Implementing C#'s "IDisposable" pattern in Typescript

disposable.ts

interface Disposable {
	dispose(): void;
}
function using<T extends Disposable>(instance: T, fn: (instance: T) => any) {
	try {
		fn(instance);
	} finally {
		instance.dispose();
	}
}

class MyDisposableClass {
	constructor(public text: string) {
	}
	public dispose() {
		delete this.text;
	}
}

// Testing:

let outsideRef: MyDisposableClass;
using(new MyDisposableClass('Test'), instance => {
	outsideRef = instance;
	console.log(instance.text); // 'Inside using: Test'
});
console.log(outsideRef.text); // undefined

let outsideRef2: MyDisposableClass;
try {
	using(new MyDisposableClass('Test2'), instance => {
		outsideRef2 = instance;
		console.log(instance.text); // 'Test2'
		throw new Error(); // What if an error happened here?
	});
} catch (ex) {
	// Ignore error
}
console.log(outsideRef2.text); // Still undefined despite the exception