Using.cs

// ReSharper disable All
namespace ValidCode
{
    using System;
    using System.IO;

    public class Using
    {
        public Using(IObservable<int> observable)
        {
            using var file = File.OpenRead(string.Empty);

            IDisposable temp;
            using (temp = new Disposable())
            {
            }

            using (new Disposable())
            {
            }

            using (var disposable = new Disposable())
            {
            }

            using (var disposable = File.OpenRead(string.Empty))
            {
            }

            using (File.OpenRead(string.Empty))
            {
            }

            using (var disposable = observable.Subscribe(x => Console.WriteLine(x)))
            {
            }

            using (observable.Subscribe(x => Console.WriteLine(x)))
            {
            }
        }
    }
}