add readable and writable traits for signal-like structs

packages/signals/src/write.rs

@@ -0,0 +1,47 @@
+use std::ops::DerefMut;
+
+use crate::read::Readable;
+
+pub trait Writable<T: 'static>: Readable<T> {
+    type Mut<R: ?Sized + 'static>: DerefMut<Target = R>;
+
+    fn map_mut<I, U: ?Sized + 'static, F: FnOnce(&mut I) -> &mut U>(
+        ref_: Self::Mut<I>,
+        f: F,
+    ) -> Self::Mut<U>;
+
+    fn try_map_mut<I, U: ?Sized + 'static, F: FnOnce(&mut I) -> Option<&mut U>>(
+        ref_: Self::Mut<I>,
+        f: F,
+    ) -> Option<Self::Mut<U>>;
+
+    fn write(&self) -> Self::Mut<T>;
+
+    #[track_caller]
+    fn with_mut<O>(&self, f: impl FnOnce(&mut T) -> O) -> O {
+        f(&mut *self.write())
+    }
+
+    /// Set the value of the signal. This will trigger an update on all subscribers.
+    #[track_caller]
+    fn set(&mut self, value: T) {
+        *self.write() = value;
+    }
+
+    /// Invert the boolean value of the signal. This will trigger an update on all subscribers.
+    fn toggle(&mut self)
+    where
+        T: std::ops::Not<Output = T> + Clone,
+    {
+        self.set(!self.cloned());
+    }
+
+    /// Index into the inner value and return a reference to the result.
+    #[track_caller]
+    fn index_mut<I>(&self, index: I) -> Self::Mut<T::Output>
+    where
+        T: std::ops::IndexMut<I>,
+    {
+        Self::map_mut(self.write(), |v| v.index_mut(index))
+    }
+}