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  • Making Modular, Reusable and Loosely Coupled MVC Components

    - by Dusan
    I am building MVC3 application and need some general guidelines on how to manage complex client side interaction between my components. Here is my definition of one component in general way: Component which has it's own controller, model and view. All of the component's logic is placed inside these three parts and component is sort of "standalone", it contains it's own form, data needed for interaction, updates itself with Ajax and so on. Beside this internal logic and behavior of the component, it needs to be able to "Talk" to the outside world. By this I mean it should provide data and events (sort of) so when this component gets embedded in pages can notify other components which then can update based on the current state and data. I have an idea to use client ViewModel (in java-script) which would hookup all relevant components on page and control interaction between them. This would make components reusable, modular - independent of the context in which they are used. How would you do this, I am a bit stuck as I do not know if this is a good approach and there is a technical possibility to achieve this using java-script/jquery. The confusing part is about update via Ajax, how to ensure that component is properly linked to ViewModel when component is Ajax updated (or even worse removed or dynamically added). Also, how should this ViewModel be constructed and which technicalities to use here and in components to work as synergy??? On the web, I have found the various examples of the similar approach, but they are oversimplified (even for dummies) or over specific and do not provide valuable resource or general solution for this kind of implementation. If you have some serious examples it would be, also, very helpful. Note: My aim is to make interactions between many components on the same page simpler and more robust and elegant.

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  • Ninject/DI: How to correctly pass initialisation data to injected type at runtime

    - by MrLane
    I have the following two classes: public class StoreService : IStoreService { private IEmailService _emailService; public StoreService(IEmailService emailService) { _emailService = emailService; } } public class EmailService : IEmailService { } Using Ninject I can set up bindings no problem to get it to inject a concrete implementation of IEmailService into the StoreService constructor. StoreService is actually injected into the code behind of an ASP.NET WebForm as so: [Ninject.Inject] public IStoreService StoreService { get; set; } But now I need to change EmailService to accept an object that contains SMTP related settings (that are pulled from the ApplicationSettings of the Web.config). So I changed EmailService to now look like this: public class EmailService : IEmailService { private SMTPSettings _smtpSettings; public void SetSMTPSettings(SMTPSettings smtpSettings) { _smtpSettings = smtpSettings; } } Setting SMTPSettings in this way also requires it to be passed into StoreService (via another public method). This has to be done in the Page_Load method in the WebForms code behind (I only have access to the Settings class in the UI layer). With manual/poor mans DI I could pass SMTPSettings directly into the constructor of EmailService and then inject EmailService into the StoreService constructor. With Ninject I don't have access to the instances of injected types outside of the objects they are injected to, so I have to set their data AFTER Ninject has already injected them via a separate public setter method. This to me seems wrong. How should I really be solving this scenario?

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  • Website Ethics / legal issues, image copyrights

    - by RailsN00b
    Ignoring the technical implementation of a website for a second, assume a website that is similar to twitter but with pictures. A user say something and puts a picture of whatever they said. As the nature of the internet, the images will most likely not be his/hers image. There are 2 options that I see for dealing with this: 1. The user will post a URL of the picture and the website will pull the picture from that URL everytime someone enters that page 2. The website will save the image in its own database of images and display the image to the visitors 'locally' The problem with option #1, while it saved storage, I see an issue with 'stealing' other websites bandwidth and if my website has many many visitors it could cost the image-hosting websites a lot and possible even crash it if the server can't handle the load. The problem with opion #2, while it saves the load to other websites, it practically takes pictures that could have copyright on them. Which option is better to implement in terms of legal issues and ethics? When do I need to contact another website to request permission to use the images from that site? Does anyone really care about that anymore. Where can I read about this?

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  • Is there such thing as a "theory of system integration"?

    - by Jeff
    There is a plethora of different programs, servers, and in general technologies in use in organizations today. We, programmers, have lots of different tools at our disposal to help solve various different data, and communication challenges in an organization. Does anyone know if anyone has done an serious thinking about how systems are integrated? Let me give an example: Hypothetically, let's say I own a company that makes specialized suits a'la Iron Man. In the area of production, I have CAD tools, machining tools, payroll, project management, and asset management tools to name a few. I also have nice design space, where designers show off their designs on big displays, some touch, some traditional. Oh, and I also have one of these new fangled LEED Platinum buildings and it has number of different computer controlled systems, like smart window shutters that close when people are in the room, a HVAC system that adjusts depending on the number of people in the building, etc. What I want to know is if anyone has done any scientific work on trying to figure out how to hook all these pieces together, so that say my access control system is hooked to my payroll system, and my phone system allowing my never to swipe a time card, and to have my phone follow me throughout the building. This problem is also more than a technology challenge. Every technology implementation enables certain human behaviours, so the human must also be considered as a part of the system. Has anyone done any work in how effectively weave these components together? FYI: I am not trying to build a system. I want to know if anyone has thoroughly studied the process of doing a large integration project, how they develop their requirements, how they studied the human behaviors, etc.

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  • Price Drop for Processor based License on Exalytics

    - by Mike.Hallett(at)Oracle-BI&EPM
    ·       33% reduction in the list `per processor` license pricing for the Oracle BI Foundation Suite ·       New capacity-based licensing which allows customers to think big & start small, significantly lowering the entry price point for an Exalytics. Oracle BI Software List Price changes In response to new powerful platforms like the in-memory Oracle Exalytics with 40 cpu cores (counted under Oracle pricing policy as 20 “processors”), the list price of “Oracle BI Foundation Suite” (BIFS) is reduced by 33% from $450K per processor to $300K per processor. Capacity-based licensing on Exalytics (Trusted Partitions) “Capacity-based pricing” for the BIFS, Endeca, Essbase and Times Ten for Exalytics software is now available for Exalytics systems. This is delivered using “Oracle VM” (OVM).  We still ship a full Exalytics machine to all customers, but they may choose to only use and license a subset of the processors installed in the machine.   Customers can license Exalytics software in units of 5 “processors”: 5, 10, 15 or the full capacity 20.   As the customer’s implementation and workload increases, it is a simple matter to license additional processors and, using OVM, make them available to the BI or EPM application. Endeca Information Discovery now available on Exalytics Oracle has also announced the certification of “Oracle Endeca Information Discovery” (EID) on the Exalytics machine.    EID can be licensed alone or in combination with the BIFS & Times Ten for an Exalytics stack, and also participates in the capacity based pricing outlined above.   The Exalytics hardware is the perfect platform for EID, and provides superb power and performance for this in-memory hybrid text-search-analytics.   For more information : Oracle Price lists Oracle Partitioning Policy Discussion by Mark Rittman (Rittman Mead Consulting ltd.) on Oracle Trusted Partitions for Oracle Engineered Systems, Oracle Exalytics and Updated BI Foundation Pricing.

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  • Should I use an interface when methods are only similar?

    - by Joshua Harris
    I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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  • Floating point undesireable in highly critical code?

    - by Kirt Undercoffer
    Question 11 in the Software Quality section of "IEEE Computer Society Real-World Software Engineering Problems", Naveda, Seidman, lists fp computation as undesirable because "the accuracy of the computations cannot be guaranteed". This is in the context of computing acceleration for an emergency braking system for a high speed train. This thinking seems to be invoking possible errors in small differences between measurements of a moving object but small differences at slow speeds aren't a problem (or shouldn't be), small differences between two measurements at high speed are irrelevant - can there be a problem with small roundoff errors during deceleration for an emergency braking system? This problem has been observed with airplane braking systems resulting in hydroplaning but could this actually happen in the context of a high speed train? The concern about fp errors seems to not be well-founded in this context. Any insight? The fp is used for acceleration so perhaps the concern is inching over a speed limit? But fp should be just fine if they use a double in whatever implementation language. The actual problem in the text states: During the inspection of the code for the emergency braking system of a new high speed train (a highly critical, real-time application), the review team identifies several characteristics of the code. Which of these characteristics are generally viewed as undesirable? The code contains three recursive functions (well that one is obvious). The computation of acceleration uses floating point arithmetic. All other computations use integer arithmetic. The code contains one linked list that uses dynamic memory allocation (second obvious problem). All inputs are checked to determine that they are within expected bounds before they are used.

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  • Linking Libraries in iOS?

    - by Bob Dole
    This is probably a totally noob question but I have missing links in my mind when thinking about linking libraries in iOS. I usually just add a new library that's been cross compiled and set the build and linker paths without really know what I'm doing. I'm hoping someone can help me fill in some gaps. Let's take the OpenCV library for instance. I have this totally working btw because of a really well written tutorial( http://niw.at/articles/2009/03/14/using-opencv-on-iphone/en ), but I'm just wanting to know what is exactly going on. What I'm thinking is happening is that when I build OpenCV for iOS is that your creating object code that gets placed in the .a files. This object code is just the implementation files( .m ) compiled. One reason you would want to do this is to make it hard to see the source code and so that you don't have to compile that source code every time. The .h files won't be put in the library ( .a ). You include the .h in your source files and these header files communicate with the object code library ( .a ) in some way. You also have to include the header files for your library in the Build Path and the Library itself in the Linker Path. So, is the way I view linking libraries correct? If , not can someone correct me on this ?

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  • BPM Solution Catalogue–promote your process templates

    - by JuergenKress
    Oracle’s BPM Solution Catalogue showcasing our solutions with partners is now live. Take a look at the initial entries here. We are planning to use this catalogue not only to publish and highlight successful BPM implementations but also will be running campaigns in industry verticals with your solutions. If you have delivered a successful implementation in BPM and think it could be reused and applied again in a similar scenario in the same industry or in a similar environment, then we are keen to know about it and will add it to the solution catalogue. The solution catalogue will showcase successful BPM solutions both inside and outside Oracle. Be in touch with us on this via this e-mail id and we will make sure to add your solution. For more information you can also read the article “Leading-Edge BPM Benefits Without Bleeding-Edge Pain” SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit  www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Mix Forum Technorati Tags: BPM,Solution Catalogue,process templates,BPM Suite,SOA Community,Oracle SOA,Oracle BPM,Community,OPN,Jürgen Kress

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  • Should you create a class within a method?

    - by Amndeep7
    I have made a program using Java that is an implementation of this project: http://nifty.stanford.edu/2009/stone-random-art/sml/index.html. Essentially, you create a mathematical expression and, using the pixel coordinate as input, make a picture. After I initially implemented this in serial, I then implemented it in parallel due to the fact that if the picture size is too large or if the mathematical expression is too complex (especially considering the fact that I made the expression recursively), it takes a really long time. During this process, I realized that I needed two classes which implemented the Runnable interface as I had to put in parameters for the run method, which you aren't allowed to do directly. One of these classes ended up being a medium sized static inner class (not large enough to make an independent class file for it though). The other though, just needed a few parameters to determine some indexes and the size of the for loop that I was making run in parallel - here it is: class DataConversionRunnable implements Runnable { int jj, kk, w; DataConversionRunnable(int column, int matrix, int wid) { jj = column; kk = matrix; w = wid; } public void run() { for(int i = 0; i < w; i++) colorvals[kk][jj][i] = (int) ((raw[kk][jj][i] + 1.0) * 255 / 2.0); increaseCounter(); } } My question is should I make it a static inner class or can I just create it in a method? What is the general programming convention followed in this case?

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  • Using a permutation table for simplex noise without storing it

    - by J. C. Leitão
    Generating Simplex noise requires a permutation table for randomisation (e.g. see this question or this example). In some applications, we need to persist the state of the permutation table. This can be done by creating the table, e.g. using def permutation_table(seed): table_size = 2**10 # arbitrary for this question l = range(1, table_size + 1) random.seed(seed) # ensures the same shuffle for a given seed random.shuffle(l) return l + l # see shared link why l + l; is a detail and storing it. Can we avoid storing the full table by generating the required elements every time they are required? Specifically, currently I store the table and call it using table[i] (table is a list). Can I avoid storing it by having a function that computes the element i, e.g. get_table_element(seed, i). I'm aware that cryptography already solved this problem using block cyphers, however, I found it too complex to go deep and implement a block cypher. Does anyone knows a simple implementation of a block cypher to this problem?

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  • In MVC, why can't a model create a view?

    - by MUY Belgium
    I have a web application written in Perl with a controller, some "views" and some "Models". Each "Model" is corresponding to one "View". The controller (one file) creates an Model object corresponding to each view (view is a CGI argument) then retrieve the view from the module it has just created. Indeed, this should be bad thing but can you argue a bit more about it. My first idea was that since the object "Model" depends upon the "view", then the "model" is actually a view. But also the fact that ALL the cgi parameters are passed to the Model causes the "Model" to become not truelly a view but to loose all interest, since it is only related to the current implementation of the web apps. On other words, that the "Model" keep model but loose its "comprehensiveness" ("Model" is not easily understandable). I'm am quite new in project analysis, so please do not be too harsh. Why is this bad? I have made a prototype with the main structures I have understood of this web application, made as short as possible. #Model.pm package Model; import { # this requires an attribute called "view" # and this require an argument which is the cgi params } ... #View1.pm package View1; ... #Model1.pm package ModelView1 ; base Model; use View1; sub new { my $class = shift; my $arg = shift; Model::DoSomething($arg); $self->view = new View1($arg); ... } #controller.cgi my $model = 0; ... $model = new Model1( cgi_param => params() ); #there is severall models here ... print $model->get_view()->get_html();

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  • Choosing open source vs. proprietary CMS

    - by jkneip
    Hi- I've been tasked with redesigning a website for a small academic library. While only in charge of the site for 6 months, we've been maintaining static html pages edited in Dreamweaver for years. Last count of our total pages is around 400. Our university is going with an enterprise level solution called Sitefinity, although we maintain our own domain and are responsible to maintain our own presense. Some background-my library has a couple Microsoft IIS servers on which this static html site has been running. I'm advocating for the implementation of a CMS while doing this redesign. The problem is I'm basically the lone webmaster so I have no one to agree or disagree with my choice. There are also only 1-2 content editors right know for the site but a CMS could change that factor. I would like to use the functionality of having servers that run .NET and MS SQL but am more experience setting up and maintaining open source software like Wordpress or Drupal on web hosts. My main concern is choosing a CMS that will be easy to update / maintain / deal with upgrades (i.e., support) in case I'm not there in the future. So I'm wondering how to factor in the open source CMS vs. a relatively inexpensive commercial CMS decision and whether choosing PHP/MySQL vs. ASP.net framework for development environment will play into my decision. Thanks for any input that can be offered based on the details I've given. Thanks, Jason

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  • The most mind-bending programming language? [closed]

    - by Xepoch
    From a reasonably common programming language, which do you find to be the most mind-bending? I have been listening to a lot of programming podcasts and taking some time to learn some new languages that are being considered upcoming, and important. I'm not necessarily talking about BrainFuck, but which language would you consider to be one that challenges the common programming paradigms? For me, I did some functional and logic (ex. Prolog) programming in the 90s, so can't say that I find anything special there. I am far from being an expert in it, but even today the most mind-bending programming language for me is Perl. Not because "Hello World" is hard to implement but rather there is so much lexical flexibility that some of the hardest solutions can be decomposed so poetically that I have to walk outside away from my terminal to clear my head. I'm not saying I'd likely sell a commercial software implementation, just that there is a distinct reason Perl is so (in)famous. Just look at the basic list of books on it. So, what is your mind-bending language that promotes your better programming and practices?

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  • Using runtime generic type reflection to build a smarter DAO

    - by kerry
    Have you ever wished you could get the runtime type of your generic class? I wonder why they didn’t put this in the language. It is possible, however, with reflection: Consider a data access object (DAO) (note: I had to use brackets b/c the arrows were messing with wordpress): public interface Identifiable { public Long getId(); } public interface Dao { public T findById(Long id); public void save(T obj); public void delete(T obj); } Using reflection, we can create a DAO implementation base class, HibernateDao, that will work for any object: import java.lang.reflect.Field; import java.lang.reflect.ParameterizedType; public class HibernateDao implements Dao { private final Class clazz; public HibernateDao(Session session) { // the magic ParameterizedType parameterizedType = (ParameterizedType) clazz.getGenericSuperclass(); return (Class) parameterizedType.getActualTypeArguments()[0]; } public T findById(Long id) { return session.get(clazz, id); } public void save(T obj) { session.saveOrUpdate(obj); } public void delete(T obj) { session.delete(obj); } } Then, all we have to do is extend from the class: public class BookDaoHibernateImpl extends HibernateDao { }

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  • sqlplus: Running "set lines" and "set pagesize" automatially

    - by katsumii
    This is a followup to my previous entry. Using the full tty real estate with sqlplus (INOUE Katsumi @ Tokyo) 'rlwrap' is widely used for adding 'sqlplus' the history function and command line editing. Here's another but again kludgy implementation. First this is the alias. alias sqlplus="rlwrap -z ~/sqlplus.filter sqlplus" And this is the file content. #!/usr/bin/env perl use lib ($ENV{RLWRAP_FILTERDIR} or "."); use RlwrapFilter; use POSIX qw(:signal_h); use strict; my $filter = new RlwrapFilter; $filter -> prompt_handler(\&prompt); sigprocmask(SIG_UNBLOCK, POSIX::SigSet->new(28)); $SIG{WINCH} = 'winchHandler'; $filter -> run; sub winchHandler { $filter -> input_handler(\&input); sigprocmask(SIG_UNBLOCK, POSIX::SigSet->new(28)); $SIG{WINCH} = 'winchHandler'; $filter -> run; } sub input { $filter -> input_handler(undef); return `resize |sed -n "1s/COLUMNS=/set linesize /p;2s/LINES=/set pagesize /p"` . $_; } sub prompt { if ($_ =~ "SQL> ") { $filter -> input_handler(\&input); $filter -> prompt_handler(undef); } return $_; } I hope I can compare these 2 implementations after testing more and getting some feedbacks.

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  • Can JSON be made easily and safely editable by the non-technical Excel crowd?

    - by glitch
    I'm looking for a data storage format that's very intuitive and easy to edit. It should be ideally targeted towards the same crowd as Excel. At the same time I would like the data structure to be a tree. Ideally this would be JSON, since it offers both the tree aspect and allows for more interesting constructs like arrays. That and parsing libraries for JSON are ubiquitous, so I don't have to reinvent the wheel. The problem is that, at least with a non-specialized text editor, JSON is a giant pain to edit for a non-technical user. I'm thinking along the lines of someone who might have used Excel in the past, but never a real text editor. Someone who might not be comfortable with the idea of preserving JSON syntax by hand. Are there data formats out there that would fit this profile? I'd very much prefer this to be a JSON actually, but then it would require a solid editing tool that would hide the underlying implementation from the user. Think Excel and how it abstracts CSV syntax from the user. The reason I'm looking for something like this is because the team has been working with pretty hierarchical data for a while now and we've hit the limits of how easy it is to represent in simple CSVs without having to create complex rules for how represent hierarchy semantics from each row. Any suggestions?

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  • ArchBeat Link-o-Rama for December 4, 2012

    - by Bob Rhubart
    Exalogic 2.0.1 Tea Break Snippets - Creating and using Distribution Groups | The Old Toxophilist "Although in many cases we, as Cloud Users, may not be to worried how the Virtualisation Algorithm decides where to place our vServers," says The Old Toxopholist, "there are cases where it is extremely important that vServers run on distinct physical compute nodes." There's plenty more on the subject in his blog post. Oracle Endeca (2.3) Record Level Security | Adam Seed Adam Sneed's blog post covers "the basics of security within Endeca Information Discovery, as these basic security objects are required in order to explain the implementation of record level security." ODI Handling DQ | Gurcan Orhan Oracle ACE Director Gurcan Orhan suggests you have fun with these scripts for Oracle Data Integrator. Parleys Testimonial at GlassFish Community Event - JavaOne 2012 Video of Parley's webmaster Stephan Janssen's presentation at the GlassFish Community Event at JavaOne 2012, in which he explains why Parley's moved from Tomcat to GlassFish. Java Spotlight Episode 109: Pete Muir on CDI 1.1 This edition of Roger Brinkley's Java Spotlight Podcast features an interview with CDI 1.1 spec lead Pete Muir of JBoss/Red Hat. Muir talks about the features in CDI 1.1 and what to expect in the future. Webcast: Java Management Extensions with Oracle WebLogic Server 12c Dr. Frank Munz and Dave Cabelus do the talking in this on-demand webcast focused on Oracle WebLogic Server 12c with Java Management Extensions (JMX). Using the Coherence API to get Portable Object Format bytes | Bruno Borges Bruno Borges shares a code snippet that illustrates how easy it is to use the Coherence API. Thought for the Day "Experience is something you don't get until just after you need it." — Anonymous Source: SoftwareQuotes.com

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  • Architecture of an action multiplayer game from scratch

    - by lcf
    Not sure whether it's a good place to ask (do point me to a better one if it's not), but since what we're developing is a game - here it goes. So this is a "real-time" action multiplayer game. I have familiarized myself with concepts like lag compensation, view interpolation, input prediction and pretty much everything that I need for this. I have also prepared a set of prototypes to confirm that I understood everything correctly. My question is about the situation when game engine must be rewind to the past to find out whether there was a "hit" (sometimes it may involve the whole 'recomputation' of the world from that moment in the past up to the present moment. I already have a piece of code that does it, but it's not as neat as I need it to be. The domain logic of the app (the physics of the game) must be separated from the presentation (render) and infrastructure tools (e.g. the remote server interaction specifics). How do I organize all this? :) Is there any worthy implementation with open sources I can take a look at? What I'm thinking is something like this: -> Render / User Input -> Game Engine (this is the so called service layer) -> Processing User Commands & Remote Server -> Domain (Physics) How would you add into this scheme the concept of "ticks" or "interactions" with the possibility to rewind and recalculate "the game"? Remember, I cannot change the Domain/Physics but only the Game Engine. Should I store an array of "World's States"? Should they be just some representations of the world, optimized for this purpose somehow (how?) or should they be actual instances of the world (i.e. including behavior and all that). Has anybody had similar experience? (never worked on a game before if that matters)

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  • "Oracle Coherence 3.5" Book - My Humble Review

    - by [email protected]
      After reviewing the book in more detail I say again that it is a great guide for sure. Lots of important concepts that sometimes can be somewhat confusing are deeply reviewed, including all types of caching schemes and backing maps, and the cache topologies with their corresponding performances and very useful "When to use it?" sections. Some functionalities that are very desirable or used a lot are reviewed with examples and best practices of implementation, including: Data affinity Querying Pagination Indexes Aggregations Event processing, listening and triggering Data persistence Security Regarding the networking and architecture topics, Coherence*Extend is exhaustively reviewed, including C++ and .NET clients, with very good tips and examples, even including source codes. Personally, I am also glad to see that the address providers (<address-provider> tag), new feature in Coherence 3.5 which is a way to programmatically provide well-known addresses in order to connect to the cluster, is mentioned on the book, because it provides new functionalities to satisfy some special configuration requirements for example: Provide a way to switch extend nodes in cases of failure Implement custom load balancing algorithms and/or dynamic discovery of TCP/IP connection acceptors Dynamically assign TCP address and port settings when binding to a server socket Another very interesting and useful section is the "Coherent Bank Sample Application", which is a great tutorial, useful to understand how Coherence interacts with third party products establishing a clear integration with them, including the use of non-Oracle products like MS Visual Studio.  

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  • Empty interface to combine multiple interfaces

    - by user1109519
    Suppose you have two interfaces: interface Readable { public void read(); } interface Writable { public void write(); } In some cases the implementing objects can only support one of these but in a lot of cases the implementations will support both interfaces. The people who use the interfaces will have to do something like: // can't write to it without explicit casting Readable myObject = new MyObject(); // can't read from it without explicit casting Writable myObject = new MyObject(); // tight coupling to actual implementation MyObject myObject = new MyObject(); None of these options is terribly convenient, even more so when considering that you want this as a method parameter. One solution would be to declare a wrapping interface: interface TheWholeShabam extends Readable, Writable {} But this has one specific problem: all implementations that support both Readable and Writable have to implement TheWholeShabam if they want to be compatible with people using the interface. Even though it offers nothing apart from the guaranteed presence of both interfaces. Is there a clean solution to this problem or should I go for the wrapper interface? UPDATE It is in fact often necessary to have an object that is both readable and writable so simply seperating the concerns in the arguments is not always a clean solution. UPDATE2 (extracted as answer so it's easier to comment on) UPDATE3 Please beware that the primary usecase for this is not streams (although they too must be supported). Streams make a very specific distinction between input and output and there is a clear separation of responsibilities. Rather, think of something like a bytebuffer where you need one object you can write to and read from, one object that has a very specific state attached to it. These objects exist because they are very useful for some things like asynchronous I/O, encodings,...

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  • Is an event loop just a for/while loop with optimized polling?

    - by Alan
    I'm trying to understand what an event loop is. Often the explanation is that in the event loop, you do something until you're notified that an event occurred. You than handle the event and continue doing what you did before. To map the above definition with an example. I have a server which 'listens' in a event loop, and when a socket connection is detected, the data from it gets read and displayed, after which the server goes to the listening it did before. However, this event happening and us getting notified 'just like that' are to much for me to handle. You can say: "It's not 'just like that' you have to register an event listener". But what's an event listener but a function which for some reason isn't returning. Is it in it's own loop, waiting to be notified when an event happens? Should the event listener also register an event listener? Where does it end? Events are a nice abstraction to work with, however just an abstraction. I believe that in the end, polling is unavoidable. Perhaps we are not doing it in our code, but the lower levels (the programming language implementation or the OS) are doing it for us. It basically comes down to the following pseudo code which is running somewhere low enough so it doesn't result in busy waiting: while(True): do stuff check if event has happened (poll) do other stuff This is my understanding of the whole idea, and i would like to hear if this is correct. I am open in accepting that the whole idea is fundamentally wrong, in which case I would like the correct explanation. Best regards

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  • What is logical cohesion, and why is it bad or undesirable?

    - by Matt Fenwick
    From the c2wiki page on coupling & cohesion: Cohesion (interdependency within module) strength/level names : (from worse to better, high cohesion is good) Coincidental Cohesion : (Worst) Module elements are unrelated Logical Cohesion : Elements perform similar activities as selected from outside module, i.e. by a flag that selects operation to perform (see also CommandObject). i.e. body of function is one huge if-else/switch on operation flag Temporal Cohesion : operations related only by general time performed (i.e. initialization() or FatalErrorShutdown?()) Procedural Cohesion : Elements involved in different but sequential activities, each on different data (usually could be trivially split into multiple modules along linear sequence boundaries) Communicational Cohesion : unrelated operations except need same data or input Sequential Cohesion : operations on same data in significant order; output from one function is input to next (pipeline) Informational Cohesion: a module performs a number of actions, each with its own entry point, with independent code for each action, all performed on the same data structure. Essentially an implementation of an abstract data type. i.e. define structure of sales_region_table and its operators: init_table(), update_table(), print_table() Functional Cohesion : all elements contribute to a single, well-defined task, i.e. a function that performs exactly one operation get_engine_temperature(), add_sales_tax() (emphasis mine). I don't fully understand the definition of logical cohesion. My questions are: what is logical cohesion? Why does it get such a bad rap (2nd worst kind of cohesion)?

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  • Automatic Generalization

    - by Nick Harrison
    I have been interested in functional programming since college. I played around a little with LISP back then, but I have not had an opportunity since then. Now that F# ships standard with VS 2010, I figured now is my chance. So, I was reading up on it a little over the weekend when I came across a very interesting topic. F# includes a concept called "Automatic Generalization". As I understand it, the compiler will look at your method and analyze how you are using parameters. It will automatically switch to a generic parameter if it is possible based on your usage. Wow! I am looking forward to playing with this. I have long been an advocate of using the most generic types possible especially when developing library classes. Use the highest level base class that you can get away with. Use an interface instead of a specific implementation. I don't advocate passing object around, but you get the idea. Tools like resharper, fxCop, and most static code analysis tools provide guidance to help you identify when a more generalized type is possible, but this is the first time I have heard about the compiler taking matters into its own hands. I like the sound of this. We'll see if it is a good idea or not. What are your thoughts? Am I missing the mark on what Automatic Generalization does in F#? How would this work in C#? Do you see any problems with this?

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  • How to deal with a CEO making all technical decision but with little technical knowledge ?

    - by anonymous
    Hi, Question posted anonymously for obvious reasons. I am working in a company with a dev group of 5-6 developers, and I am in a situation which I have a hard time dealing with. Every technical choice (language, framework, database, database scheme, configuration scheme, etc...) is decided by the CEO, often without much rationale. It is very hard to modify those choices, and his main argument consists in "I don't like this", even though we propose several alternative with detailed pros/cons. He will also decide to rewrite from scratch our core product without giving a reason why, and he never participates to dev meetings because he considers it makes things slower... I am already looking at alternative job opportunities, but I was wondering if there anything we (the developers) could do to improve the situation. Two examples which shocked me: he will ask us to implement something akin to configuration management, but he reject any existing framework because they are not written in the language he likes (even though the implementation language is irrelevant). He also expects us to be able to write those systems in a couple of days, "because it is very simple". he keeps rewriting from scratch on his own our core product because the current codebase is too bad (codebase whose design was his). We are at our third rewrite in one year, each rewrite worse than the previous one. Things I have tried so far is doing elaborate benchmarks on our product (he keeps complaining that our software is too slow, and justifies rewrites to make it faster), implement solutions with existing products as working proof instead of just making pros/cons charts, etc... But still 90 % of those efforts go to the trashbox (never with any kind of rationale behind he does not like it, again), and often get reprimanded because I don't do exactly as he wants (not realizing that what he wants is impossible).

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