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  • Podcast interview with Michael Kane

    - by mhornick
    In this podcast interview with Michael Kane, Data Scientist and Associate Researcher at Yale University, Michael discusses the R statistical programming language, computational challenges associated with big data, and two projects involving data analysis he conducted on the stock market "flash crash" of May 6, 2010, and the tracking of transportation routes bird flu H5N1. Michael also worked with Oracle on Oracle R Enterprise, a component of the Advanced Analytics option to Oracle Database Enterprise Edition. In the closing segment of the interview, Michael comments on the relationship between the data analyst and the database administrator and how Oracle R Enterprise provides secure data management, transparent access to data, and improved performance to facilitate this relationship. Listen now...

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  • A new SQL, a new Analysis Services, a new Workshop! #ssas #sql2012

    - by Marco Russo (SQLBI)
    One week ago Microsoft SQL Server 2012 finally debuted with a virtual launch event and you can find many intro sessions there (20 minutes each). There is a lot of new content available if you want to learn more about SQL 2012 and in this blog post I’d like to provide a few link to sessions, documents, bits and courses that are available now or very soon. First of all, the release of Analysis Services 2012 has finally released PowerPivot 2012 (many of us called it PowerPivot v2 before this official name) and also the new Data Mining Add-in for Microsoft Office 2010, now available also for Excel 64bit! And, of course, don’t miss the Microsoft SQL Server 2012 Feature Pack, there are a lot of upgrades for both DBAs and developers. I just discovered there is a new LocalDB version of SQL Express that can run in user mode without any setup. Is this the end of SQL CE? But now, back to Analysis Services: if you want some tutorial on Tabular, the Microsoft Virtual Academy has a whole track dedicated to Analysis Services 2012 but you will probably be interested also in the one about Reporting Services 2012. If you think that virtual is good but it’s not enough, there are plenty of conferences in the coming months – these are just those where I and Alberto will deliver some SSAS Tabular presentations: SQLBits X, London, March 29-31, 2012: if you are in London or want a good reason to go, this is the most important SQL Server event in Europe this year, no doubts about it. And not only because of the high number of attendees, but also because there is an impressive number of speakers (excluding me, of course) coming from all over the world. This is an event second only to PASS Summit in Seattle so there are no good reasons to not attend it. Microsoft SQL Server & Business Intelligence Conference 2012, Milan, March 28-29, 2012: this is an Italian conference so the language might be a barrier, but many of us also speak English and the food is good! Just a few seats still available. TechEd North America, Orlando, June 11-14, 2012: you know, this is a big event and it contains everything – if you want to spend a whole day learning the SSAS Tabular model with me and Alberto, don’t miss our pre-conference day “Using BISM Tabular in Microsoft SQL Server Analysis Services 2012” (be careful, it is on June 10, a nice study-Sunday!). TechEd Europe, Amsterdam, June 26-29, 2012: the European version of TechEd provides almost the same content and you don’t have to go overseas. We also run the same pre-conference day “Using BISM Tabular in Microsoft SQL Server Analysis Services 2012” (in this case, it is on June 25, that’s a regular Monday). I and Alberto will also speak at some user group meeting around Europe during… well, we’re going to travel a lot in the next months. In fact, if you want to get a complete training on SSAS Tabular, you should spend two days with us in one of our SSAS Tabular Workshop! We prepared a 2-day seminar, a very intense one, that start from the simple tabular modeling and cover architecture, DAX, query, advanced modeling, security, deployment, optimization, monitoring, relationships with PowerPivot and Multidimensional… Really, there are a lot of stuffs here! We announced the first dates in Europe and also an online edition optimized for America’s time zone: Apr 16-17, 2012 – Amsterdam, Netherlands Apr 26-27, 2012 – Copenhagen, Denmark May 7-8, 2012 – Online for America’s time zone May 14-15, 2012 – Brussels, Belgium May 21-22, 2012 – Oslo, Norway May 24-25, 2012 – Stockholm, Sweden May 28-29, 2012 – London, United Kingdom May 31-Jun 1, 2012 – Milan, Italy (Italian language) Also Chris Webb will join us in this workshop and in every date you can find who is the speaker on the web site. The course is based on our upcoming book, almost 600 pages (!) about SSAS Tabular, an incredible effort that will be available very soon in a preview (rough cuts from O’Reilly) and will be on the shelf in May. I will provide a link to order it as soon as we have one! And if you think that this is not enough… you’re right! Do you know what is the only thing you can do to optimize your Tabular model? Optimize your DAX code. Learning DAX is easy, mastering DAX requires some knowledge… and our DAX Advanced Workshop will provide exactly the required content. Public classes will be available later this year, by now we just deliver it on demand.

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  • Pure virtual or abstract, what's in a name?

    - by Steven Jeuris
    While discussing a question about virtual functions on Stack Overflow, I wondered whether there was any official naming for pure (abstract) and non-pure virtual functions. I always relied on wikipedia for my information, which states that pure and non-pure virtual functions are the general term. Unfortunately, the article doesn't back it up with a origin or references. To quote Jon Skeet's answer to my reply that pure and non-pure are the general term used: @Steven: Hmm... possibly, but I've only ever seen it in the context of C++ before. I suspect anyone talking about them is likely to have a C++ background :) Did the terms originate from C++, or were they first defined or implemented in a earlier language, and are they the 'official' scientific terms?

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  • See the Geeky Work Done Behind the Scenes to Add Sounds to Movies [Video]

    - by Asian Angel
    Ever wondered about all the work that goes into adding awesome sound effects large and small to your favorite movies? Then here is your chance! Watch as award-winning Foley artist Gary Hecker shows how it is done using the props in his studio. SoundWorks Collection: Gary Hecker – Veteran Foley Artist [via kottke.org & Michal Csanaky] Latest Features How-To Geek ETC What Can Super Mario Teach Us About Graphics Technology? Windows 7 Service Pack 1 is Released: But Should You Install It? How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) How To Remove People and Objects From Photographs In Photoshop Make Efficient Use of Tab Bar Space by Customizing Tab Width in Firefox See the Geeky Work Done Behind the Scenes to Add Sounds to Movies [Video] Use a Crayon to Enhance Engraved Lettering on Electronics Adult Swim Brings Their Programming Lineup to iOS Devices Feel the Chill of the South Atlantic with the Antarctica Theme for Windows 7 Seas0nPass Now Offers Untethered Apple TV Jailbreaking

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  • What Agile Model do you use at Work?

    - by Kyle Rozendo
    I am looking to start pushing for more Agile processes to be brought into play in the work place and do my best to outlaw cowboy coding as much as possible. I understand many of the different models and am just looking to see which model has the higher uptake (or which parts of the model as well), and in what industry it is being used. Extreme Programming (XP) Adaptive Software Development (ASD) Scrum Dynamic Systems Development Model (DSDM) Crystal Feature Driven Development (FDD) Lean Software Development (LSD) Agile Modelling (AM) Agile Unified Process (AUP) Kanban If you care to add to your answer with comments about what you don't like, do like or have tried and it hadn't worked, that would also be appreciated.

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  • Hiring a Junior Developer, What should I ask?

    - by Jeremy
    We are currently hiring a junior developer to help me out, as I have more projects than I can currently manage. I have never hired anyone who wasn't a friend or at least an acquaintance. I have a phone interview with the only applicant that actually stood out to me (on paper), but I have never done this before. Our projects are all high scalability, data intensive web applications that process millions of transactions an hour, across multiple servers and clients. To be language/stack specific, we use ASP.Net MVC2, WebForms and C# 4, MSSQL 2008 R2, all running atop Windows Server 2008 R2 What should I ask him? How should I structure the phone call?

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  • Why Ubuntu Server asks to insert a CD-ROM when installed from PXE?

    - by MainMa
    I set up a PXE server which hosts both Ubuntu Desktop and Ubuntu Server. Ubuntu Desktop is installed successfully from PXE. Ubuntu Server seems to successfully load vmlinuz and initrd.gz, asks for the language, then the location, then the keyboard layout, and finally complains that it can't mount the CD-ROM: The content of /var/lib/tftpboot/pxelinux.cfg/default is the following: default ubuntu-installer/amd64/boot-screens/vesamenu.c32 menu title Ubuntu setup label ubuntu-14.04-desktop-amd64 menu label ubuntu-14.04-desktop-amd64 kernel ubuntu-14.04-desktop-amd64/vmlinuz.efi append initrd=ubuntu-14.04-desktop-amd64/initrd.lz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.1.41:/exports/ubuntu-14.04-desktop-amd64 splash -- label ubuntu-14.04-server-amd64 menu label ubuntu-14.04-server-amd64 kernel ubuntu-14.04-server-amd64/vmlinuz append initrd=ubuntu-14.04-server-amd64/initrd.gz root=/dev/nfs boot=install netboot=nfs nfsroot=192.168.1.41:/exports/ubuntu-14.04-server-amd64 splash -- What explains the fact that it requests the CD-ROM and how to avoid it?

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  • How to render axometric/isometric tiles that are a 2d array in logic, but inclined 45º visually?

    - by TheLima
    I am making a tile-based strategy game which i plan to have 2.5D visuals in an axometric/isometric fashion. Right now i'm programming it's logic and rendering it as a literal 2-dimensional array (perfect squares, like an isometric top-down-view). In short, i have something like this: And i want to turn it to something like this: Do i keep going on the 2d-array logic? Is it all just a change in rendering behavior, as i'm thinking it is? or 2d-array is the wrong approach for my objective and I should change before it's too late? What are the ways of doing it, anyways? How should i apply the 2.5D axometric/isometric view (45º rotation to the side, and 45º rotation upwards)?

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  • What do neglected O'Reilly book topics tell us about that topic?

    - by Peter Turner
    Does anybody know how O'Reilly chooses topics to publish? For some reason, I don't see how it can be based on demand. The reason, I ask, is because they haven't published a Delphi book in almost 12 years and Object Pascal is at least as esoteric as Erlang and as practical as PHP and as robust as C++. So, maybe someone knows what rationale is behind O'Reilly's publishing methodology or what it is supposed to tell us about the relative popularity or usefulness of any given language or programming technique? Oh, I forgot about pig and robotlegs

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  • Why does Clojure neglect the uniform access principle?

    - by Alexey
    My background is Ruby, C#, JavaScript and Java. And now I'm learning Clojure. What makes me feel uncomfortable about the later is that idiomatic Clojure seems to neglect the Uniform access principle (wiki, c2) and thus to a certain degree encapsulation as well by suggesting to use maps instead of some sort of "structures" or "classes". It feels like step back. So a couple of questions, if anyone informed: Which other design decisions/concerns it conflicted with and why it was considered less important? Did you have the same concern as well and how it end up when you switched from a language supporting UAP by default (Ruby, Eiffel, Python, C#) to Clojure?

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  • Rhythmbox not saving the album art permanently

    - by Nik
    I run ubuntu 10.10 and use rhythmbox (version 0.13.1) regularly with the albumartsearch plugin installed. However when I change the album art it is only temporary. On moving to the next song it automatically removes the previous song's album art cover. (I do know about banshee but would like to use rhythmbox). The cover art plugin is also installed by default however it cannot display some of the album covers since the songs are in my local language (tamil) hence it cannot retrieve the album cover from the internet. However the albumartsearch plugin seems to do the job although only temporarily. Any reason why it might be? I have tried looking for other rhythmbox plugins which might be similar to albumartsearch but in vain. Any help would be appreciated. I have filed a bug in the albumartsearch plugin's website. Waiting for the reply.

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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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  • Adaptative interface with Open GL and machine learning in C#

    - by Afnan
    For my Semester project I have to go for any Adaptative Interface Design. My language is C# and I have to Use OpenTK (wrapper for OpenGL). I have an idea that I should show two points and some obstacles and my subject (user) would drag an object from one place to the final place avoiding the Obstacles. Also (s)he can place obstacles randomly. My software should be able to learn some paths by doing test runs and then after learning it should be able to predict the shortest path. I do not know how stupid this idea sounds but it is just an idea. I need help regarding any ideas for adaptative interface possible small projects or if my idea is ok then please can you tell me what should be used to implement it? I mean that along with OpenGl for the Graphics what can I use for machine learning?

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  • 'Development dashboard' web application

    - by espais
    Hi all, I am not sure if something like this exists in that it is ready out of the box. I currently have some web space that I use for various projects, and I would like to setup an area for some friends and I to develop web applications together. My ideal setup would be to create a folder, say, webdev.domain.com. We could all go to this domain, login, and then be able to setup new applications, pick which language will be used, setup database tables, allow HTML based file uploading, and create sub-folders to basically have a test bed for the applications. In retrospect, it seems like I'm describing a limited version of cpanel. I could come up with something in Drupal I'm sure, but I don't want to have to really spend time configuring much. Like I said, I want to install it and have minimal configuration. Does something like this exist (preferably in open-source)?

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  • Passing the CAML thru the EY of the NEEDL

    - by PointsToShare
    © 2011 By: Dov Trietsch. All rights reserved Passing the CAML thru the EY of the NEEDL Definitions: CAML (Collaborative Application Markup Language) is an XML based markup language used in Microsoft SharePoint technologies  Anonymous: A camel is a horse designed by committee  Dov Trietsch: A CAML is a HORS designed by Microsoft  I was advised against putting any Camel and Sphinx rhymes in here. Look it up in Google!  _____ Now that we have dispensed with the dromedary jokes (BTW, I have many more, but they are not fit to print!), here is an interesting problem and its solution.  We have built a list where the title must be kept unique so I needed to verify the existence (or absence) of a list item with a particular title. Two methods came to mind:  1: Span the list until the title is found (result = found) or until the list ends (result = not found). This is an algorithm of complexity O(N) and for long lists it is a performance sucker. 2: Use a CAML query instead. Here, for short list we’ll encounter some overhead, but because the query results in an SQL query on the content database, it is of complexity O(LogN), which is significantly better and scales perfectly. Obviously I decided to go with the latter and this is where the CAML s--t hit the fan.   A CAML query returns a SPListItemCollection and I simply checked its Count. If it was 0, the item did not already exist and it was safe to add a new item with the given title. Otherwise I cancelled the operation and warned the user. The trouble was that I always got a positive. Most of the time a false positive. The count was greater than 0 regardles of the title I checked (except when the list was empty, which happens only once). This was very disturbing indeed. To solve my immediate problem which was speedy delivery, I reverted to the “Span the list” approach, but the problem bugged me, so I wrote a little console app by which I tested and tweaked and tested, time and again, until I found the solution. Yes, one can pass the proverbial CAML thru the ey of the needle (e’s missing on purpose).  So here are my conclusions:  CAML that does not work:  Note: QT is my quote:  char QT = Convert.ToChar((int)34); string titleQuery = "<Query>><Where><Eq>"; titleQuery += "<FieldRef Name=" + QT + "Title" + QT + "/>"; titleQuery += "<Value Type=" + QT + "Text" + QT + ">" + uniqueID + "</Value></Eq></Where></Query>"; titleQuery += "<ViewFields><FieldRef Name=" + QT + "Title" + QT + "/></ViewFields>";  Why? Even though U2U generates it, the <Query> and </Query> tags do not belong in the query that you pass. Start your query with the <Where> clause.  Also the <ViewFiels> clause does not belong. I used this clause to limit the returned collection to a single column, and I still wish to do it. I’ll show how this is done a bit later.   When you use the <Query> </Query> tags in you query, it’s as if you did not specify the query at all. What you get is the all inclusive default query for the list. It returns evey column and every item. It is expensive for both server and network because it does all the extra processing and eats plenty of bandwidth.   Now, here is the CAML that works  string titleQuery = "<Where><Eq>"; titleQuery += "<FieldRef Name=" + QT + "Title" + QT + "/>"; titleQuery += "<Value Type=" + QT + "Text" + QT + ">" + uniqueID + "</Value></Eq></Where>";  You’ll also notice that inside the unusable <ViewFields> clause above, we have a <FieldRef> clause. This is what we pass to the SPQuery object. Here is how:  SPQuery query = new SPQuery(); query.Query = titleQuery; query.ViewFields = "<FieldRef Name=" + QT + "Title" + QT + "/>"; query.RowLimit = 1; SPListItemCollection col = masterList.GetItems(query);  Two thing to note: we enter the view fields into the SPQuery object and we also limited the number of rows that the query returns. The latter is not always done, but in an existence test, there is no point in returning hundreds of rows. The query will now return one item or none, which is all we need in order to verify the existence (or non-existence) of items. Limiting the number of columns and the number of rows is a great performance enhancer. That’s all folks!!

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  • O&rsquo;Reilly Deal of the Day 4/Aug/2014 - Windows PowerShell 4.0 for .NET Developers

    - by TATWORTH
    Originally posted on: http://geekswithblogs.net/TATWORTH/archive/2014/08/04/orsquoreilly-deal-of-the-day-4aug2014---windows-powershell-4.0.aspxToday’s half-price Deal of the Day from O’Reilly at http://shop.oreilly.com/product/9781849688765.do?code=MSDEAL is Windows PowerShell 4.0 for .NET Developers. “The world of technology is growing faster than ever, and the business needs are getting more complex every day. With PowerShell in your toolbox, you have an object-based scripting language, task-based shell, along with a powerful automation engine. PowerShell is built on top of .NET framework which gives an edge over the other tools when it comes to integration and automation of Microsoft product and technologies.”

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  • A Quick Primer on SharePoint Customization

    - by PeterBrunone
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";} This one goes out to all the people who have been asked to change the way a SharePoint site looks.  Management wants to know how long it will take, and you can whip that out by tomorrow, right?  If you don't have time to prepare a treatise on what's involved, or if you just want to lend some extra weight to your case by quoting a blogger who was an MVP for seven years, then dive right in; this post is for you. There are three main components of SharePoint visual customization:   1)       Theme – A theme encompasses all the standardized text formatting and coloring (borders, fonts, etc), including the background images of various sections. All told, there could be around 50 images involved, and a few hundred CSS (style) classes.  Installing a theme once it’s been created is no great feat.  Given the number of pieces, of course, creating a new theme could take anywhere from a day to a week… once decisions have been made about the desired appearance. 2)      Master Page – A master page provides the framework for page layout.  This includes all the top and side menus, where content shows up, et cetera.  Master pages have been around for a long time in ASP.NET (Microsoft’s web development platform), and they do require some .NET programming knowledge.  Beyond that, in SharePoint, there are a few dozen controls which the system expects find on a given page.  They’re not all used at once, but if they’re not there when they’re needed, chaos ensues.  Estimating a custom master page is difficult, as it depends on the level of customization.  I’ve been on projects where I was brought in simply to fix some problems and add a few finishing touches, and it took 2-3 weeks.  Master page customization requires a large amount of testing time to make sure that the HTML, JavaScript, CSS, and control placement all work well together. 3)      Individual page layout – Each page (ideally) uses a master page for its template, but within the content areas defined by the master page, web parts can be added, removed, and configured from within the browser.  The wireframe that Brent provided could most likely be completed simply by manipulating the content on the home page in this fashion, and we had allowed about a day of effort for the task.  If needed, further functionality can be provided by an experienced ASP.NET developer; custom forms are a common example.  This of course is a bit more in-depth than simple content manipulation and could take several days per page (or more; there’s really no way to quantify this without a set of requirements).   That’s basically it.  To recap:  Fonts and coloring are done with themes, and can take anywhere from a day to a week to create (not counting creative time); required technical skills include HTML, CSS, and image manipulation.  Templated layout is done with master pages, and generally requires a developer familiar with both ASP.NET and SharePoint in particular; it can have far-reaching consequences depending on the complexity of the changes, and could add weeks or months to a project.  Page layout can be as simple as content manipulation in the web browser, taking a few hours per page, or it can involve more detail, like custom forms, and can require programming expertise and significantly more development time.

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  • How I understood monads, part 1/2: sleepless and self-loathing in Seattle

    For some time now, I had been noticing some interest for monads, mostly in the form of unintelligible (to me) blog posts and comments saying oh, yeah, thats a monad about random stuff as if it were absolutely obvious and if I didnt know what they were talking about, I was probably an uneducated idiot, ignorant about the simplest and most fundamental concepts of functional programming. Fair enough, I am pretty much exactly that. Being the kind of guy who can spend eight years in college just to...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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  • 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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  • 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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  • Lua & Javascript documentation generation

    - by Tiddo
    I am in the beginning phase of create a mobile MMO with my team. The server software will be written in JavaScript using NodeJS, and the client software in Lua using Corona. We need a tool to auto-generate documentation for both the server-side and client-side code. Are there any tools which can generate documentation for both Lua and Javascript? And as a bonus: we are hosting our project on Bitbucket and the Bitbucket Wiki uses the Creole markup language. So if it's possible I want the tool to export to Creole.

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  • Internationalization of non-english application

    - by Jacket
    I know there are lots of posts for internationalization, but this is something I didn't found while searching. I have a PHP Web application, which is pretty big right now. It's developed actively for 4 years and wasn't built with internationalization in mind. Text is everywhere - in plain HTML, in PHP variables, in echo's, in the DB... Now I'm familiar with the concept of gettext and this is what i plan to use for the internationalization project of the application. However the app is not written in English and here is my question: Should I first translate everything to English while wrapping every string in gettext() function, or I can use my native language as a base? P.S. also any quick suggestions (links maybe) on making my life easier with the whole i18n project will be greatly appreciated!

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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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  • AJI Report with Nat Ryan&ndash;Discussion about Game Development with Corona Labs SDK

    - by Jeff Julian
    We sat down with Nat Ryan of Fully Croisened to talk about Game Development and the Corona Labs framework. The Corona SDK is a platform that allows you to write mobile games or applications using the Lua language and deploy to the iOS and Android platforms. One of the great features of Corona is the compilation output is a native application and not a hybrid application. Corona is very centered around their developer community and there are quite a few local meetups focused on the helping other developers use the platform. The community and Corona site offers a great number of resources and samples that will help you get started in a matter of a few days. If you are into Game Development and want to move towards mobile, or a business developer looking to turn your craft back into a hobby, check out this recording and Corona Labs to get started.   Download the Podcast   Site: AJI Report – @AJISoftware Site: Fully Croisened Twitter: @FullyCroisened Site: Corona Labs

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  • The Frustrations of Resetting Your Password Online [Video]

    - by Asian Angel
    We have all been there…finding ourselves needing to reset a password and suffering through the process of creating a password that the online service will accept. You will certainly feel some sympathy watching this young woman reset the password for her favorite web service before she can log in and have fun. Note: Video contains some language that may be considered inappropriate. Have you had similar bad or extremely frustrating experiences while resetting a password? Let us know in the comments! Reset Your Password [via MakeUseOf] HTG Explains: What Is RSS and How Can I Benefit From Using It? HTG Explains: Why You Only Have to Wipe a Disk Once to Erase It HTG Explains: Learn How Websites Are Tracking You Online

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