In addition, if the caller itself is a long-lived object it can remember the object and implement dispose itself by delegating. Then the user of the long-lived object can manage it.
That doesn't help. Not if the function that wants to return the disposable object in the happy path also wants to destroy the disposable object in the error path.
readonly record struct Result<TResult, TDisposable>(TResult? IfHappy, TDisposable? Disposable): IDisposable where TDisposable : IDisposable
{
public void Dispose() => Disposable?.Dispose();
} using (var result = foo.GetSomethingIfLucky())
{
if (result.IfHappy is {} success)
{
// do something
}
}