn test_or() {
assert_eq!(op1().or(Ok(667)).unwrap(), 666);
assert_eq!(op1().or(Err(~"bad")).unwrap(), 666);
assert_eq!(op2().or(Ok(667)).unwrap(), 667);
assert_eq!(op2().or(Err(~"bad")).unwrap_err(), ~"bad");
}
#[test]
pub fn test_or_else() {
assert_eq!(op1().or_else(|_| Ok::<int, ~str>(667)).unwrap(), 666);
assert_eq!(op1().or_else(|e| Err::<int, ~str>(e + "!")).unwrap(), 666);
assert_eq!(op2().or_else(|_| Ok::<int, ~str>(667)).unwrap(), 667);
assert_eq!(op2().or_else(|e| Err::<int, ~str>(e + "!")).unwrap_err(), ~"sadface!");
}
#[test]
pub fn test_impl_map() {
assert_eq!(Ok::<~str, ~str>(~"a").map(|x| x + "b"), Ok(~"ab"));
assert_eq!(Err::<~str, ~str>(~"a").map(|x| x + "b"), Err(~"a"));
}
#[test]
pub fn test_impl_map_err() {
assert_eq!(Ok::<~str, ~str>(~"a").map_err(|x| x + "b"), Ok(~"a"));
assert_eq!(Err::<~str, ~str>(~"a").map_err(|x| x + "b"), Err(~"ab"));
}
#[test]
fn test_collect() {
let v: Result<~[int], ()> = collect(range(0, 0).map(|_| Ok::<int, ()>(0)));
assert_eq!(v, Ok(~[]));
let v: Result<~[int], ()> = collect(range(0, 3).map(|x| Ok::<int, ()>(x)));
assert_eq!(v, Ok(~[0, 1, 2]));
let v: Result<~[int], int> = collect(range(0, 3)
.map(|x| if x > 1 { Err(x) } else { Ok(x) }));
assert_eq!(v, Err(2));
// test that it does not take more elements than it needs
let functions = [|| Ok(()), || Err(1), || fail!()];
let v: Result<~[()], int> = collect(functions.iter().map(|f| (*f)()));
assert_eq!(v, Err(1));
}
#[test]
fn test_fold() {
assert_eq!(fold_(range(0, 0)
.map(|_| Ok::<(), ()>(()))),
Ok(()));
assert_eq!(fold(range(0, 3)
.map(|x| Ok::<int, ()>(x)),
0, |a, b| a + b),
Ok(3));
assert_eq!(fold_(range(0, 3)
.map(|x| if x > 1 { Err(x) } else { Ok(()) })),
Err(2));
// test that it does not take more elements than it needs
let functions = [|| Ok(()), || Err(1), || fail!()];
assert_eq!(fold_(functions.iter()
.map(|f| (*f)())),
Err(1));
}
#[test]
pub fn test_to_str() {
let ok: Result<int, ~str> = Ok(100);
let err: Result<int, ~str> = Err(~"Err");
assert_eq!(ok.to_str(), ~"Ok(100)");
assert_eq!(err.to_str(), ~"Err(Err)");
}
#[test]
pub fn test_fmt_default() {
let ok: Result<int, ~str> = Ok(100);
let err: Result<int, ~str> = Err(~"Err");
assert_eq!(format!("{}", ok), ~"Ok(100)");
assert_eq!(format!("{}", err), ~"Err(Err)");
}
}