add ArraySet

src/vs/base/common/set.ts

+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+export class ArraySet<T> {
+
+	private _elements: T[];
+
+	constructor(elements: T[] = []) {
+		this._elements = elements.slice();
+	}
+
+	set(element: T): void {
+		this.unset(element);
+		this._elements.push(element);
+	}
+
+	unset(element: T): void {
+		const index = this._elements.indexOf(element);
+
+		if (index > -1) {
+			this._elements.splice(index, 1);
+		}
+	}
+
+	get elements(): T[] {
+		return this._elements;
+	}
+}
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