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pub use super::pend_once::PendOnce;
pub use decurse_macro::decurse_sound;
use pfn::PFnOnce;
use pinned_vec::PinnedVec;
use scoped_tls::scoped_thread_local;
use std::{any::Any, cell::RefCell, future::Future, task::Poll};
pub struct Context<F: Future> {
next: RefCell<Option<F>>,
result: RefCell<Option<F::Output>>,
}
impl<F: Future + 'static> Context<F> {
pub fn new() -> Self {
Self {
next: RefCell::new(None),
result: RefCell::new(None),
}
}
pub fn set_next(self_ptr: &Box<dyn Any>, fut: F) {
let this: &Self = self_ptr.downcast_ref().unwrap();
*this.next.borrow_mut() = Some(fut);
}
pub fn get_result(self_ptr: &Box<dyn Any>) -> F::Output {
let this: &Self = self_ptr.downcast_ref().unwrap();
this.result.borrow_mut().take().unwrap()
}
}
scoped_thread_local! (static CONTEXT: Box<dyn Any>);
pub fn set_next<F: Future + 'static>(fut: F) {
CONTEXT.with(|c| Context::set_next(c, fut))
}
pub fn get_result<A, R, F>(_phantom: R) -> F::Output
where
R: PFnOnce<A, PFnOutput = F>,
F: Future + 'static,
{
CONTEXT.with(|c| Context::<F>::get_result(c))
}
pub fn execute<F>(fut: F) -> F::Output
where
F: Future + 'static,
{
let dummy_waker = waker_fn::waker_fn(|| {});
let mut dummy_async_cx: std::task::Context = std::task::Context::from_waker(&dummy_waker);
let ctx: Context<F> = Context::new();
let any_ctx: Box<dyn Any> = Box::new(ctx);
let ctx: &Context<F> = any_ctx.downcast_ref().unwrap();
let output = CONTEXT.set(&any_ctx, || {
let mut heap_stack: PinnedVec<F> = PinnedVec::new();
heap_stack.push(fut);
loop {
let len = heap_stack.len();
let fut = heap_stack.get_mut(len - 1).unwrap();
let polled = fut.poll(&mut dummy_async_cx);
match polled {
Poll::Ready(r) => {
if len == 1 {
break r;
} else {
let mut bm = ctx.result.borrow_mut();
*bm = Some(r);
heap_stack.pop();
}
}
Poll::Pending => {
heap_stack.push(ctx.next.borrow_mut().take().unwrap());
}
}
}
});
output
}
#[macro_export]
macro_rules! for_macro_only_recurse_sound {
($func:path, ($($args:expr),*)) => {
({
$crate::for_macro_only::sound::set_next($func ($($args),*));
$crate::for_macro_only::sound::PendOnce::new().await;
$crate::for_macro_only::sound::get_result($func)
})
};
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn stack_factorial() {
fn factorial(x: u32) -> u32 {
if x == 0 {
1
} else {
x * factorial(x - 1)
}
}
assert_eq!(factorial(6), 720);
}
#[test]
fn stack_fibonacci() {
fn fibonacci(x: u32) -> u32 {
if x == 0 || x == 1 {
1
} else {
fibonacci(x - 1) + fibonacci(x - 2)
}
}
assert_eq!(fibonacci(10), 89);
}
#[test]
fn factorial() {
async fn factorial(x: u32) -> u32 {
if x == 0 {
1
} else {
for_macro_only_recurse_sound!(factorial, (x - 1)) * x
}
}
assert_eq!(execute(factorial(6)), 720);
}
#[test]
fn fibonacci() {
async fn fibonacci(x: u32) -> u32 {
if x == 0 || x == 1 {
1
} else {
for_macro_only_recurse_sound!(fibonacci, (x - 1))
+ for_macro_only_recurse_sound!(fibonacci, (x - 2))
}
}
assert_eq!(execute(fibonacci(10)), 89);
}
#[test]
fn triangular() {
fn triangular(x: u64) -> u64 {
async fn decurse_triangular(x: u64) -> u64 {
if x == 0 {
0
} else {
for_macro_only_recurse_sound!(decurse_triangular, (x - 1)) + x
}
}
execute(decurse_triangular(x))
}
assert_eq!(20000100000, triangular(200000));
}
}