Pattern to build actions for ngrx

ngrx_actions.ts

interface Action<T> {
	type: T;
}

interface PayloadAction<T, R> {
	readonly type: T;
	payload: R;
}

interface ActionFactory<T> {
	(): Action<T>;
	type: T;
}

interface PayloadActionFactory<T, R> {
	(payload: R): PayloadAction<T, R>;
	type: T;
}

function newActionFactory<T extends string>(type: T|''): ActionFactory<T>;
function newActionFactory<T extends string, R>(type: T|'', payloadFunc: (payload: R) => R): PayloadActionFactory<T, R>;
function newActionFactory<T extends string, R>(type: T|'', payloadFunc?: (payload: R) => R): ActionFactory<T> | PayloadActionFactory<T, R>  {
	const actionBuilder = payloadFunc ?
		<PayloadActionFactory<T, R>> function(payload: R): PayloadAction<T, R> {
			return {
				payload: payloadFunc(payload),
				type: <T>type
			};
		} :
		<ActionFactory<T>> function(): Action<T> {
			return { type: <T>type };
		}
	;

	actionBuilder.type = <T>type;

	return actionBuilder;
}
  
//usage 
  
const Action1 = newActionFactory('ACTION1');
/* Here we have to use a function mostly for typings but also allow user to define some logic to build the payload */
const Action2 = newActionFactory('ACTION2', (p: number) => p);

/* Here we need to do some boilerplate by repeting the structure or our actions
 * This should be replaced with ts 2.3 with something like :
 * `type Actions = returnType Action1 | returnType Action2`
 */
type Actions = Action<'ACTION1'> | PayloadAction<'ACTION2', number>;