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#![cfg_attr(not(test), no_std)]
use core::cell::UnsafeCell;
pub struct LateStatic<T> {
val: UnsafeCell<Option<T>>
}
unsafe impl<T: Send> core::marker::Send for LateStatic<T> {}
unsafe impl<T: Send> core::marker::Sync for LateStatic<T> {}
impl<T> LateStatic<T> {
pub const fn new() -> Self {
LateStatic {
val: UnsafeCell::new(None),
}
}
pub unsafe fn assign(&self, val: T) {
let option: &mut Option<T> = &mut *self.val.get();
if option.is_some() {
panic!("Second assignment to late static");
}
else {
*option = Some(val);
}
}
}
impl<T> core::ops::Deref for LateStatic<T> {
type Target = T;
fn deref(&self) -> &T {
unsafe {
let option: &Option<T> = &*self.val.get();
match option {
Some(ref val) => val,
None => panic!("Dereference of late static before a value was assigned"),
}
}
}
}
impl<T> core::ops::DerefMut for LateStatic<T> {
fn deref_mut(&mut self) -> &mut T {
unsafe {
let option: &mut Option<T> = &mut *self.val.get();
match option {
Some(ref mut val) => val,
None => panic!("Dereference of late static before a value was assigned"),
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
static ASSIGN_ONCE_TEST: LateStatic<u32> = LateStatic::new();
#[test]
fn assign_once() {
unsafe {
ASSIGN_ONCE_TEST.assign(42);
}
}
static ASSIGN_TWICE_TEST: LateStatic<u32> = LateStatic::new();
#[test]
#[should_panic]
fn assign_twice() {
unsafe {
ASSIGN_TWICE_TEST.assign(42);
ASSIGN_TWICE_TEST.assign(37);
}
}
struct Foo {
pub value: u32,
}
static DEREF_CONST_TEST: LateStatic<Foo> = LateStatic::new();
#[test]
fn deref_const() {
unsafe {
DEREF_CONST_TEST.assign(Foo { value: 42 });
}
assert_eq!(DEREF_CONST_TEST.value, 42);
}
static mut DEREF_MUT_TEST: LateStatic<Foo> = LateStatic::new();
#[test]
fn deref_mut() {
unsafe {
DEREF_MUT_TEST.assign(Foo { value: 42 });
assert_eq!(DEREF_MUT_TEST.value, 42);
DEREF_MUT_TEST.value = 37;
assert_eq!(DEREF_MUT_TEST.value, 37);
}
}
}