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• Can't understand example using continuations

  - by Matt Fenwick

  I'm reading the r6rs Scheme report and am confused by the explanation of continuations (I find it to be too dense and lacking of examples for a beginner). What is this code doing and how does it evaluate to 4? Why does call/cc want an argument that's a function of one argument? How is call/cc's argument used? (+ 1 (call-with-current-continuation (lambda (escape) (+ 2 (escape 3))))) =? 4 This example is from section 1.11 - Continuations.

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• Is there something better than a StringBuilder for big blocks of SQL in the code

  - by Eduardo Molteni

  I'm just tired of making a big SQL statement, test it, and then paste the SQL into the code and adding all the sqlstmt.append(" at the beginning and the ") at the end. It's 2011, isn't there a better way the handle a big chunk of strings inside code? Please: don't suggest stored procedures or ORMs. edit Found the answer using XML literals and CData. Thanks to all the people that actually tried to answer the question without questioning me for not using ORM, SPs and using VB edit 2 the question leave me thinking that languages could try to make a better effort for using inline SQL with color syntax, etc. It will be cheaper that developing Linq2SQL. Just something like: dim sql = <sql> SELECT * ... </sql>

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• What is Object Oriented Programming ill-suited for?

  - by Richard JP Le Guen

  In Martin Fowler's book Refactoring, Fowler speaks of how when developers learn something new, they don't consider when it's inappropriate for the job: Ten years ago it was like that with objects. If someone asked me when not to use objects, it was hard to answer. [...] It was just that I didn't know what those limitations were, although I knew what the benefits were. Reading this, it occurred to me I don't know what the limitations or potential disadvantages of Object-Oriented Programming are. What are the limitations of Object Oriented Programming? When should one look at a project and think "OOP is not best suited for this"?

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• How can an SQL relational database be used to model a thesaurus? [closed]

  - by Miles O'Keefe

  I would like to design a web app that functions as a simple thesaurus: a long list of words with attributes, all of which are linked to each other. This thesaurus data model can be defined as: a controlled vocabulary arranged in a known order in which equivalence, hierarchical, and associative relationships among terms are clearly displayed and identified by standardized relationship indicators. My idea so far is to have one database in which every word is a table, and every table contains all words related to that word. e.g. Thesaurus(database) - happy(table) - excited(row)|cheerful(row)|lively(row) Is there are more efficient way to store words and their relationship to other words in a relational SQL database?

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• How to Detect Sprites in a SpriteSheet?

  - by IAE

  I'm currently writing a Sprite Sheet Unpacker such as Alferds Spritesheet Unpacker. Now, before this is sent to gamedev, this isn't necessarily about games. I would like to know how to detect a sprite within a spriitesheet, or more abstactly, a shape inside of an image. Given this sprite sheet: I want to detect and extract all individual sprites. I've followed the algorithm detailed in Alferd's Blog Post which goes like: Determine predominant color and dub it the BackgroundColor Iterate over each pixel and check ColorAtXY == BackgroundColor If false, we've found a sprite. Keep going right until we find a BackgroundColor again, backtrack one, go down and repeat until a BackgroundColor is reached. Create a box from location to ending location. Repeat this until all sprites are boxed up. Combined overlapping boxes (or within a very short distance) The resulting non-overlapping boxes should contain the sprite. This implementation is fine, especially for small sprite sheets. However, I find the performance too poor for larger sprite sheets and I would like to know what algorithms or techniques can be leveraged to increase the finding of sprites. A second implementation I considered, but have not tested yet, is to find the first pixel, then use a backtracking algorithm to find every connected pixel. This should find a contiguous sprite (breaks down if the sprite is something like an explosion where particles are no longer part of the main sprite). The cool thing is that I can immediately remove a detected sprite from the sprite sheet. Any other suggestions?

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• what's the point of method overloading?

  - by David

  I am following a textbook in which I have just come across method overloading. It briefly described method overloading as: when the same method name is used with different parameters its called method overloading. From what I've learned so far in OOP is that if I want different behaviors from an object via methods, I should use different method names that best indicate the behavior, so why should I bother with method overloading in the first place?

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• Books, resources and so on about GUI architecture [on hold]

  - by Moses

  I'm making first steps in GUI programming. Earlier I've had little experience with GUI and I remember that it was kind of pain. Code was either coupled or to verbose with tons of "Listeners". It seems to me that problem in me and not in a library that I used(Swing). So, could you recommend me some books, tutorials or resources where I can find how to design gui programms? Emphasize that I'm interested in architecture and not in how to use components of some framework(which about 90% of tutorials that I've ever seen).

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• Subsumption architecture vs. perceptual control theory

  - by Yasir G.

  I'm a new person to AI field and I have to research and compare 2 different architectures for a thesis I'm writing. Before you scream (homework thread), I've been reading on these 2 topics only to find that I'm confusing myself more.. let me first start with stating briefly what I know so far. Subsumption is based on the fact that targets of a system are different in sophistication, thus that requires them to be added as layers, each layer can suppress (modify) the command of the layers below it, and there are inhibitors to stop signals from execution lets say. PCT stresses on the fact that there are nodes to handle environmental changes (negative feedback), so the inputs coming from an environment go through a comparator node and then an action is generated by that node, HPCT or (Hierarchical PCT) is based on nesting these cycles inside each other so a small cycle to avoid crashing would be nested in a more sophisticated cycle that targets a certain location for example. My questions, am I getting this the right way? am I missing any critical understanding about these 2 models? also any idea where I can find simplified explanations for each theory (so far been struggling trying to understand the papers from Google scholar :< ) /Y

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• Development-led security vs administration-led security in a software product?

  - by haylem

  There are cases where you have the opportunity, as a developer, to enforce stricter security features and protections on a software, though they could very well be managed at an environmental level (ie, the operating system would take care of it). Where would you say you draw the line, and what elements do you factor in your decision? Concrete Examples User Management is the OS's responsibility Not exactly meant as a security feature, but in a similar case Google Chrome used to not allow separate profiles. The invoked reason (though it now supports multiple profiles for a same OS user) used to be that user management was the operating system's responsibility. Disabling Web-Form Fields A recurrent request I see addressed online is to have auto-completion be disabled on form fields. Auto-completion didn't exist in old browsers, and was a welcome feature at the time it was introduced for people who needed to fill in forms often. But it also brought in some security concerns, and so some browsers started to implement, on top of the (obviously needed) setting in their own preference/customization panel, an autocomplete attribute for form or input fields. And this has now been introduced into the upcoming HTML5 standard. For browsers that do not listen to this attribute, strange hacks* are offered, like generating unique IDs and names for fields to avoid them from being suggested in future forms (which comes with another herd of issues, like polluting your local auto-fill cache and not preventing a password from being stored in it, but instead probably duplicating its occurences). In this particular case, and others, I'd argue that this is a user setting and that it's the user's desire and the user's responsibility to enable or disable auto-fill (by disabling the feature altogether). And if it is based on an internal policy and security requirement in a corporate environment, then substitute the user for the administrator in the above. I assume it could be counter-argued that the user may want to access non-critical applications (or sites) with this handy feature enabled, and critical applications with this feature disabled. But then I'd think that's what security zones are for (in some browsers), or the sign that you need a more secure (and dedicated) environment / account to use these applications. * I obviously don't deny the ingeniosity of the people who were forced to find workarounds, just the necessity of said workarounds. Questions That was a tad long-winded, so I guess my questions are: Would you in general consider it to be the application's (hence, the developer's) responsiblity? Where do you draw the line, if not in the "general" case?

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• Good Practices for writing large (team/solo) projects (In C)

  - by Moshe Magnes

  Since I started learning C a few years ago, I have never been a part of a team that worked on a project. Im very interested to know what are the best practices for writing large projects in C. One of the things i want to know, is when (not how) do I split my project into different source files. My previous experience is with writing a header-source duo (the functions defined in the header are written in the source). I want to know what are the best practices for splitting a project, and some pointers on important things when writing a project as part of a team.

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• How to refactor an OO program into a functional one?

  - by Asik

  I'm having difficulty finding resources on how to write programs in a functional style. The most advanced topic I could find discussed online was using structural typing to cut down on class hierarchies; most just deal with how to use map/fold/reduce/etc to replace imperative loops. What I would really like to find is an in-depth discussion of an OOP implementation of a non-trivial program, its limitations, and how to refactor it in a functional style. Not just an algorithm or a data structure, but something with several different roles and aspects - a video game perhaps. By the way I did read Real-World Functional Programming by Tomas Petricek, but I'm left wanting more.

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• Dependency Checker/ Installer With Java/Ant

  - by jsn

  I need some kind of software to easily roll out code on new servers. I use Apache Ant for builds. However, say I want to set-up a new server fast and my Java program depends on GhostScript, if there any software that can automatically check the computer for it (and then maybe the PATH) and add it if is not there? I have already looked at Maven and Apache Ivy, however, I think these are only for .jar files (from what I saw). Thanks for any help.

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• Using an AGPL 3.0-licensed library for extra functionality in an iOS app

  - by Arnold Sakhnov

  I am building an iOS application, and I am planning to incorporate an AGPL 3.0-licensed library to it to provide some extra (non-essential) functionality. I’ve got a couple of questions regarding this: Do I understand it right that this still obliges me to publish the source of my app open? If yes, does it have to be open to the general public, or only to those who have downloaded the app? Does this allow me to distribute the app for a fee?

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• Notifying a separate application of an event

  - by TomDestry

  I have an application that runs through various tasks as an automated process. My client would like me to create a file in a given folder for each task as a way to flag when each task completes. They prefer this to a database flag because they can be notified by the file system rather than continually polling a database table. I can do this but creating and deleting files as flags feels clunky. Is there a more elegant approach to notifying a third-party of an event?

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• Languages/Methods to Learn for Scientific Computing?:

  - by Zéychin

  I'm a second-semester Junior working towards a Computer Science degree with a Scientific Computing concentration and a Mathematics degree with a concentration on Applied Discrete Mathematics. So, number crunching and such rather than a bunch of regular expressions, interface design, and networking. I've found that I'm not learning new relevant languages from my coursework and am interested in what the community would recommend me to learn. I know as far as programming methods go, I need to learn more about parallelizing programs, but if there's anything else you can recommend, I would appreciate it. Here's a list of the languages with which I am very experienced (web technologies omitted as they barely apply here). Any recommendations for additional languages I should learn would be very much appreciated!: Java C C++ Fortran77/90/95 Haskell Python MATLAB

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• Difference between jquery.clone() and simple concatenation of string [closed]

  - by Francis Cebu

  Which of the following code samples is faster in generating HTML code using jQuery? Sample 1: var div = $("<div>"); $.each(data,function(count,item){ var Elem = div.clone().addClass("message").html(item.Firstname); $(".container").append(Elem); }); Sample 2: $.each(data,function(count,item){ var Elem = "<div class = 'Elem'>" + item.Firstname + "</div>"; $(".container").append(Elem); });

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• Dual Inspection / Four Eyes Principle

  - by Ralf

  I have the requirement to implement some kind of dual inspection or four-eyes principle as a feature of my software, meaning that every change of an object done by user A has to be checked by user B. A trivial example would be a publishing system where an author writes an article and another has to proofread it before it is published. I am a little bit surprised that you find nearly nothing about it on the net. No patterns, no libraries (besides cibet), no workflow solutions etc. Is this requirement really so uncommon? Or am I searching for the wrong terms? I am not looking for a specific solution. More for a pattern or best practice approach. Update: the above example is really trivial. Let's add some more complexity to it. The article has been published, but it now needs an update. Putting the article offline for the update is not an option, but the update has to be proof read, too.

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• Best practice for marking a bug as resolved in Bugzilla ?

  - by Vincent B.

  I am wondering what is the best way to handle the situation of marking a bug as resolved and providing a version of component/product in which this fix can be found. Context For a project I am working on, we are using Bugzilla for issue tracking, and we have the following: A product "A" with a version number like vA.B.C.D, This product "A" have the following components: Component "C1" with a version number like vA.B.C.D, Component "C2" with a version number like vA.B.C.D, Component "C3" with a version number like vA.B.C.D. Internally we keep track of which component versions have been used to generate the product A version vA.B.C.D. Example: Product "A" version v1.0.0.0 has been produced from component "C1" v1.0.0.3, component "C2" v1.3.0.0 and component "C3" v2.1.3.5. And Product "A" version v1.0.1.0 has been produced from component "C1" v1.0.0.4, component "C2" v1.3.0.0 and component "C3" v2.1.3.5. Each component is a SVN repository. The person in charge of generating the product "A" have only access to the different components tags folder in SVN, and not the trunk of each component repository. Problem Now the problem is the following, when a bug is found in the product "A", and that the bug is related to Component "C1", the version of product "A" is chosen (e.g. v1.0.0.0), and this version allow the developer to know which version of component "C1" has the bug (here it will be v1.0.0.3). A bug report is created. Now let's say that the developer responsible for component "C1" corrects the bug, then when the bug seems to be fixed and after some test and validation, the developer generates a new tag for component "C1", with the version v1.0.0.4. At this time, the developer of component "C1" needs to update the bug report, but what is the best to do: Mark the bug as resolved/fixed and add a comment saying "This bug has been fixed in the tags v1.0.0.4 of C1 component" ? Keep the bug as assigned, add a comment saying "This bug has been fixed in the tags v1.0.0.4 of C1 component, update this bug status to resolved for the next version of the product that will be generated with the newest version (v1.0.0.4 of C1)" ? Another possible way to deal with this problem. Right now the problem is that when a product component CX is fixed, it is not sure in which future version of the product A it will be included, so it is for me not possible to say in which version of the product it will be solved, but it is possible to say in which version of the Component CX it has been solved. So when do we need to mark a bug as solved, when the product A version include the fixed version of CX, or only when CX component has been fixed ? Thanks for your personal feedback and ideas about this !

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• from Java to SAS

  - by Giovanni Rossi

  I am a seasoned python,java,...other programmer having a (fairly advanced) mathematical education (so I do understand statistics and data mining, for example) . For various reasons I am thinking to switch to SAS/BI area (I am naming SAS because it might be, for me, a possible way to enter in BI). My question, for whoever might have an experience of both: is it, in BI current state, worth it? I mean, the days of big ideas in BI for business seem to be over (there are the APIs, managers think that they know what you can do with them), and my mathematical background might turn out to be superflous. Also, the big companies now have their data organized, have their BI procedures well established, and trying to analyze it from a different standpoint might not be what they want. Another difference is: while in Java etc. development one codes and codes and codes, I don't know if this is the case for BI; in fact, from what I read on the net, a BI (or OLAP, ...etc) developer, in a big organization, is usually in a state of standby, and does in fact little coding. Any opinions, and in particular strong opinions, will be appreciated.

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• Would Using a PHP Framework Be Beneficial in My Context?

  - by Fractal

  I've just started work at a small start-up company who mainly uses PHP to develop their front-end apps. I had no prior PHP experience before joining, and this has led to my apps becoming large pieces of spaghetti code. I essentially started by adding code to implement an initial feature, and then continued to hack in more code to implement further features – without much thought for the overall design. The apps themselves output XML to render on small mobile devices. I recently started looking into frameworks that I could use. I reckon an advantage would be that they seem to force developers to modularise their programs using good-practice design patterns. This seems great for someone in my position. The extra functions they provide, for example: interfacing with databases in such a way as to make SQL injection impossible, would be very useful too. The downside I can see is that there will be a lot of overhead for me in terms of the time taken to learn the framework itself (while still getting to grips with PHP itself). I'm also worried that it will be overkill for the scale of the apps we develop. They tend to be programs that interface with a fairly simple back-end DB, and will generate about 5 different XML screens. Probably around 1 or 2 thousand lines of code. The time it takes just to configure the frameworks may not be worth it. The final problem I can see is that developers in the company – who have to go over my code, and who do not know the PHP framework I may use – will have a much harder time understanding it. Given those pros and cons, I'm still not sure on what the best course of action will be; so any advice will be greatly appreciated.

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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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• Business Logic Layer in MVC Application

  - by Subin Jacob

  In my ASP MVC application I decided to add another Business Layer and made the model only to have properties. All other functionality like save to db, get from db is done on this new Business layer. So now the controller will be calling this business layer and model for various operations. Is it a good approach to design like this? I decided not to use model for this purpose because I would need a number of models for different actions. (for eg, one for edit and other for create)

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• Design pattern for client/server sessions?

  - by nonot1

  Are there any common patterns or general guidance I can learn from for how to design a client/server system where the both the client and server must maintain some kind per-client session state? I've found any number of libraries that can help with some of the plumbing, but it's the overall design I'm wondering about. Open issues in my mind: How to structure the client/server communication so that bidirectional synchronous and asynchronous requests are possible? The server side needs to spawn a couple of per-connected-client session-long helper process. How to manage that? How to manage the mapping from a given client (and any of it's requests) to server state and helper process instances in the face of multiple clients and intermittent network connectivity. Most communication can be simple blocking request/reply, but some will be long running processing tasks that the client will want to keep tabs on. To the extent that it matters, the platform is Linux/C/C++. Not web based. Just an existing thick-client software app being modified to talk to backend servers for some tasks.

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• How can I separate the user interface from the business logic while still maintaining efficiency?

  - by Uri

  Let's say that I want to show a form that represents 10 different objects on a combobox. For example, I want the user to pick one hamburguer from 10 different ones that contain tomatoes. Since I want to separate UI and logic, I'd have to pass the form a string representation of the hamburguers in order to display them on the combobox. Otherwise, the UI would have to dig into the objects fields. Then the user would pick a hamburguer from the combobox, and submit it back to the controller. Now the controller would have to find again said hamburguer based on the string representation used by the form (maybe an ID?). Isn't that incredibly inefficient? You already had the objects you wanted to pick one from. If you submited to the form the whole objects, and then returned a specific object, you wouldn't have to refind it later on since the form already returned a reference to that object. Moreover, if I'm wrong and you actually should send the whole object to the form, how can I isolate UI from logic?

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• Improving the running time of Breadth First Search and Adjacency List creation

  - by user45957

  We are given an array of integers where all elements are between 0-9. have to start from the 1st position and reach end in minimum no of moves such that we can from an index i move 1 position back and forward i.e i-1 and i+1 and jump to any index having the same value as index i. Time Limit : 1 second Max input size : 100000 I have tried to solve this problem use a single source shortest path approach using Breadth First Search and though BFS itself is O(V+E) and runs in time the adjacency list creation takes O(n2) time and therefore overall complexity becomes O(n2). is there any way i can decrease the time complexity of adjacency list creation? or is there a better and more efficient way of solving the problem? int main(){ vector<int> v; string str; vector<int> sets[10]; cin>>str; int in; for(int i=0;i<str.length();i++){ in=str[i]-'0'; v.push_back(in); sets[in].push_back(i); } int n=v.size(); if(n==1){ cout<<"0\n"; return 0; } if(v[0]==v[n-1]){ cout<<"1\n"; return 0; } vector<int> adj[100001]; for(int i=0;i<10;i++){ for(int j=0;j<sets[i].size();j++){ if(sets[i][j]>0) adj[sets[i][j]].push_back(sets[i][j]-1); if(sets[i][j]<n-1) adj[sets[i][j]].push_back(sets[i][j]+1); for(int k=j+1;k<sets[i].size();k++){ if(abs(sets[i][j]-sets[i][k])!=1){ adj[sets[i][j]].push_back(sets[i][k]); adj[sets[i][k]].push_back(sets[i][j]); } } } } queue<int> q; q.push(0); int dist[100001]; bool visited[100001]={false}; dist[0]=0; visited[0]=true; int c=0; while(!q.empty()){ int dq=q.front(); q.pop(); c++; for(int i=0;i<adj[dq].size();i++){ if(visited[adj[dq][i]]==false){ dist[adj[dq][i]]=dist[dq]+1; visited[adj[dq][i]]=true; q.push(adj[dq][i]); } } } cout<<dist[n-1]<<"\n"; return 0; }

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