Question

I want to make util classes for System.Io (such as File, Directory etc).

Since inheritance cannot be done for static classes i want to know how would be a proper way to wrap lets say System.Io.File.

Answer 1

I would create three types:

• An interface containing all the methods you want to be able to test etc, e.g.

  public interface IFileSystem
  {
      Stream OpenWrite(string filename);
      TextReader OpenText(string filename);
      // etc
  }
  

• An implementation which delegates to the system implementation:

  public class FrameworkFileSystem : IFileSystem
  {
      public Stream OpenWrite(string filename)
      {
          return File.OpenWrite(filename);
      }
      // etc
  }
  

• A fake implementation for testing:

  public class FakeFileSystem : IFileSystem
  {
      // Probably all kinds of things to allow in-memory files
      // to be created etc
  }
  

You may well not want to put everything from File in there though – as many of the operations can be composed from the “core” ones. Of course, that would mean reimplementing the operations yourself, which may be undesirable…