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