feat: expose observables.createState and provideState

Author: Duke

src/index.ts

@@ -1,4 +1,4 @@
-import { observables, pipe, pushObservable, type Operator, type PushObservable, type Subscribable } from "./rx"
+import { observables, pipe, pushObservable, type Operator, type PushObservable, type Subscribable, type Subscriber } from "./rx"
 
 declare const ExecutorIdBrand: unique symbol
 export type ExecutorId = string & { readonly [ExecutorIdBrand]: never }
@@ -842,6 +842,28 @@ export function providePushObservable<Value>(
     })
 }
 
+/**
+ * Utility to integrate state with submodule ecosystem
+ * @param pValue - value that will be used as initial state
+ * @param controller - api to control the state
+ * @returns 
+ */
+export function provideState<
+  Value,
+  Controller,
+  ControllerFn extends (sub: Subscriber<Value>, get: () => Value) => Controller
+>(
+  pValue: Value | Executor<Value>,
+  controller: ControllerFn | Executor<ControllerFn>
+): Executor<readonly [Subscribable<Value>, Controller]> {
+  return map(
+    { value: normalize(pValue), controller: normalize(controller) },
+    ({ value, controller }) => {
+      return observables.createState<Value, Controller>(value, controller)
+    }
+  )
+}
+
 export type OperatorLike<S, A> = Operator<S, A> | Executor<Operator<S, A>>
 
 /**

src/rx.ts

@@ -627,6 +627,19 @@ export const observables = {
       }
     }
   },
+
+  /** Simplified version of push observable that focusing on providing a shaped api */
+  createState: <T, C>(
+    initialValue: T,
+    fn: (subscriber: Subscriber<T>, get: () => T) => C
+  ): readonly [Subscribable<T>, C] => {
+    const [observable, subscriber] = pushObservable<T>(initialValue);
+    // biome-ignore lint/style/noNonNullAssertion: <explanation>
+    const get = () => observable.lastValue!;
+
+    const controller = fn(subscriber, get);
+    return [observable, controller] as const;
+  },
   /**
    * Combines the latest values from multiple observables into a single observable.
    * @template T The type of the combined value.