Did it with .NET - Twelve Days of Refactor! X-mas, Day Two: Make Explicit

Friday, December 21, 2007

Twelve Days of Refactor! X-mas, Day Two: Make Explicit

Fireplace

Season's greetings! Welcome back for another dose of Yuletide cheer! Yesterday, I sang to you about one way in which Refactor! Pro can be used to leverage the new features of C# 3.0 and Visual Basic 9 right now. Today, I'm back with another verse to warm your hearts this holiday season.

So, strike up the band! Rouse the drunken carolers! It's time to go a wassailing once more.

"On the second day of X-mas my true love (DevExpress) gave to me..."

Make Explicit

Like its sister refactoring, Make Explicit enables developers to manipulate implicitly-typed local variables. However, it performs the opposite operation as Make Implicit. It converts implicitly-typed local variables to explicit ones. In other words, Make Explicit will transform the following code:

	var number = 42ul;

Like so:

	ulong number = 42ul;

Make Explicit must do a great deal of work to determine the type of the expression that an implicitly-typed local variable is assigned to. Consider the following code (which I found lurking in some corner of the 'net):

using System;

using System.Linq;

using System.ServiceProcess;

namespace TwelveDaysOfXmas

{

  class MakeExplicit

  {

    static void DisplayServices()

    {

      var services = from service in ServiceController.GetServices()

                     where service.Status == ServiceControllerStatus.Running

                     orderby service.ServiceName ascending

                     select service;

      foreach (ServiceController aService in services)

      {

        Console.WriteLine(aService.ServiceName);

      }

      Console.ReadLine();

    }

  }

}

In order to determine the type of services, Make Explicit must have a full understanding of LINQ. First, it must transform the query expression into the appropriate extension methods and lambda expressions like so:

var services = ServiceController.GetServices()

                 .Where(service => service.Status == ServiceControllerStatus.Running)

                 .OrderBy(service => service.ServiceName)

Next, Make Explicit must be able to resolve the extension methods and infer the types of the lambda expressions. Once this is done, the type of the expression can finally be determined. That's an awful lot of work, but it's required to ensure that the type is inferred accurately. Fortunately, Make Explicit executes all of this with blazing speed and infers the correct type:

IOrderedEnumerable<ServiceController> services = from service in ServiceController.GetServices()

                                                 where service.Status == ServiceControllerStatus.Running

                                                 orderby service.ServiceName ascending

                                                 select service;

View Screencast of Make Explicit in Action! (#1)

If you have any doubt that Make Explicit is really doing this much work behind the scenes, try commenting out the orderby clause. Make Explicit will infer the correct type even after the query expression has changed:

IEnumerable<ServiceController> services = from service in ServiceController.GetServices()

                                          where service.Status == ServiceControllerStatus.Running

                                          //orderby service.ServiceName ascending

                                          select service;

View Screencast of Make Explicit in Action! (#2)

Finally, I should mention that Make Explicit works just as handily with Visual Basic.

Dim services = From service In ServiceController.GetServices() _

               Where service.Status = ServiceControllerStatus.Running _

               Order By service.ServiceName Ascending

In the above code, Make Explicit properly infers the type of services as IOrderedEnumerable<ServiceController>. Awesome.

One last closing thought: some of you might be thinking right now, "Why would I want to do this? Aren't implicitly-typed local variables better?" There are a few scenarios in which Make Explicit is useful:

Specifying the type name sometimes makes code easier to read.
It simplifies porting code backwards (e.g. to compile in an earlier version of Visual Studio).
It can be helpful for learning and understanding code.

For these reasons, Make Explicit takes its rightful place among the refactorings that support Visual Studio 2008.

"And a partridge in a pear tree..."

And so concludes today's verse. It's time to settle back with a warm mug of spiked eggnog and kick up your feet. Join me tomorrow as we take a peek at another way in which Refactor! Pro brings the X-mas love.

posted on Friday, December 21, 2007 1:44:12 PM (Eastern Standard Time, UTC-05:00)