MSDN Magazine - February 2009 - (Page 19)

queue and doesn’t have any idea what to do with a QueueEmptyException. But the programmer who wrote GenerateGrades() doesn’t want the program to crash without saving the data that’s been computed so far. Everything is written safely to the disk and the program exits. The problem with this program is that it makes a number of assumptions that could be incorrect. What’s to say that the missing entry in the student queue is at the end? Maybe the first student record got skipped, or the tenth. The exception only tells the programmer that the program is incorrect. Taking any action—sav- Guerrilla .NET: w/ 3.0 & 3.5 content November 3rd-7th London Call 800.699.1932 to register today! or visit www.develop.com Guerrilla .NET w/3.0 & 3.5 content LOS ANGELES February 16–20 New The exception only tells the programmer that the program is incorrect. Taking any action is just plain wrong. ing data to disk or “recovering” and continuing execution—is just plain wrong. No correct action is possible without knowledge of the context in which the exception was raised. If the program had caught a specific exception close to where the exception was raised, it might have been able to take proper action. The program knows what a QueueEmptyException means in the function that attempts to dequeue students. If the function catches that exception by type—rather than catching a whole class of exception types—it would be in a much better position to try to make the program state correct. In general, catching a specific exception is the correct thing to do because it provides the most context to your exception handler. If your code can potentially catch two exceptions, then it has to be able to deal with both. Writing code that says catch (Exception e) has to be able to deal with literally any exceptional situation. That’s a promise that is very hard to keep. Some languages try to prevent programmers from catching a broad class of exceptions. For example, C++ has exception specifications, a mechanism that allows a programmer to specify what exceptions can be raised in that function. Java takes this a step further with checked exceptions, a compiler-enforced requirement that a certain class of exceptions be specified. In both languages, you list the exceptions that can flow out of this function in the function declaration and callers are required to handle those exceptions. Exception specifications are a good idea, but they have had mixed results in practice. There’s vigorous debate as to whether or not any managed code should be able to handle CSEs. These exceptions normally denote a systems-level error and should only be handled by code that understands the systems-level context. While most people don’t need the ability to handle CSEs, there are a couple of scenarios where it’s necessary. One scenario is when you are very close to where the exception msdnmagazine.com Hands-on .NET 3.0/3.5 Training Upcoming Courses What’s New in .NET 3.0-3.5 w/LINQ What’s New in .NET 3.0-3.5 featuring LINQ DALLAS 6th - Boston OctoberFebruary 23-27 LOS ANGELES March 23-27 Windows Communication Foundation Essential LINQ with w/ 3.5 content the Entity Framework October 13th - Los Angeles November 3rd- Chicago Essential Silverlight 2 November 17th- New York LOS ANGELES February 24–27 BOSTON March 17-20 Windows Presentation Foundation BOSTON March 23-27 w/ 3.5 content Enhancing Web October 13th - Development with .NET 3.5 Los Angeles LOS ANGELES February 9–12 November 10th - Austin Essential Windows Presentation Foundation Windows WorkFlow Foundation CHICAGO February 23–27 November 3rd - Los Angeles LOS ANGELES March 2-6 NEW COURSE Essential F# Learn to create reliable software on the .NET framework Business Intelligence Learn to leverage the power of Microsoft’s BI platform Essential Skills for the Business Analyst New Courses in 2009 October 29th - Los Angeles On-Site Training Essential OSLO Learn how OSLO can be used to create model driven apps Essential AZURE For groups of students, DevelopMentor’s Learn how to develop scalable AZURE hosted applications On-Site course delivery may offer the CALL most800.699.1932 FOR MORE INFORMATION. cost-effective solution – at your location, at the time you need it. OnOn-Site Training For Groups! Sites also offer the ability to customize a For group’s of students, DevelopMentor’s On-Site course course to your group’s needs, including delivery may offer the most cost-effective solution—at course content, labsneed it. run on your that On-Sites also offer your location, at the time you programming platform and needs,exercises the ability to customize a course to your lab including course content, labs that run on your or project. tailored to your business programming platform and lab exercises tailored to your business or project. CALL US TODAY TO DISCUSS YOUR TRAINING NEEDS Call us today to discuss your training needs! US -800.699.1932 UK -(0)8000.562.265 Developing people Europe-(0)01242.525.108who develop software 19 February 2009 http://www.develop.com http://www.develop.com http://www.msdnmagazine.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - February 2009

MSDN Magazine - February 2009 Contents Toolbox CLR Inside Out Data Points Cutting Edge Patterns In Practice Best Practices .Net Interop "Oslo" Basics Patterns Silverlight Under The Table Foundations Windows With C++ .NET Matters Going Places { End Bracket }

MSDN Magazine - February 2009

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