fix: Idempotent start

README.md

@@ -135,6 +135,12 @@ You add the ViewModel as a property wrapper to your view:
 @ViewModel var model: AnyReactor = MyViewModel().eraseToAnyReactor()
 ```
 
+`AnyReactor` does not start the wrapped reactor automatically. Start it explicitly:
+
+```swift
+.task { model.start() }
+```
+
 To access the current `State` you use:
 
 ```swift
@@ -200,4 +206,3 @@ You can easily mock state for Xcode Previews by using `Stub` reactor implementat
 
 # License
 GoodReactor repository is released under the MIT license. See [LICENSE](LICENSE.md) for details.
-

Sources/GoodReactor/Core/Erased/AnyReactor.swift

@@ -25,7 +25,8 @@ import SwiftUI
 ///
 /// Behavior:
 /// - State is accessed dynamically and mutated by reducing events on a concrete underlying reactor.
-/// - Lifecycle: external subscriptions start automatically when `AnyReactor` is initialized (by `start()`-ing the base reactor).
+/// - Lifecycle: `AnyReactor` does not automatically start the wrapped reactor.
+///   Call `start()` explicitly to initialize external subscriptions.
 /// - Events from `send(action:)`, `send(action:) async`, and `send(destination:)` are forwarded to the base reactor.
 ///
 /// Example:
@@ -58,9 +59,11 @@ import SwiftUI
 
     // MARK: - Initialization
 
+    /// Creates a type-erased wrapper around `base`.
+    ///
+    /// - note: This initializer does not call `start()` on `base`.
     public init<R: Reactor>(_ base: R) where R.Action == Action, R.Destination == Destination, R.State == State {
         self._box = AnyReactorBox(base)
-        base.start()
     }
 
 }
@@ -151,4 +154,3 @@ public extension Reactor {
     }
 
 }
-

Sources/GoodReactor/Core/Reactor.swift

@@ -155,6 +155,9 @@ import SwiftUI
     /// of the reactor.
     ///
     /// You can use multiple subscriptions to multiple external events.
+    ///
+    /// - important: Keep this function free of side effects, except calls to
+    /// ``subscribe(to:map:)``. This function may be invoked multiple times.
     func transform()
 
     #if canImport(Combine)
@@ -329,6 +332,11 @@ public extension Reactor {
     /// uses Combine, subscribes the event stream and publishes the
     /// initial state.
     func start() {
+        let hasSubscriptions = MapTables.subscriptions.value(forKey: self)?.isEmpty == false
+        guard !hasSubscriptions else {
+            return
+        }
+
         self.transform()
 
         #if canImport(Combine)