Added reducer generator

Author: piotrwitek

README.md

@@ -1106,11 +1106,10 @@ export default combineReducers<TodosState, TodosAction>({
         return [...state, action.payload];
 
       case TOGGLE:
-        return state.map(
-          item =>
-            item.id === action.payload
-              ? { ...item, completed: !item.completed }
-              : item
+        return state.map(item =>
+          item.id === action.payload
+            ? { ...item, completed: !item.completed }
+            : item
         );
 
       default:

playground/package-lock.json

@@ -56,7 +56,7 @@
     "ts-jest": "22.4.6",
     "tslint": "5.12.1",
     "tslint-react": "3.6.0",
-    "typescript": "3.1.6",
+    "typescript": "3.0.3",
     "webpack": "3.11.0",
     "webpack-blocks": "1.0.0"
   }

playground/package.json

@@ -19,11 +19,10 @@ export default combineReducers<TodosState, TodosAction>({
         return [...state, action.payload];
 
       case TOGGLE:
-        return state.map(
-          item =>
-            item.id === action.payload
-              ? { ...item, completed: !item.completed }
-              : item
+        return state.map(item =>
+          item.id === action.payload
+            ? { ...item, completed: !item.completed }
+            : item
         );
 
       default:

playground/src/features/todos/reducer.ts

@@ -0,0 +1,36 @@
+import { ActionType, getType } from 'typesafe-actions';
+
+import { Todo } from '../features/todos/models';
+import * as actions from '../features/todos/actions';
+
+export type TodosAction = ActionType<typeof actions>;
+
+function createReducer<S, A extends { type: string }>(
+  initialState: S,
+  handlers: {
+    [P in A['type']]?: A extends { type: P }
+      ? (state: S, action: A) => S
+      : never
+  }
+) {
+  return (state: S = initialState, action: A): S => {
+    if (handlers.hasOwnProperty(action.type)) {
+      return (handlers as any)[action.type](state, action);
+    } else {
+      return state;
+    }
+  };
+}
+
+export const todos = createReducer<Todo[], TodosAction>([], {
+  ['todos/ADD' as 'todos/ADD']: (state, action) => {
+    return [...state, action.payload];
+  },
+  ['todos/TOGGLE']: (state, action) => {
+    return state.map(item =>
+      item.id === action.payload
+        ? { ...item, completed: !item.completed }
+        : item
+    );
+  },
+});