rename memo to selector

packages/signals/src/selector.rs

@@ -0,0 +1,45 @@
+use dioxus_core::prelude::*;
+
+use crate::{get_effect_stack, signal::SignalData, CopyValue, Effect, ReadOnlySignal, Signal};
+
+pub fn use_selector<R: PartialEq>(
+    cx: &ScopeState,
+    f: impl FnMut() -> R + 'static,
+) -> ReadOnlySignal<R> {
+    *cx.use_hook(|| selector(f))
+}
+
+pub fn selector<R: PartialEq>(mut f: impl FnMut() -> R + 'static) -> ReadOnlySignal<R> {
+    let state = Signal::<R> {
+        inner: CopyValue::invalid(),
+    };
+    let effect = Effect {
+        callback: CopyValue::invalid(),
+    };
+
+    {
+        get_effect_stack().effects.write().push(effect);
+    }
+    state.inner.value.set(SignalData {
+        subscribers: Default::default(),
+        effect_subscribers: Default::default(),
+        update_any: schedule_update_any().expect("in a virtual dom"),
+        value: f(),
+    });
+    {
+        get_effect_stack().effects.write().pop();
+    }
+
+    effect.callback.value.set(Box::new(move || {
+        let value = f();
+        let changed = {
+            let old = state.inner.read();
+            value != old.value
+        };
+        if changed {
+            state.set(value)
+        }
+    }));
+
+    ReadOnlySignal::new(state)
+}