ref-with-flag: Update for 2nd edition.

pull/13/head
Jim Blandy 3 years ago
parent dc2350d9da
commit 5cea569df2

@ -2,5 +2,6 @@
name = "ref-with-flag"
version = "0.1.0"
authors = ["You <you@example.com>"]
edition = "2018"
[dependencies]

@ -10,41 +10,44 @@ mod ref_with_flag {
/// If you're the kind of programmer who's never met a pointer whose
/// 2⁰-bit you didn't want to steal, well, now you can do it safely!
/// ("But it's not nearly as exciting this way...")
pub struct RefWithFlag<'a, T: 'a> {
pub struct RefWithFlag<'a, T> {
ptr_and_bit: usize,
behaves_like: PhantomData<&'a T> // occupies no space
}
impl<'a, T: 'a> RefWithFlag<'a, T> {
pub fn new(ptr: &'a T, bit: bool) -> RefWithFlag<T> {
pub fn new(ptr: &'a T, flag: bool) -> RefWithFlag<T> {
assert!(align_of::<T>() % 2 == 0);
RefWithFlag {
ptr_and_bit: ptr as *const T as usize | bit as usize,
ptr_and_bit: ptr as *const T as usize | flag as usize,
behaves_like: PhantomData
}
}
pub fn as_ref(&self) -> &'a T {
let ptr = (self.ptr_and_bit & !1) as *const T;
pub fn get_ref(&self) -> &'a T {
unsafe {
let ptr = (self.ptr_and_bit & !1) as *const T;
&*ptr
}
}
pub fn as_bool(&self) -> bool {
pub fn get_flag(&self) -> bool {
self.ptr_and_bit & 1 != 0
}
}
}
#[cfg(test)]
mod ref_with_flag_tests {
use super::ref_with_flag;
#[test]
fn use_ref_with_flag() {
use ref_with_flag::RefWithFlag;
let vec = vec![10, 20, 30];
let pab = RefWithFlag::new(&vec, true);
assert_eq!(pab.as_ref()[1], 20);
assert_eq!(pab.as_bool(), true);
let flagged = RefWithFlag::new(&vec, true);
assert_eq!(flagged.get_ref()[1], 20);
assert_eq!(flagged.get_flag(), true);
}
}

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