2012-12-03 18:48:01 -06:00
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// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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2013-03-24 20:59:04 -05:00
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//! A mutable, nullable memory location
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2013-04-02 16:15:04 -05:00
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use cast::transmute_mut;
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2013-02-25 15:23:16 -06:00
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use prelude::*;
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2013-05-05 23:42:54 -05:00
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use util::replace;
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2012-12-23 16:41:37 -06:00
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2013-03-24 20:59:04 -05:00
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/*
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A dynamic, mutable location.
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Similar to a mutable option type, but friendlier.
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*/
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2012-08-09 21:06:06 -05:00
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2013-05-05 14:42:03 -05:00
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#[mutable]
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2012-09-28 16:55:31 -05:00
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pub struct Cell<T> {
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2013-04-22 12:01:32 -05:00
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priv value: Option<T>
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}
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2013-03-16 13:11:31 -05:00
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impl<T:cmp::Eq> cmp::Eq for Cell<T> {
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2013-03-21 23:20:48 -05:00
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fn eq(&self, other: &Cell<T>) -> bool {
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(self.value) == (other.value)
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}
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fn ne(&self, other: &Cell<T>) -> bool { !self.eq(other) }
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}
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2012-08-09 21:06:06 -05:00
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/// Creates a new full cell with the given value.
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2012-10-03 14:21:48 -05:00
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pub fn Cell<T>(value: T) -> Cell<T> {
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2013-02-15 01:30:30 -06:00
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Cell { value: Some(value) }
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}
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2013-03-21 23:20:48 -05:00
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pub fn empty_cell<T>() -> Cell<T> {
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2012-08-20 14:23:37 -05:00
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Cell { value: None }
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}
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2013-02-26 19:47:41 -06:00
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pub impl<T> Cell<T> {
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/// Yields the value, failing if the cell is empty.
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2013-03-04 21:36:15 -06:00
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fn take(&self) -> T {
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2013-05-10 17:15:06 -05:00
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let this = unsafe { transmute_mut(self) };
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if this.is_empty() {
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2013-05-05 17:18:51 -05:00
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fail!("attempt to take an empty cell");
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}
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2012-08-12 18:36:07 -05:00
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2013-05-10 17:15:06 -05:00
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replace(&mut this.value, None).unwrap()
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}
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/// Returns the value, failing if the cell is full.
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fn put_back(&self, value: T) {
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let this = unsafe { transmute_mut(self) };
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if !this.is_empty() {
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fail!("attempt to put a value back into a full cell");
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}
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this.value = Some(value);
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2012-08-09 21:06:06 -05:00
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}
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/// Returns true if the cell is empty and false if the cell is full.
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fn is_empty(&self) -> bool {
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self.value.is_none()
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}
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2012-08-16 21:36:49 -05:00
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// Calls a closure with a reference to the value.
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2013-03-07 16:38:38 -06:00
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fn with_ref<R>(&self, op: &fn(v: &T) -> R) -> R {
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2012-08-13 17:06:13 -05:00
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let v = self.take();
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let r = op(&v);
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self.put_back(v);
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r
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}
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2013-04-04 12:34:35 -05:00
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// Calls a closure with a mutable reference to the value.
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fn with_mut_ref<R>(&self, op: &fn(v: &mut T) -> R) -> R {
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let mut v = self.take();
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let r = op(&mut v);
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self.put_back(v);
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r
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}
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2012-08-09 21:06:06 -05:00
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}
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2012-08-12 18:36:07 -05:00
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#[test]
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fn test_basic() {
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let value_cell = Cell(~10);
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2013-03-28 20:39:09 -05:00
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assert!(!value_cell.is_empty());
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let value = value_cell.take();
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assert!(value == ~10);
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assert!(value_cell.is_empty());
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2013-02-15 01:30:30 -06:00
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value_cell.put_back(value);
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2013-03-28 20:39:09 -05:00
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assert!(!value_cell.is_empty());
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2012-08-12 18:36:07 -05:00
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}
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#[test]
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#[should_fail]
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#[ignore(cfg(windows))]
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fn test_take_empty() {
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let value_cell = empty_cell::<~int>();
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value_cell.take();
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}
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#[test]
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#[should_fail]
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#[ignore(cfg(windows))]
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fn test_put_back_non_empty() {
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let value_cell = Cell(~10);
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value_cell.put_back(~20);
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2012-08-16 21:36:49 -05:00
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}
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2013-04-04 12:34:35 -05:00
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#[test]
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fn test_with_ref() {
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let good = 6;
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let c = Cell(~[1, 2, 3, 4, 5, 6]);
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let l = do c.with_ref() |v| { v.len() };
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assert!(l == good);
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}
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#[test]
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fn test_with_mut_ref() {
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let good = ~[1, 2, 3];
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2013-04-12 00:10:01 -05:00
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let v = ~[1, 2];
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2013-04-04 12:34:35 -05:00
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let c = Cell(v);
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do c.with_mut_ref() |v| { v.push(3); }
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let v = c.take();
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assert!(v == good);
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}
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