Restore set compare hook (#2287)

* restore set compare hook

* fix use_set_compare doc example

* add a hook to compare a value with a set

* implement partialeq for SetCompare

* export the new hook

* fix the use_set_compare hook

packages/signals/src/set_compare.rs

@@ -0,0 +1,99 @@
+use crate::{write::Writable, ReactiveContext};
+use std::hash::Hash;
+
+use crate::read::Readable;
+use dioxus_core::prelude::*;
+use futures_util::StreamExt;
+use generational_box::{Storage, UnsyncStorage};
+
+use crate::{CopyValue, ReadOnlySignal, Signal, SignalData};
+use rustc_hash::FxHashMap;
+
+/// An object that can efficiently compare a value to a set of values.
+#[derive(Debug)]
+pub struct SetCompare<R: 'static, S: Storage<SignalData<bool>> = UnsyncStorage> {
+    subscribers: CopyValue<FxHashMap<R, Signal<bool, S>>>,
+}
+
+impl<R: Eq + Hash> SetCompare<R> {
+    /// Creates a new [`SetCompare`] which efficiently tracks when a value changes to check if it is equal to a set of values.
+    ///
+    /// Generally, you shouldn't need to use this hook. Instead you can use [`crate::use_memo`]. If you have many values that you need to compare to a single value, this hook will change updates from O(n) to O(1) where n is the number of values you are comparing to.
+    #[track_caller]
+    pub fn new(f: impl FnMut() -> R + 'static) -> SetCompare<R> {
+        Self::new_maybe_sync(f)
+    }
+}
+
+impl<R: Eq + Hash, S: Storage<SignalData<bool>>> SetCompare<R, S> {
+    /// Creates a new [`SetCompare`] that may be `Sync + Send` which efficiently tracks when a value changes to check if it is equal to a set of values.
+    ///
+    /// Generally, you shouldn't need to use this hook. Instead you can use [`crate::use_memo`]. If you have many values that you need to compare to a single value, this hook will change updates from O(n) to O(1) where n is the number of values you are comparing to.
+    #[track_caller]
+    pub fn new_maybe_sync(mut f: impl FnMut() -> R + 'static) -> SetCompare<R> {
+        let subscribers: CopyValue<FxHashMap<R, Signal<bool>>> =
+            CopyValue::new(FxHashMap::default());
+        let mut previous = CopyValue::new(None);
+
+        let mut recompute = move || {
+            let subscribers = subscribers.read();
+            let mut previous = previous.write();
+
+            if let Some(previous) = previous.take() {
+                if let Some(mut value) = subscribers.get(&previous).cloned() {
+                    *value.write() = false;
+                }
+            }
+
+            let current = f();
+
+            if let Some(mut value) = subscribers.get(&current).cloned() {
+                *value.write() = true;
+            }
+
+            *previous = Some(current);
+        };
+        let (rc, mut changed) = ReactiveContext::new();
+        spawn(async move {
+            loop {
+                // Recompute the value
+                rc.run_in(&mut recompute);
+
+                // Wait for context to change
+                let _ = changed.next().await;
+            }
+        });
+
+        SetCompare { subscribers }
+    }
+
+    /// Returns a signal which is true when the value is equal to the value passed to this function.
+    pub fn equal(&mut self, value: R) -> ReadOnlySignal<bool, S> {
+        let subscribers = self.subscribers.write();
+
+        match subscribers.get(&value) {
+            Some(&signal) => signal.into(),
+            None => {
+                drop(subscribers);
+                let mut subscribers = self.subscribers.write();
+                let signal = Signal::new_maybe_sync(false);
+                subscribers.insert(value, signal);
+                signal.into()
+            }
+        }
+    }
+}
+
+impl<R: 'static, S: Storage<SignalData<bool>>> PartialEq for SetCompare<R, S> {
+    fn eq(&self, other: &Self) -> bool {
+        self.subscribers == other.subscribers
+    }
+}
+
+impl<R, S: Storage<SignalData<bool>>> Clone for SetCompare<R, S> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<R, S: Storage<SignalData<bool>>> Copy for SetCompare<R, S> {}