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// build-pass
#![allow(incomplete_features)]
#![feature(generic_const_exprs)]
trait Collate<Op> {
type Pass;
type Fail;
fn collate(self) -> (Self::Pass, Self::Fail);
}
impl<Op> Collate<Op> for () {
type Pass = ();
type Fail = ();
fn collate(self) -> ((), ()) {
((), ())
}
}
trait CollateStep<X, Prev> {
type Pass;
type Fail;
fn collate_step(x: X, prev: Prev) -> (Self::Pass, Self::Fail);
}
impl<X, P, F> CollateStep<X, (P, F)> for () {
type Pass = (X, P);
type Fail = F;
fn collate_step(x: X, (p, f): (P, F)) -> ((X, P), F) {
((x, p), f)
}
}
struct CollateOpImpl<const MASK: u32>;
trait CollateOpStep {
type NextOp;
type Apply;
}
impl<const MASK: u32> CollateOpStep for CollateOpImpl<MASK>
where
CollateOpImpl<{ MASK >> 1 }>: Sized,
{
type NextOp = CollateOpImpl<{ MASK >> 1 }>;
type Apply = ();
}
impl<H, T, Op: CollateOpStep> Collate<Op> for (H, T)
where
T: Collate<Op::NextOp>,
Op::Apply: CollateStep<H, (T::Pass, T::Fail)>,
{
type Pass = <Op::Apply as CollateStep<H, (T::Pass, T::Fail)>>::Pass;
type Fail = <Op::Apply as CollateStep<H, (T::Pass, T::Fail)>>::Fail;
fn collate(self) -> (Self::Pass, Self::Fail) {
<Op::Apply as CollateStep<H, (T::Pass, T::Fail)>>::collate_step(self.0, self.1.collate())
}
}
fn collate<X, const MASK: u32>(x: X) -> (X::Pass, X::Fail)
where
X: Collate<CollateOpImpl<MASK>>,
{
x.collate()
}
fn main() {
dbg!(collate::<_, 5>(("Hello", (42, ('!', ())))));
}
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