add readable and writable traits for signal-like structs

packages/signals/src/read.rs

@@ -0,0 +1,72 @@
+use std::ops::Deref;
+
+pub trait Readable<T: 'static> {
+    type Ref<R: ?Sized + 'static>: Deref<Target = R>;
+
+    fn map_ref<I, U: ?Sized, F: FnOnce(&I) -> &U>(ref_: Self::Ref<I>, f: F) -> Self::Ref<U>;
+
+    fn try_map_ref<I, U: ?Sized, F: FnOnce(&I) -> Option<&U>>(
+        ref_: Self::Ref<I>,
+        f: F,
+    ) -> Option<Self::Ref<U>>;
+
+    fn read(&self) -> Self::Ref<T>;
+
+    fn peek(&self) -> Self::Ref<T>;
+
+    fn cloned(&self) -> T
+    where
+        T: Clone,
+    {
+        self.read().clone()
+    }
+
+    fn with<O>(&self, f: impl FnOnce(&T) -> O) -> O {
+        f(&*self.read())
+    }
+
+    fn with_peek<O>(&self, f: impl FnOnce(&T) -> O) -> O {
+        f(&*self.peek())
+    }
+
+    /// Index into the inner value and return a reference to the result.
+    #[track_caller]
+    fn index<I>(&self, index: I) -> Self::Ref<T::Output>
+    where
+        T: std::ops::Index<I>,
+    {
+        Self::map_ref(self.read(), |v| v.index(index))
+    }
+}
+
+pub trait ReadableVecExt<T: 'static>: Readable<Vec<T>> {
+    /// Returns the length of the inner vector.
+    #[track_caller]
+    fn len(&self) -> usize {
+        self.with(|v| v.len())
+    }
+
+    /// Returns true if the inner vector is empty.
+    #[track_caller]
+    fn is_empty(&self) -> bool {
+        self.with(|v| v.is_empty())
+    }
+
+    /// Get the first element of the inner vector.
+    #[track_caller]
+    fn first(&self) -> Option<Self::Ref<T>> {
+        Self::try_map_ref(self.read(), |v| v.first())
+    }
+
+    /// Get the last element of the inner vector.
+    #[track_caller]
+    fn last(&self) -> Option<Self::Ref<T>> {
+        Self::try_map_ref(self.read(), |v| v.last())
+    }
+
+    /// Get the element at the given index of the inner vector.
+    #[track_caller]
+    fn get(&self, index: usize) -> Option<Self::Ref<T>> {
+        Self::try_map_ref(self.read(), |v| v.get(index))
+    }
+}