From 007754892d25c92292531b17945aa6b9faf2c26f Mon Sep 17 00:00:00 2001
From: Angus MacDonald <amacdonald@google.com>
Date: Fri, 27 Nov 2020 12:37:58 -0600
Subject: [PATCH] Add setf.subtract

---
 src/set/setf.ts | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 src/set/setf.ts

diff --git a/src/set/setf.ts b/src/set/setf.ts
new file mode 100644
index 0000000000..b653da3de4
--- /dev/null
+++ b/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;
+  }
+}