Keep last non-nil value around for ForEachStore (#668)

Author: stephencelis

Sources/ComposableArchitecture/SwiftUI/ForEachStore.swift

@@ -101,10 +101,13 @@ where Data: Collection, ID: Hashable, Content: View {
           //     views for elements no longer in the collection.
           //
           // Feedback filed: https://gist.github.com/stephencelis/cdf85ae8dab437adc998fb0204ed9a6b
-          let element = store.state.value[id: id]!
+          var element = store.state.value[id: id]!
           return content(
             store.scope(
-              state: { $0[id: id] ?? element },
+              state: {
+                element = $0[id: id] ?? element
+                return element
+              },
               action: { (id, $0) }
             )
           )

Sources/ComposableArchitecture/SwiftUI/IfLetStore.swift

@@ -51,11 +51,15 @@ public struct IfLetStore<State, Action, Content>: View where Content: View {
   ) where Content == _ConditionalContent<IfContent, ElseContent> {
     self.store = store
     self.content = { viewStore in
-      if viewStore.state != nil {
-        let unwrapper = Optional<State>.lastWrappedValue
-        // Force unwrap is safe here because first value from scope is non-nil and scoped store
-        // is dismanteled after last nil value.
-        return ViewBuilder.buildEither(first: ifContent(store.scope(state: { unwrapper($0)! })))
+      if var state = viewStore.state {
+        return ViewBuilder.buildEither(
+          first: ifContent(
+            store.scope {
+              state = $0 ?? state
+              return state
+            }
+          )
+        )
       } else {
         return ViewBuilder.buildEither(second: elseContent())
       }
@@ -75,11 +79,15 @@ public struct IfLetStore<State, Action, Content>: View where Content: View {
   ) where Content == IfContent? {
     self.store = store
     self.content = { viewStore in
-      viewStore.state.map { _ in
-        let unwrapper = Optional<State>.lastWrappedValue
-        // Force unwrap is safe here because first value from scope is non-nil and scoped store
-        // is dismanteled after last nil value.
-        return ifContent(store.scope(state: { unwrapper($0)! }))
+      if var state = viewStore.state {
+        return ifContent(
+          store.scope {
+            state = $0 ?? state
+            return state
+          }
+        )
+      } else {
+        return nil
       }
     }
   }
@@ -92,13 +100,3 @@ public struct IfLetStore<State, Action, Content>: View where Content: View {
     )
   }
 }
-
-extension Optional {
-  static var lastWrappedValue: (Self) -> Self {
-    var lastWrapped: Wrapped?
-    return {
-      lastWrapped = $0 ?? lastWrapped
-      return lastWrapped
-    }
-  }
-}