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use std::cell::RefCell;
use std::fmt;
use std::rc::Rc;
pub enum Callback<IN> {
Callback(Rc<dyn Fn(IN)>),
CallbackOnce(Rc<CallbackOnce<IN>>),
}
type CallbackOnce<IN> = RefCell<Option<Box<dyn FnOnce(IN)>>>;
impl<IN, F: Fn(IN) + 'static> From<F> for Callback<IN> {
fn from(func: F) -> Self {
Callback::Callback(Rc::new(func))
}
}
impl<IN> Clone for Callback<IN> {
fn clone(&self) -> Self {
match self {
Callback::Callback(cb) => Callback::Callback(cb.clone()),
Callback::CallbackOnce(cb) => Callback::CallbackOnce(cb.clone()),
}
}
}
#[allow(clippy::vtable_address_comparisons)]
impl<IN> PartialEq for Callback<IN> {
fn eq(&self, other: &Callback<IN>) -> bool {
match (&self, &other) {
(Callback::Callback(cb), Callback::Callback(other_cb)) => Rc::ptr_eq(cb, other_cb),
(Callback::CallbackOnce(cb), Callback::CallbackOnce(other_cb)) => {
Rc::ptr_eq(cb, other_cb)
}
_ => false,
}
}
}
impl<IN> fmt::Debug for Callback<IN> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let data = match self {
Callback::Callback(_) => "Callback<_>",
Callback::CallbackOnce(_) => "CallbackOnce<_>",
};
f.write_str(data)
}
}
impl<IN> Callback<IN> {
pub fn emit(&self, value: IN) {
match self {
Callback::Callback(cb) => cb(value),
Callback::CallbackOnce(rc) => {
let cb = rc.replace(None);
let f = cb.expect("callback in CallbackOnce has already been used");
f(value)
}
};
}
pub fn once<F>(func: F) -> Self
where
F: FnOnce(IN) + 'static,
{
Callback::CallbackOnce(Rc::new(RefCell::new(Some(Box::new(func)))))
}
pub fn noop() -> Self {
Self::from(|_| {})
}
}
impl<IN> Default for Callback<IN> {
fn default() -> Self {
Self::noop()
}
}
impl<IN: 'static> Callback<IN> {
pub fn reform<F, T>(&self, func: F) -> Callback<T>
where
F: Fn(T) -> IN + 'static,
{
let this = self.clone();
let func = move |input| {
let output = func(input);
this.emit(output);
};
Callback::from(func)
}
}
#[cfg(test)]
pub(crate) mod test_util {
use super::*;
use std::cell::RefCell;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll, Waker};
struct CallbackHandle<T> {
waker: Option<Waker>,
output: Option<T>,
}
impl<T> Default for CallbackHandle<T> {
fn default() -> Self {
CallbackHandle {
waker: None,
output: None,
}
}
}
pub(crate) struct CallbackFuture<T>(Rc<RefCell<CallbackHandle<T>>>);
impl<T> Clone for CallbackFuture<T> {
fn clone(&self) -> Self {
Self(self.0.clone())
}
}
impl<T> Default for CallbackFuture<T> {
fn default() -> Self {
Self(Rc::default())
}
}
impl<T: 'static> Into<Callback<T>> for CallbackFuture<T> {
fn into(self) -> Callback<T> {
Callback::from(move |r| self.finish(r))
}
}
impl<T> Future for CallbackFuture<T> {
type Output = T;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
if let Some(output) = self.ready() {
Poll::Ready(output)
} else {
self.0.borrow_mut().waker = Some(cx.waker().clone());
Poll::Pending
}
}
}
impl<T> CallbackFuture<T> {
fn ready(&self) -> Option<T> {
self.0.borrow_mut().output.take()
}
fn finish(&self, output: T) {
self.0.borrow_mut().output = Some(output);
if let Some(waker) = self.0.borrow_mut().waker.take() {
waker.wake();
}
}
}
}