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• Examples of Liskov Substitution

  - by james lewis

  I'm facilitating a session next week on the Liskov Substitution Principle and I was wondering if anyone had any examples of violations 'from the trenches'? I'm looking for something other than uncle Bob's rectangle - square problem and the persistent set problem he talks about in A-PPP (although that is a great example). So far I'm using the example of a (very simple) List and an IndexedList as the 'correct' use of inheritance. And the addition of a Set to this hierarchy as a violation (as a Set is distinct; strengthening the pre condition of the Add method). I've also taken this great example and it's solution from this question Both those examples are great but I'm looking for something more subtle and harder to spot. So far I've come up with nothing so if you've got a great, subtle example post it up. Also, any metaphors you've come across that helped you understand LSP would be really useful too.

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• Variable declaration versus assignment syntax

  - by rwallace

  Working on a statically typed language with type inference and streamlined syntax, and need to make final decision about syntax for variable declaration versus assignment. Specifically I'm trying to choose between: // Option 1. Create new local variable with :=, assign with = foo := 1 foo = 2 // Option 2. Create new local variable with =, assign with := foo = 1 foo := 2 Creating functions will use = regardless: // Indentation delimits blocks square x = x * x And assignment to compound objects will do likewise: sky.color = blue a[i] = 0 Which of options 1 or 2 would people find most convenient/least surprising/otherwise best?

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• Objective C - Aggro with Images

  - by Will

  I have three UIImageViews. enemy1, enemy1AggroBox and mainSprite. What I want to do is when mainSprite and enemy1AggroBox interect, I want enemy1 to start moving towards mainSprite. Basically creating aggro for a game. if(CGRectIntersectsRect(mainSprite.frame, enemy1AggroBox.frame)){ //Code here// } My plan would be to call this method in viewDidLoad. I'm not using any sort of framework like cocos2d or OpenGLES. If you need to see any more code just ask.

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• Is true multithreading really necessary?

  - by Jonathan Graef

  So yeah, I'm creating a programming language. And the language allows multiple threads. But, all threads are synchronized with a global interpreter lock, which means only one thread is allowed to execute at a time. The only way to get the threads to switch off is to explicitly tell the current thread to wait, which allows another thread to execute. Parallel processing is of course possible by spawning multiple processes, but the variables and objects in one process cannot be accessed from another. However the language does have a fairly efficient IPC interface for communicating between processes. My question is: Would there ever be a reason to have multiple, unsynchronized threads within a single process (thus circumventing the GIL)? Why not just put thread.wait() statements in key positions in the program logic (presuming thread.wait() isn't a CPU hog, of course)? I understand that certain other languages that use a GIL have processor scheduling issues (cough Python), but they have all been resolved.

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• how to write high quality GUI software with qt?

  - by Opetmar

  I want to write a project using QT library, so after learning the library and mastering it how should I start, what other libraries or things that I should learn? are there any other tools that will help me during the development or tools well help the end user to install the software and using it? What are the things that I should be aware? what are the things that I should avoid so it can run efficiently?

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• UML - Class Diagrams Order -> Products

  - by Phorce

  I have a class diagram that is like this: < Order > (1) CAN HAVE (M) < products > But therefore "Order" has the following: Order_Id Customer_Id Order_date_day Order_date_month Order_date_yeah But I do not know how it would handle the Products? Because, I couldn't have "ProductID" because that would mean that each item in this class would have to have a separate instance for each product (E.g. someone ordered 100 products, but only placed 1 order). Could I have an Product object in class Order? If so, how do you represent that in UML? Thank you

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• Cyclic Dependencies.

  - by PhilCK

  Are cyclic dependencies a common thing in games dev? I ask as I keep getting into situation where I'm using and have been told more than once that they should be avoided. I am wondering if this is just a what people say as a general rule of thumb in the software development business. and that the nature of game programming produces such dependencies. // Foo #include <Bar.hpp> class Foo { bar& m_bar; }; and // Bar class Foo; class Bar { Foo* m_foo; }; I do this alot in Ruby, but dynamic languages are more forgiving in this instance, where as static ones, not so much.

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• String patterns that can be used to filter and group files

  - by Louis Rhys

  One of our application filters files in certain directory, extract some data from it and export a document from the extracted data. The algorithm for extracting the data depends on the file, and so far we use regex to select the algorithm to be used, for example .*\.txt will be processed by algorithm A, foo[0-5]\.xml will be processed by algo B, etc. However now we need some files to be processed together. For example, in one case we need two files, foo.*\.xml and bar.*\.xml. Part of the information to be extracted exist in the foo file, and the other part in the bar file. Moreover, we need to make sure the wild card is compatible. For example, if there are 6 files foo1.xml foo23.xml bar1.xml bar9.xml bar23.xml foo4.xml I would expect foo1 and bar1 to be identified as a group, and foo23 and bar23 as another group. bar9 and foo4 has no pair, so they will not be treated. Now, since the filter is configured by user, we need to have a pattern that can express the above requirement. I don't think you can express meaning like above in standard regex. (foo|bar).*\.xml will match all 6 file above and we can't identify which file is paired for a particular file. Is there any standard pattern that can express it? Or any idea how to modify regex to support this, that can be implemented easily?

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• Gamification: designing cooperation in an RPG like game based on Scrum methodology

  - by Grzegorz Slawecki

  I have implemented with 3 friends a gamified system at my work (development company) which builds an fantasy rpg game over scrum project methodology. Generally, the tasks are the missions, each player is represented by a character. They earn XPs for completing tasks and they advance to the next levels which gives them badges, titles and (this is in planning phase) new privileges (e.g. priority in choosing tasks). Since the very beginning we try to do everything to avoid rivalisation between players because it would ruin the project if the players started to compete. There are no explicit leaderboards, we also plan to give bonuses for helping other players. I have a feeling that this is still not enough to really encourage cooperation. I would like to ask You for any ideas that come to Your mind that would help.

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• Good free CSS Sprite for icons

  - by Saif Bechan

  I am working on a small project where I need some of the basic icons: edit, favorite, delete. You know them. Now i can download them all seperate, and put them together in a sprite, but I was wondering if there are ready to download sprites which I can use. Now I am working on an accounting app, so it would be nice if the icons were not too childish. A little but of fancy business type icons. Thanks

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• Create Outlook Appointments from PowerShell

  - by BuckWoody

  I've been toying around with a script to create a special set of calendar objects in Outlook that show when my SQL Server Agent Jobs are scheduled to run. I haven't finished yet, but I thought I would share the part that creates the Outlook Appointments.I have yet to fill a variable with the start and end times, and then loop through that to create the appointments. I'm thinking I'll make the script below into a function, and feed it those variables in a loop. The script below creates a whole new Calendar Folder in Outlook called "SQL Server Agent Jobs". I also use categories quite a bit, so you'll see that too. Caution: If you plan to play with this script, do it on an isolated workstation, not on your "regular" Outlook calendar. Otherwise, you'll have lots of appointments in there that you don't care about!  # Add a new calendar item to a new Outlook folder called "SQL Server Agent Jobs" $outlook = new-object -com Outlook.Application $calendar = $outlook.Session.folders.Item(1).Folders.Item("SQL Server Agent Jobs") $appt = $calendar.Items.Add(1) # == olAppointmentItem $appt.Start = [datetime]"03/11/2010 11:00" $appt.End = [datetime]"03/11/2009 12:00" $appt.Subject = "JobName" $appt.Location = "ServerName" $appt.Body = "Job Details" $appt.Categories = "SQL server Agent Job" $appt.Save()   Script Disclaimer, for people who need to be told this sort of thing: Never trust any script, including those that you find here, until you understand exactly what it does and how it will act on your systems. Always check the script on a test system or Virtual Machine, not a production system. All scripts on this site are performed by a professional stunt driver on a closed course. Your mileage may vary. Void where prohibited. Offer good for a limited time only. Keep out of reach of small children. Do not operate heavy machinery while using this script. If you experience blurry vision, indigestion or diarrhea during the operation of this script, see a physician immediately.   Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Balancing game difficulty against player progression

  - by Raven Dreamer

  It seems that the current climate of games seems to cater to an obvious progression of player power, whether that means getting a bigger, more explosive gun in Halo, leveling up in an RPG, or unlocking new options in Command and Conquer 4. Yet this concept is not exclusive to video or computer games -- even in Dungeons and Dragons players can strive to acquire a +2 sword to replace the +1 weapon they've been using. Yet as a systems designer, the concept of player progression is giving me headache after headache. Should I balance around the players exact capabilities and give up on a simple linear progression? (I think ESIV:Oblivion is a good example of this) Is it better to throw the players into an "arms race" with their opponents, where if the players don't progress in an orderly manner, it is only a matter of time until gameplay is unbearably difficult? (4th Edition DnD strikes me as a good example of this) Perhaps it would make most sense to untether the core gameplay mechanics from progression at all -- give them flashier, more interesting (but not more powerful!) ways to grow?

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• How is game development different from other software development?

  - by Davy8

  For a solid general purpose software developer, what specifically is different about game development, either fundamentally or just differences in degree? I've done toy games like Tic-tac-toe, Tetris, and a brute-force sudoku solver (with UI) and I'm now embarking on a mid-sized project (mid-sized for being a single developer and not having done many games) and one thing I've found with this particular project is that separation of concerns is a lot harder since everything affects state, and every object can interact with every other object in a myriad of ways. So far I've managed to keep the code reasonably clean for my satisfaction but I find that keeping clean code in non-trivial games is a lot harder than it is for my day job. The game I'm working on is turn-based and the graphics are going to be fairly simple (web-based, mostly through DOM manipulation) so real time and 3d work aren't really applicable to me, but I'd still be interested in answers regarding those if they're interesting. Mostly interested in general game logic though. P.S. Feel free to retag this, I'm not really sure what tags are applicable.

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• Beginning HTML and CSS [closed]

  - by romani

  My goal of learning HTML and CSS is to be able to modify popular scripts such as Wordpress, vBulletin, Drupal, etc. I haven't started yet learning CSS and HTML or XHTML. I see many, many books and tutorials out there so it is difficult to make a choice. I think most of web designers were like me in the past and have read many books. So, could you tell me about 1 good book for HTML and 1 good book for CSS? and if I should read the book from cover to cover or only learning the basics is enough for modifying Wordpress, for example!

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• Permissions and MVC

  - by not-rightfold

  I’m in the progress of developing a web application. This web application is mostly a CRUD interface, although some users are only allowed to perform some actions and see only some parts of views. What would be a reasonable way to handle user permissions, given that some parts of views are not available to users? I was thinking of having a function hasPermission(permission) that returns true iff the current user has the given permission, although it would require conditionals around all parts of views that are only visible to some users. For example: {% if has_permission('view_location') %} {{ product.location }} {% endif %} I’m fearing this will become an ugly and unreadable mess, especially since these permissions can get kind of complicated. How is this problem commonly solved in web applications? I’m considering using Haskell with Happstack or Python with Django.

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• Advantages of Singleton Class over Static Class?

  Point 1) Singleton We can get the object of singleton and then pass to other methods. Static Class We can not pass static class to other methods as we pass objects Point 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed. Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use. Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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• When is a Use Case layer needed?

  - by Meta-Knight

  In his blog post The Clean Architecture Uncle Bob suggests a 4-layer architecture. I understand the separation between business rules, interfaces and infrastructure, but I wonder if/when it's necessary to have separate layers for domain objects and use cases. What added value will it bring, compared to just having the uses cases as "domain services" in the domain layer? The only useful info I've found on the web about a use case layer is an article by Martin Fowler, who seems to contradict Uncle Bob about its necessity: At some point I may run into the problems, and then I'll make a Use Case Controller - but only then. And even when I do that I rarely consider the Use Case Controllers to occupy a separate layer in the system architecture. Edit: I stumbled upon a video of Uncle Bob's Architecture: The Lost Years keynote, in which he explains this architecture in depth. Very informative.

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• How to manage own bots at the server?

  - by Nikolay Kuznetsov

  There is a game server and people can play in game rooms of 2, 3 or 4. When a client connects to server he can send a request specifying a number of people or range he wants to play with. One of this value is valid: {2-4, 2-3, 3-4, 2, 3, 4} So the server maintains 3 separate queues for game room with 2, 3 and 4 people. So we can denote queues as #2, #3 and #4. It work the following way. If a client sends request, 3-4, then two separate request are added to queues #3 and #4. If queue #3 now have 3 requests from different people then game room with 3 players is created, and all other requests from those players are removed from all queues. Right now not many people are online simultaneously, so they apply for a game wait for some time and quit because game does not start in a reasonable time. That's a simple bot for beginning has been developed. So there is a need to patch server code to run a bot, if some one requests a game, but humans are not online. Input: request from human {2-4, 2-3, 3-4, 2, 3, 4} Output: number of bots to run and time to wait for each before connecting, depending on queues state. The problem is that I don't know how to manage bots properly at the server? Example: #3 has 1 request and #4 has 1 request Request from user is {3,4} then server can add one bot to play game with 3 people or two bots to play game of 4. Example: #3 has 1 request and #4 has 2 requests Request from user is {3,4} then in each case just one bot is needed so game with 4 players is more preferrable.

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• How to refactor and improve this XNA mouse input code?

  - by Andrew Price

  Currently I have something like this: public bool IsLeftMouseButtonDown() { return currentMouseState.LeftButton == ButtonState.Pressed && previousMouseSate.LeftButton == ButtonState.Pressed; } public bool IsLeftMouseButtonPressed() { return currentMouseState.LeftButton == ButtonState.Pressed && previousMouseSate.LeftButton == ButtonState.Released; } public bool IsLeftMouseButtonUp() { return currentMouseState.LeftButton == ButtonState.Released && previousMouseSate.LeftButton == ButtonState.Released; } public bool IsLeftMouseButtonReleased() { return currentMouseState.LeftButton == ButtonState.Released && previousMouseSate.LeftButton == ButtonState.Pressed; } This is fine. In fact, I kind of like it. However, I'd hate to have to repeat this same code five times (for right, middle, X1, X2). Is there any way to pass in the button I want to the function so I could have something like this? public bool IsMouseButtonDown(MouseButton button) { return currentMouseState.IsPressed(button) && previousMouseState.IsPressed(button); } public bool IsMouseButtonPressed(MouseButton button) { return currentMouseState.IsPressed(button) && !previousMouseState.IsPressed(button); } public bool IsMouseButtonUp(MouseButton button) { return !currentMouseState.IsPressed(button) && previousMouseState.IsPressed(button); } public bool IsMouseButtonReleased(MouseButton button) { return !currentMouseState.IsPressed(button) && previousMouseState.IsPressed(button); } I suppose I could create some custom enumeration and switch through it in each function, but I'd like to first see if there is a built-in solution or a better way.. Thanks!

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• how do you read from system.out in Java [closed]

  - by Dan

  I'm trying to create a word scramble game and so far I have taken a vector of randomly assorted strings that contains both words and hints and split them into two vectors. I have randomly scrambled the word and set this all up in text boxes. Right now I'm stuck because I have a text box that takes input but I'm not sure how to read that in? I want the user to type the unscrambled word into the text box and have it calculate as correct and move on to the next word immediately. I also don't know how to get the keys working. I want the "?" character to be the hint button that shows the hint. At the moment the hint box works if I type the question mark in using the System.in but it doesn't work if I type it directly in to the text box. The characters are showing up in the text box but nothing is working after that.

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• What to include in metadata?

  - by shyam

  I'm wondering if there are any general guidelines or best practices regarding when to split data into a metadata format, as oppose to directly embedding it within the data. (Specific example below). My understanding of metadata is that it describes data (without the need to actually look at the data), allowing for data to be quickly search/filtered for easy access. Let's take for example a simple 3D model format. The actual data file itself is a binary file containing vertices and colors. Things like creation date, modified data and author name would be things that describe the binary data, so I would say these belong as metadata (outside of the binary file). But what if the application had no need to search or filter by these fields? Would it be acceptable to embed these fields directly into the binary data itself? Could they be duplicated in both the binary data and the meta data, or would this be considered bad practice? What about more ambiguous fields such as the model name, which could be considered part of the data itself, but also as data describing the binary data?... How do you decide which data to embed in the actual binary file, as opposed to separating into a more flexible metadata format? Thanks!

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• Ideas for attack damage algorithm (language irrelevant)

  - by Dillon

  I am working on a game and I need ideas for the damage that will be done to the enemy when your player attacks. The total amount of health that the enemy has is called enemyHealth, and has a value of 1000. You start off with a weapon that does 40 points of damage (may be changed.) The player has an attack stat that you can increase, called playerAttack. This value starts off at 1, and has a possible max value of 100 after you level it up many times and make it farther into the game. The amount of damage that the weapon does is cut and dry, and subtracts 40 points from the total 1000 points of health every time the enemy is hit. But what the playerAttack does is add to that value with a percentage. Here is the algorithm I have now. (I've taken out all of the gui, classes, etc. and given the variables very forward names) double totalDamage = weaponDamage + (weaponDamage*(playerAttack*.05)) enemyHealth -= (int)totalDamage; This seemed to work great for the most part. So I statrted testing some values... //enemyHealth ALWAYS starts at 1000 weaponDamage = 50; playerAttack = 30; If I set these values, the amount of damage done on the enemy is 125. Seemed like a good number, so I wanted to see what would happen if the players attack was maxed out, but with the weakest starting weapon. weaponDamage = 50; playerAttack = 100; the totalDamage ends up being 300, which would kill an enemy in just a few hits. Even with your attack that high, I wouldn't want the weakest weapon to be able to kill the enemy that fast. I thought about adding defense, but I feel the game will lose consistency and become unbalanced in the long run. Possibly a well designed algorithm for a weapon decrease modifier would work for lower level weapons or something like that. Just need a break from trying to figure out the best way to go about this, and maybe someone that has experience with games and keeping the leveling consistent could give me some ideas/pointers.

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• How can I make an MMORPG appeal to casual players?

  - by Philipp

  I believe that there is a significant market of players who would enjoy the exploration and interaction aspects of MMORPGs, but simply don't have the time for the endless grinding marathons which are part of the average MMORPG. MMORPGs are all about interaction between players. But when different players have different amounts of time to invest into a game, those with less time to spend will soon lack behind their power-leveling friends and won't be able to interact with them anymore. One way to solve this would be to limit the progress a player can achieve per day, so that it simply doesn't make sense to play more than one or two hours a day. But even the busiest casual players sometimes like to spend a whole sunday afternoon playing a video game. Just stopping them after two hours would be really frustrating. It also creates a pressure to use the daily progress limit every day, because otherwise the player would feel like wasting something. This pressure would be detrimental for casual gamers. What else could be done to level the playing field between those players who play 40+ hours a week and those who can't play more than 10?

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• CircuitLab Offers Easy Circuit Building on the Web and iPad

  - by Jason Fitzpatrick

  If you like to sketch out your circuit designs rapidly, cleanly, and on the web or your iPad, CircuitLab makes it dead simple. The free tool includes an easy drag-and-drop interface, circuit analysis, easy printing, and more. Watch the video above to see the creators of CircuitLab whipping up a simple circuit to showcase the app, then hit up the link below to try it out. CircuitLab [via Hacked Gadgets] How to Make Your Laptop Choose a Wired Connection Instead of Wireless HTG Explains: What Is Two-Factor Authentication and Should I Be Using It? HTG Explains: What Is Windows RT and What Does It Mean To Me?

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• When to use abstract classes instead of interfaces and extension methods in C#?

  - by Gulshan

  "Abstract class" and "interface" are similar type of ideas, while interface being more abstract. One need of abstract classes was to provide method implementations for the derived classes. But in C#, that need has also been reduced by lately introduced extension methods. So, in C#, when should we use abstract classes instead of using interfaces and extension methods associated with the interface? And now, we can use 'Properties' in interfaces also. A notable example of interface+ extension methods is the Heavily used IEnumerable and it's helper methods. You use Linq and it's all by this extension methods!

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