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  • How to Elegantly convert switch+enum with polymorphism

    - by Kyle
    I'm trying to replace simple enums with type classes.. that is, one class derived from a base for each type. So for example instead of: enum E_BASE { EB_ALPHA, EB_BRAVO }; E_BASE message = someMessage(); switch (message) { case EB_ALPHA: applyAlpha(); case EB_BRAVO: applyBravo(); } I want to do this: Base* message = someMessage(); message->apply(this); // use polymorphism to determine what function to call. I have seen many ways to do this which all seem less elegant even then the basic switch statement. Using dyanimc_pointer_cast, inheriting from a messageHandler class that needs to be updated every time a new message is added, using a container of function pointers, all seem to defeat the purpose of making code easier to maintain by replacing switches with polymorphism. This is as close as I can get: (I use templates to avoid inheriting from an all-knowing handler interface) class Base { public: template<typename T> virtual void apply(T* sandbox) = 0; }; class Alpha : public Base { public: template<typename T> virtual void apply(T* sandbox) { sandbox->applyAlpha(); } }; class Bravo : public Base { public: template<typename T> virtual void apply(T* sandbox) { sandbox->applyBravo(); } }; class Sandbox { public: void run() { Base* alpha = new Alpha; Base* bravo = new Bravo; alpha->apply(this); bravo->apply(this); delete alpha; delete bravo; } void applyAlpha() { // cout << "Applying alpha\n"; } void applyBravo() { // cout << "Applying bravo\n"; } }; Obviously, this doesn't compile but I'm hoping it gets my problem accross.

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  • Using table-of-contents in code?

    - by AareP
    Do you use table-of-contents for listing all the functions (and maybe variables) of a class in the beginning of big source code file? I know that alternative to that kind of listing would be to split up big files into smaller classes/files, so that their class declaration would be self-explanatory enough.. but some complex tasks require a lot of code. I'm not sure is it really worth it spending your time subdividing implementation into multiple of files? Or is it ok to create an index-listing additionally to the class/interface declaration?

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  • Is my method for avoiding dynamic_cast<> faster than dynamic_cast<> itself ?

    - by ereOn
    Hi, I was answering a question a few minutes ago and it raised to me another one: In one of my projects, I do some network message parsing. The messages are in the form of: [1 byte message type][2 bytes payload length][x bytes payload] The format and content of the payload are determined by the message type. I have a class hierarchy, based on a common class Message. To instanciate my messages, i have a static parsing method which gives back a Message* depending on the message type byte. Something like: Message* parse(const char* frame) { // This is sample code, in real life I obviously check that the buffer // is not NULL, and the size, and so on. switch(frame[0]) { case 0x01: return new FooMessage(); case 0x02: return new BarMessage(); } // Throw an exception here because the mesage type is unknown. } I sometimes need to access the methods of the subclasses. Since my network message handling must be fast, I decived to avoid dynamic_cast<> and I added a method to the base Message class that gives back the message type. Depending on this return value, I use a static_cast<> to the right child type instead. I did this mainly because I was told once that dynamic_cast<> was slow. However, I don't know exactly what it really does and how slow it is, thus, my method might be as just as slow (or slower) but far more complicated. What do you guys think of this design ? Is it common ? Is it really faster than using dynamic_cast<> ? Any detailed explanation of what happen under the hood when one use dynamic_cast<> is welcome !

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  • What are the worst examples of moral failure in the history of software engineering?

    - by Amanda S
    Many computer science curricula include a class or at least a lecture on disasters caused by software bugs, such as the Therac-25 incidents or Ariane 5 Flight 501. Indeed, Wikipedia has a list of software bugs with serious consequences, and a question on StackOverflow addresses some of them too. We study the failures of the past so that we don't repeat them, and I believe that rather than ignoring them or excusing them, it's important to look at these failures squarely and remind ourselves exactly how the mistakes made by people in our profession cost real money and real lives. By studying failures caused by uncaught bugs and bad process, we learn certain lessons about rigorous testing and accountability, and we make sure that our innocent mistakes are caught before they cause major problems. There are kinds of less innocent failure in software engineering, however, and I think it's just as important to study the serious consequences caused by programmers motivated by malice, greed, or just plain amorality. Thus we can learn about the ethical questions that arise in our profession, and how to respond when we are faced with them ourselves. Unfortunately, it's much harder to find lists of these failures--the only one I can come up with is that apocryphal "DOS ain't done 'til Lotus won't run" story. What are the worst examples of moral failure in the history of software engineering?

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  • Should I define a single "DataContext" and pass references to it around or define muliple "DataConte

    - by Nate Bross
    I have a Silverlight application that consists of a MainWindow and several classes which update and draw images on the MainWindow. I'm now expanding this to keep track of everything in a database. Without going into specifics, lets say I have a structure like this: MainWindow Drawing-Surface Class1 -- Supports Drawing DataContext + DataServiceCollection<T> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) Class3 Each "Class" is passed a reference to the Drawing Surface so they can interact with it independently. I'm starting to use WCF Data Services in Class1 and its working well; however, the other classes are also going to need access to the WCF Data Services. (Should I define my "DataContext" in MainWindow and pass a reference to each child class?) Class1 will need READ access to the "transactions" data, and Class2 will need READ access to some of the drawing data. So my question is, where does it make the most sense to define my DataContext? Does it make sense to: Define a "global" WCF Data Service "Context" object and pass references to that in all of my subsequent classes? Define an instance of the "Context" for each Class1, Class2, etc Have each method that requires access to data define its own instance of the "Context" and use closures handle the async load/complete events? Would a structure like this make more sense? Is there any danger in keeping an active "DataContext" open for an extended period of time? Typical usecase of this application could range from 1 minute to 40+ minutes. MainWindow Drawing-Surface DataContext Class1 -- Supports Drawing DataServiceCollection<DrawingType> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) DataServiceCollection<TransactionType> w/events Class3 DataServiceCollection<T> w/events

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  • PHP MVC Framework Structure

    - by bigstylee
    I am sorry about the amount of code here. I have tried to show enough for understanding while avoiding confusion (I hope). I have included a second copy of the code at Pastebin. (The code does execute without error/notice/warning.) I am currently creating a Content Management System while trying to implement the idea of Model View Controller. I have only recently come across the concept of MVC (within the last week) and trying to implement this into my current project. One of the features of the CMS is dynamic/customisable menu areas and each feature will be represented by a controller. Therefore there will be multiple versions of the Controller Class, each with specific extended functionality. I have looked at a number of tutorials and read some open source solutions to the MVC Framework. I am now trying to create a lightweight solution for my specific requirements. I am not interested in backwards compatibility, I am using PHP 5.3. An advantage of the Base class is not having to use global and can directly access any loaded class using $this->Obj['ClassName']->property/function();. Hoping to get some feedback using the basic structure outlined (with performance in mind). Specifically; a) Have I understood/implemented the concept of MVC correctly? b) Have I understood/implemented Object Orientated techniques with PHP 5 correctly? c) Should the class propertise of Base be static? d) Improvements? Thank you very much in advance! <?php /* A "Super Class" that creates/stores all object instances */ class Base { public static $Obj = array(); // Not sure this is the correct use of the "static" keyword? public static $var; static public function load_class($directory, $class) { echo count(self::$Obj)."\n"; // This does show the array is getting updated and not creating a new array :) if (!isset(self::$Obj[$class]) && !is_object(self::$Obj[$class])) //dont want to load it twice { /* Locate and include the class file based upon name ($class) */ return self::$Obj[$class] = new $class(); } return TRUE; } } /* Loads general configuration objects into the "Super Class" */ class Libraries extends Base { public function __construct(){ $this->load_class('library', 'Database'); $this->load_class('library', 'Session'); self::$var = 'Hello World!'; //testing visibility /* Other general funciton classes */ } } class Database extends Base { /* Connects to the the database and executes all queries */ public function query(){} } class Session extends Base { /* Implements Sessions in database (read/write) */ } /* General functionality of controllers */ abstract class Controller extends Base { protected function load_model($class, $method) { /* Locate and include the model file */ $this->load_class('model', $class); call_user_func(array(self::$Obj[$class], $method)); } protected function load_view($name) { /* Locate and include the view file */ #include('views/'.$name.'.php'); } } abstract class View extends Base { /* ... */ } abstract class Model extends Base { /* ... */ } class News extends Controller { public function index() { /* Displays the 5 most recent News articles and displays with Content Area */ $this->load_model('NewsModel', 'index'); $this->load_view('news', 'index'); echo $this->var; } public function menu() { /* Displays the News Title of the 5 most recent News articles and displays within the Menu Area */ $this->load_model('news/index'); $this->load_view('news/index'); } } class ChatBox extends Controller { /* ... */ } /* Lots of different features extending the controller/view/model class depending upon request and layout */ class NewsModel extends Model { public function index() { echo $this->var; self::$Obj['Database']->query(/*SELECT 5 most recent news articles*/); } public function menu() { /* ... */ } } $Libraries = new Libraries; $controller = 'News'; // Would be determined from Query String $method = 'index'; // Would be determined from Query String $Content = $Libraries->load_class('controller', $controller); //create the controller for the specific page if (in_array($method, get_class_methods($Content))) { call_user_func(array($Content, $method)); } else { die('Bad Request'. $method); } $Content::$var = 'Goodbye World'; echo $Libraries::$var . ' - ' . $Content::$var; ?> /* Ouput */ 0 1 2 3 Goodbye World! - Goodbye World

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  • PHP Database connection practice

    - by Phill Pafford
    I have a script that connects to multiple databases (Oracle, MySQL and MSSQL), each database connection might not be used each time the script runs but all could be used in a single script execution. My question is, "Is it better to connect to all the databases once in the beginning of the script even though all the connections might not be used. Or is it better to connect to them as needed, the only catch is that I would need to have the connection call in a loop (so the database connection would be new for X amount of times in the loop). Yeah Example Code #1: // Connections at the beginning of the script $dbh_oracle = connect2db(); $dbh_mysql = connect2db(); $dbh_mssql = connect2db(); for ($i=1; $i<=5; $i++) { // NOTE: might not use all the connections $rs = queryDb($query,$dbh_*); // $dbh can be any of the 3 connections } Yeah Example Code #2: // Connections in the loop for ($i=1; $i<=5; $i++) { // NOTE: Would use all the connections but connecting multiple times $dbh_oracle = connect2db(); $dbh_mysql = connect2db(); $dbh_mssql = connect2db(); $rs_oracle = queryDb($query,$dbh_oracle); $rs_mysql = queryDb($query,$dbh_mysql); $rs_mssql = queryDb($query,$dbh_mssql); } now I know you could use a persistent connection but would that be one connection open for each database in the loop as well? Like mysql_pconnect(), mssql_pconnect() and adodb for Oracle persistent connection method. I know that persistent connection can also be resource hogs and as I'm looking for best performance/practice.

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  • jquery - detect if selector returns null

    - by peirix
    What is the best way to detect if a jQuery-selector returns an empty object. If you do: alert($('#notAnElement')); you get [object Object], so the way I do it now is: alert($('#notAnElement').get(0)); which will write "undefined", and so you can do a check for that. But it seems very bad. What other way is there?

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  • What's the best method in ASP.NET to obtain the current domain?

    - by Graphain
    Hi, I am wondering what the best way to obtain the current domain is in ASP.NET? For instance: http://www.domainname.com/subdir/ should yield http://www.domainname.com http://www.sub.domainname.com/subdir/ should yield http://sub.domainname.com As a guide, I should be able to add a url like "/Folder/Content/filename.html" (say as generated by Url.RouteUrl() in ASP.NET MVC) straight onto the URL and it should work.

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  • SVN Best practice for a "branch" of your main product ?

    - by Steffen
    At my job we develop websites - however now we're going to make a "whitelabelled" version of a site, which basically means it's the same site, however with a different logo and hosted on a different domain. Also it'll have minor graphical differences, but overall the engine is the same. My initial thought for keeping this in SVN, was to just make a branch for it - however I'm not quite certain if this could give me trouble later on. Normally I keep my branches somewhat short lived - mainly used for developing a new feature, without disturbing trunk. We need to be able to merge trunk changes into this "whitelabel" version, which I why I thought about branching it in the first place. So what's the best way to archive this ?

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  • Practical rules for premature optimization

    - by DougW
    It seems that the phrase "Premature Optimization" is the buzz-word of the day. For some reason, iphone programmers in particular seem to think of avoiding premature optimization as a pro-active goal, rather than the natural result of simply avoiding distraction. The problem is, the term is beginning to be applied more and more to cases that are completely inappropriate. For example, I've seen a growing number of people say not to worry about the complexity of an algorithm, because that's premature optimization (eg http://stackoverflow.com/questions/2190275/help-sorting-an-nsarray-across-two-properties-with-nssortdescriptor/2191720#2191720). Frankly, I think this is just laziness, and appalling to disciplined computer science. But it has occurred to me that maybe considering the complexity and performance of algorithms is going the way of assembly loop unrolling, and other optimization techniques that are now considered unnecessary. What do you think? Are we at the point now where deciding between an O(n^n) and O(n!) complexity algorithm is irrelevant? What about O(n) vs O(n*n)? What do you consider "premature optimization"? What practical rules do you use to consciously or unconsciously avoid it? This is a bit vague, but I'm curious to hear other peoples' opinions on the topic.

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  • ASP.Net MVC: Showing the same data using different layouts...

    - by vdh_ant
    Hi guys I'm wanting to create a page that allows the users to select how they would like to view their data - i.e. summary (which supports grouping), grid (which supports grouping), table (which supports grouping), map, time line, xml, json etc. Now each layout would probably have different use a different view model, which inherit from a common base class/view model. The reason being that each layout needs the object structure that it deals with to be different (some need hierarchical others a flatter structure). Each layout would call the same repository method and each layout would support the same functionality, i.e. searching and filtering (hence these controls would be shared between layouts). The main exception to this would be sorting which only grid and table views would need to support. Now my question is given this what do people think is the best approach. Using DisplayFor to handle the rendering of the different types? Also how do I work this with the actions... I would imagine that I would use the one action, and pass in the layout types, but then how does this support the grouping required for the summary, grid and table views. Do i treat each grouping as just a layout type Also how would this work from a URL point of view - what do people think is the template to support this layout functionality Cheers Anthony

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  • Should image size be defined in the img tag height/width attributes or in CSS?

    - by Benjamin Manns
    Is it better coding practice to define an images size in the img tag's width and height attributes? <img src="images/academia_vs_business.png" width="740" height="382" alt="" /> Or in the CSS style with width/height? <img src="images/academia_vs_business.png" style="width:740px; height:382px;" alt="" /> Or both? <img src="images/academia_vs_business.png" width="740" height="382" style="width:740px; height:382px" alt="" />

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  • How do you go from an abstract project description to actual code?

    - by Jason
    Maybe its because I've been coding around two semesters now, but the major stumbling block that I'm having at this point is converting the professor's project description and requirements to actual code. Since I'm currently in Algorithms 101, I basically do a bottom-up process, starting with a blank whiteboard and draw out the object and method interactions, then translate that into classes and code. But now the prof has tossed interfaces and abstract classes into the mix. Intellectually, I can recognize how they work, but am stubbing my toes figuring out how to use these new tools with the current project (simulating a web server). In my professors own words, mapping the abstract description to Java code is the real trick. So what steps are best used to go from English (or whatever your language is) to computer code? How do you decide where and when to create an interface, or use an abstract class?

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  • Passing arguments and values form HTML to jQuery (events)

    - by Jaroslav Moravec
    What is the practice to pass arguments from HTML to jQuery events function. For example getting id of row from db: <tr class="jq_killMe" id="thisItemId-id"> ... </tr> and jQuery: $(".jq_killMe").click(function () { var tmp = $(this).attr('id).split("-"); var id = tmp[0] // ... } What's the best practise, if I want to pass more than one argument? Is it better not to use jQuery? For example: <tr onclick="killMe('id')"> ... </tr> I didn't find the answer on my question, I will be glad even for links. Thanks.

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  • How sophisticated should be DAL?

    - by Andrew Florko
    Basically, DAL (Data Access Layer) should provide simple CRUD (Create/Read/Update/Delete) methods but I always have a temptation to create more sophisticated methods in order to minimize database access roundtrips from Business Logic Layer. What do you think about following extensions to CRUD (most of them are OK I suppose): Read: GetById, GetByName, GetPaged, GetByFilter... e.t.c. methods Create: GetOrCreate methods (model entity is returned from DB or created if not found and returned), Create(lots-of-relations) instead of Create and multiple AssignTo methods calls Update: Merge methods (entities list are updated, created and deleted in one call) Delete: Delete(bool children) - optional children delete, Cleanup methods Where do you usually implement Entity Cache capabilities? DAL or BLL? (My choice is BLL, but I have seen DAL implementations also) Where is the boundary when you decide: this operation is too specific so I should implement it in Business Logic Layer as DAL multiple calls? I often found insufficient BLL operations that were implemented in dozen database roundtrips because developer was afraid to create a bit more sophisticated DAL. Thank you in advance!

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  • Scaffold default files are the best practice?

    - by antpaw
    Hey, i have some experience with MVC. but I'm new to rails. I'm using the scaffold command to generate some default files. The model looks clean and nice, but the controller and the views aren't really dry. The contents of new.html.erb and edit.html.erb are almost the same and the methods new/edit and create/update are doing almost the same thing. In other frameworks i've used only one view for updating and creating new entries and also the same method in my controller by setting the id as an optional parameter. Do they use this structure to keep things RESTful (i have not much of a clue about rest :()? Is it the best practice to use this default stuff for crud?

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  • Common programming mistakes in .Net when handling exceptions?

    - by Jared Coleson
    What are some of the most common mistakes you've seen made when handling exceptions? It seems like exception handling can be one of the hardest things to learn how to do "right" in .Net. Especially considering the currently #1 ranked answer to Common programming mistakes for .NET developers to avoid? is related to exception handling. Hopefully by listing some of the most common mistakes we can all learn to handle exceptions better.

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  • How to organize code using an optional assembly reference?

    - by apoorv020
    I am working on a project and want to optionally use an assembly if available. This assembly is only available on WS 2008 R2, and my ideal product whould be a common binary for both computers with and without the assembly. However, I'm primarily developing on a Windows 7 machine, where I cannot install the assembly. How can I organize my code so that I can (with minimum changes) build my code on a machine without the assembly and secondly, how do I ensure that I call the assembly functions only when it is present. (NOTE : The only use of the optional assembly is to instantiate a class in the library and repeatedly call a (single) function of the class, which returns a boolean. The assembly is fsrmlib, which exposes advanced file system management operations on WS08R2.) I'm currently thinking of writing a wrapper class, which will always return true if the assembly is not present. Is this the right way to go about doing this?

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  • Specification: Use cases for CRUD

    - by Mario Ortegón
    I am writing a Product requirements specification. In this document I must describe the ways that the user can interact with the system in a very high level. Several of these operations are "Create-Read-Update-Delete" on some objects. The question is, when writing use cases for these operations, what is the right way to do so? Can I write only one Use Case called "Manage Object x" and then have these operations as included Use Cases? Or do I have to create one use case per operation, per object? The problem I see with the last approach is that I would be writing quite a few pages that I feel do not really contribute to the understanding of the problem. What is the best practice?

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