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  • Properly Label Your Dangerous Projects

    - by Jason Fitzpatrick
    In the pursuit of science, fun, and laser-fueled hijinks, we often undertake projects that really should be labeled more properly. Download this effective label to visually warn “No really, you’ll burn the house down”. Courtesy of Flattr at Thingiverse, you can grab a copy of the “Warning: Will Burn Your House Down” graphic in high resolution image formats suitable for silk screening, laser engraving, or plain old fashioned sign printing. Warning: Will Burn Your House Down [Thingiverse via Make] How To Encrypt Your Cloud-Based Drive with BoxcryptorHTG Explains: Photography with Film-Based CamerasHow to Clean Your Dirty Smartphone (Without Breaking Something)

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  • Ever helpful Windows&hellip;

    - by John Breakwell
    I’m doing some troubleshooting for a relative and asked them to send me a zipped copy of their registry which they dutifully did. When I tried to extract the registry file, though, Windows jumped in the way and said “No”. This made sense as registry files are dangerous things in the hands of the ignorant. So I clicked the link to see if it would tell me how to get at the reg file but found the result less than helpful. So off to the Internet and found an excellent answer on how to get round this: Now on to the much harder part of fixing the original problems.

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  • CLR via C# 3rd Edition is out

    - by Abhijeet Patel
    Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

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  • The Modern Marketer’s Guide to Connected Customer Journeys

    - by Richard Lefebvre
    By Amanda Batista on Thursday, August 14, 2014 in Marketing Efficiency Organizations are striving to deliver consistent experiences but very few feel they are there yet. It’s a simple consideration for marketers, really. Not only does industry data continue to support that customers demand personalized experiences when engaging with brands, but if you think about your own consumer driven shopping experiences, you, too, expect that stellar experience at every touch point. And when you don’t get it, that brand has potentially alienated the experience, as well as their shot at engaging with you in more meaningful ways. Oracle Marketing Cloud partnered with marketingfinder.co.uk to conduct a survey exploring how marketers are adapting to this new age of the customer and the challenges they face. Less than half (40%) of marketers in the study were able to track the customer journey across channels. These findings, as well as other data points showcasing marketers’ challenges, are explored in our latest eBook, “The Modern Marketer's Guide to Connected Customer Journeys.” Read the entire article and order your copy of the full report here

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  • New Exadata Book Available Soon

    - by Rob Reynolds
    Oracle Press is set to released the first book on data warehouse performance and Exadata on March 14th. Achieving Extreme Performance with Oracle Exadata , by my colleagues Rick Greenwald, Robert Stackowiak, Maqsood Alam, and Mans Bhuller will be available at your favorite booksellers next week. I've seen a sneak peak of the content in this book and its a great way to fully grasp the power of Exadata and how to best apply it to achieve extreme data warehouse performance. From the publisher's description: Achieving Extreme Performance with Oracle Exadata and the Sun Oracle Database Machine is filled with best practices for deployments, hardware sizing, architecting the database machine environments for maximum availability, and backup and recovery. Oracle Database 11gR2 features used within these offerings, as well as migration options and paths for Oracle and non-Oracle databases to Oracle Exadata are covered. This Oracle Press guide also discusses architecture, administration, maintenance, monitoring, and tuning of Oracle Exadata Storage Servers and the Sun Oracle Database Machine. If your company is considering Exadata, or if you need more horsepower out of your data warehouse, I highly recommend grabbing a copy of this book next week.

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  • NTFS Issues in Windows 7 and 2008 R2 - 'Is it a Bug?'

    - by renewieldraaijer
    I have been using the various versions of the Microsoft Windows product line since NT4 and I really thought I knew the ins and outs about the NTFS filesystem by now. There were always a few rules of thumb to understand what happens if you move data around. These rules were: "If you copy data, the copied data will inherit the permissions of the location it is being copied to. The same goes for moving data between disk partitions. Only when you move data within the same partition, the permissions are kept."  Recently I was asked to assist in troubleshooting some NTFS related issues. This forced me to have another good look at this theory. To my surprise I found out that this theory does not completely stand anymore. Apparently some things have changed since the release of Windows Vista / Windows 2008. Since the release of these Operating Systems, a move within the same disk partition results in the data inheriting the permissions of the location it is being copied into. A major change in the NTFS filesystem you would think!  Not quite! The above only counts when the move operation is being performed by using Windows Explorer. A move by using the 'move' command from within a cmd prompt for example, retains the NTFS permissions, just like before in Windows XP and older systems. Conclusion: The Windows Explorer is responsible for changing the ACL's of the moved data. This is a remarkable change, but if you follow this theory, the resulting ACL after a move operation is still predictable.  We could say that since Windows Vista and Windows 2008, a new rule set applies: "If you copy data, the copied data will inherit the permissions of the location it is being copied to. Same goes for moving data between disk partitions and within disk partitions. Only when you move data within the same partition by using something else than the Windows Explorer, the permissions are kept." The above behavior should be unchanged in Windows 7 / Windows 2008 R2, compared to Windows Vista / 2008. But somehow the NTFS permissions are not so predictable in Windows 7 and Windows 2008 R2. Moving data within the same disk partition the one time results in the permissions being kept and the next time results in inherited permissions from the destination location. I will try to demonstrate this in a few examples: Example 1 (Incorrect behavior): Consider two folders, 'Folder A' and 'Folder B' with the following permissions configured.                    Now we create the test file 'test file 1.txt' in 'Folder A' and afterwards move this file to 'Folder B' using Windows Explorer.                       According to the new theory, the file should inherit the permissions of 'Folder B' and therefore 'Group B' should appear in the ACL of 'test file 1.txt'. In the screenshot below the resulting permissions are displayed. The permissions from the originating location are kept, while the permissions of 'Folder B' should be inherited.                   Example 2 (Correct behavior): Again, consider the same two folders. This time we make a small modification to the ACL of 'Folder A'. We add 'Group C' to the ACL and again we create a file in 'Folder A' which we name 'test file 2.txt'.                    Next, we move 'test file 2.txt' to 'Folder B'.                       Again, we check the permissions of 'test file 2.txt' at the target location. We can now see that the permissions are inherited. This is what should be happening, and can be considered 'correct behavior' for Windows Vista / 2008 / 7 / 2008 R2. It remains uncertain why this behavior is so inconsistent. At this time, this is under investigation with Microsoft Support. The investigation has been going for the last two weeks and it is beginning to look like there is no rational reason for this, other than a bug in the Windows Explorer in Windows 7 and 2008 R2. As soon as there is any certainty on this, I will note it here in this blog.                   The examples above are harmless tests, by using my own laptop. If you would create the same set of folders and groups, and configure exactly the same permissions, you will see exactly the same behavior. Be sure to use Windows 7 or Windows 2008 R2.   Initially the problem arose at a customer site where move operations on data on the fileserver by users would result in unpredictable results. This resulted in the wrong set of people having àccess permissions on data that they should not have permissions to. Off course this is something we want to prevent at all costs.   I have also done several tests with move operations by using the move command in a cmd prompt. This way the behavior is always consistent. The inconsistent behavior is only exposed when using the Windows Explorer to initiate the move operation, and only when using Windows 7 or Windows 2008 R2 systems. It is evident that this behavior changes when the ACL of a folder has been changed, for example by adding an extra entry. The reason for this remains uncertain though. To be continued…. A dutch version of this post can be found at: http://blogs.platani.nl/?p=612

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  • What should web programmers know about cryptography?

    - by davidhaskins
    Should programmers who build websites/web applications understand cryptography? I have no idea how most crypographic algorithms work, and I really don't understand the differences between md5/des/aes/etc. Have any of you found any need for an in-depth understanding of cryptography? I haven't needed it, but I wonder if perhaps I'm missing something. I've used salt + md5 hash to encrypt passwords, and I tell webservers to use SSL. Beyond that, I can't say I've used much else, nor can I say with any certainty how secure these methods are. I only use them because other people claim they are safe. Have you ever found a need to use cryptography in web programming aside from these two simple examples?

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  • APress Deal of the Day 13/August/2014 - Pro ASP.NET MVC 4

    - by TATWORTH
    Originally posted on: http://geekswithblogs.net/TATWORTH/archive/2014/08/13/apress-deal-of-the-day-13august2014---pro-asp.net-mvc.aspxToday’s $10 Deal of the Day from APress at http://www.apress.com/9781430242369 is Pro ASP.NET MVC 4. Adam Freeman is an excellent author and I recommend this book to all my readers. “The ASP.NET MVC 4 Framework is the latest evolution of Microsoft’s ASP.NET web platform. It provides a high-productivity programming model that promotes cleaner code architecture, test-driven development, and powerful extensibility, combined with all the benefits of ASP.NET.”

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  • Why do we need fork to create new process

    - by user3671483
    In Unix whenever we want to create a new process, we fork the current process i.e. we create a new child process which is exactly the same as the parent process and then we do exec system call to replace the child process with a new process i.e. we replace all the data for the parent process eith that for the new process. Why do we create a copy of the parent process in the first place and why don't we create a new process directly? I am new to Unix please explain in lay-man terms.

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  • Bing Desktop Automatically Downloads Bing Wallpapers to Your Computer

    - by Jason Fitzpatrick
    Windows 7: Bing Desktop is a new and lightweight offering from Microsoft that automatically swaps your desktop background every day and offers quick access to the Bing search engine. In addition to downloading the Bing wallpaper, Bing Desktop also includes a small search box that allows you to search Bing from your desktop–although most users will likely grab the app simply to get the daily wallpaper update. Hit up the link below to download a copy. Bing Desktop is free, Windows 7 only. Bing Desktop [via Quick Online Tips] How to Stress Test the Hard Drives in Your PC or Server How To Customize Your Android Lock Screen with WidgetLocker The Best Free Portable Apps for Your Flash Drive Toolkit

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  • WebForms vs MVC (again)

    There's a new video up on www.asp.net which aims to help developers pick between ASP.NET WebForms and ASP.NET MVC. The video boils down to 5 benefits per technology which Microsoft thinks you should consider. Let's go over the points, shall we? First, ASP.NET WebForms: 1 - Familiar control and event base programming model The claim here is that the ASP.NET model is comfortable for WinForm programmers (thankfully this unbiased analysis left out who it's more familiar for). This is largely...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Teamwork 101 for the solo newbie

    - by clankercrusher
    Forgive my newbishness but I have a question to ask about teamwork...mainly because I stink at it. Most of my projects up until this point have been solo so I have a very limited experience with teamwork. I did make graphics for a game that was being developed by several people, but that was completely different than programming with several different people. Right now I'm working with someone else on an indie MMO along with a few other team members. I've already made some pretty stupid mistakes, (like rewriting EVERYTHING) so I have two questions for you guys: 1) What are some of the most common mistakes that people make in a team environment and how can they be avoided? 2) How can the structure of your program be altered to allow for multiple teams members to work on different parts of the program at the same time? P.S. Is this the right stack exchange site for this type of question? (if not, where does it go? Thanks)

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  • Computer Science or Computer Engineering for Data Science and Machine Learning

    - by ATMathew
    I'm a 25 year old data consultant who is considering returning to school to get a second bachelors degree in computer science or engineering. My interest is data science and machine learning. I use programming as a means to an end, and use languages like Python, R, C, Java, and Hadoop to find meaning in large data sets. Would a computer science or computer engineering degree be better for this? I realize that a statistics degree may be even more beneficial, but I'll be at a school which dosn't have a stats department or a computational math department.

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  • Prevent service from starting

    - by Evan Plaice
    So, I do Arduino development on my system to program arduinos using the FTDI USB programming interface (if you have no idea what this means don't worry). The issue arises because the FTDI interface uses tty to communicate and it conflicts with one of the default ubuntu services. The default service in question is called brltty (which enables braille accessibility for people with impaired vision). Considering that I don't have any particular use for this service and it's annoying to stop it manually (using 'service brltty stop') after I restart my system... Where would I configure this (or any) service to prevent it from loading on startup? Note: I also have this issue with qemu-kvm conflicting with virtualbox.

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  • How to Sync Any Folder With SkyDrive on Windows 8.1

    - by Chris Hoffman
    Before Windows 8.1, it was possible to sync any folder on your computer with SkyDrive using symbolic links. This method no longer works now that SkyDrive is baked into Windows 8.1, but there are other tricks you can use. Creating a symbolic link or directory junction inside your SkyDrive folder will give you an empty folder in your SkyDrive cloud storage. Confusingly, the files will appear inside the SkyDrive Modern app as if they were being synced, but they aren’t. The Solution With SkyDrive refusing to understand and accept symbolic links in its own folder, the best option is probably to use symbolic links anyway — but in reverse. For example, let’s say you have a program that automatically saves important data to a folder anywhere on your hard drive — whether it’s C:\Users\USER\Documents\, C:\Program\Data, or anywhere else. Rather than trying to trick SkyDrive into understanding a symbolic link, we could instead move the actual folder itself to SkyDrive and then use a symbolic link at the folder’s original location to trick the original program. This may not work for every single program out there. But it will likely work for most programs, which use standard Windows API calls to access folders and save files. We’re just flipping the old solution here — we can’t trick SkyDrive anymore, so let’s try to trick other programs instead. Moving a Folder and Creating a Symbolic Link First, ensure no program is using the external folder. For example, if it’s a program data or settings folder, close the program that’s using the folder. Next, simply move the folder to your SkyDrive folder. Right-click the external folder, select Cut, go to the SkyDrive folder, right-click and select Paste. The folder will now be located in the SkyDrive folder itself, so it will sync normally. Next, open a Command Prompt window as Administrator. Right-click the Start button on the taskbar or press Windows Key + X and select Command Prompt (Administrator) to open it. Run the following command to create a symbolic link at the original location of the folder: mklink /d “C:\Original\Folder\Location” “C:\Users\NAME\SkyDrive\FOLDERNAME\” Enter the correct paths for the exact location of the original folder and the current location of the folder in your SkyDrive. Windows will then create a symbolic link at the folder’s original location. Most programs should hopefully be tricked by this symbolic location, saving their files directly to SkyDrive. You can test this yourself. Put a file into the folder at its original location. It will be saved to SkyDrive and sync normally, appearing in your SkyDrive storage online. One downside here is that you won’t be able to save a file onto SkyDrive without it taking up space on the same hard drive SkyDrive is on. You won’t be able to scatter folders across multiple hard drives and sync them all. However, you could always change the location of the SkyDrive folder on Windows 8.1 and put it on a drive with a larger amount of free space. To do this, right-click the SkyDrive folder in File Explorer, select Properties, and use the options on the Location tab. You could even use Storage Spaces to combine the drives into one larger drive. Automatically Copy the Original Files to SkyDrive Another option would be to run a program that automatically copies files from another folder on your computer to your SkyDrive folder. For example, let’s say you want to sync copies of important log files that a program creates in a specific folder. You could use a program that allows you to schedule automatic folder-mirroring, configuring the program to regularly copy the contents of your log folder to your SkyDrive folder. This may be a useful alternative for some use cases, although it isn’t the same as standard syncing. You’ll end up with two copies of the files taking up space on your system, which won’t be ideal for large files. The files also won’t be instantly uploaded to your SkyDrive storage after they’re created, but only after the scheduled task runs. There are many options for this, including Microsoft’s own SyncToy, which continues to work on Windows 8. If you were using the symbolic link trick to automatically sync copies of PC game save files with SkyDrive, you could just install GameSave Manager. It can be configured to automatically create backup copies of your computer’s PC game save files on a schedule, saving them to SkyDrive where they’ll be synced and backed up online. SkyDrive support was completely rewritten for Windows 8.1, so it’s not surprising that this trick no longer works. The ability to use symbolic links in previous versions of SkyDrive was never officially supported, so it’s not surprising to see it break after a rewrite. None of the methods above are as convenient and quick as the old symbolic link method, but they’re the best we can do with the SkyDrive integration Microsoft has given us in Windows 8.1. It’s still possible to use symbolic links to easily sync other folders with competing cloud storage services like Dropbox and Google Drive, so you may want to consider switching away from SkyDrive if this feature is critical to you.     

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  • HFS+ hard drive being mounted as read only

    - by DNA
    This is a recurring problem and occurs a few times a week. I have an external hard drive which is hfs+. Every couple of weeks, for no obviuous reason, when I mount it by pluggin it in to my Ubuntu 11.10, it is read only and I can't copy any files into it. I gksudo nautlius and change the ownership and it magically works in some time. But returns to the read only state soon in a few hours-days without any rhyme or reason. Right now my fstab doesn't have any entry for my hard drive. What gives? What in the world is going on with Linux/HFS+? This is frustrating. I can't reformat my hard drive because I have almost a terrabyte of data in it and no receptacle to hold it while I reformat it.

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  • how should I network my turn based game?

    - by ddriver1
    I'm writing a very basic turn based strategy game which allows a player to select units and attack enemy units on their turn. The game is written in Java using the slick2d library and I plan to use kyronet for the networking api. I want the game to be networked, but I do not know how I should go about it. My current idea is to connect two users together, and the first one to join the game becomes the game host, while the other becomes the client. However after reading http://gafferongames.com/networking-for-game-programmers/what-every-programmer-needs-to-know-about-game-networking/ it seems my game would be suited to a peer to peer lockstep model. Would that make programming the networking side much easier? Any suggestions on how I should structure my networking would be greatly appreciated

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  • Why are there so many spaces and line breaks in Unicode?

    - by maaartinus
    Unicode has maybe 50 spaces \u0009\u000A-\u000D\u0020\u0085\u00A0\u1680\u180E\u2000-\u200A\u2028\u2029\u202F\u205F\u3000][\u0009\u000A-\u000D\u0020\u0085\u00A0\u1680\u180E\u2000-\u200A\u2028\u2029\u202F\u205F\u3000 and 6 line breaks not only CRLF, LF, CR, but also NEL (U+0085), PS (U+2029) and LS (U+2028). Maybe I could understand most of the spaces and PS ("Paragraph separator"), but what are "Next Line" and "Line separator" good for? It all looks like invented by a very big committee where everybody wanted their own space and the leaders were granted one line break each. But seriously, how do you deal with it when your programming language doesn't support it (or does it wrong as e.g. Java does)?

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  • How to keep menu in a single place without using frames

    - by TJ Ellis
    This is probably a duplicate, but I can't find the answer anywhere (maybe I'm searching for the wrong thing?) and so I'm going to go ahead and ask. What is the accepted standard practice for creating a menu that is stored in a single file, but is included on every page across a site? Back in the day, one used frames, but this seems to be taboo now. I can get things layed out just the way I want, but copy/pasting across every page is a pain. I have seen php-based solutions, but my cheap-o free hosting doesn't support php (which is admittedly a pain, but it's a fairly simple webpage...). Any ideas for doing this that does not require server-side scripting?

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  • Liskov Substitution Principle and the Oft Forgot Third Wheel

    - by Stacy Vicknair
    Liskov Substitution Principle (LSP) is a principle of object oriented programming that many might be familiar with from the SOLID principles mnemonic from Uncle Bob Martin. The principle highlights the relationship between a type and its subtypes, and, according to Wikipedia, is defined by Barbara Liskov and Jeanette Wing as the following principle:   Let be a property provable about objects of type . Then should be provable for objects of type where is a subtype of .   Rectangles gonna rectangulate The iconic example of this principle is illustrated with the relationship between a rectangle and a square. Let’s say we have a class named Rectangle that had a property to set width and a property to set its height. 1: Public Class Rectangle 2: Overridable Property Width As Integer 3: Overridable Property Height As Integer 4: End Class   We all at some point here that inheritance mocks an “IS A” relationship, and by gosh we all know square IS A rectangle. So let’s make a square class that inherits from rectangle. However, squares do maintain the same length on every side, so let’s override and add that behavior. 1: Public Class Square 2: Inherits Rectangle 3:  4: Private _sideLength As Integer 5:  6: Public Overrides Property Width As Integer 7: Get 8: Return _sideLength 9: End Get 10: Set(value As Integer) 11: _sideLength = value 12: End Set 13: End Property 14:  15: Public Overrides Property Height As Integer 16: Get 17: Return _sideLength 18: End Get 19: Set(value As Integer) 20: _sideLength = value 21: End Set 22: End Property 23: End Class   Now, say we had the following test: 1: Public Sub SetHeight_DoesNotAffectWidth(rectangle As Rectangle) 2: 'arrange 3: Dim expectedWidth = 4 4: rectangle.Width = 4 5:  6: 'act 7: rectangle.Height = 7 8:  9: 'assert 10: Assert.AreEqual(expectedWidth, rectangle.Width) 11: End Sub   If we pass in a rectangle, this test passes just fine. What if we pass in a square?   This is where we see the violation of Liskov’s Principle! A square might "IS A” to a rectangle, but we have differing expectations on how a rectangle should function than how a square should! Great expectations Here’s where we pat ourselves on the back and take a victory lap around the office and tell everyone about how we understand LSP like a boss. And all is good… until we start trying to apply it to our work. If I can’t even change functionality on a simple setter without breaking the expectations on a parent class, what can I do with subtyping? Did Liskov just tell me to never touch subtyping again? The short answer: NO, SHE DIDN’T. When I first learned LSP, and from those I’ve talked with as well, I overlooked a very important but not appropriately stressed quality of the principle: our expectations. Our inclination is to want a logical catch-all, where we can easily apply this principle and wipe our hands, drop the mic and exit stage left. That’s not the case because in every different programming scenario, our expectations of the parent class or type will be different. We have to set reasonable expectations on the behaviors that we expect out of the parent, then make sure that those expectations are met by the child. Any expectations not explicitly expected of the parent aren’t expected of the child either, and don’t register as a violation of LSP that prevents implementation. You can see the flexibility mentioned in the Wikipedia article itself: A typical example that violates LSP is a Square class that derives from a Rectangle class, assuming getter and setter methods exist for both width and height. The Square class always assumes that the width is equal with the height. If a Square object is used in a context where a Rectangle is expected, unexpected behavior may occur because the dimensions of a Square cannot (or rather should not) be modified independently. This problem cannot be easily fixed: if we can modify the setter methods in the Square class so that they preserve the Square invariant (i.e., keep the dimensions equal), then these methods will weaken (violate) the postconditions for the Rectangle setters, which state that dimensions can be modified independently. Violations of LSP, like this one, may or may not be a problem in practice, depending on the postconditions or invariants that are actually expected by the code that uses classes violating LSP. Mutability is a key issue here. If Square and Rectangle had only getter methods (i.e., they were immutable objects), then no violation of LSP could occur. What this means is that the above situation with a rectangle and a square can be acceptable if we do not have the expectation for width to leave height unaffected, or vice-versa, in our application. Conclusion – the oft forgot third wheel Liskov Substitution Principle is meant to act as a guidance and warn us against unexpected behaviors. Objects can be stateful and as a result we can end up with unexpected situations if we don’t code carefully. Specifically when subclassing, make sure that the subclass meets the expectations held to its parent. Don’t let LSP think you cannot deviate from the behaviors of the parent, but understand that LSP is meant to highlight the importance of not only the parent and the child class, but also of the expectations WE set for the parent class and the necessity of meeting those expectations in order to help prevent sticky situations.   Code examples, in both VB and C# Technorati Tags: LSV,Liskov Substitution Principle,Uncle Bob,Robert Martin,Barbara Liskov,Liskov

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  • Uploading to a PPA using quickly

    - by Andres
    I am trying to participate in ubuntu showdown. I followed Jono's tutorial to do a browser using quickly. I did some modifications including choosing license (gpl v3), putting my name in copy right ( without special spanish charecters since quicky does not like it) $quickly run to make sure it worked I used bazaar to commit a change with a line of comment. I packaged it using quickly. Managed to install it ignoring some warnings but it would not run. I want to share code to get feedback. I have a launchpad account, signed terms and coditions, created a ppa. I got my commandline to talk to lauchpad using the encription key. But when I run $quickly release or $quickly share and it says the project does not exist. There seems to be another command $dput ... But i don't seem to get the wording right because it requests some sort of signed file that i cannot manage to add the correct way.

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  • Win a free pass for Silverlight Tour in Vancouver, D-10!!

    - by pluginbaby
    As you may know, the Silverlight Tour Training is coming to Vancouver in may. If you plan to attend, this might be interesting: you can win one free pass to this Vancouver Silverlight 4 workshop in May 3-6, 2010 ($1,995 CAD value) by visiting the SilverlightShow.net community website and participate in the draw! (the pass does not include travel and hotel, only the course). Take the chance to get an intensive course on Silverlight 4 in this four-day training! Learn the ins and outs of design, development and server-side programming with Silverlight in an exciting way, through a mix of lessons, demonstrations and hands-on labs. Enter the draw before April 1st, 2010! The winner will be announced on April 2nd, 2010 in www.silverlightshow.net. Good Luck! Technorati Tags: Silverlight training,Silverlight Tour

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  • Do Not Optimize Without Measuring

    - by Alois Kraus
    Recently I had to do some performance work which included reading a lot of code. It is fascinating with what ideas people come up to solve a problem. Especially when there is no problem. When you look at other peoples code you will not be able to tell if it is well performing or not by reading it. You need to execute it with some sort of tracing or even better under a profiler. The first rule of the performance club is not to think and then to optimize but to measure, think and then optimize. The second rule is to do this do this in a loop to prevent slipping in bad things for too long into your code base. If you skip for some reason the measure step and optimize directly it is like changing the wave function in quantum mechanics. This has no observable effect in our world since it does represent only a probability distribution of all possible values. In quantum mechanics you need to let the wave function collapse to a single value. A collapsed wave function has therefore not many but one distinct value. This is what we physicists call a measurement. If you optimize your application without measuring it you are just changing the probability distribution of your potential performance values. Which performance your application actually has is still unknown. You only know that it will be within a specific range with a certain probability. As usual there are unlikely values within your distribution like a startup time of 20 minutes which should only happen once in 100 000 years. 100 000 years are a very short time when the first customer tries your heavily distributed networking application to run over a slow WIFI network… What is the point of this? Every programmer/architect has a mental performance model in his head. A model has always a set of explicit preconditions and a lot more implicit assumptions baked into it. When the model is good it will help you to think of good designs but it can also be the source of problems. In real world systems not all assumptions of your performance model (implicit or explicit) hold true any longer. The only way to connect your performance model and the real world is to measure it. In the WIFI example the model did assume a low latency high bandwidth LAN connection. If this assumption becomes wrong the system did have a drastic change in startup time. Lets look at a example. Lets assume we want to cache some expensive UI resource like fonts objects. For this undertaking we do create a Cache class with the UI themes we want to support. Since Fonts are expensive objects we do create it on demand the first time the theme is requested. A simple example of a Theme cache might look like this: using System; using System.Collections.Generic; using System.Drawing; struct Theme { public Color Color; public Font Font; } static class ThemeCache { static Dictionary<string, Theme> _Cache = new Dictionary<string, Theme> { {"Default", new Theme { Color = Color.AliceBlue }}, {"Theme12", new Theme { Color = Color.Aqua }}, }; public static Theme Get(string theme) { Theme cached = _Cache[theme]; if (cached.Font == null) { Console.WriteLine("Creating new font"); cached.Font = new Font("Arial", 8); } return cached; } } class Program { static void Main(string[] args) { Theme item = ThemeCache.Get("Theme12"); item = ThemeCache.Get("Theme12"); } } This cache does create font objects only once since on first retrieve of the Theme object the font is added to the Theme object. When we let the application run it should print “Creating new font” only once. Right? Wrong! The vigilant readers have spotted the issue already. The creator of this cache class wanted to get maximum performance. So he decided that the Theme object should be a value type (struct) to not put too much pressure on the garbage collector. The code Theme cached = _Cache[theme]; if (cached.Font == null) { Console.WriteLine("Creating new font"); cached.Font = new Font("Arial", 8); } does work with a copy of the value stored in the dictionary. This means we do mutate a copy of the Theme object and return it to our caller. But the original Theme object in the dictionary will have always null for the Font field! The solution is to change the declaration of struct Theme to class Theme or to update the theme object in the dictionary. Our cache as it is currently is actually a non caching cache. The funny thing was that I found out with a profiler by looking at which objects where finalized. I found way too many font objects to be finalized. After a bit debugging I found the allocation source for Font objects was this cache. Since this cache was there for years it means that the cache was never needed since I found no perf issue due to the creation of font objects. the cache was never profiled if it did bring any performance gain. to make the cache beneficial it needs to be accessed much more often. That was the story of the non caching cache. Next time I will write something something about measuring.

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  • Pricing options at O’Reilly

    - by Nick Harrison
    I was browsing through the new options for books on O'Reilly and Associates and noticed something kind of cool    If you buy the print edition of a book, you can get the ebook for just a couple dollars more.  This is pure genius marketing. I may question whether or not I want the ebook at 20 or the print copy at 25, but to get them both for 28, well that's a no brainer.  This is actually a strategy examined at great depth in Predictably Rational In all honesty, $20 is probably over priced for the ebook, but $3 if you are already buying the print edition is actually a pretty good deal  .

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  • Are technical books easy to read on the Kindle (or other small screens) [closed]

    - by Peter Recore
    Possible Duplicate: eBook editions of programming books I am considering getting a kindle or other e reader. (Kindle is my top choice for the eink vs lcd factor) I have been able to try reading fiction on a Kindle, and it seemed pretty nice, even with the small screen. However, most books I buy are actually technical books, which tend to have figures, code samples, and other odd things. How well do the various ereaders handle books like this? In particular, does the kindle render code samples or figures in an easy to read way?

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