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Welcome Microsoft Delegate! Lambda expressions right this way… July 3, 2010

Posted by codinglifestyle in C#, CodeProject, linq, Uncategorized.
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Delegates are deceptively great.  Without them something as simple as the OnClick event of a button would cease to work.  In a nutshell, they offer a simple way to pass a function as a parameter which in turn can be invoked anywhere, anytime.  Pointers for functions, very useful!

In .NET v2.0 the anonymous delegate was quietly introduced, well at least it slipped my notice.  I read about them at the same time I read about Lambda functions.  I saw them laid bare without the syntactic sugar in all they’re simple glory.  As I was stuck on a .NET v2.0 project I found sugar-free anonymous delegates useful to, say, recursively find all controls of a given Type and execute a function on the matching controls.

More recently, I was working on a robust Windows service responsible for various IO operations.  It was vitally important each file operation (heretofore fileop) had its own comprehensive try/catch block.  As the number of fileops increased the code looked like one huge catch block.

It was clear it would be nice to have just one try/catch block in a static utility class which could catch every IO exception conceivable.  Then I could replace each try/catch block with one-line:

bool isBackedUp = FileUtil.FileOp(_logger, () => File.Copy(latestFilename, backupFilename, true));

Notice the file copy on the other side of the lambda function syntax, () =>, is what is executed in the try block below:

public delegate void FileOperation();

internal static bool FileOp(ILogger logger, FileOperation fileOp)

{

bool success = false;

try

{

fileOp.DynamicInvoke();

success = true;

}

catch (ArgumentException argEx)

{

logger.Error(argEx, “Bad arguement(s) passed”);

}

catch (DirectoryNotFoundException dirEx)

{

logger.Error(dirEx, “The specified path is invalid”);

}

catch (FileNotFoundException fileEx)

{

logger.Error(fileEx, “The specified file was not found”);

}

catch (PathTooLongException pathEx)

{

logger.Error(pathEx, “The specified path, file name, or both exceed the system-defined maximum length”);

}

catch (IOException ioEx)

{

logger.Error(ioEx, “An I/O error has occurred”);

}

catch (NotSupportedException supportEx)

{

logger.Error(supportEx, “The requested operation was not supported”);

}

catch (SecurityException secEx)

{

logger.Error(secEx, “The caller does not have the required permission.”);

}

catch (UnauthorizedAccessException accessEx)

{

logger.Error(accessEx, “The caller does not have the required permission”);

}

catch (Exception ex)

{

logger.Error(ex, “General fileop exception”);

}

return success;

}

Not only was this an elegant way to catch a comprehensive set of exceptions, but the resulting code was much more readable.

Of course we could pass bigger hunks of code and this is fine in moderation.  But the flip-side can mean less readable code when lambda functions (and especially lambda expressions) are used without restraint.  Readability for the whole team is paramount.  After all, too much syntactic sugar will rot your teeth!

The brilliant thing about C# is the mind set of “I’m sure there’s a way to do this” is often rewarded with a little research.

Visual Studio 2008 JumpStart December 18, 2007

Posted by codinglifestyle in ASP.NET, C#, Javascript, jQuery, linq.
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Yesterday I attended the Visual Studio 2008 Jumpstart at Microsoft in Dublin.  This was a one-day course, presented by David Ryan, introducing some of the new features in C# 3.0 and VS2008.

 

I approach every release with excitement and trepidation.  There are some fantastic new features like JavaScript debugging, nested MasterPages, improved IDE for both coding and web design, and multi-target runtime support.  With multi-targeting support we can use VS2008 to continue to code or support .NET 2.  If you open a VS2005 project, you will be prompted to upgrade your project even if you continue to use .NET 2.  I asked was there any risk associated with this for those who need to continue to support .NET 2 and was told only the SLN file is changed.  So theoretically, there is no reason to keep VS2005 installed!  Do you believe it??  If only we could get rid of VS2003 as well.

 

Now, the reason I also approach each release with trepidation is because you know there is going to be some big, new, ghastly feature which will be force-feed to us like geese in a pâté factory.  This time that feature in LINQ.  Open wide because there is a big push behind LINQ and you’ll notice a using System.Linq statement in every new class (which is a real pain if you change target framework back to .NET 2).  But first, let’s review some of the changes made to C#:

 

  • Anonymous types
    • var dt = DateTime.Today;
    • Anything can be assigned to a var, but once it’s assigned its strongly typed and that type can’t be changed.  So I can’t reuse local variable dt and assign string “Hello” like I could with object.
  • Automatic Properties
    • This:

      private int m_nID;

         public int ID

         {

             get

             {

                 return m_nID;

             }

             set

             {

                 m_nID = value;

             }

         }

 

  •  
    • becomes this:

public int ID { get; set; }

 

  •  
    • The problem is in practice I prefer to use the private variables in code leaving properties for external access only.  Many times the get/set is doing something interesting, like reading the value from a cache or performing some complex operation.  We don’t necessarily want/need this code to execute every time it is accessed from within the class so I use the private variable.  Automatic Properties has us using the public property directly everywhere in the class.  So, personally, this will cause inconsistency in my coding style.
    • You can also specify the get as public but keep the set to just be accessible from within the class like this:

public int ID { get; private set; }

 

  • Object initalizers
    • Ever have to instantiate your own class and have to initialize it with a dozen properties?  Do you add 13 lines of code or go overload the constructor?  Now you don’t have to, imagine a simple Person class with 3 properties:

Person person = new Person { FirstName=“Chris”, LastName=“Green”, Age=33 };

 

  •  
    • Only initialize what you properties you want:

Person person2 = new Person { FirstName = “Chris”, LastName = “Green” };

 

  • Collection initalizers

List<Person> people = new List<Person>

         {

new Person { FirstName = “Chris”, LastName = “Green”, Age = 33 },

new Person { FirstName = “Bill”, LastName = “Bob”, Age = 46 },

new Person { FirstName = “Foo”, LastName = “Bar”, Age = 26 }

         };

 

  • Extension methods
    • This is a way of adding new inherent functionality to existing classes.  The objective is to add a new method to the DateTime type called LastDay() which will return the last day of the given date’s month.

public static class DateTimeUtils

{

        public static int LastDay (this DateTime dt)

        {

            return DateTime.DaysInMonth(dt.Year, dt.Month);

        }

}

 

  •  
    • Notice the this before the first parameter argument.  This tells the compiler that this is an extension method for the DateTime type.  We can now use this method as if it was built in to the DateTime class:
      • int nLastDay = dt.LastDay();
  • Lambda expressions
    • Too lazy or couldn’t be arsed to write a small 2 line function?  This is for you:

Func<string, bool> CheckName = sName => sName == “Bob”;

bool bBob = CheckName(person.FirstName);

Func<int, int> Square = x => x * x;

int nSquare = Square(5);

 

The fact is there’s an ulterior reason var, Lamda expressions, and many of above additions have been added to C# 3.0.  C# had been bent in order to accommodate LINQ.  LINQ allows you to perform queries on objects, DataSets, XML, and databases.  It’s interesting in that it offers an independent layer of abstraction for performing these types of operations.  This has actually occurred to me before when looking at data layers chock full of embedded SQL not being particularly ideal.  LINQ offers a generic and powerful alternative.  Let’s take a look at a simple example based on the people collection from above:

 

var matches = from person in people

              where person.FirstName == “Bob”

              select person;

 

The first thing that caught my attention was the select was last.  One reason they likely did this was to force us to state what we were querying first (the from clause) so that Intellisense could kick-in for the rest of the expression.  Notice person.FirstName was fully supported by Intellisense so the Person class was automatically inferred from the people collection.

 

You can create objects on-the-go from your expression.  For example:

 

var matches = from employee in people

              where employee.FirstName == “Bob”

              select new Person(employee.FirstName, employee.LastName);

 

 

Notice how var is inherently handy here (but bad practice for nearly everything else) as our LINQ expression returns System.Collections.Generic.IEnumerable.  Lambda expressions as well play a key part in LINQ:

 

var matchesBob = people.Select(CheckName => CheckName.LastName == “Bob”);

 

matchesBob.ToArray()

{bool[3]}

    [0]: false

    [1]: true

    [2]: false

 

var matchesInitials = people.Select(ChopName => ChopName.FirstName.Remove(1) + ChopName.LastName.Remove(1));

 

matchesInitials.ToArray()

{string[3]}

    [0]: “CG”

    [1]: “BB”

    [2]: “FB”

 

There is so much more to LINQ that I won’t attempt to cover any more.  Rest assured you will hear much more about LINQ in the months to come (fatten up those livers).  One thing is obvious, C# took a heavy hit in order to support it.  Let’s hope it’s worth it as every release we lean more and more towards VB.  A colleague recently remarked, “C# is all VB under the covers anyhow”.  He might be right.

 

Some other interesting new additions:

  • XElement – for anyone who has programmatically built XML before you will appreciate this quicker alternative
  • ASP.NET ListView – the singular new control this release.  Its basically a Repeater but with design-time support
  • Script Manager Proxy – typically the Ajax ScriptManager will be placed in the MasterPage.  When the content page needs to access the ScriptManager a ScriptManagerProxy can be used to get around the restriction of only one ScriptManager allowed per page.
  • Javascript enhancements – built-in libraries which extend string, add StringBuilder, and a number of other enhancements to make writing JavaScript more .NET-like
  • CLR Add-In Framework: essentially a pattern for loading modules (only from a specified directory) vs. using reflection, iterating classes for a specified type, and using the activator to instantiate the object
  • Transparent Intellisense: In VS2005 Intellisense went in to hyperdrive and our tab keys have never been the same.  However, I often found myself cursing it as it often got in the way.  So when VS is being too helpful and you can’t see what you’re doing press CTRL rather than ESC to turn Intellisense transparent.
  • Right-click the code and you will see an Organize Using menu below Refactor.  Here is a feature I’ve often dreamed of: Remove Unused Usings.  Pinch me!  Also, if you right-click the interface in a class’s definition (public class MyClass : Interface) there is an Implement interface option.   Last, if you are coding away and using a class before adding a using statement use ALT-Shift-F10 to automatically resolve the class and add the using statement to your file.
  • Improved support for debugging multithreaded applications
  • SQL Database Publishing Wizard is now integrated in the VS
  • Did I mention JavaScript debugging??!

 

You may notice I’ve omitted a few big topics.  I didn’t mention Ajax because that’s old news now.  However, there are new versions of the Ajax Control Toolkit and web deployment projects for VS2008.

 

I also didn’t mention Silverlight although I may find some interesting applications for it in the future.  For example, if you really hate writing JavaScript you could use Silverlight’s built-in mini CLR to write C# code which executes in the browser.  Oh, I hear it does some UI stuff too.

 

References: ScottGu 19-11-2007, ScottGu 13-03-2007, ScottGu 08-03-2007, C# 3.0 In a Nutshell, Pro ASP.NET 3.5 in C# 2008, and CodeProject.