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// check-pass
// FamilyType (GAT workaround)
pub trait FamilyLt<'a> {
type Out;
}
struct RefMutFamily<T>(std::marker::PhantomData<T>, ());
impl<'a, T: 'a> FamilyLt<'a> for RefMutFamily<T> {
type Out = &'a mut T;
}
pub trait Execute {
type E: Inject;
fn execute(self, value: <<Self::E as Inject>::I as FamilyLt>::Out);
}
pub trait Inject
where
Self: Sized,
{
type I: for<'a> FamilyLt<'a>;
fn inject(_: &()) -> <Self::I as FamilyLt>::Out;
}
impl<T: 'static> Inject for RefMutFamily<T> {
type I = Self;
fn inject(_: &()) -> <Self::I as FamilyLt>::Out {
unimplemented!()
}
}
// This struct is only used to give a hint to the compiler about the type `Q`
struct Annotate<Q>(std::marker::PhantomData<Q>);
impl<Q> Annotate<Q> {
fn new() -> Self {
Self(std::marker::PhantomData)
}
}
// This function annotate a closure so it can have Higher-Rank Lifetime Bounds
//
// See 'annotate' workaround: https://github.com/rust-lang/rust/issues/58052
fn annotate<F, Q>(_q: Annotate<Q>, func: F) -> impl Execute + 'static
where
F: for<'r> FnOnce(<<Q as Inject>::I as FamilyLt<'r>>::Out) + 'static,
Q: Inject + 'static,
{
let wrapper: Wrapper<Q, F> = Wrapper(std::marker::PhantomData, func);
wrapper
}
struct Wrapper<Q, F>(std::marker::PhantomData<Q>, F);
impl<Q, F> Execute for Wrapper<Q, F>
where
Q: Inject,
F: for<'r> FnOnce(<<Q as Inject>::I as FamilyLt<'r>>::Out),
{
type E = Q;
fn execute(self, value: <<Self::E as Inject>::I as FamilyLt>::Out) {
(self.1)(value)
}
}
struct Task {
_processor: Box<dyn FnOnce()>,
}
// This function consume the closure
fn task<P>(processor: P) -> Task
where P: Execute + 'static {
Task {
_processor: Box::new(move || {
let q = P::E::inject(&());
processor.execute(q);
})
}
}
fn main() {
task(annotate(
Annotate::<RefMutFamily<usize>>::new(),
|value: &mut usize| {
*value = 2;
}
));
}
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