servo/components/script/dom/bindings/cell.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

use dom::bindings::trace::JSTraceable;
use js::jsapi::{JSTracer};

use std::cell;
use std::cell::RefCell;
use std::mem;

/// A mutable field in DOM for large sized value.
/// This has a special method to return the pointer of itself
/// for used in layout task.
/// This simply wraps `RefCell<T>` to add the special method.
pub struct DOMRefCell<T> {
    base: RefCell<T>,
}

pub type Ref<'a, T> = cell::Ref<'a, T>;
pub type RefMut<'a, T> = cell::RefMut<'a, T>;


impl<T> DOMRefCell<T> {
    #[inline(always)]
    pub fn new(value: T) -> DOMRefCell<T> {
        DOMRefCell {
            base: RefCell::new(value),
        }
    }

    #[inline(always)]
    pub fn unwrap(self) -> T {
        self.base.unwrap()
    }

    #[inline(always)]
    pub fn try_borrow<'a>(&'a self) -> Option<Ref<'a, T>> {
        self.base.try_borrow()
    }

    #[inline(always)]
    pub fn borrow<'a>(&'a self) -> Ref<'a, T> {
        self.base.borrow()
    }

    #[inline(always)]
    pub fn try_borrow_mut<'a>(&'a self) -> Option<RefMut<'a, T>> {
        self.base.try_borrow_mut()
    }

    #[inline(always)]
    pub fn borrow_mut<'a>(&'a self) -> RefMut<'a, T> {
        self.base.borrow_mut()
    }

    /// This returns the pointer which refers T in `RefCell<T>` directly.
    pub unsafe fn borrow_for_layout<'a>(&'a self) -> &'a T {
        let val = mem::transmute::<&RefCell<T>, &T>(&self.base);
        val
    }
}

impl<T: JSTraceable> JSTraceable for DOMRefCell<T> {
    fn trace(&self, trc: *mut JSTracer) {
        (*self).base.borrow().trace(trc)
    }
}