fix: build

packages/collection-utils/src/difference.ts

@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2022 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Returns the difference between two arrays.
+ */
+export function differenceBy<T>(a: T[], b: T[], transform: (item: T) => unknown) {
+  const disallowed = new Set(b.map(transform));
+
+  return a.filter(item => !disallowed.has(transform(item)));
+}