131 lines
3.3 KiB
Rust
131 lines
3.3 KiB
Rust
// Copyright 2012-2013 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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//! A mutable, nullable memory location
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#[missing_doc];
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use cast::transmute_mut;
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use unstable::finally::Finally;
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use prelude::*;
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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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#[no_freeze]
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#[deriving(Clone, DeepClone, Eq)]
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#[allow(missing_doc)]
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pub struct Cell<T> {
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priv value: Option<T>
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}
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impl<T> Cell<T> {
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/// Creates a new full cell with the given value.
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pub fn new(value: T) -> Cell<T> {
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Cell { value: Some(value) }
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}
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/// Creates a new empty cell with no value inside.
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pub fn new_empty() -> Cell<T> {
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Cell { value: None }
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}
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/// Yields the value, failing if the cell is empty.
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pub fn take(&self) -> 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 take an empty cell");
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}
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this.value.take_unwrap()
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}
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/// Yields the value if the cell is full, or `None` if it is empty.
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pub fn take_opt(&self) -> Option<T> {
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let this = unsafe { transmute_mut(self) };
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this.value.take()
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}
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/// Returns the value, failing if the cell is full.
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pub 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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}
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/// Returns true if the cell is empty and false if the cell is full.
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pub fn is_empty(&self) -> bool {
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self.value.is_none()
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}
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/// Calls a closure with a reference to the value.
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pub fn with_ref<R>(&self, op: &fn(v: &T) -> R) -> R {
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do self.with_mut_ref |ptr| { op(ptr) }
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}
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/// Calls a closure with a mutable reference to the value.
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pub fn with_mut_ref<R>(&self, op: &fn(v: &mut T) -> R) -> R {
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let mut v = Some(self.take());
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do (|| {
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op(v.get_mut_ref())
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}).finally {
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self.put_back(v.take_unwrap());
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}
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}
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}
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#[test]
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fn test_basic() {
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let value_cell = Cell::new(~10);
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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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value_cell.put_back(value);
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assert!(!value_cell.is_empty());
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}
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#[test]
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#[should_fail]
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fn test_take_empty() {
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let value_cell = Cell::new_empty::<~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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fn test_put_back_non_empty() {
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let value_cell = Cell::new(~10);
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value_cell.put_back(~20);
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}
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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::new(~[1, 2, 3, 4, 5, 6]);
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let l = do c.with_ref() |v| { v.len() };
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assert_eq!(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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let v = ~[1, 2];
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let c = Cell::new(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_eq!(v, good);
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}
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