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Make equality works on noop callbacks of same type #3430

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Make equality works on noop callbacks of same type #3430

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Make equality works on noop callbacks of same type
cecton Sep 30, 2023
28fc872
CLEANUP
cecton Sep 30, 2023
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35 changes: 31 additions & 4 deletions packages/yew/src/callback.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,10 @@
//! - [Counter](https://github.com/yewstack/yew/tree/master/examples/counter)
//! - [Timer](https://github.com/yewstack/yew/tree/master/examples/timer)

use std::fmt;
use std::cell::RefCell;
use std::collections::HashMap;
use std::rc::Rc;
use std::{any, fmt};

use crate::html::ImplicitClone;

Expand Down Expand Up @@ -33,6 +35,8 @@ macro_rules! generate_callback_impls {
}
}

impl<IN, OUT> Eq for $callback<IN, OUT> {}

impl<IN, OUT> fmt::Debug for $callback<IN, OUT> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "$callback<_>")
Expand All @@ -46,15 +50,31 @@ macro_rules! generate_callback_impls {
}
}

impl<IN> $callback<IN> {
impl<IN: 'static> $callback<IN> {
/// Creates a "no-op" callback which can be used when it is not suitable to use an
/// `Option<$callback>`.
pub fn noop() -> Self {
Self::from(|_: $in_ty| ())
thread_local! {
static NOOP: RefCell<HashMap<any::TypeId, Box<dyn any::Any>>> = RefCell::new(Default::default());
}

Self {
cb: NOOP.with(|noop| {
noop.borrow_mut()
.entry(any::TypeId::of::<$in_ty>())
.or_insert_with(|| {
let func: Rc<dyn Fn($in_ty)> = Rc::new(|_: $in_ty| ());
Box::new(func) as Box<dyn any::Any>
})
.downcast_ref::<Rc<dyn Fn($in_ty)>>()
.unwrap()
.clone()
}),
}
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Is there really no other solution other than unwrapping and modifying a HashMap in a RefCell? that seems to me like too much work for a Default::default() value

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Since the function is doing nothing I think it might be possible to do something with unsafe that would be much faster? But I'm really no expert so I won't write that lol

One alternative would be to wrap the Rc into an Option like this:

pub struct Callback<IN, OUT = ()> {
    /// A callback which can be called multiple times
    pub(crate) cb: Option<Rc<dyn Fn(IN) -> OUT>>,
}

(Or using an enum instead of struct)

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But I'm afraid using Option will have a cost at runtime because every call will need to check the option.

}
}

impl<IN> Default for $callback<IN> {
impl<IN: 'static> Default for $callback<IN> {
fn default() -> Self {
Self::noop()
}
Expand Down Expand Up @@ -300,4 +320,11 @@ mod test {
reformed.emit(&mut value).expect("is some");
assert_eq!(value, 45);
}

#[test]
fn test_noop_eq() {
assert_eq!(Callback::<u32>::noop(), Callback::<u32>::noop());
assert_eq!(CallbackRef::<u32>::noop(), CallbackRef::<u32>::noop());
assert_eq!(CallbackRefMut::<u32>::noop(), CallbackRefMut::<u32>::noop());
}
}
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