1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
14 /// A write-once variable. When constructed, it is empty, and
15 /// can only be set once.
17 /// Ivars ensure that data that can only be initialised once. A full
18 /// implementation is used for concurrency and blocks on a read of an
19 /// unfulfilled value. This implementation is more minimal and panics
20 /// if you attempt to read the value before it has been set. It is also
21 /// not `Sync`, but may be extended in the future to be usable as a true
24 pub struct Ivar<T: Copy> {
28 impl<T: Copy> Ivar<T> {
29 pub fn new() -> Ivar<T> {
35 pub fn get(&self) -> Option<T> {
39 pub fn fulfill(&self, value: T) {
40 assert!(self.data.get().is_none(),
41 "Value already set!");
42 self.data.set(Some(value));
45 pub fn is_fulfilled(&self) -> bool {
46 self.data.get().is_some()
49 pub fn unwrap(&self) -> T {
54 impl<T: Copy+fmt::Debug> fmt::Debug for Ivar<T> {
55 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
57 Some(val) => write!(f, "Ivar({:?})", val),
58 None => f.write_str("Ivar(<unfulfilled>)")
63 impl<T: Copy> Clone for Ivar<T> {
64 fn clone(&self) -> Ivar<T> {
66 Some(val) => Ivar { data: Cell::new(Some(val)) },