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option.rs
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option.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.
//! Optionally nullable values (`Option` type)
//!
//! Type `Option` represents an optional value.
//!
//! Every `Option<T>` value can either be `Some(T)` or `None`. Where in other
//! languages you might use a nullable type, in Rust you would use an option
//! type.
//!
//! Options are most commonly used with pattern matching to query the presence
//! of a value and take action, always accounting for the `None` case.
//!
//! # Example
//!
//! ```
//! let msg = Some(~"howdy");
//!
//! // Take a reference to the contained string
//! match msg {
//! Some(ref m) => println!("{}", *m),
//! None => ()
//! }
//!
//! // Remove the contained string, destroying the Option
//! let unwrapped_msg = match msg {
//! Some(m) => m,
//! None => ~"default message"
//! };
//! ```
use any::Any;
use clone::Clone;
use clone::DeepClone;
use cmp::{Eq, TotalEq, TotalOrd};
use default::Default;
use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSize};
use kinds::Send;
use mem;
use vec;
/// The option type
#[deriving(Clone, DeepClone, Eq, Ord, TotalEq, TotalOrd, Show)]
pub enum Option<T> {
/// No value
None,
/// Some value `T`
Some(T)
}
/////////////////////////////////////////////////////////////////////////////
// Type implementation
/////////////////////////////////////////////////////////////////////////////
impl<T> Option<T> {
/////////////////////////////////////////////////////////////////////////
// Querying the contained values
/////////////////////////////////////////////////////////////////////////
/// Returns true if the option contains a `Some` value
#[inline]
pub fn is_some(&self) -> bool {
match *self {
Some(_) => true,
None => false
}
}
/// Returns true if the option equals `None`
#[inline]
pub fn is_none(&self) -> bool {
!self.is_some()
}
/////////////////////////////////////////////////////////////////////////
// Adapter for working with references
/////////////////////////////////////////////////////////////////////////
/// Convert from `Option<T>` to `Option<&T>`
#[inline]
pub fn as_ref<'r>(&'r self) -> Option<&'r T> {
match *self { Some(ref x) => Some(x), None => None }
}
/// Convert from `Option<T>` to `Option<&mut T>`
#[inline]
pub fn as_mut<'r>(&'r mut self) -> Option<&'r mut T> {
match *self { Some(ref mut x) => Some(x), None => None }
}
/// Convert from `Option<T>` to `&[T]` (without copying)
#[inline]
pub fn as_slice<'r>(&'r self) -> &'r [T] {
match *self {
Some(ref x) => vec::ref_slice(x),
None => &[]
}
}
/// Convert from `Option<T>` to `&[T]` (without copying)
#[inline]
pub fn as_mut_slice<'r>(&'r mut self) -> &'r mut [T] {
match *self {
Some(ref mut x) => vec::mut_ref_slice(x),
None => &mut []
}
}
/////////////////////////////////////////////////////////////////////////
// Getting to contained values
/////////////////////////////////////////////////////////////////////////
/// Unwraps an option, yielding the content of a `Some`
/// Fails if the value is a `None` with a custom failure message provided by `msg`.
#[inline]
pub fn expect<M: Any + Send>(self, msg: M) -> T {
match self {
Some(val) => val,
None => fail!(msg),
}
}
/// Moves a value out of an option type and returns it.
///
/// Useful primarily for getting strings, vectors and unique pointers out
/// of option types without copying them.
///
/// # Failure
///
/// Fails if the value equals `None`.
///
/// # Safety note
///
/// In general, because this function may fail, its use is discouraged.
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
#[inline]
pub fn unwrap(self) -> T {
match self {
Some(val) => val,
None => fail!("called `Option::unwrap()` on a `None` value"),
}
}
/// Returns the contained value or a default
#[inline]
pub fn unwrap_or(self, def: T) -> T {
match self {
Some(x) => x,
None => def
}
}
/// Returns the contained value or computes it from a closure
#[inline]
pub fn unwrap_or_else(self, f: || -> T) -> T {
match self {
Some(x) => x,
None => f()
}
}
/////////////////////////////////////////////////////////////////////////
// Transforming contained values
/////////////////////////////////////////////////////////////////////////
/// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value.
#[inline]
pub fn map<U>(self, f: |T| -> U) -> Option<U> {
match self { Some(x) => Some(f(x)), None => None }
}
/// Applies a function to the contained value or returns a default.
#[inline]
pub fn map_or<U>(self, def: U, f: |T| -> U) -> U {
match self { None => def, Some(t) => f(t) }
}
/// Apply a function to the contained value or do nothing.
/// Returns true if the contained value was mutated.
pub fn mutate(&mut self, f: |T| -> T) -> bool {
if self.is_some() {
*self = Some(f(self.take_unwrap()));
true
} else { false }
}
/// Apply a function to the contained value or set it to a default.
/// Returns true if the contained value was mutated, or false if set to the default.
pub fn mutate_or_set(&mut self, def: T, f: |T| -> T) -> bool {
if self.is_some() {
*self = Some(f(self.take_unwrap()));
true
} else {
*self = Some(def);
false
}
}
/////////////////////////////////////////////////////////////////////////
// Iterator constructors
/////////////////////////////////////////////////////////////////////////
/// Return an iterator over the possibly contained value
#[inline]
pub fn iter<'r>(&'r self) -> Item<&'r T> {
match *self {
Some(ref x) => Item{opt: Some(x)},
None => Item{opt: None}
}
}
/// Return a mutable iterator over the possibly contained value
#[inline]
pub fn mut_iter<'r>(&'r mut self) -> Item<&'r mut T> {
match *self {
Some(ref mut x) => Item{opt: Some(x)},
None => Item{opt: None}
}
}
/// Return a consuming iterator over the possibly contained value
#[inline]
pub fn move_iter(self) -> Item<T> {
Item{opt: self}
}
/////////////////////////////////////////////////////////////////////////
// Boolean operations on the values, eager and lazy
/////////////////////////////////////////////////////////////////////////
/// Returns `None` if the option is `None`, otherwise returns `optb`.
#[inline]
pub fn and<U>(self, optb: Option<U>) -> Option<U> {
match self {
Some(_) => optb,
None => None,
}
}
/// Returns `None` if the option is `None`, otherwise calls `f` with the
/// wrapped value and returns the result.
#[inline]
pub fn and_then<U>(self, f: |T| -> Option<U>) -> Option<U> {
match self {
Some(x) => f(x),
None => None,
}
}
/// Returns the option if it contains a value, otherwise returns `optb`.
#[inline]
pub fn or(self, optb: Option<T>) -> Option<T> {
match self {
Some(_) => self,
None => optb
}
}
/// Returns the option if it contains a value, otherwise calls `f` and
/// returns the result.
#[inline]
pub fn or_else(self, f: || -> Option<T>) -> Option<T> {
match self {
Some(_) => self,
None => f(),
}
}
/////////////////////////////////////////////////////////////////////////
// Misc
/////////////////////////////////////////////////////////////////////////
/// Take the value out of the option, leaving a `None` in its place.
#[inline]
pub fn take(&mut self) -> Option<T> {
mem::replace(self, None)
}
/// Filters an optional value using a given function.
#[inline(always)]
pub fn filtered(self, f: |t: &T| -> bool) -> Option<T> {
match self {
Some(x) => if f(&x) {Some(x)} else {None},
None => None
}
}
/// Applies a function zero or more times until the result is `None`.
#[inline]
pub fn while_some(self, blk: |v: T| -> Option<T>) {
let mut opt = self;
while opt.is_some() {
opt = blk(opt.unwrap());
}
}
/////////////////////////////////////////////////////////////////////////
// Common special cases
/////////////////////////////////////////////////////////////////////////
/// The option dance. Moves a value out of an option type and returns it,
/// replacing the original with `None`.
///
/// # Failure
///
/// Fails if the value equals `None`.
#[inline]
pub fn take_unwrap(&mut self) -> T {
if self.is_none() {
fail!("called `Option::take_unwrap()` on a `None` value")
}
self.take().unwrap()
}
/// Gets an immutable reference to the value inside an option.
///
/// # Failure
///
/// Fails if the value equals `None`
///
/// # Safety note
///
/// In general, because this function may fail, its use is discouraged
/// (calling `get` on `None` is akin to dereferencing a null pointer).
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
#[inline]
pub fn get_ref<'a>(&'a self) -> &'a T {
match *self {
Some(ref x) => x,
None => fail!("called `Option::get_ref()` on a `None` value"),
}
}
/// Gets a mutable reference to the value inside an option.
///
/// # Failure
///
/// Fails if the value equals `None`
///
/// # Safety note
///
/// In general, because this function may fail, its use is discouraged
/// (calling `get` on `None` is akin to dereferencing a null pointer).
/// Instead, prefer to use pattern matching and handle the `None`
/// case explicitly.
#[inline]
pub fn get_mut_ref<'a>(&'a mut self) -> &'a mut T {
match *self {
Some(ref mut x) => x,
None => fail!("called `Option::get_mut_ref()` on a `None` value"),
}
}
}
impl<T: Default> Option<T> {
/// Returns the contained value or default (for this type)
#[inline]
pub fn unwrap_or_default(self) -> T {
match self {
Some(x) => x,
None => Default::default()
}
}
}
/////////////////////////////////////////////////////////////////////////////
// Trait implementations
/////////////////////////////////////////////////////////////////////////////
impl<T> Default for Option<T> {
#[inline]
fn default() -> Option<T> { None }
}
/////////////////////////////////////////////////////////////////////////////
// The Option Iterator
/////////////////////////////////////////////////////////////////////////////
/// An iterator that yields either one or zero elements
#[deriving(Clone, DeepClone)]
pub struct Item<A> {
priv opt: Option<A>
}
impl<A> Iterator<A> for Item<A> {
#[inline]
fn next(&mut self) -> Option<A> {
self.opt.take()
}
#[inline]
fn size_hint(&self) -> (uint, Option<uint>) {
match self.opt {
Some(_) => (1, Some(1)),
None => (0, Some(0)),
}
}
}
impl<A> DoubleEndedIterator<A> for Item<A> {
#[inline]
fn next_back(&mut self) -> Option<A> {
self.opt.take()
}
}
impl<A> ExactSize<A> for Item<A> {}
/////////////////////////////////////////////////////////////////////////////
// Free functions
/////////////////////////////////////////////////////////////////////////////
/// Takes each element in the `Iterator`: if it is `None`, no further
/// elements are taken, and the `None` is returned. Should no `None` occur, a
/// vector containing the values of each `Option` is returned.
///
/// Here is an example which increments every integer in a vector,
/// checking for overflow:
///
/// fn inc_conditionally(x: uint) -> Option<uint> {
/// if x == uint::MAX { return None; }
/// else { return Some(x+1u); }
/// }
/// let v = [1u, 2, 3];
/// let res = collect(v.iter().map(|&x| inc_conditionally(x)));
/// assert!(res == Some(~[2u, 3, 4]));
#[inline]
pub fn collect<T, Iter: Iterator<Option<T>>, V: FromIterator<T>>(iter: Iter) -> Option<V> {
// FIXME(#11084): This should be twice as fast once this bug is closed.
let mut iter = iter.scan(false, |state, x| {
match x {
Some(x) => Some(x),
None => {
*state = true;
None
}
}
});
let v: V = FromIterator::from_iterator(&mut iter);
if iter.state {
None
} else {
Some(v)
}
}
/////////////////////////////////////////////////////////////////////////////
// Tests
/////////////////////////////////////////////////////////////////////////////
#[cfg(test)]
mod tests {
use super::*;
use prelude::*;
use iter::range;
use str::StrSlice;
use kinds::marker;
use vec::ImmutableVector;
#[test]
fn test_get_ptr() {
unsafe {
let x = ~0;
let addr_x: *int = ::cast::transmute(&*x);
let opt = Some(x);
let y = opt.unwrap();
let addr_y: *int = ::cast::transmute(&*y);
assert_eq!(addr_x, addr_y);
}
}
#[test]
fn test_get_str() {
let x = ~"test";
let addr_x = x.as_ptr();
let opt = Some(x);
let y = opt.unwrap();
let addr_y = y.as_ptr();
assert_eq!(addr_x, addr_y);
}
#[test]
fn test_get_resource() {
use rc::Rc;
use cell::RefCell;
struct R {
i: Rc<RefCell<int>>,
}
#[unsafe_destructor]
impl ::ops::Drop for R {
fn drop(&mut self) {
let ii = self.i.borrow();
ii.set(ii.get() + 1);
}
}
fn R(i: Rc<RefCell<int>>) -> R {
R {
i: i
}
}
let i = Rc::new(RefCell::new(0));
{
let x = R(i.clone());
let opt = Some(x);
let _y = opt.unwrap();
}
assert_eq!(i.borrow().get(), 1);
}
#[test]
fn test_option_dance() {
let x = Some(());
let mut y = Some(5);
let mut y2 = 0;
for _x in x.iter() {
y2 = y.take_unwrap();
}
assert_eq!(y2, 5);
assert!(y.is_none());
}
#[test] #[should_fail]
fn test_option_too_much_dance() {
let mut y = Some(marker::NoPod);
let _y2 = y.take_unwrap();
let _y3 = y.take_unwrap();
}
#[test]
fn test_and() {
let x: Option<int> = Some(1);
assert_eq!(x.and(Some(2)), Some(2));
assert_eq!(x.and(None::<int>), None);
let x: Option<int> = None;
assert_eq!(x.and(Some(2)), None);
assert_eq!(x.and(None::<int>), None);
}
#[test]
fn test_and_then() {
let x: Option<int> = Some(1);
assert_eq!(x.and_then(|x| Some(x + 1)), Some(2));
assert_eq!(x.and_then(|_| None::<int>), None);
let x: Option<int> = None;
assert_eq!(x.and_then(|x| Some(x + 1)), None);
assert_eq!(x.and_then(|_| None::<int>), None);
}
#[test]
fn test_or() {
let x: Option<int> = Some(1);
assert_eq!(x.or(Some(2)), Some(1));
assert_eq!(x.or(None), Some(1));
let x: Option<int> = None;
assert_eq!(x.or(Some(2)), Some(2));
assert_eq!(x.or(None), None);
}
#[test]
fn test_or_else() {
let x: Option<int> = Some(1);
assert_eq!(x.or_else(|| Some(2)), Some(1));
assert_eq!(x.or_else(|| None), Some(1));
let x: Option<int> = None;
assert_eq!(x.or_else(|| Some(2)), Some(2));
assert_eq!(x.or_else(|| None), None);
}
#[test]
fn test_option_while_some() {
let mut i = 0;
Some(10).while_some(|j| {
i += 1;
if j > 0 {
Some(j-1)
} else {
None
}
});
assert_eq!(i, 11);
}
#[test]
fn test_unwrap() {
assert_eq!(Some(1).unwrap(), 1);
assert_eq!(Some(~"hello").unwrap(), ~"hello");
}
#[test]
#[should_fail]
fn test_unwrap_fail1() {
let x: Option<int> = None;
x.unwrap();
}
#[test]
#[should_fail]
fn test_unwrap_fail2() {
let x: Option<~str> = None;
x.unwrap();
}
#[test]
fn test_unwrap_or() {
let x: Option<int> = Some(1);
assert_eq!(x.unwrap_or(2), 1);
let x: Option<int> = None;
assert_eq!(x.unwrap_or(2), 2);
}
#[test]
fn test_unwrap_or_else() {
let x: Option<int> = Some(1);
assert_eq!(x.unwrap_or_else(|| 2), 1);
let x: Option<int> = None;
assert_eq!(x.unwrap_or_else(|| 2), 2);
}
#[test]
fn test_filtered() {
let some_stuff = Some(42);
let modified_stuff = some_stuff.filtered(|&x| {x < 10});
assert_eq!(some_stuff.unwrap(), 42);
assert!(modified_stuff.is_none());
}
#[test]
fn test_iter() {
let val = 5;
let x = Some(val);
let mut it = x.iter();
assert_eq!(it.size_hint(), (1, Some(1)));
assert_eq!(it.next(), Some(&val));
assert_eq!(it.size_hint(), (0, Some(0)));
assert!(it.next().is_none());
}
#[test]
fn test_mut_iter() {
let val = 5;
let new_val = 11;
let mut x = Some(val);
{
let mut it = x.mut_iter();
assert_eq!(it.size_hint(), (1, Some(1)));
match it.next() {
Some(interior) => {
assert_eq!(*interior, val);
*interior = new_val;
}
None => assert!(false),
}
assert_eq!(it.size_hint(), (0, Some(0)));
assert!(it.next().is_none());
}
assert_eq!(x, Some(new_val));
}
#[test]
fn test_ord() {
let small = Some(1.0);
let big = Some(5.0);
let nan = Some(0.0/0.0);
assert!(!(nan < big));
assert!(!(nan > big));
assert!(small < big);
assert!(None < big);
assert!(big > None);
}
#[test]
fn test_mutate() {
let mut x = Some(3i);
assert!(x.mutate(|i| i+1));
assert_eq!(x, Some(4i));
assert!(x.mutate_or_set(0, |i| i+1));
assert_eq!(x, Some(5i));
x = None;
assert!(!x.mutate(|i| i+1));
assert_eq!(x, None);
assert!(!x.mutate_or_set(0i, |i| i+1));
assert_eq!(x, Some(0i));
}
#[test]
fn test_collect() {
let v: Option<~[int]> = collect(range(0, 0)
.map(|_| Some(0)));
assert_eq!(v, Some(~[]));
let v: Option<~[int]> = collect(range(0, 3)
.map(|x| Some(x)));
assert_eq!(v, Some(~[0, 1, 2]));
let v: Option<~[int]> = collect(range(0, 3)
.map(|x| if x > 1 { None } else { Some(x) }));
assert_eq!(v, None);
// test that it does not take more elements than it needs
let functions = [|| Some(()), || None, || fail!()];
let v: Option<~[()]> = collect(functions.iter().map(|f| (*f)()));
assert_eq!(v, None);
}
}