Add setf.subtract

src/set/setf.ts

@@ -0,0 +1,20 @@
+export class setf {
+  /**
+   * Creates and returns copy of the minuend with values from the subtrahend
+   * removed.
+   *
+   * ```
+   * // Returns new Set(['b']);
+   * setf.subtract(new Set(['a', 'b', 'c']), new Set(['a', 'c']));
+   * ```
+   */
+  static subtract<T>(minuend: Set<T>, subtrahend: Set<T>): Set<T> {
+    const result = new Set<T>();
+    minuend.forEach((value) => {
+      if (!subtrahend.has(value)) {
+        result.add(value);
+      }
+    });
+    return result;
+  }
+}