You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
51 lines
1.4 KiB
Rust
51 lines
1.4 KiB
Rust
#![allow(dead_code)]
|
|
|
|
mod ref_with_flag {
|
|
use std::marker::PhantomData;
|
|
use std::mem::align_of;
|
|
|
|
/// A `&T` and a `bool`, wrapped up in a single word.
|
|
/// The type `T` must require at least two-byte alignment.
|
|
///
|
|
/// 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> {
|
|
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> {
|
|
assert!(align_of::<T>() % 2 == 0);
|
|
RefWithFlag {
|
|
ptr_and_bit: ptr as *const T as usize | bit as usize,
|
|
behaves_like: PhantomData
|
|
}
|
|
}
|
|
|
|
pub fn as_ref(&self) -> &'a T {
|
|
let ptr = (self.ptr_and_bit & !1) as *const T;
|
|
unsafe {
|
|
&*ptr
|
|
}
|
|
}
|
|
|
|
pub fn as_bool(&self) -> bool {
|
|
self.ptr_and_bit & 1 != 0
|
|
}
|
|
}
|
|
}
|
|
|
|
mod ref_with_flag_tests {
|
|
#[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);
|
|
}
|
|
}
|