feat(spread): Add a spread helper.

source/operators/index.ts

@@ -25,6 +25,7 @@ export * from "./refCountDelay";
 export * from "./refCountForever";
 export * from "./refCountOn";
 export * from "./reschedule";
+export * from "./spread";
 export * from "./startWithDeferred";
 export * from "./startWithTimeout";
 export * from "./subsequent";

source/operators/spread-spec.ts

@@ -0,0 +1,27 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/rxjs-etc
+ */
+/*tslint:disable:no-unused-expression*/
+
+import { filter, map } from "rxjs/operators";
+import { marbles } from "rxjs-marbles";
+import { spread } from "./spread";
+
+describe("spread", () => {
+
+    it("should pipe the specified operators", marbles((m) => {
+
+        const source =   m.cold("-a-b-c-|");
+        const subs =            "^------!";
+        const expected = m.cold("-A---C-|)");
+
+        const operators = [
+            filter(value => value !== "b"),
+            map((value: string) => value.toUpperCase())
+        ];
+        const destination = source.pipe(spread(...operators));
+        m.expect(destination).toBeObservable(expected);
+        m.expect(source).toHaveSubscriptions(subs);
+    }));
+});

source/operators/spread.ts

@@ -0,0 +1,10 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/rxjs-etc
+ */
+
+import { OperatorFunction } from "rxjs";
+
+export function spread<T, R>(...operations: OperatorFunction<any, any>[]): OperatorFunction<T, R> {
+    return source => operations.reduce((acc, operator) => acc.pipe(operator), source);
+}