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• Is there a Design Pattern for preventing dangling references?

  - by iFreilicht

  I was thinking about a design for custom handles. The thought is to prevent clients from copying around large objects. Now a regular handle class would probably suffice for that, but it doesn't solve the "dangling reference problem"; If a client has multiple handles of the same object and deletes the object via one of them, all the others would be invalid, but not know it, so the client could write or read parts of the memory he shouldn't have access to. Is there a design pattern to prevent this from happening? Two ideas: An observer-like pattern where the destructor of an object would notify all handles. "Handle handles" (does such a thing even exist?). All the handles don't really point to the object, but to another handle. When the object gets destroyed, this "master-handle" invalidates itself and therefore all that point to it.

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• Find points whose pairwise distances approximate a given distance matrix

  - by Stephan Kolassa

  Problem. I have a symmetric distance matrix with entries between zero and one, like this one: D = ( 0.0 0.4 0.0 0.5 ) ( 0.4 0.0 0.2 1.0 ) ( 0.0 0.2 0.0 0.7 ) ( 0.5 1.0 0.7 0.0 ) I would like to find points in the plane that have (approximately) the pairwise distances given in D. I understand that this will usually not be possible with strictly correct distances, so I would be happy with a "good" approximation. My matrices are smallish, no more than 10x10, so performance is not an issue. Question. Does anyone know of an algorithm to do this? Background. I have sets of probability densities between which I calculate Hellinger distances, which I would like to visualize as above. Each set contains no more than 10 densities (see above), but I have a couple of hundred sets. What I did so far. I did consider posting at math.SE, but looking at what gets tagged as "geometry" there, it seems like this kind of computational geometry question would be more on-topic here. If the community thinks this should be migrated, please go ahead. This looks like a straightforward problem in computational geometry, and I would assume that anyone involved in clustering might be interested in such a visualization, but I haven't been able to google anything. One simple approach would be to randomly plonk down points and perturb them until the distance matrix is close to D, e.g., using Simulated Annealing, or run a Genetic Algorithm. I have to admit that I haven't tried that yet, hoping for a smarter way. One specific operationalization of a "good" approximation in the sense above is Problem 4 in the Open Problems section here, with k=2. Now, while finding an algorithm that is guaranteed to find the minimum l1-distance between D and the resulting distance matrix may be an open question, it still seems possible that there at least is some approximation to this optimal solution. If I don't get an answer here, I'll mail the gentleman who posed that problem and ask whether he knows of any approximation algorithm (and post any answer I get to that here).

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• How to organise projects with dependencies on BitBucket?

  - by Timwi

  Both Mercurial and BitBucket make one fundamental assumption: 1 repo = 1 project. If I have a project that has a dependency (a library) which is shared by many projects, this assumption gets in the way. Now it is no longer possible to have a separate BitBucket page for each project while still being able to commit atomic revisions to multiple projects. If I put all the projects into one repo, they all become one “project” on BitBucket. If I put them in separate repos, it is no longer possible to know which version of the library project was in use at revision X of a dependent project. How is this situation normally solved on BitBucket, or is there explicitly no support for this common scenario?

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• Is it bad practice to pass instances through several layers?

  - by Puckl

  In my program design, I often come to the point where I have to pass object instances through several classes. For example, if I have a controller that loads an audio file, and then passes it to a player, and the player passes it to the playerRunnable, which passes it again somewhere else etc. It looks kind of bad, but I don´t know how to avoid it. Or is it OK to do this? EDIT: Maybe the player example is not the best because I could load the file later, but in other cases that does not work.

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• I think client's project will be a flop; should I discuss with him? [closed]

  - by WeaklyTyped

  I have a meeting with a prospective client tomorrow for a certain e-commerce project he wants to commission. I had an overview of it over the phone and from what I understand there are gazillion such concepts already floating and most of them are disasters and I have reasons to believe that his project is significantly likely to have the same fate. Should I raise/discuss the commercial feasibility of his idea with him or simply accept the project, give my best and leave out all the rest?

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• PHP and performance

  - by Naif

  I always hear that PHP is for medium and small websites whereas .NET and Java for enterprise applications. My question is about PHP. Why is PHP not a good option for enterprise web applications? Is it because if the web application becomes bigger then PHP will be slower as it is an interpreted language? I know that corporate world will choose .NET or J2EE because of the integration with their products and because of back end services, etc. However, if we just have PHP for building sites and web applications then how can we use it to perform well with big sites? In short, Is there a relationship between the performance of PHP and the size of the website? What are the factors that make PHP not appropriate option for big sites?

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• Why use sealed instead of static on a class?

  - by sq33G

  Our system has several utility classes. Some people on our team use (A) a class with all-static methods and a private constructor. Others use (B) a class with all-static methods (these the juniors). On code analysis, (A) and (B) raise warning CA1052, which recommends marking the class as sealed. Included in the MSDN documentation there is the following advice: If you are targeting .NET Framework 2.0 or earlier, a better approach is to mark the type as static. Why does this make any sense? I would have thought the opposite; AFAIK, previous to 2.0 there was no way to mark a class as static.

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• How do you encode Algebraic Data Types in a C#- or Java-like language?

  - by Jörg W Mittag

  There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f Empty = Empty consmap f (ConsCell a b) = ConsCell (f a) (consmap f b) l = ConsCell 1 (ConsCell 2 (ConsCell 3 Empty)) consmap (+1) l This particular example is in Haskell, but it would be similar in other languages with native support for Algebraic Data Types. It turns out that there is an obvious mapping to OO-style subtyping: the datatype becomes an abstract base class and every data constructor becomes a concrete subclass. Here's an example in Scala: sealed abstract class ConsList[+T] { def map[U](f: T => U): ConsList[U] } object Empty extends ConsList[Nothing] { override def map[U](f: Nothing => U) = this } final class ConsCell[T](first: T, rest: ConsList[T]) extends ConsList[T] { override def map[U](f: T => U) = new ConsCell(f(first), rest.map(f)) } val l = (new ConsCell(1, new ConsCell(2, new ConsCell(3, Empty))) l.map(1+) The only thing needed beyond naive subclassing is a way to seal classes, i.e. a way to make it impossible to add subclasses to a hierarchy. How would you approach this problem in a language like C# or Java? The two stumbling blocks I found when trying to use Algebraic Data Types in C# were: I couldn't figure out what the bottom type is called in C# (i.e. I couldn't figure out what to put into class Empty : ConsList< ??? >) I couldn't figure out a way to seal ConsList so that no subclasses can be added to the hierarchy What would be the most idiomatic way to implement Algebraic Data Types in C# and/or Java? Or, if it isn't possible, what would be the idiomatic replacement?

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• May I remove ads from feed in my news reader app?

  - by Mahdi Ghiasi

  I'm creating a News Reader app for Tablets and PCs. My app is fetching data from news sources by RSS feed of websites (in the server-side). But some of these sites are showing some advertising banners at the end of each article. Should I remove those banners from the feed? Am I legally/ethically allowed to do this? And what about If I want to put some other ads in my application? (Right at the end of each article) I mean, If I want to have my own advertising service... Update: And what if I use feed for content titles and summaries, but use other thing, like Readability API to show full article, and then put my own ads below content? (Readability gets the HTML page, and gives you a clean page without any ads and such.)

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• Registering as developer on Google Play store

  - by ChosenOne

  I am registering as a Developer to sell paid applications on the Google Play store and have run into a slight issue: After I paid, I clicked on "Setup merchant details" link. I filled out the business address section, but in the "Public contact" section, Google says this: How can your customers get in touch with you? This information will be made available to your customers when they make a purchase. I work from home. I do not want customers knowing my home address, nor do I want it displayed anywhere online or even accessible by anyone. Should I just enter NA in each of the following fields? Surely Google understands that we have a right to keep such things private? How can I get around this while not getting my account suspended or risk not being approved?

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• What is the best way to track / record the current programming project you work on? [duplicate]

  - by user2424160

  This question already has an answer here: Methodology for Documenting Existing Code Base 6 answers When do you start documenting the code? 13 answers Where should a programmer explain the extended logic behind the code? 5 answers I have been in this problem for long time and I want to know how it's done in real / big companies project? Suppose I have the project to build a website. Now I divide the project into sub tasks and do it. But you know that suppose I have task1 in hand like export the page to pdf. Now I spend 3 days to do that , came across various problems, many Stack Overflow questions and in the end I solve it. Now 4 months after someone told me that there is some error in the code. Now by that I completely forgot about (60%) of how I did it and why I do this way. I document the code but I can't write the whole story of that in the code. Then I have to spend much time on code to find what was the problem so that I added this line etc. I want to know that is there any way that i can log steps in completing the project. So that I can see how I end up with code, what errors I got, what questions I asked on SO and etc. How people do it in real time? Which software to use? I know in our project management software called JIRA we have tasks but that does not cover what steps I took to solve that tasks. What is the best way so that when I look back at my 2 year old project, I know how I solve particular task?

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• Are Java servers really more preferable for web-development? [closed]

  - by Gerald Goward

  Many experienced people I know tell me that many web-projects, including enterprise ones, are better to develop with Java being back-end. Reasons: Ubuntu servers being cheaper and more reliable. MySql being much more "light" rather than "heavyweighted" MS Sql. I heard some more, but I really cant remember all of them. My question: I believe ASP.NET and Java are BOTH good for web-development and its just holywar subject. Am I right or not?

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• What should happen at the start of a software project startup?

  - by Willem

  A quick introduction My college semesters include a 8 week project working for an actual company with a software need in order to get some much needed practical experience. I have just started such a project with 5 other students. We're required to spend roughly 40 hours a week per student on this project. We're working with SCRUM as the software development method, this was assigned by our teachers. The question Day one of the project just ended which has created some questions for me as to how to start a project in the 'real world'. Our first day included working on a project planning document (not sure what the English term is), creating a appointment with the company for an introduction and the opportunity to start specifying the requirements and setting up some standards for the behavior within the group. However these items didn't take that long to finish. We've made some concrete plans for tomorrow and the day after we'll meet the company. This still leaves several hours of 'work-time' unspent. Is it usual not being able to fill every hour of a day for work at the start of a project or are we simply too inexperienced to see what work needs to be done at this stage of a project, or are we, perhaps, going through the above list too fast? How does this work in the 'real world'? Do you spend your time wondering 'what should I do now', or do you have a clear view of what you're supposed to do at that moment?

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• Using an open source non-free license

  - by wagglepoons

  Are there any projects/products out there that use an open source license that basically says "free for small companies" and "cost money for larger companies" in addition to "make modifications available"? (And are there any standard licenses with such a wording?) If I were to release a project under such a license, would it be automatically shunned by every developer on the face of the earth, or, assuming it is actually a useful project, does it have a fair chance at getting contributions from Joe Programmer? The second part of this question can easily become subjective, but any well argued point of view will be highly appreciated. For example, do dual licensed projects made by commercial entities have success with the open source communities?

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• Generic Repositories with DI & Data Intensive Controllers

  - by James

  Usually, I consider a large number of parameters as an alarm bell that there may be a design problem somewhere. I am using a Generic Repository for an ASP.NET application and have a Controller with a growing number of parameters. public class GenericRepository<T> : IRepository<T> where T : class { protected DbContext Context { get; set; } protected DbSet<T> DbSet { get; set; } public GenericRepository(DbContext context) { Context = context; DbSet = context.Set<T>(); } ...//methods excluded to keep the question readable } I am using a DI container to pass in the DbContext to the generic repository. So far, this has met my needs and there are no other concrete implmentations of IRepository<T>. However, I had to create a dashboard which uses data from many Entities. There was also a form containing a couple of dropdown lists. Now using the generic repository this makes the parameter requirments grow quickly. The Controller will end up being something like public HomeController(IRepository<EntityOne> entityOneRepository, IRepository<EntityTwo> entityTwoRepository, IRepository<EntityThree> entityThreeRepository, IRepository<EntityFour> entityFourRepository, ILogError logError, ICurrentUser currentUser) { } It has about 6 IRepositories plus a few others to include the required data and the dropdown list options. In my mind this is too many parameters. From a performance point of view, there is only 1 DBContext per request and the DI container will serve the same DbContext to all of the Repositories. From a code standards/readability point of view it's ugly. Is there a better way to handle this situation? Its a real world project with real world time constraints so I will not dwell on it too long, but from a learning perspective it would be good to see how such situations are handled by others.

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• How can I get started using TDD to code some simple functionality?

  - by Gabriel

  I basically have the gist of TDD. I'm sold that it's useful and I've got a reasonable command of the MSTEST framework. However, to date I have not been able to graduate to using it as a primary development method. Mostly, I use it as a surrogate for writing console apps as test drivers (my traditional approach). The most useful thing about it for me is the way it absorbs the role of regression testing. I have not yet built anything yet that specifically isolates various testable behaviors, which is another big part of the picture I know. So this question is to ask for pointers on what the first test(s) I might write for the following development task: I want to produce code that encapsulates task execution in the fashion of producer/consumer. I stopped and decided to write this question after I wrote this code (wondering if I could actually use TDD for real this time) Code: interface ITask { Guid TaskId { get; } bool IsComplete { get; } bool IsFailed { get; } bool IsRunning { get; } } interface ITaskContainer { Guid AddTask(ICommand action); } interface ICommand { string CommandName { get; } Dictionary<string, object> Parameters { get; } void Execute(); }

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• Designing an API on top with Java RMI and Rest APIs

  - by user1303881

  I'm working on the backend of a java web application. We have a document repository (Fedora Commons specifically) where we house xml files. I want to abstract the API of the repository internally so that we aren't tightly coupled to one product. I'd also like to give the flexibility of connecting to to a repository via Java RMI or REST APIs. I was hoping to get advice or resources on how to implement something like this. My thought it that I'd have some abstract repository class that had methods like getRecord, updateRecord, and deleteRecord. In the constructor I would pass the URI for the repository and the API method and port. This would allow some flexibility in the future so that if the REST api became more practical, but allow the flexibility or using RMI which could (should?) have better performance. Am I over thinking this or am I on the right path?

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• Understanding how memory contents map into a struct

  - by user95592

  I am not able to understand how bytes in memory are being mapped into a struct. My machine is a little-endian x86_64. The code was compiled with gcc 4.7.0 from the Win64 mingw32-64 distribution for Win64. These are contents of the relevant memory fragment: ...450002cf9fe5000040115a9fc0a8fe... And this is the struct definition: typedef struct ip4 { unsigned int ihl :4; unsigned int version :4; uint8_t tos; uint16_t tot_len; uint16_t id; uint16_t frag_off; // flags=3 bits, offset=13 bits uint8_t ttl; uint8_t protocol; uint16_t check; uint32_t saddr; uint32_t daddr; /*The options start here. */ } ip4_t; When a pointer to such an structure (let it be *ip4) is initialized to the starting address of the above pasted memory region, this is what the debugger shows for the struct's fields: ip4: address=0x8da36ce ip4->ihl: address=0x8da36ce, value=0x5 ip4->version: address=0x8da36ce, value=0x4 ip4->tos: address=0x8da36d2, value=0x9f ip4->tot_len: address=0x8da36d4, value=0x0 ... I see how ihl and version are mapped: 4 bytes for a long integer, little-endian. But I don't understand how tos and tot_len are mapped; which bytes in memory correspond to each one of them. Thank you in advance.

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• Analyzing Memory Usage: Java vs C++ Negligible?

  - by Anthony

  How does the memory usage of an integer object written in Java compare\contrast with the memory usage of a integer object written in C++? Is the difference negligible? No difference? A big difference? I'm guessing it's the same because an int is an int regardless of the language (?) The reason why I asked this is because I was reading about the importance of knowing when a program's memory requirements will prevent the programmer from solving a given problem. What fascinated me is the amount of memory required for creating a single Java object. Take for example, an integer object. Correct me if I'm wrong but a Java integer object requires 24 bytes of memory: 4 bytes for its int instance variable 16 bytes of overhead (reference to the object's class, garbage collection info & synchronization info) 4 bytes of padding As another example, a Java array (which is implemented as an object) requires 48+bytes: 24 bytes of header info 16 bytes of object overhead 4 bytes for length 4 bytes for padding plus the memory needed to store the values How do these memory usages compare with the same code written in C++? I used to be oblivious about the memory usage of the C++ and Java programs I wrote, but now that I'm beginning to learn about algorithms, I'm having a greater appreciation for the computer's resources.

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• Architecture for subscription based application

  - by John

  This is about the architecture of my application I think. I have a Rails application where companies can administrate all things related to clients. Companies can buy a subscription and their users can access the application online. Hopefully I will get multiple companies subscribing to my appplication/service. Thing is, what should I do with my code and database? Seperate app code base and database per company One app code base but seperate database per company One app code base and one database The decision I am to make involves security (e.g. user from company X should not see any data from company Y) performance (let's suppose it becomes successful, it should have a good performance) and scalability (again, if successful, it should have a good performance but also easy for me to handle all the companies, code changes, etc) For sake of maintainability, I tend to opt for the one code base. For the database I really don't know at this moment. So what do you think is the best option?

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• Application layer vs domain layer?

  - by Louis Rhys

  I am reading Domain-Driven Design by Evans and I am at the part discussing the layered architecture. I just realized that application and domain layers are different and should be separate. In the project I am working on, they are kind of blended and I can't tell the difference until I read the book (and I can't say it's very clear to me now), really. My questions, since both of them concerns the logic of the application and are supposed to be clean of technical and presentation aspects, what are the advantages of drawing a boundary these two?

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• Dependency injection and IOC containers in a closed project

  - by Puckl

  Does it make sense to assemble my project with dependency injection containers if I am the only one who will use the code of that project? The question came up when I read this IOC Article http://martinfowler.com/articles/injection.html The justification for using dependency injection in this article is that friends can reuse a class, and replace depending classes with their own classes because they get injected and not instantiated in the class. I would only use it to inject objects where they are needed instead of passing them through layers to their target. (Which is not so bad I learned here: Is it bad practice to pass instances through several layers?) (Maybe I will reuse parts of the project, who knows, but I don´t know if that is a good justification)

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• Consultant - Google Cloud Endpoints

  - by Marc M.

  How does when go along finding a consultant to hire for a few hours for particular technologies? Lets say Google Cloud Endpoints, basically a professional at the library that can answer anything I need to know about it? How much might this cost. Can you hire them for only a couple hours at a time? Or even for a 20 minute phone call like a lawyer? P.S. I could use someone on call for Objectify questions too.

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• Incorporating GPL Code in my Open Source Project

  - by rutherford

  I have downloaded a currently inactive GPL project with a view to updating it and releasing the completed codebase as open source. I'm not really a fan of GPL though and would rather licence my project under BSD. What are my options? Is it just a case of keeping any existing non-touched code under the GPL and any updated stuff can be BSD (messy)? The source will essentially be the same codebase i.e. there is no logical separation between the two and they certainly can't be split into anything resembling different libraries. Are my only realistic options to either GPL the whole thing or seek the original author's permission to release everthing under BSD?

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• The next step for a graduate?

  - by Michael Hobbs

  I will complete my degree in Computer Science in July of 2013 however I will have two years of military service left. I would like to get some hands on C#/C++ programming experience in the mean time. I have been looking around the web at all the open source project that are out there. There are literally 10's of thousands. How would you go about picking one that is: A) good for a graduate level programmer B) will probably go somewhere, and C) are willing to take a novice under their wing. I would even be happy to work for a company for free, remotely as a debugger, tester, or what have you. As a side note would prefer to stick in the C# realm but understand I need to branch out at the same time.

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