Microsoft just published a new version of C# : 5.0 beta with CLR version 4.5 (Visual Studio 11 beta). 
In order to get a big picture of the whole evolution of C# language, I summarized all the key features 
into a C# Evolution Matrix for your reference as below diagram shows:

In C# version 5.0, there are two key features: Async Programming and Caller Information.

Two new key words are used for Async feature: async modifier and await operator. Method marked 
with async modifier is called async method. This new feature will help us a lot in async programming. 
For example, in the programming of Winform, the UI thread will be blocked while we use 
HttpWebRequest synchronously request any resource in the Internet. From the perspective of user 
experience, we cannot interact with the form before the request is done.

private void
btnTest_Click(object sender, EventArgs e) 

{ 

var request = WebRequest.Create(txtUrl.Text.Trim()); 

var content=new MemoryStream(); 

using (var response = request.GetResponse()) 

{ 

using (var responseStream = response.GetResponseStream()) 

{ 

responseStream.CopyTo(content); 

} 

} 

txtResult.Text = content.Length.ToString(); 

}

In the above example, after we clicked the Test button, we cannot not make any change to the form
before the txtResult textbox shows the result.

In the past, we can also use BeginGetResponse method to send async request as this sample in MSDN
shows: 
http://msdn.microsoft.com/zh-cn/library/system.net.httpwebrequest.begingetresponse(v=vs.80).aspx. But it 
will takes us a lot effort to realize it.

Now, we can simply use below code to do request asynchronously :

private async void
btnTest_Click(object sender, EventArgs e) 

{ 

var request = WebRequest.Create(txtUrl.Text.Trim()); 

var content = new MemoryStream(); 

Task<WebResponse> responseTask = request.GetResponseAsync(); 

using (var response = await responseTask) 

{

using (var
responseStream = response.GetResponseStream()) 

{ 

Task copyTask = responseStream.CopyToAsync(content); 

//await operator to supends the excution of the method until the task is completed. In the meantime, 
the control is returned the UI thread. 

await copyTask; 

} 

} 

txtResult.Text = content.Length.ToString(); 

}

The await operator is applied to the returned task. The await operator suspends execution of the
method until the task is completed. Meanwhile, control is returned to the caller of the suspended 
method.

Caller Information can help us in tracing, debugging and creating diagnose tools. It will help us
to avoid duplicate codes which are generally invoked in many methods for same purpose, such 
as logging and tracing.

We could get the below information of caller method :

• CallerFilePathAttribute Full path of the source
  file that contains the caller. This is the file path at compile time.
• CallerLineNumberAttribute Line number in the
  source file at which the method is called.
• CallerMemberNameAttribute Method or property
  name of the caller.

Below example are a common practice prior to the new feature of Caller Information:

using System; 

using System.Collections.Generic; 

using System.Linq; 

using System.Text; 

using System.Threading.Tasks;

namespace
ConsoleApplicationTest 

{ 

class Program 

{ 

static void Main(string[] args) 

{ 

InsertLog("Main"); 

MethodB(); 

Console.ReadLine(); 

}

static void MethodA()


{ 

InsertLog("MethodA"); 

MethodB(); 

}

static void MethodB()


{ }

static void
InsertLog(string methodName) 

{ 

Console.WriteLine("{0} called method B at {1}", methodName,
DateTime.Now); 

} 

} 

}

In both Main and MethodA methods, method InsertLog is invoked for logging. Now we can change the
codes to be as per below lines:

using System; 

using System.Collections.Generic; 

using System.Linq; 

using System.Runtime.CompilerServices; 

using System.Text; 

using System.Threading.Tasks;

namespace
ConsoleApplicationTest 

{ 

class Program 

{ 

static void Main(string[] args) 

{ 

//InsertLog("Main"); 

MethodB(); 

Console.ReadLine(); 

}

static void MethodA()


{ 

//InsertLog("MethodA"); 

MethodB(); 

}

static void MethodB( 

[CallerMemberName] string memberName = "", 

[CallerFilePath] string sourceFilePath = "", 

[CallerLineNumber] int sourceLineNumber = 0) 

{ 

InsertLog(memberName); 

}

static void
InsertLog(string methodName) 

{ 

Console.WriteLine("{0} called method B at {1}", methodName,
DateTime.Now); 

} 

} 

}

The new features in C# 5.0 will help us to code more easily and improve the productivity. Have a nice 
experience with the new release of Visual Studio 11!