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#![cfg_attr(not(test), no_std)]
use core::{fmt, marker::PhantomData};
#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
pub struct Id<'id> {
phantom: PhantomData<&'id mut &'id fn(&'id ()) -> &'id ()>,
}
impl<'id> Id<'id> {
pub unsafe fn new() -> Self {
Id {
phantom: PhantomData,
}
}
}
impl<'id> fmt::Debug for Id<'id> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("#[invariant] 'id").finish()
}
}
impl<'id> From<Guard<'id>> for Id<'id> {
fn from(_guard: Guard<'id>) -> Self {
Id {
phantom: PhantomData,
}
}
}
#[derive(Eq, PartialEq)]
pub struct Guard<'id> {
#[allow(unused)]
id: Id<'id>,
}
impl<'id> Guard<'id> {
pub unsafe fn new(id: Id<'id>) -> Guard<'id> {
Guard { id }
}
}
impl<'id> fmt::Debug for Guard<'id> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("#[unique] 'id").finish()
}
}
#[macro_export]
macro_rules! make_guard {
($name:ident) => {
let tag = unsafe { $crate::Id::new() };
let _guard;
let $name = unsafe { $crate::Guard::new(tag) };
{
if false {
#[allow(non_camel_case_types)]
struct make_guard<'id>(&'id $crate::Id<'id>);
impl<'id> ::core::ops::Drop for make_guard<'id> {
fn drop(&mut self) {}
}
_guard = make_guard(&tag);
}
}
};
}
#[test]
#[allow(clippy::eq_op)]
fn dont_error_in_general() {
make_guard!(a);
make_guard!(b);
dbg!(a == a);
dbg!(b == b);
}