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• Scalable solution for website polling

  - by Tom Irving

  I'm looking to add push notifications to one of my iOS apps. The app is a client for a website which doesn't offer push notifications. What I've come up with so far: App sends a message to home server when transitioning to background, asking the server to start polling the website for the logged in user. The home server starts a new process to poll for that user. Polling happens every so many seconds / minutes. When the user returns to the iOS app, the app sends a message to the home server to stop polling. The home server kills the process polling for the user. Repeat. The problem is that this soon becomes stupid: 100s of users means 100s of different processes. It's just not scalable in the slighest. What I've written so far is in PHP, using CURL to do the polling and I started with PHP a few days ago, so maybe I'm missing something obvious that could help me with this. Some advice would be great.

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• How to create single integer index value based on two integers where first is unlimited?

  - by Jan Doggen

  I have table data containing an integer value X ranging from 1.... unknown, and an integer value Y ranging from 1..9 The data need to be presented in order 'X then Y'. For one visual component I can set multiple index names: X;Y But for another component I need a one-dimensional integer value as index (sort order). If X were limited to an upper bound of say 100, the one-dimensional value could simply be X*100 + Y. If the one-dimensional value could have been a real, it could be X + Y/10. But if I want to keep X unlimited, is there a way to calculate a single integer 'indexing' value from X and Y? [Added] Background information: I have a Gantt/TreeList component where the tasks are ordered on a TaskIndex integer. This does not need to be a real database field, I can make it a calculated field in the underlying client dataset. My table data is e.g. as follows: ID Baseline ParentID 1 0 0 (task) 5 2 1 (baseline) 8 1 1 (baseline) 9 0 0 (task) 12 0 0 (task) 16 1 12 (baseline) Task 1 has two baselines numbered 1 and 2 (IDs 8 and 5) Task 9 has no baselines Task 12 has one baseline numbered 1 (ID 16) Baselines number 1-9 (the Y variable from my question); 0 or null identify the tasks ID's are unlimited (the X variable) The user plays with visibility of baselines, e.g. he wants to see all tasks with all baselines labeled 1. This is done by updating a filter on the table. Right now I constantly have to recalculate TaskIndex after changing the filter (looping through records). It would be nice if TaskIndex could be calculated on the fly for each record knowing only the data in the current record (I work in Delphi where a client dataset has an OnCalcFields event handler, that is triggered for each record when necessary). I have no control over the inner workings of the visual component.

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• DDD and filtering

  - by tikhop

  I am developing an app in ddd maner. So I have a complex domain model. Suppose I have a Fare object and Airline. Each Airline should contain several or much more Fares. My UI should represent Model (only small part of complex model) as a list of Airline, when the user select the Airline, I must show the list of Fares. User can filtering the Fares (by travel time, cost, etc.). What is the appropriate place for filtering Fares and Airlines? I am assuming that I should do it in ViewModel. Like: My domain model has wrapped with Service Layer - UI works with ViewModel - ViewModel obtain data from Service Layer filtering it and create DTO objects for UI. Or I'm wrong?

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• Installing Perl modules and dependencies with non-root and without CPAN [migrated]

  - by Eegabooga

  I have been writing Perl scripts for my work and the machine that I have been given to work on makes installing Perl modules difficult: We cannot have gcc on my machine for security reasons, so I cannot use CPAN to install modules, for most modules. I do not have access to the root account. Usually, when I want to install a module, I put in a request and I have to wait a day or two before it gets installed. I know that nobody would have a problem with me installing them myself, so to save everyone's time and my sanity I would like to install them myself. It's just an issue of how to best do that. I have talked to various people and they said to use an RPM to install them (to get around not having gcc). However, when trying to install modules from RPMs, it does not handle the dependencies so I would manually need to handle the dependencies, which could take a while. How can I best install Perl modules with these limitations?

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• How to fill certain application design learning "gaps"?

  - by e4rthdog

  In life it doesnt matter if you do one thing for 15 years. You will end up waking one day and asking stuff that are equal to "how do i walk?" :) My specific question is that as a new entrant to C# and OOP i am stepping into many little "details" that need to be addressed. Written a lot of code in VB.NET / cobol / simple php e.t.c surely does not help much into the OOP world... So , even after reading entry level books for C# and watching some videos i recently found out about the "factory model design" for applications. I would appreciate if any of you guys recomment some reading on application design architecture for further reading...

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• how a pure functional programming language manage without assignment statements?

  - by Gnijuohz

  When reading the famous SICP,I found the authors seem rather reluctant to introduce the assignment statement to Scheme in Chapter 3.I read the text and kind of understand why they feel so. As Scheme is the first functional programming language I ever know something about,I am kind of surprised that there are some functional programming languages(not Scheme of course) can do without assignments. Let use the example the book offers,the bank account example.If there is no assignment statement,how can this be done?How to change the balance variable?I ask so because I know there are some so-called pure functional languages out there and according to the Turing complete theory,this must can be done too. I learned C,Java,Python and use assignments a lot in every program I wrote.So it's really an eye-opening experience.I really hope someone can briefly explain how assignments are avoided in those functional programming languages and what profound impact(if any) it has on these languages. The example mentioned above is here: (define (make-withdraw balance) (lambda (amount) (if (>= balance amount) (begin (set! balance (- balance amount)) balance) "Insufficient funds"))) This changed the balance by set!.To me it looks a lot like a class method to change the class member balance. As I said,I am not familiar with functional programming languages,so if I said something wrong about them,feel free to point out.

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• What guidelines do you suggest for using Objective-C Properties?

  - by adarsha

  Objective-C 2.0 introduced properties. While I personally think properties are nice addition to the language, I have seen a trend of making every instance variable as a property. Apple sample codes are no exceptions to this. I believe this is against the spirit of OOP, and since it exposes a lot more implementation details of a class to the client than they need to know. What guidelines do you suggest for the proper usage properties in Objective C?

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• C++ and function pointers assessment: lack of inspiration

  - by OlivierDofus

  I've got an assessment to give to my students. It's about C++ and function pointers. Their skill is middle: it the first year of a programming school after bachelor. To give you something precise, here's a sample of a solution of one of 3 exercices they had to do in 30 minutes (the question was: "here's a version of a code that could be written with function pointers, write down the same thing but with function pointers"): typedef void (*fcPtr) (istream &); fcPtr ArrayFct [] = { Delete , Insert, Swap, Move }; void HandleCmd (const string && Cmd) { string AvalaibleCommands ("DISM"); string::size_type Pos; istringstream Flux (Cmd); char CodeOp; Flux >> CodeOp; Pos = AvalaibleCommands.find (toupper (CodeOp)); if (Pos != string::npos) { ArrayFct [Pos](Flux); } } Any idea where I could find some inspiration? Some of the students have understood the principles, even though it's very hard for them to write C++ code. I know them, I know they're clever, and I'm pretty sure they should be very good project managers. So, writing C++ code is not that important after all. Understanding is the most important part (IMHO). I'm wondering about maybe break the habits, and give half of the questions about the principle, or even better, give some sample in other language and ask them why it's better to use function pointers instead of classical programming (usually a big switch case). Any idea where I could look? Find some inspiration?

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• How should I determine my rates for writing custom software?

  - by Carson Myers

  For a custom software that will likely take a year or more to develop, how would I go about determining what to charge as a consultant? I'm having a hard time coming up with a number, and searches online are providing vastly different numbers (between $55/hr and $300/hr). I don't want to shoot too low because it's going to take me so much time (and I'm deferring my education for this project). I also don't want to shoot too high and get unpleasant looks and demand for justification. FWIW I live in Canada, and have approx. 10 years of development experience. I've read the "take your salary and divide it by 1000" rule of thumb, but the thing is I don't have a salary. Currently I'm just doing fairly small programming tasks for a friend who is starting a marketing company, pricing each task fairly arbitrarily. I don't know what I would make over the course of a year doing it, but it would be incredibly low. My responsibilities for the project would be the architecture, programming, database, server, and UX to some degree. It's going to be a public facing web service so I will also need to put a lot of effort into security and scalability. Any advice or experience?

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• documentation of typescript code

  - by Max Beikirch

  my question is rather short: How do I document typescript code properly? I found out that for projects becoming bigger and bigger, it is important to look at a function and immediately know parameters, what it returns and side-effects etc. It is tiring to have just a bunch of comments before a function, most of the time these 'blocks' even look differently in style. What I am looking for is a documentation tool like javadoc or doxygen for typescript. Is there anything out there? Or is it possible to 'abuse' a documentation tool and get it to work with typescript?

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• Is there a variable width font that does not change width when adding effects like bold, italic?

  - by George Bailey

  NetBeans has a word wrap feature now - but if the font changes width when bold then it gets all jumpy and sometimes hard to work with. Edit: It turns out that even with Courier New that NetBeans word wrap still jumps up and down lines at a time at random. I guess that this question no longer cares for an answer. However,, it seems that there is no answer. (at least nobody has brought one up yet) I am currently using Comic Sans MS which gets wider when bold.

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• What does your Lisp workflow look like?

  - by Duncan Bayne

  I'm learning Lisp at the moment, coming from a language progression that is Locomotive BASIC - Z80 Assembler - Pascal - C - Perl - C# - Ruby. My approach is to simultaneously: write a simple web-scraper using SBCL, QuickLisp, closure-html, and drakma watch the SICP lectures I think this is working well; I'm developing good 'Lisp goggles', in that I can now read Lisp reasonably easily. I'm also getting a feel for how the Lisp ecosystem works, e.g. Quicklisp for dependencies. What I'm really missing, though, is a sense of how a seasoned Lisper actually works. When I'm coding for .NET, I have Visual Studio set up with ReSharper and VisualSVN. I write tests, I implement, I refactor, I commit. Then when I'm done enough of that to complete a story, I write some AUATs. Then I kick off a Release build on TeamCity to push the new functionality out to the customer for testing & hopefully approval. If it's an app that needs an installer, I use either WiX or InnoSetup, obviously building the installer through the CI system. So, my question is: as an experienced Lisper, what does your workflow look like? Do you work mostly in the REPL, or in the editor? How do you do unit tests? Continuous integration? Packaging & deployment? When you sit down at your desk, steaming mug of coffee to one side and a framed photo of John McCarthy to the other, what is it that you do? Currently, I feel like I am getting to grips with Lisp coding, but not Lisp development ...

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• Brief explanation for executables in a GNU/Clang Toolchain?

  - by ZhangChn

  I roughly understand that cc, ld and other parts are called in a certain sequence according to schemes like Makefiles etc. Some of those commands are used to generate those configs and Makefiles. And some other tools are used to deal with libraries. But what are other parts used for? How are they called in this process? Which tool would use various parser generators? Which part is optional? Why? Is there a brief summary get these explained on how the tools in a GNU or LLVM/Clang toolchain are organised and called in a C/C++ project building? Thanks in advance. EDIT: Here is a list of executables for Clang/LLVM on Mac OS X: ar clang dsymutil gperf libtool nmedit rpcgen unwinddump as clang++ dwarfdump gprof lorder otool segedit vgrind asa cmpdylib dyldinfo indent m4 pagestuff size what bison codesign_allocate flex install_name_tool mig ranlib strip yacc c++ ctags flex++ ld mkdep rebase unifdef cc ctf_insert gm4 lex nm redo_prebinding unifdefall

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• Pythonic use of the isinstance function?

  - by Pace

  Whenever I find myself wanting to use the isinstance() function I usually know that I'm doing something wrong and end up changing my ways. However, in this case I think I have a valid use for it. I will use shapes to illustrate my point although I am not actually working with shapes. I am parsing XML configuration files that look like the following: <square> <width>7</width> </square> <rectangle> <width>5</width> <height>7</height> </rectangle> <circle> <radius>4</radius> </circle> For each element I create an instance of the Shape class and build up a list of Shape objects in a class called the ShapeContainer. Different parts of the rest of my application need to refer to the ShapeContainer to get certain shapes. Depending on what the code is doing it might need just rectangles, or it might operate on all quadrangles, or it might operate on all shapes. I have created the following function in the ShapeContainer class (the actual function uses a list comprehension but I have expanded it here for readability): def locate(self, shapeClass): result = [] for shape in self.__shapes: if isinstance(shape,shapeClass): result.append(shape) return result Is this a valid use of the isinstance function? Is there another way I can do this which might be more pythonic?

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• Class Design for special business rules

  - by Samuel Front

  I'm developing an application that allows people to place custom manufacturing orders. However, while most require similar paperwork, some of them have custom paperwork that only they require. My current class design has a Manufacturer class, of which of one of the member variables is an array of RequiredSubmission objects. However, there are two issues that I am somewhat concerned about. First, some manufacturers are willing to accept either a standard form or their own custom form. I'm thinking of storing this in the RequiredSubmission object, with an array of alternate forms that are a valid substitute. I'm not sure that this is ideal, however. The major issue, however, is that some manufacturers have deadline cycles. For example, forms A, B and C have to be delivered by January 1, while payment must be rendered by January 10. If you miss those, you'll have to wait until the next cycle. I'm not exactly sure how I can get this to work with my existing classes—how can I say "this set of dates all belong to the same cycle, with date A for form A, date B for form B, etc." I would greatly appreciate any insights on how to best design these classes.

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• Why use link classes in oql instead of classes that contain links

  - by Isaac

  itop abstracts its very complex database design with an object query language (oql). For this there are classes definded, like 'Ticket' and 'Server'. Now a Ticket usually is linked to a Server. In my naive way I would give the Ticket class an attribute 'affected_server_list', where I could reference the affected servers. itop does it different: neither Servers nor Tickets know of each other. Instead there is a class 'linkTicketToServer', which provides the link between the two. The first thing I noticed is that it makes oql queries more complex. So I wondered why they designed it this way. One thing that occured to me is that it allows for more flexiblity, in that I can add links without modifying the original classes. Is this allready why one would implement it this way, or are there other reasons for this kind of design?

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• Reading source code to learn

  - by perl.j

  As you develop as a programmer, IMO, you begin to see different practices, different Algorithms, and "more than one way to do it". Seeing this code can be a great learning experience for you, even though you did not write the code. But is doing this only going to confuse you? For example, let's say you have a library in any language that was created by a colleague, and you have been using it for a while. You decide to look at the actual source code, regardless of how extensive it is, and get a better look at how this library is written. For the sake of example, the function you use most often from this library is the max function, which finds the largest of two numbers. But this function is a lot more complicated than it needs to be. The way it is written is confusing the heck out of you, and you don't know how this works. Will this make you a better programmer, because you realize how complicated it is for such a simple function, or will it make you a worse coder because you feel less confidant? So my question, in general, is does reading source code make you a better programmer and if so how? If not why do people still do it?.

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• Somewhere to get inspiration - Pair up the creative with the tech

  - by Morten Bergfall

  I am a somewhat green developer; some work experience, last year of school. As most of you, I am constantly working on an assortment of personal projects. Since my mind often has a somewhat drifting characteristic; I am not always able to keep the projects in check. After some time they all exhibit the moral fiber of Vikings, harlots and chain-letter-knitters. This includes constant forking, round-abouting, eating of school assignments of rather mundane, and hence pretty yawn-inducing, specifications, and of course quite a bit of gathering of folder dust. Well, on to my question....is there a place, forum... or something with the purpose of linking people with ideas to the people actually being able to bring said ideas to life? Of course, I know of the professional ones, like rent-a-coder and such. And there seem to be a lot of open source projects available for participation. What I'm looking for doesn't really fit into any of those categories....the form would be somewhat like rent-a-coder, but this is ideas&inspiration, not bubble-sort-my-quarterly-for-a-buck. The possibilities for developing bonds, spicy code, and plain old fun seem quite possible.As I see it, the main benefit would be that we (that is the tech-flipside of the proverbial eCoin) get something worthwhile to do, rather than squeeze the last creative grain out of our code-heavy brains.To give it some perspective...: My last project consists of an absurd jQuery-plugin that includes animated png-robots migrating from Google Earth to drag a html-element of your choosing onto the map, where it gets color, for so to be dragged back by this poorly animated robot.... Often, the line between the creative and the tech is blurred, to say the least. I wouldn't think that would be a problem. Think someone who has developed a nifty little windows application, then sees possibility for a broader use, perhaps some sort of networking functionality. This fellow sadly lacks the skill to implememet this. So he, she or it would then seek a developer with the know-how and they could complete this project together. So, do any of you know of such a place, or can nudge in the right direction? And yes, I understand completely that I should be dedicating myself to doing school work, or applying for mundane developer positions, so please.... :-) UPDATE Sadly, I'm situated in Oslo, Norway, and the number of developers are somewhat limited...and I have had quite some ahem personality issues with the ones who are available ;-) So I feel I must go deeper; search the multitude of the web...

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• How to start competitive programming?

  - by Vaibhav Agarwal

  I am practicing coding for a while but the problem is that it takes me a lot of time to write a solution for the problems. I want to ask if competitive programming can help me in improving this? If yes, then how should I start and from what site like TopCoder? I would obviously won't be able to solve very hard problems for now. What should I do? If no, what else should I do? I also have another problem that I want to learn coding but the thing is that I feel that I am not very good at it. What should I do? It's like bugging me from inside. I know some people may not find this question informative but please at least allow me to get an answer.

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• How to solve SocketException: Permission denied: connect

  - by luxinxian

  I recently encountered a problem getting a headache, need help... System consists of: Two subsystems, called A, B (each running on a standalone tomcat instance), currently running on the same machine. A invoke B's service via spring httpInvoker(http). B system also invoke other system's services via http. Symptoms: 1, the system starts to run normally after 10-15 days; 2, the system will run for a period of time after an exception: org.springframework.remoting.RemoteAccessException: Could not access HTTP invoker remote service at [http://xxx.xxx.xxx.xxx/remoting/call]; nested exception is java. net.SocketException: Permission denied: connect 3, when the exception occour, it continues, not only occasional .(it looks like some resources exhausted, but cpu rate < 5%, memory < 15%, network < 5%) 4, A, B when the system call fails, B system via http call to an external service also failed for the same exception. 5, closed two tomcat services, restart, and working properly. So repeatedly (step 1 - 5), has not found the root reason. Emvironment: windows 2008 R2 tomcat7.0.42 x86_64 oralce-jdk-1.7.0_40 Any ideas?

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• What technique to use when trying to drag elements around on a canvas

  - by choise

  I want to achieve two things in my java swing application: First, i need a canvas zone where i can drag elements (a rectangle or a circle) from the outside of a pane inside the canvas and place it at the position where they where dropped. also it should be possible to select an element on the canvas and move it around and drop it on another location on the canvas. what techniques would fit best to do such a job? Please leave a comment if something is unclear.

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• Starting web development with ASP.Net [closed]

  - by nayef harb

  Possible Duplicate: Fastest way to get up to speed on webapp development with ASP.NET? If you develop with ASP.NET, which other technologies do you use? How much do i need to learn in order to get an entry level asp.net job? training plan for asp.net and c# Trying to learn ASP.NET What should every programmer know about web development? I learned web development in ASP.Net couple of month ago in college, nothing serious just couple of general lessons. But now I am confused where to start, should I start with HTML and JavaScript before ASP.Net?

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• Need help with this question [closed]

  - by Jaime

  Occasionally, multiplying the sizes of nested loops can give an overestimate for the Big-Oh running time. This result happens when an innermost loop is infrequently executed. Give the Big-O analysis of the running time. Implement the following code and run for several values of N, and compare your analysis with the actual running times. for(int i = 1; i <= n; i++) for(int j = 1; j<=i * i; j++) if(j%i == 0) for(int k = 0; k < j; k++) sum++;

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• Card deck and sparse matrix interview questions

  - by MrDatabase

  I just had a technical phone screen w/ a start-up. Here's the technical questions I was asked ... and my answers. What do think of these answers? Feel free to post better answers :-) Question 1: how would you represent a standard 52 card deck in (basically any language)? How would you shuffle the deck? Answer: use an array containing a "Card" struct or class. Each instance of card has some unique identifier... either it's position in the array or a unique integer member variable in the range [0, 51]. Shuffle the cards by traversing the array once from index zero to index 51. Randomly swap ith card with "another card" (I didn't remember how this shuffle algorithm works exactly). Watch out for using the same probability for each card... that's a gotcha in this algorithm. I mentioned the algorithm is from Programming Pearls. Question 2: how to represent a large sparse matrix? the matrix can be very large... like 1000x1000... but only a relatively small number (~20) of the entries are non-zero. Answer: condense the array into a list of the non-zero entries. for a given entry (i,j) in the array... "map" (i,j) to a single integer k... then use k as a key into a dictionary or hashtable. For the 1000x1000 sparse array map (i,j) to k using something like f(i, j) = i + j * 1001. 1001 is just one plus the maximum of all i and j. I didn't recall exactly how this mapping worked... but the interviewer got the idea (I think). Are these good answers? I'm wondering because after I finished the second question the interviewer said the dreaded "well that's all the questions I have for now." Cheers!

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• What is the diffference between "data hiding" and "encapsulation"?

  - by john smith optional

  I'm reading "Java concurrency in practice" and there is said: "Fortunately, the same object-oriented techniques that help you write well-organized, maintainable classes - such as encapsulation and data hiding -can also help you crate thread-safe classes." The problem #1 - I never heard about data hiding and don't know what it is. The problem #2 - I always thought that encapsulation is using private vs public, and is actually the data hiding. Can you please explain what data hiding is and how it differs from encapsulation?

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