rust/src/libstd/cell.rs

// Copyright 2012-2013 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.

//! Runtime move semantics

#[missing_doc];

use cast::transmute_mut;
use prelude::*;

/*
A dynamic, mutable location.

Similar to a mutable option type, but friendlier.
*/

#[no_freeze]
#[deriving(Clone, DeepClone, Eq)]
#[allow(missing_doc)]
pub struct Cell<T> {
    priv value: Option<T>
}

impl<T> Cell<T> {
    /// Creates a new full cell with the given value.
    pub fn new(value: T) -> Cell<T> {
        Cell { value: Some(value) }
    }

    /// Yields the value, failing if the cell is empty.
    pub fn take(&self) -> T {
        let this = unsafe { transmute_mut(self) };
        if this.is_empty() {
            fail!("attempt to take an empty cell");
        }

        this.value.take_unwrap()
    }

    /// Yields the value if the cell is full, or `None` if it is empty.
    pub fn take_opt(&self) -> Option<T> {
        let this = unsafe { transmute_mut(self) };
        this.value.take()
    }

    /// Returns true if the cell is empty and false if the cell is full.
    pub fn is_empty(&self) -> bool {
        self.value.is_none()
    }
}

#[test]
fn test_basic() {
    let value_cell = Cell::new(~10);
    assert!(!value_cell.is_empty());
    let value = value_cell.take();
    assert!(value == ~10);
    assert!(value_cell.is_empty());
}

#[test]
#[should_fail]
fn test_take_empty() {
    let value_cell: Cell<~int> = Cell::new(~0);
    value_cell.take();
    value_cell.take();
}