Defer in C#

In C#, we use the using statement or try-finally blocks to ensure that resources are properly disposed of, which is similar to the concept of defer in other languages. Here’s how we can achieve similar functionality:

using System;
using System.IO;

class Program
{
    static void Main()
    {
        // We use a using statement to ensure the file is closed
        // when we're done, similar to defer
        using (var f = CreateFile("/tmp/defer.txt"))
        {
            WriteFile(f);
        } // The file is automatically closed here
    }

    static StreamWriter CreateFile(string path)
    {
        Console.WriteLine("creating");
        try
        {
            return new StreamWriter(path);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
            Environment.Exit(1);
            return null; // This line is never reached
        }
    }

    static void WriteFile(StreamWriter f)
    {
        Console.WriteLine("writing");
        f.WriteLine("data");
    }
}

In this C# version:

1. We use a using statement to ensure that the file is properly closed when we’re done with it. This is similar to the defer functionality in other languages.

2. The CreateFile method returns a StreamWriter object, which is used for writing to the file.

3. The WriteFile method writes to the file using the StreamWriter.

4. Error handling is done using try-catch blocks. In C#, we don’t typically use panic for error handling.

5. The using statement automatically calls the Dispose method on the StreamWriter when the block is exited, which closes the file. This happens even if an exception is thrown within the block.

Running the program will produce output similar to this:

creating
writing

The file is automatically closed when the using block is exited, so we don’t see an explicit “closing” message.

It’s worth noting that in C#, resource management is typically handled through the IDisposable interface and the using statement, which provides a more structured approach to resource cleanup compared to explicit defer statements.