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• Starting to Program C++ and Java

  - by user0321

  So as the title states, I'm trying to start programming in C++ and Java. I took C++ and Java courses in high school and I'm trying to get back into it. Of course all I want to get working now is a simple "Hello World" program. Couple of things: I want to use an IDE. I've decided on Eclipse. I'm just confused about how I go about downloading/using it. For Java: I get stuck right on their download page. They show Eclipse Classic, Eclipse IDE for Java developers and Eclipse IDE for Java EE Developers. I only programmed in Notepad and compiled in command prompt. Question 1: Which version of Eclipse should I download? Question 2: Do I need to install the Java JDK or does it come built into Eclipse? For C++: I guess I download the separate Eclipse IDE for C/C++ developers? I'm not too sure. I remember using Microsoft Visual for C++. I remember it being weird though. Anyways Question 3: Which version of Eclipse should I download? Question 4: Does C++ have a Development Kit or does it come built into Eclipse?

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• Is There a Real Advantage to Generic Repository?

  - by Sam

  Was reading through some articles on the advantages of creating Generic Repositories for a new app (example). The idea seems nice because it lets me use the same repository to do several things for several different entity types at once: IRepository repo = new EfRepository(); // Would normally pass through IOC into constructor var c1 = new Country() { Name = "United States", CountryCode = "US" }; var c2 = new Country() { Name = "Canada", CountryCode = "CA" }; var c3 = new Country() { Name = "Mexico", CountryCode = "MX" }; var p1 = new Province() { Country = c1, Name = "Alabama", Abbreviation = "AL" }; var p2 = new Province() { Country = c1, Name = "Alaska", Abbreviation = "AK" }; var p3 = new Province() { Country = c2, Name = "Alberta", Abbreviation = "AB" }; repo.Add<Country>(c1); repo.Add<Country>(c2); repo.Add<Country>(c3); repo.Add<Province>(p1); repo.Add<Province>(p2); repo.Add<Province>(p3); repo.Save(); However, the rest of the implementation of the Repository has a heavy reliance on Linq: IQueryable<T> Query(); IList<T> Find(Expression<Func<T,bool>> predicate); T Get(Expression<Func<T,bool>> predicate); T First(Expression<Func<T,bool>> predicate); //... and so on This repository pattern worked fantastic for Entity Framework, and pretty much offered a 1 to 1 mapping of the methods available on DbContext/DbSet. But given the slow uptake of Linq on other data access technologies outside of Entity Framework, what advantage does this provide over working directly with the DbContext? I attempted to write a PetaPoco version of the Repository, but PetaPoco doesn't support Linq Expressions, which makes creating a generic IRepository interface pretty much useless unless you only use it for the basic GetAll, GetById, Add, Update, Delete, and Save methods and utilize it as a base class. Then you have to create specific repositories with specialized methods to handle all the "where" clauses that I could previously pass in as a predicate. Is the Generic Repository pattern useful for anything outside of Entity Framework? If not, why would someone use it at all instead of working directly with Entity Framework? Edit: Original link doesn't reflect the pattern I was using in my sample code. Here is an (updated link).

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• An alternative to multiple inheritance when creating an abstraction layer?

  - by sebf

  In my project I am creating an abstraction layer for some APIs. The purpose of the layer is to make multi-platform easier, and also to simplify the APIs to the feature set that I need while also providing some functionality, the implementation of which will be unique to each platform. At the moment, I have implemented it by defining and abstract class, which has methods which creates objects that implement interfaces. The abstract class and these interfaces define the capabilities of my abstraction layer. The implementation of these in my layer should of course be arbitrary from the POV view of my application, but I have done it, for my first API, by creating chains of subclasses which add more specific functionality as the features of the APIs they expose become less generic. An example would probably demonstrate this better: //The interface as seen by the application interface IGenericResource { byte[] GetSomeData(); } interface ISpecificResourceOne : IGenericResource { int SomePropertyOfResourceOne {get;} } interface ISpecificResourceTwo : IGenericResource { string SomePropertyOfResourceTwo {get;} } public abstract class MyLayer { ISpecificResourceOne CreateResourceOne(); ISpecificResourceTwo CreateResourceTwo(); void UseResourceOne(ISpecificResourceOne one); void UseResourceTwo(ISpecificResourceTwo two); } //The layer as created in my library public class LowLevelResource : IGenericResource { byte[] GetSomeData() {} } public class ResourceOne : LowLevelResource, ISpecificResourceOne { int SomePropertyOfResourceOne {get{}} } public class ResourceTwo : ResourceOne, ISpecificResourceTwo { string SomePropertyOfResourceTwo {get {}} } public partial class Implementation : MyLayer { override UseResourceOne(ISpecificResourceOne one) { DoStuff((ResourceOne)one); } } As can be seen, I am essentially trying to have two inheritance chains on the same object, but of course I can't do this so I simulate the second version with interfaces. The thing is though, I don't like using interfaces for this; it seems wrong, in my mind an interface defines a contract, any class that implements that interface should be able to be used where that interface is used but here that is clearly not the case because the interfaces are being used to allow an object from the layer to masquerade as something else, without the application needing to have access to its definition. What technique would allow me to define a comprehensive, intuitive collection of objects for an abstraction layer, while their implementation remains independent? (Language is C#)

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• How to Implement a Parallel Workflow

  - by Paul

  I'm trying to implement a parallel split task using a workflow system. I'm using .NET but my process is very simple and I don't want to use WF or anything heavy like that. I've tried using Stateless. So far is was easy to set up and run, but I may be using the wrong tool for the job because I'm not sure how you're supposed to model parallel split workflows, where you have multiple sub-tasks required before you can advance to the next state, but the steps don't require being performed in any particular order. I can easily use the dynamic configuration options to check my data model manually to see if the model is in the correct state (all sub-tasks completed) and can transition to the next state, but this seems to completely break the workflow paradigm. What is the proper, orthodox way to implement a parallel split process? Thanks

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• What is the role of C++ today?

  - by hades

  Currently I'm an IT student and I'm wondering what is still important in C++ today, what for is it used? I completed basic C++ course in my university but I can't imagine where can I use my knowledge and in which direction should I go learning C++. In other words what should I learn to become a successful C++ programmer? Currently I'm learning Java just because I don't see clearly in which area C++ could be useful today, but I clearly know which kind of work I'll be doing as a Java programmer. But I still hope that C++ isn't dead.

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• what does composition example vs aggregation

  - by meWantToLearn

  Composition and aggregation both are confusion to me. Does my code sample below indicate composition or aggregation? class A { public static function getData($id) { //something } public static function checkUrl($url) { // something } class B { public function executePatch() { $data = A::getData(12); } public function readUrl() { $url = A::checkUrl('http/erere.com'); } public function storeData() { //something not related to class A at all } } } Is class B a composition of class A or is it aggregation of class A? Does composition purely mean that if class A gets deleted class B does not works at all and aggregation if class A gets deleted methods in class B that do not use class A will work?

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• Algorithm to reduce calls to mapping API

  - by aidan

  A random distribution of points lies on a map. This data lies behind an API, and I want to grab the complete set of points within a given bounding box. I can query the API with the bounding box and the API will return the set of points that fall within that box. The problem is that the API will limit the result set to 10 items, with no pagination and no indication if there are more points that have been omitted. So I made a recursive algorithm that takes a bounding box and requests the points that lie within it. If the result set is exactly 10 items, then I split the bounding box into four quadrants and recurse. It works fine but my question is this: if want to minimize the number of API calls, what is the optimal way to split the bounding box? Splitting it into quadrants was just an arbitrary decision. When there are a lot of points on the map, I have to drill down many levels before I start getting meaningful results. So I imagine it might be faster to split the box into, say, 9, 16, or more sections. But if I do that, then I eventually get to a point where a lot of requests are returning 0 results which isn't so efficient. Also, does the size of the limit on the results set affect the answer? (This is all assuming that I have no prior knowledge of nominal point density in the bounding box)

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• Commenting Code AS3 - Not being an API

  - by Marcelo Noronha

  How should I comment a method? What are the best practices on commenting code? Example: /* Checks if a color is allowed in a given point * of the bitmapdata of the current floor * @param value - color to be checked * @return boolean - if color is allowed returns true, else, return false */ private function isAllowed(value:uint):Boolean { //code... } Is that the best way to comment a method? I´ve heard there´s the use of the tag @see. What should be on this tag? I wonder if it could be something that has a relation to the method, is that right? Thanks.

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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 to write constructors which might fail to properly instantiate an object

  - by whitman

  Sometimes you need to write a constructor which can fail. For instance, say I want to instantiate an object with a file path, something like obj = new Object("/home/user/foo_file") As long as the path points to an appropriate file everything's fine. But if the string is not a valid path things should break. But how? You could: 1. throw an exception 2. return null object (if your programming language allows constructors to return values) 3. return a valid object but with a flag indicating that its path wasn't set properly (ugh) 4. others? I assume that the "best practices" of various programming languages would implement this differently. For instance I think ObjC prefers (2). But (2) would be impossible to implement in C++ where constructors must have void as a return type. In that case I take it that (1) is used. In your programming language of choice can you show how you'd handle this problem and explain why?

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• Result class dependency

  - by Stefano Borini

  I have an object containing the results of a computation. This computation is performed in a function which accepts an input object and returns the result object. The result object has a print method. This print method must print out the results, but in order to perform this operation I need the original input object. I cannot pass the input object at printing because it would violate the signature of the print function. One solution I am using right now is to have the result object hold a pointer to the original input object, but I don't like this dependency between the two, because the input object is mutable. How would you design for such case ?

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• Erlang web frameworks survey

  - by Zachary K

  (Inspired by similar question on Haskel) There are several web frameworks for Erlang like Nitrogen, Chicago Boss, and Zotonic, and a few more. In what aspects do they differ from each other? For example: features (e.g. server only, or also client scripting, easy support for different kinds of database) maturity (e.g. stability, documentation quality) scalability (e.g. performance, handy abstraction) main targets Also, what are examples of real-world sites / web apps using these frameworks?

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• Big Oh notation does not mention constant value

  - by user883561

  I am a programmer and have just started reading Algorithms. I am not completely convinced with the notations namely Bog Oh, Big Omega and Big Theta. The reason is by definition of Big Oh, it states that there should be a function g(x) such that it is always greater than or equal to f(x). Or f(x) <= c.n for all values of n n0. My doubt is the why dont we mention the constant value in the definition? For example. lets say a function 6n+4, we denote it as O(n). but its not true that the definition holds good for all constant value. this holds good only when c = 10 and n = 1. For lesser values of c than 6, the value of n0 increases. So why we do not mention the constant value as a part of the definition.

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• Open source ASP.NET MVC project for a SaaS application

  - by DotnetDude

  I am working on a personal project that offers a service online. I'd like put this out to the public. I don't want to reinvent the wheel and use an existing template/open source project and add my service specific functionality. The features I am looking for are: Support for different roles (I need to have an admin role, customer and preferred customer roles) An admin section where admins can manage user accounts, login as with users credentials for providing support Customer pages that are role specific (Ex: Some functionality can be used by preferred customers but not non preferred ones) Preferably a pricing/plans page with payment gateway integration These are some of the basic pages available in most of service sites online. Is there a MVC 3 (preferably 4) written in C# that I can use as a shell to build upon? Thanks

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• Maintainability of Boolean logic - Is nesting if statements needed?

  - by Vaccano

  Which of these is better for maintainability? if (byteArrayVariable != null) if (byteArrayVariable .Length != 0) //Do something with byteArrayVariable OR if ((byteArrayVariable != null) && (byteArrayVariable.Length != 0)) //Do something with byteArrayVariable I prefer reading and writing the second, but I recall reading in code complete that doing things like that is bad for maintainability. This is because you are relying on the language to not evaluate the second part of the if if the first part is false and not all languages do that. (The second part will throw an exception if evaluated with a null byteArrayVariable.) I don't know if that is really something to worry about or not, and I would like general feedback on the question. Thanks.

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• What is the precise definition of programming paradigm?

  - by Kazark

  Wikipedia defines programming paradigm thus: a fundamental style of computer programming which is echoed in the descriptive text of the paradigms tag on this site. I find this a disappointing definition. Anyone who knows the words programming and paradigm could do about that well without knowing anything else about it. There are many styles of computer programming at many level of abstraction; within any given programming paradigm, multiple styles are possible. For example, Bob Martin says in Clean Code (13), Consider this book a description of the Object Mentor School of Clean Code. The techniques and teachings within are the way that we practice our art. We are willing to claim that if you follow these teachings, you will enjoy the benefits that we have enjoyed, and you will learn to write code that is clean and professional. But don't make the mistake of thinking that we are somehow "right" in any absolute sense. Thus Bob Martin is not claiming to have the correct style of Object-Oriented programming, even though he, if anyone, might have some claim to doing so. But even within his school of programming, we might have different styles of formatting the code (K&R, etc). There are many styles of programming at many levels. So how can we define programming paradigm rigorously, to distinguish it from other categories of programming styles? Fundamental is somewhat helpful, but not specific. How can we define the phrase in a way that will communicate more than the separate meanings of each of the two words—in other words, how can we define it in a way that will provide additional meaning for someone who speaks English but isn't familiar with a variety of paradigms?

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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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• converting dates things from visual basic to c-sharp

  - by sinrtb

  So as an excercise in utility i've taken it upon myself to convert one of our poor old vb .net 1.1 apps to C# .net 4.0. I used telerik code conversion for a starting point and ended up with ~150 errors (not too bad considering its over 20k of code and rarely can i get it to run without an error using the production source) many of which deal with time/date in vb versus c#. my question is this how would you represent the following statement in VB If oStruct.AH_DATE <> #1/1/1900# Then in C#? The converter gave me if (oStruct.AH_DATE != 1/1/1900 12:00:00 AM) { which is of course not correct but I cannot seem to work out how to make it correct.

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• What are the advantages of programming to under an OS as opposed to bare metal executive?

  - by gby

  Assume you are presented with an embedded system application to program, in C, on a multi-core environment (think a Cavium or Tilera) and need to choose between two environments: Code the application under Linux in SMP mode or code the application under a thin bare metal executive (something like a very minimal RTOS), perhaps with a single core running UP Linux that can serve control tasks. For the purpose of this question, assume that both environment provide the same level of performance guarantees in any measurable aspects of run time performance, including number of meaningful action per second, jitter, latency, real time considerations - the works. (and yes, I realize this is by far not a trivial assumption at all, bare with me). How would you justify going with a Linux SMP based solution rather then a bare metal thin executive solution? The question may seems silly. It certainly seems obvious to me - but I have to convince someone that does not think the same. Could you help make a list of arguments in favor of choosing a real SMP aware OS (Linux) vs. a bare metal executive assuming performance guarantees are NOT an issue? Many thanks

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• Authenticating users for a website

  - by MCB

  I'm working on a website and I want to validate that an individual is an employee at one of a large number of companies (probably using their company's email address, which I don't know before hand). The idea being some users are the general public and others are from these companies. And I need some way to authenticate that the users claiming to be employees are being honest while still having a friendly enough UI. I did an informal survey of people I know and the domains and emails will match in a majority of cases but they might not always match exactly so you might have a company with a website foo.com and an email [email protected] (although foobar.com did redirect back to foo.com). And while I can easily check that I'm not sure what other variations might be out there (maybe fooLA.com and email [email protected], etc.)

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• Application qos involving priority and bandwidth

  - by Steve Peng

  Our manager wants us to do applicaiton qos which is quite different from the well-known system qos. We have many services of three types, they have priorites, the manager wants to suspend low priority services requests when there are not enough bandwidth for high priority services. But if the high priority services requests decrease, the bandwidth for low priority services should increase and low priority service requests are allowed again. There should be an algorithm involving priority and bandwidth. I don't know how to design the algorithm, is there any example on the internet? Somebody can give suggestion? Thanks. UPDATE All these services are within a same process. We are setting the maximum bandwidth for the three types of services via ports of services via TC (TC is the linux qos tool whose name means traffic control).

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• Packages organisation with MVC design pattern

  - by Oltarus

  I have been programming quite a lot now and still can't decide which of these packages hierachies was the best: package1 Class1Controller Class1Model Class1View package2 Class2Controller Class2Model Class2View or controller Class1Controller Class2Contoller model Class1Model Class2Model view Class1View Class2View In other words, is it better to apply the MVC design pattern to classes or to packages? Is there any reason to choose one over the other? My question is language-agnostic, but I'm mostly a Java programmer, if it does any difference.

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• What is a good way to share internal helpers?

  - by toplel32

  All my projects share the same base library that I have build up over quite some time. It contains utilities and static helper classes to assist them where .NET doesn't exactly offer what I want. Originally all the helpers were written mainly to serve an internal purpose and it has to stay that way, but sometimes they prove very useful to other assemblies. Now making them public in a reliable way is more complicated than most would think, for example all methods that assume nullable types must now contain argument checking while not charging internal utilities with the price of doing so. The price might be negligible, but it is far from right. While refactoring, I have revised this case multiple times and I've come up with the following solutions so far: Have an internal and public class for each helper The internal class contains the actual code while the public class serves as an access point which does argument checking. Cons: The internal class requires a prefix to avoid ambiguity (the best presentation should be reserved for public types) It isn't possible to discriminate methods that don't need argument checking   Have one class that contains both internal and public members (as conventionally implemented in .NET framework). At first, this might sound like the best possible solution, but it has the same first unpleasant con as solution 1. Cons: Internal methods require a prefix to avoid ambiguity   Have an internal class which is implemented by the public class that overrides any members that require argument checking. Cons: Is non-static, atleast one instantiation is required. This doesn't really fit into the helper class idea, since it generally consists of independent fragments of code, it should not require instantiation. Non-static methods are also slower by a negligible degree, which doesn't really justify this option either. There is one general and unavoidable consequence, alot of maintenance is necessary because every internal member will require a public counterpart. A note on solution 1: The first consequence can be avoided by putting both classes in different namespaces, for example you can have the real helper in the root namespace and the public helper in a namespace called "Helpers".

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• Programming languages specifications ebooks

  - by Oxinabox

  In this talk Jon Skeet talks about the advantages of reading programming language specifications. I have an Ebook Reader (a Sony, one of the better ones for PDF's, though EPub is still much better). Does anyone know any sources for specifications, optimised for ebook readersm that can be downloaded? I expect someone would have gone through the effort of optimising the websites for ebook reader reading, ideally: EPUB Format (though pdf will do) Annotated (eg XML) Most specifications I find don't have obvious download links. I'm having trouble googling because everytime I seach for say: "F# Spec EPUB" or "Python Spec PDF" most of the results are for the EPUB or PDF specifications.

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• How do you achieve a numeric versioning scheme with Git?

  - by Erlend

  My organization is considering moving from SVN to Git. One argument against moving is as follows: How do we do versioning? We have an SDK distribution based on the NetBeans Platform. As the svn revisions are simple numbers we can use them to extend the version numbers of our plugins and SDK builds. How do we handle this when we move to Git? Possible solutions: Using the build number from hudson (Problem: you have to check hudson to correlate that to an actual git version) Manually upping the version for nightly and stable (Problem: Learning curve, human error) If someone else has encountered a similar problem and solved it, we'd love to hear how.

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