5.0

C# 5.0, released with .NET Framework 4.5 in August 2012, focused primarily on asynchronous programming and improving the performance of applications that perform I/O-bound or CPU-bound operations. Here are the key features introduced in C# 5.0, along with examples and comparisons to earlier versions of C#:

1. Async/Await

The async and await keywords were introduced to simplify writing asynchronous code, making it more readable and maintainable by avoiding callback "pyramids of doom" and making asynchronous code appear more like its synchronous counterpart.

C# 5.0

public async Task<string> GetWebPageAsync(string url)
{
    using (HttpClient client = new HttpClient())
    {
        string content = await client.GetStringAsync(url);
        return content;
    }
}

This method asynchronously downloads the content of a web page, and the await keyword is used to await the completion of the asynchronous operation without blocking the calling thread.

C# < 5.0 Before C# 5.0, asynchronous programming involved more complex patterns, such as the use of callbacks, the IAsyncResult pattern, or the Event-based Asynchronous Pattern (EAP).

public void GetWebPage(string url, Action<string> callback)
{
    WebClient client = new WebClient();
    client.DownloadStringCompleted += (sender, e) =>
    {
        if (e.Error == null)
        {
            callback(e.Result);
        }
    };
    client.DownloadStringAsync(new Uri(url));
}

This approach is more cumbersome and harder to read, especially when dealing with multiple asynchronous operations.

2. Caller Information Attributes

C# 5.0 introduced Caller Information attributes (CallerFilePath, CallerLineNumber, CallerMemberName) that allow you to obtain information about the caller of a method, which is particularly useful for diagnostic purposes.

C# 5.0

public void LogMessage(string message,
    [CallerMemberName] string memberName = "",
    [CallerFilePath] string filePath = "",
    [CallerLineNumber] int lineNumber = 0)
{
    Console.WriteLine($"{filePath}({lineNumber}) {memberName}: {message}");
}

This method logs a message along with information about the caller, without the caller needing to supply this information explicitly.

C# < 5.0 In earlier versions, obtaining caller information required manual input, such as passing the file name, line number, and member name as parameters, making logging and diagnostics more tedious and error-prone.

public void LogMessage(string message, string memberName, string filePath, int lineNumber)
{
    Console.WriteLine($"{filePath}({lineNumber}) {memberName}: {message}");
}
// Usage (manual and prone to errors)
LogMessage("An error occurred.", nameof(MyMethod), "MyFile.cs", 42);