Deterministic cleanup with using

The idea

Some objects own resources that need timely cleanup, such as file handles. IDisposable exposes Dispose, and a using statement arranges disposal when control leaves its scope, including ordinary exception paths. This is separate from garbage collection: unreachable managed memory and an external resource’s usable lifetime are different concerns.

A using declaration disposes its resource at the end of the containing scope, not immediately after its last apparent use. A nested using block can make an earlier lifetime boundary explicit. Do not return a resource that has already been disposed by a local using. Also distinguish cleanup from rollback: disposing a stream does not undo data it already wrote, and a resource operation can still throw.

using System;
using (var resource = new Marker()) {
  Console.WriteLine("work");
}
Console.WriteLine("after");
sealed class Marker : IDisposable {
  public void Dispose() => Console.WriteLine("dispose");
}

work
dispose
after

Leaving the using block calls Dispose before the subsequent statement.