Question

I am a .NET developer and recently started learning ruby with ruby_koans. Some of Ruby’s syntaxes are amazing and one of them is the way it handles “Sandwich” code.

The following is ruby sandwich code.

  def file_sandwich(file_name)
    file = open(file_name)
    yield(file)
  ensure
    file.close if file
  end

  def count_lines2(file_name)
    file_sandwich(file_name) do |file|
      count = 0
      while line = file.gets
        count += 1
      end
      count
    end
  end

  def test_counting_lines2
    assert_equal 4, count_lines2("example_file.txt")
  end

I am fascinated that I can get rid of the cumbersome “file open and close code” each time I access a file but cannot think of any C# equivalent code. Maybe, I can use IoC’s dynamic proxy to do the same thing, but is there any way I can do it purely with C#?

Many thanks in advance.

Answer 1

You certainly don’t need anything IoC-related here. How about:

public T ActOnFile<T>(string filename, Func<Stream, T> func)
{
    using (Stream stream = File.OpenRead(stream))
    {
        return func(stream);
    }
}

public int CountLines(string filename)
{
    return ActOnFile(filename, stream =>
    {
        using (StreamReader reader = new StreamReader(stream))
        {
            int count = 0;
            while (reader.ReadLine() != null)
            {
                count++;
            }
            return count;
        }
    });
}

In this case it doesn’t help very much, as the using statement already does most of what you want… but the general principle holds. Indeed, that’s how LINQ is so flexible. If you haven’t looked at LINQ yet, I strongly recommend that you do.

Here’s the act CountLines method I’d use:

public int CountLines(string filename)
{
    return File.ReadLines(filename).Count();
}

Note that this will still only read a line at a time… but the Count extension method acts on the returned sequence.

In .NET 3.5 it would be:

public int CountLines(string filename)
{
    using (var reader = File.OpenText(filename))
    {
        int count = 0;
        while (reader.ReadLine() != null)
        {
            count++;
        }
        return count;
    }
}

… still pretty simple.