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• Why is rvalue write in shared memory array serialised?

  - by CJM

  I'm using CUDA 4.0 on a GPU with computing capability 2.1. One of my device functions is the following: device void test(int n, int* itemp) // itemp is shared memory pointer { const int tid = threadIdx.x; const int bdim = blockDim.x; int i, j, k; bool flag = 0; itemp[tid] = 0; for(i=tid; i<n; i+=bdim) { // { code that produces some values of "flag" } } itemp[tid] = flag; } Each thread is checking some conditions and producing a 0/1 flag. Then each thread is writing flag at the tid-th location of a shared int array. The write statement "itemp[tid] = flag;" gets serialized -- though "itemp[tid] = 0;" is not. This is causing huge performance lag which technically should not be there -- I want to avoid it. Please help.

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• How should I structure moving from overworld to menu system / combat?

  - by persepolis

  I'm making a text-based "Arena" game where the player is the owner of 5 creatures that battle other teams for loot, experience and glory. The game is very simple, using Python and a curses emulator. I have a static ASCII map of an "overworld" of sorts. My character, represented by a glyph, can move about this static map. There are locations all over the map that the character can visit, that break down into two types: 1) Towns, which are a series of menus that will allow the player to buy equipment for his team, hire new recruits or do other things. 2) Arenas, where the player's team will have a "battle" interface with actions he can perform, messages about the fight, etc. Maybe later, an ASCII representation of the fight but for now, just screens of information with action prompts. My main problem is what kind of design or structure I should use to implement this? Right now, the game goes through a master loop which waits for keyboard input and then moves the player about the screen. My current thinking is this: 1) Upon keyboard input, the Player coordinates are checked against a list of Location objects and if the Player coords match the Location coords then... 2) ??? I'm not sure if I should then call a seperate function to initiate a "menu" or "combat" mode. Or should I create some kind of new GameMode object that contains a method itself for drawing the screen, printing the necessary info? How do I pass my player's team data into this object? My main concern is passing around the program flow into all these objects. Should I be calling straight functions for different parts of my game, and objects to represent "things" within my game? I was reading about the MVC pattern and how this kind of problem might benefit - decouple the GUI from the game logic and user input but I have no idea how this applies to my game.

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• Dealing with the node callback pyramid

  - by thecoop

  I've just started using node, and one thing I've quickly noticed is how quickly callbacks can build up to a silly level of indentation: doStuff(arg1, arg2, function(err, result) { doMoreStuff(arg3, arg4, function(err, result) { doEvenMoreStuff(arg5, arg6, function(err, result) { omgHowDidIGetHere(); }); }); }); The official style guide says to put each callback in a separate function, but that seems overly restrictive on the use of closures, and making a single object declared in the top level available several layers down, as the object has to be passed through all the intermediate callbacks. Is it ok to use function scope to help here? Put all the callback functions that need access to a global-ish object inside a function that declares that object, so it goes into a closure? function topLevelFunction(globalishObject, callback) { function doMoreStuffImpl(err, result) { doMoreStuff(arg5, arg6, function(err, result) { callback(null, globalishObject); }); } doStuff(arg1, arg2, doMoreStuffImpl); } and so on for several more layers... Or are there frameworks etc to help reduce the levels of indentation without declaring a named function for every single callback? How do you deal with the callback pyramid?

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• What language and topics should be covered when teaching non-CS college students how to program?

  - by michaelcarrano

  I have been asked by many of my non-computer science friends to teach them how to program. I have agreed to hold a seminar for them that will last for approximately 1 to 2 hours. My thoughts are to use Python as the language to teach them basic programming skills. I figured Python is relatively easier to learn from what I have researched. It is also a language I want to learn which will make holding this seminar all the more enjoyable. The topics I plan to cover are as followed: Variables / Arrays Logic - If else statements, switch case, nested statements Loops - for, while, do-while and nested loops Functions - pass by value, pass by reference (is this the correct terms for Python? I am mostly a C/C++ person) Object Oriented Programming Of course, I plan to have code examples for all topics and I will try to have each example flow into each other so that at the end of the seminar everyone will have a complete working program. I suppose my question is, if you were given 1 to 2 hours to teach a group of college students how to program, what language would you choose and what topics would you cover? Update: Thank you for the great feedback. I should have mentioned in my earlier post above that a majority of the students attending the seminar have some form of programming experience whether it was with Java or using Matlab. Most of these students are 3rd/4th year Engineering students who want to get a refresher on programming before they graduate.

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• How do you handle animations that are for transitioning between states?

  - by yaj786

  How does one usually handle animations that are for going between a game object's states? For example, imagine a very simple game in which a character can only crouch or stand normally. Currently, I use a custom Animation class like this: class Animation{ int numFrames; int curFrame; Bitmap spriteSheet; //... various functions for pausing, returning frame, etc. } and an example Character class class Character{ int state; Animation standAni; Animation crouchAni; //... etc, etc. } Thus, I use the state of the character to draw the necessary animation. if(state == STATE_STAND) draw(standAni.updateFrame()); else if(state == STATE_CROUCH) draw(crouchAni.updateFrame()); Now I've come to the point where I want to draw "in-between" animations, because right now the character will just jump immediately into a crouch instead of bending down. What is a good way to handle this? And if the way that I handle storing Animations in the Character class is not a good way, what is? I thought of creating states like STATE_STANDING_TO_CROUCHING but I feel like that may get messy fast.

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• Parsing an header with two different version [ID3] avoiding code duplication?

  - by user66141

  I really hope you could give me some interesting viewpoints for my situation, my ways to approach my issue are not to my liking . I am writing an mp3 parser , starting with an ID3v2 parser . Right now I`m working on the extended header parsing , my issue is that the optional header is defined differently in version 2.3 and 2.4 of the tag . The 2.3 version optional header is defined as follows : struct ID3_3_EXTENDED_HEADER{ DWORD dwExtHeaderSize; //Extended header size (either 6 or 8 bytes , excluded) WORD wExtFlags; //Extended header flags DWORD dwSizeOfPadding; //Size of padding (size of the tag excluding the frames and headers) }; While the 2.4 version is defined : struct ID3_4_EXTENDED_HEADER{ DWORD dwExtHeaderSize; //Extended header size (synchsafe int) BYTE bNumberOfFlagBytes; //Number of flag bytes BYTE bFlags; //Flags }; How could I parse the header while minimizing code duplication ? Using two different functions to parse each version sounds less great , using a single function with a different flow for each occasion is similar , any good practices for this kind of issues ? any tips for avoiding code duplication ? anything would be great .

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• Why it is called "hash table", or "hash function"? Hash doesn't make any sense to me here

  - by Saeed Neamati

  It's now about 4 years of development that I'm using, hearing, talking about, and implementing hash tables and hash functions. But I really never understand why it's called hash? I remember the first days I started programming, this term was kind'of cumbersome terminology to me. I never figured out what is it, based on its name. I just experimentally understood what it does and why and when should we use it. However, I still sometimes try to figure out why it's called hash. I have no problem with table or function and to be honest, they are pretty deductive, rational terms. However, I think better words could be used instead of hash, like key, or uniqueness. Don't key table or uniqueness table. According to my dictionary, hash means: Fried dish of potato and meats (highly irrelevant) # symbol (AKA number sign, pound sign, etc.) (still irrelevant, maybe just a mis-nomenclature) Apply algorithm to character string (still has nothing to do with uniqueness, which is the most important feature of a hash table) Cut food Another term for hashish Does anyone know why it's called hash?

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• Debugger for file I/O development?

  - by datenwolf

  Okay, the question title may be a bit cryptic. But it aptly describes what I'm looking for: I think every experienced coder went through this numerous times: You get a binary file format specification, you implement the reader for it, and… nothing works like expected. So you run your code in the debugger, go execute through the code line by line, every header field is read in seemingly correct, but when it comes to the bulk data, offset and indices no longer match up. What would really help in this situation was a binary file viewer, that shows you the progress of your file pointer, as you step through the code, and ideally would also highlight all memory maps. Then you could see the context of the current I/O operations, most notably those darn "off-by-one" mistakes, which are even more annoying when reading a file. Implementing such a debugger should not be too hard. traces on the process' file descriptors/handles and triggers on the I/O functions, to update the display. Only: I don't know of such a kind of debugger to exist. Do I just lack knowledge about the existance of such a tool, or is there really no such thing?

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• I can't program because the code I am using uses old coding styles. Is this normal to programmers? [closed]

  - by Renato Dinhani Conceição

  I'm in my first real job as programmer, but I can't solve any problems because of the coding style used. The code here: Does not have comments Does not have functions (50, 100, 200, 300 or more lines executed in sequence) Uses a lot of if statements with a lot of paths Has variables that make no sense (eg.: cf_cfop, CF_Natop, lnom, r_procod) Uses an old language (Visual FoxPro 8 from 2002), but there are new releases from 2007. I feel like I have gone back to 1970. Is it normal for a programmer familiar with OOP, clean-code, design patterns, etc. to have trouble with coding in this old-fashion way? EDIT: All the answers are very good. For my (un)hope, appears that there are a lot of this kind of code bases around the world. A point mentioned to all answers is refactor the code. Yeah, I really like to do it. In my personal project, I always do this, but... I can't refactor the code. Programmers are only allowed to change the files in the task that they are designed for. Every change in old code must be keep commented in the code (even with Subversion as version control), plus meta informations (date, programmer, task) related to that change (this became a mess, there are code with 3 used lines and 50 old lines commented). I'm thinking that is not only a code problem, but a management of software development problem.

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• PHP Calculating Text to Content Ratio

  - by James

  I am using the following code to calculate text to code ratio. I think it is crazy that no one can agree on how to properly calculate the result. I am looking any suggestions or ideas to improve this code that may make it more accurate. <?php // Returns the size of the content in bytes function findKb($content){ $count=0; $order = array("\r\n", "\n", "\r", "chr(13)", "\t", "\0", "\x0B"); $content = str_replace($order, "12", $content); for ($index = 0; $index < strlen($content); $index ++){ $byte = ord($content[$index]); if ($byte <= 127) { $count++; } else if ($byte >= 194 && $byte <= 223) { $count=$count+2; } else if ($byte >= 224 && $byte <= 239) { $count=$count+3; } else if ($byte >= 240 && $byte <= 244) { $count=$count+4; } } return $count; } // Collect size of entire code $filesize = findKb($content); // Remove anything within script tags $code = preg_replace("@<script[^>]*>.+</script[^>]*>@i", "", $content); // Remove anything within style tags $code = preg_replace("@<style[^>]*>.+</style[^>]*>@i", "", $content); // Remove all tags from the system $code = strip_tags($code); // Remove Extra whitespace from the content $code = preg_replace( '/\s+/', ' ', $code ); // Find the size of the remaining code $codesize = findKb($code); // Calculate Percentage $percent = $codesize/$filesize; $percentage = $percent*100; echo $percentage; ?> I don't know the exact calculations that are used so this function is just my guess. Does anyone know what the proper calculations are or if my functions are close enough for a good judgement.

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• How to suggest changes as a recently-hired employee ?

  - by ereOn

  Hi, I was recently hired in a big company (thousands of people, to give an idea of the size). They said they hired me because of my rigor and because I was, despite my youngness (i'm 25), experienced as a C/C++ programer. Now that I'm in, I can see that the whole system is old and often uses obsolete technologies. There is no naming convention (files, functions, variables, ...), they don't use Version Control, don't use exceptions or polymorphism and it seems like almost everybody lost his passion (some of them are only 30 years old). I'd like to suggest somes changes but i don't want to be "the new guy that wants to change everything just because he doesn't want to fit in". I tried to "fit in", but actually, It takes me one week to do what I would do in one afternoon, just because of the poor tools we're forced to use. A lot my collegues never look at the new "things" and techniques that people use nowadays. It's like they just given up. The situation is really frustrating. Have you ever been in a similar situation and, if so, what advices would you give me ? Is there a subtle way of changing things without becoming the black sheep here ? Or should I just give up my passion and energy as well ? Thank you. Updates Just in case (if anyone cares): following your precious advices I was able to suggest changes and am now in charge of the team that must create and deploy Subversion :D Thanks to all of you !

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• Teach Your Kid to Code Coming to Philly.NET

  - by Steve Michelotti

  Originally posted on: http://geekswithblogs.net/michelotti/archive/2014/05/20/teach-your-kid-to-code-coming-to-philly.net.aspxTomorrow night (Wednesday, May 21) my son and I will be at Philly.NET presenting Teach Your Kid to Code. Bring your kid out to Philly.NET with you for a fun evening! After our first talk, I’ll then be giving an introduction to TypeScript. Of any presentation I’ve ever given, this is my favorite: Have you ever wanted a way to teach your kid to code? For that matter, have you ever wanted to simply be able to explain to your kid what you do for a living? Putting things in a context that a kid can understand is not as easy as it sounds. If you are someone curious about these concepts, this is a “can’t miss” presentation that will be co-presented by Justin Michelotti (6th grader) and his father. Bring your kid with you to Philly.NET for this fun and educational session. We will show tools you may not have been aware of like SmallBasic and Kodu – we’ll even throw in a little Visual Studio and JavaScript. Concepts such as variables, conditionals, loops, and functions will be covered while we introduce object oriented concepts without any of the confusing words. Kids are not required for entry!

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• Is it possible to generate Events and Hooks in Lua for any game without built-in support?

  - by pr0tocol

  Does a game have to have built-in functions to accept and run lua scripts, or can I design Events and Hooks using Lua on any game I please, akin to the days where C code could be used to hook into the WinAPI using dlls? The reason I ask is, I am trying to create a background application that will perform events and hooks on a particular game that does not currently support lua in-game. Brief examples: Events: - An action executed by the PLAYER is detected. For instance, hitting the Q key will normally make my character use an ability, but with my Lua script running in the background, will cause a sound to play on my computer (or something). Hooks: - An action within the GAME is detected. For instance, the game spawns an enemy every minute. When an enemy spawns, the script will detect this and perform an action, for instance playing a sound locally on the computer. I would like to do both, but I know for games like Garry's Mod, the game already has built-in support for running lua scripts. Is there a way to do either events OR hooks using lua similarly to how C/C++ can connect to a game using WinAPI dlls?

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• Floating point undesirable in highly critical code?

  - by Kirt Undercoffer

  Question 11 in the Software Quality section of "IEEE Computer Society Real-World Software Engineering Problems", Naveda, Seidman, lists fp computation as undesirable because "the accuracy of the computations cannot be guaranteed". This is in the context of computing acceleration for an emergency braking system for a high speed train. This thinking seems to be invoking possible errors in small differences between measurements of a moving object but small differences at slow speeds aren't a problem (or shouldn't be), small differences between two measurements at high speed are irrelevant - can there be a problem with small roundoff errors during deceleration for an emergency braking system? This problem has been observed with airplane braking systems resulting in hydroplaning but could this actually happen in the context of a high speed train? The concern about fp errors seems to not be well-founded in this context. Any insight? The fp is used for acceleration so perhaps the concern is inching over a speed limit? But fp should be just fine if they use a double in whatever implementation language. The actual problem in the text states: During the inspection of the code for the emergency braking system of a new high speed train (a highly critical, real-time application), the review team identifies several characteristics of the code. Which of these characteristics are generally viewed as undesirable? The code contains three recursive functions (well that one is obvious). The computation of acceleration uses floating point arithmetic. All other computations use integer arithmetic. The code contains one linked list that uses dynamic memory allocation (second obvious problem). All inputs are checked to determine that they are within expected bounds before they are used.

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• Serializing network messages

  - by mtsvetkov

  I am writing a network wrapper around boost::asio and was wondering what is a good and simple way to serialize my messages. I have a message factory which can take care of dispatching the data to the correct builder, but I want to know if there are any established solutions for getting the binary data on the sender side and consequently passing the data for deserialization on the receiver end. Some options I've explored are: passing a pointer to a char[] to the serialize/deserialize functions (for serialize to write to, and deserialize to read from), but it's difficult to enforce buffer size this way; building on that, I decided to have the serialize function return a boost::asio::mutable_buffer, however ownership of the memory gets blurred between multiple classes, as the network wrapper needs to clean up the memory allocated by the message builder. I have also seen solutions involving streambuf's and stringstream's, but manipulating binary data in terms of its string representation is something I want to avoid. Is there some sort of binary stream I can use instead? What I am looking for is a solution (preferrably using boost libs) that lets the message builder dictate the amount of memory allocated during serialization and what that would look like in terms of passing the data around between the wrapper and message factory/message builders. PS. Messages contain almost exclusively built-in types and PODs and form a shallow but wide hierarchy for the sake of going through a factory. Note: a link to examples of using boost::serialization for something like this would be appreciated as I'm having difficulties figuring out the relation between it and buffers.

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• How to Integrate Dropbox with Pages, Keynote, and Numbers on iPad

  - by The Geek

  The iWork apps are some of the best apps on the iPad, and each show just how powerful a touchscreen device can be with the most basic of computing functions. In fact, there’s not much to dislike about the iWork apps, except for one thing: importing and exporting files. You can open documents from email attachments, download them from websites, or import them from other apps like Dropbox. Once you’ve opened your file in Pages, Keynote, or Numbers on iPad, though, you can only send it via email, upload it to a WebDAV server or Apple’s iDisk service, or wait to sync it with iTunes on your computer. Most other iOS office apps don’t offer nearly as many features as the iWork apps, but they do offer deep integration with Dropbox which makes it easy to view and edit your documents no matter where you are. Dropbox is the most popular file sync and sharing solution, and makes it absolutely painless to share folders with anyone around the world and keep your computers in sync. That is, computers and applications that integrate with Dropbox. However, you don’t need to give up on using Dropbox with iWork apps on iPad. Today we’re going to look at how you can enable WebDAV compatibility on your Dropbox account to let Pages integrate nearly the whole way with Dropbox. It’s not a perfect solution, but it’s much better than the default setup. So let’s get started Latest Features How-To Geek ETC How to Integrate Dropbox with Pages, Keynote, and Numbers on iPad RGB? CMYK? Alpha? What Are Image Channels and What Do They Mean? How to Recover that Photo, Picture or File You Deleted Accidentally How To Colorize Black and White Vintage Photographs in Photoshop How To Get SSH Command-Line Access to Windows 7 Using Cygwin The How-To Geek Video Guide to Using Windows 7 Speech Recognition Stylebot Customizes Web Pages in Chrome, Now Has Downloadable Styles Blackberry, Dell, Apple, and Motorola Tablets Compared [Infographic] Encrypt Your Google Search Queries Vintage Posters Showcase the History of Tech Advertising Google Cloud Print Extension Lets You Print Doc/PDF/Txt Files from Web Sites Hack a $10 Flashlight into an Ultra-bright Premium One

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• Web application interacts bi-directional with server program?

  - by Roelof Berkepeis

  I want to write a web application to play chess against the engine Crafty. I'm not new to PHP and javascript, but must learn how to interact with a server process : how can a web application and/or (jQuery) ajax interact bi-directionally with a (linux) program running on the server? At this moment i am developing on (Apache) local host. Crafty is installed on my Ubuntu PC. This well-known chess engine has no GUI, it runs in terminal by the command $ /usr/games/crafty and so you can play chess against it and even see it's calculations. I can make Crafty run by PHP, using the functions proc_open() or exec(), and most documentation i found states that the output stream should be a file .. But i think i don't want such setup, because then the webpage should be constanty polling that file (eg. by ajax) to see if some new data was appended, right? How can Crafty talk to the web page directly, saying "i have calculated another variation" or "i have decided a move" etc, then display this info on the web page and let the user give some counter move, just like in terminal. Isn't it possible to use some session / stream / listener? I have no clue at all, can anybody point me in a right direction?

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• What is a 'good number' of exceptions to implement for my library?

  - by Fuzz

  I've always wondered how many different exception classes I should implement and throw for various pieces of my software. My particular development is usually C++/C#/Java related, but I believe this is a question for all languages. I want to understand what is a good number of different exceptions to throw, and what the developer community expect of a good library. The trade-offs I see include: More exception classes can allow very fine grain levels of error handling for API users (prone to user configuration or data errors, or files not being found) More exception classes allows error specific information to be embedded in the exception, rather than just a string message or error code More exception classes can mean more code maintenance More exception classes can mean the API is less approachable to users The scenarios I wish to understand exception usage in include: During 'configuration' stage, which might include loading files or setting parameters During an 'operation' type phase where the library might be running tasks and doing some work, perhaps in another thread Other patterns of error reporting without using exceptions, or less exceptions (as a comparison) might include: Less exceptions, but embedding an error code that can be used as a lookup Returning error codes and flags directly from functions (sometimes not possible from threads) Implemented an event or callback system upon error (avoids stack unwinding) As developers, what do you prefer to see? If there are MANY exceptions, do you bother error handling them separately anyway? Do you have a preference for error handling types depending on the stage of operation?

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• Announcing Two Papers Addressing the RPAS Fusion Client

  - by Oracle Retail Documentation Team

  Oracle Retail has published two documents to My Oracle Support addressing the Retail Predictive Application Server (RPAS) Fusion Client, a web-based rich client developed using the latest Oracle Application Development Framework (ADF). The Fusion Client provides an enhanced user experience for communicating with the RPAS server. Oracle Retail Predictive Application Server Fusion Client Getting Started Guide Doc ID 1492759.1The Retail Predictive Application Server (RPAS) is a configurable platform that provides capabilities such as a multidimensional database structure, batch and online processing, a configurable user interface, a configurable calculation engine, user security, and utility functions such as importing and exporting, all on a highly scalable technical environment that can be deployed on a variety of hardware. This paper addresses typical questions that arise during setting up and deploying the Fusion Client, provides performance recommendations, and highlights the differences between the Classic Client and the Fusion Client. Oracle Retail RPAS Fusion Client Performance Issue Report Doc ID 1493747.1Performance issues can be frustrating for customers, and Oracle Retail will strive to assist you as you attempt to enhance the performance of your systems. To ensure the timeliest processing of your issue, retailers and partners are encouraged to respond as thoroughly as possible to each question in this document, which can be sent back for analysis by logging a Service Request and following typical Customer Support processes. The sections of the document solicit information about the following: Performance Issue Description Performance Issue Details System Configuration Data Application Configuration Data Performance Log Files

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• How do I drag my widgets without dragging other widgets?

  - by Cypher

  I have a bunch of drag-able widgets on screen. When I am dragging one of the widgets around, if I drag the mouse over another widget, that widget then gets "snagged" and is also dragged around. While this is kind of a neat thing and I can think of a few game ideas based on that alone, that was not intended. :-P Background Info I have a Widget class that is the basis for my user interface controls. It has a bunch of properties that define it's size, position, image information, etc. It also defines some events, OnMouseOver, OnMouseOut, OnMouseClick, etc. All of the event handler functions are virtual, so that child objects can override them and make use of their implementation without duplicating code. Widgets are not aware of each other. They cannot tell each other, "Hey, I'm dragging so bugger off!" Source Code Here's where the widget gets updated (every frame): public virtual void Update( MouseComponent mouse, KeyboardComponent keyboard ) { // update position if the widget is being dragged if ( this.IsDragging ) { this.Left -= (int)( mouse.LastPosition.X - mouse.Position.X ); this.Top -= (int)( mouse.LastPosition.Y - mouse.Position.Y ); } ... // define and throw other events if ( !this.WasMouseOver && this.IsMouseOver && mouse.IsButtonDown( MouseButton.Left ) ) { this.IsMouseDown = true; this.MouseDown( mouse, new EventArgs() ); } ... // define and throw other events } And here's the OnMouseDown event where the IsDraggable property gets set: public virtual void OnMouseDown( object sender, EventArgs args ) { if ( this.IsDraggable ) { this.IsDragging = true; } } Problem Looking at the source code, it's obvious why this is happening. The OnMouseDown event gets fired whenever the mouse is hovered over the Widget and when the left mouse button is "down" (but not necessarily in that order!). That means that even if I hold the mouse down somewhere else on screen, and simply move it over anything that IsDraggable, it will "hook" onto the mouse and go for a ride. So, now that it's obvious that I'm Doing It Wrong™, how do I do this correctly?

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• Does it make sense to write tests for legacy code when there is no time for a complete refactoring?

  - by is4

  I usually try to follow the advice of the book Working Effectively with Legacy Code. I break dependencies, move parts of the code to @VisibleForTesting public static methods and to new classes to make the code (or at least some part of it) testable. And I write tests to make sure that I don't break anything when I'm modifying or adding new functions. A colleague says that I shouldn't do this. His reasoning: The original code might not work properly in the first place. And writing tests for it makes future fixes and modifications harder since devs have to understand and modify the tests too. If it's GUI code with some logic (~12 lines, 2-3 if/else block, for example), a test isn't worth the trouble since the code is too trivial to begin with. Similar bad patterns could exist in other parts of the codebase, too (which I haven't seen yet, I'm rather new); it will be easier to clean them all up in one big refactoring. Extracting out logic could undermine this future possibility. Should I avoid extracting out testable parts and writing tests if we don't have time for complete refactoring? Is there any disadvantage to this that I should consider?

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• How are objects modelled in a functional programming language?

  - by Giorgio

  In an answer to this question (written by Pete) there are some considerations about OOP versus FP. In particular, it is suggested that FP languages are not very suitable for modelling (persistent) objects that have an identity and a mutable state. I was wondering if this is true or, in other words, how one would model objects in a functional programming language. From my basic knowledge of Haskell I thought that one could use monads in some way, but I really do not know enough on this topic to come up with a clear answer. So, how are entities with an identity and a mutable persistent state normally modelled in a functional language? EDIT Here are some further details to clarify what I have in mind. Take a typical Java application in which I can (1) read a record from a database table into a Java object, (2) modify the object in different ways, (3) save the modified object to the database. How would this be implemented e.g. in Haskell? I would initially read the record into a record value (defined by a data definition), perform different transformations by applying functions to this initial value (each intermediate value is a new, modified copy of the original record) and then write the final record value to the database. Is this all there is to it? How can I ensure that at each moment in time only one copy of the record is valid / accessible? One does not want to have different immutable values representing different snapshots of the same object to be accessible at the same time.

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• How to visualize code?

  - by gablin

  I've mostly only had to read my own code. As such, I've had no need to visualize the code as I already know how each and every class and module communicate with one another. But the few times I've had to read someone else's code - let us now assume we are talking about at least one larger module which contains several internal classes - I've almost always found myself wishing "This would have been so much easier to understand if I could just visualize it!" So what are the common methods or tools for enabling this? Which do you use, and why do you prefer them over the others? I've heard stuff like UML, module and class diagrams, but I imagine there are more. Furthermore, any of these is most likely better than anything I can devise on my own. EDIT: For those who answer with "Use pen and paper and just draw it": This isn't very helpful unless you explain this further. What exactly am I supposed to draw? A box for each class? Should I include the public methods? What about its fields? How should I draw connections that explain how one class uses another? What about modules? What if the language isn't object-oriented but functional or logical, or even just imperative (C, for instance)? What about global variables and functions? Is there an already-standardized way of drawing this, or do I need to think up of a method of my own? You get the drift.

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• Design in "mixed" languages: object oriented design or functional programming?

  - by dema80

  In the past few years, the languages I like to use are becoming more and more "functional". I now use languages that are a sort of "hybrid": C#, F#, Scala. I like to design my application using classes that correspond to the domain objects, and use functional features where this makes coding easier, more coincise and safer (especially when operating on collections or when passing functions). However the two worlds "clash" when coming to design patterns. The specific example I faced recently is the Observer pattern. I want a producer to notify some other code (the "consumers/observers", say a DB storage, a logger, and so on) when an item is created or changed. I initially did it "functionally" like this: producer.foo(item => { updateItemInDb(item); insertLog(item) }) // calls the function passed as argument as an item is processed But I'm now wondering if I should use a more "OO" approach: interface IItemObserver { onNotify(Item) } class DBObserver : IItemObserver ... class LogObserver: IItemObserver ... producer.addObserver(new DBObserver) producer.addObserver(new LogObserver) producer.foo() //calls observer in a loop Which are the pro and con of the two approach? I once heard a FP guru say that design patterns are there only because of the limitations of the language, and that's why there are so few in functional languages. Maybe this could be an example of it? EDIT: In my particular scenario I don't need it, but.. how would you implement removal and addition of "observers" in the functional way? (I.e. how would you implement all the functionalities in the pattern?) Just passing a new function, for example?

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• A few questions about how JavaScript works

  - by KayoticSully

  I originally posted on Stack Overflow and was told I might get some better answers here. I have been looking deeply into JavaScript lately to fully understand the language and have a few nagging questions that I can not seem to find answers to (Specifically dealing with Object Oriented programming. I know JavaScript is meant to be used in an OOP manner I just want to understand it for the sake of completeness). Assuming the following code: function TestObject() { this.fA = function() { // do stuff } this.fB = testB; function testB() { // do stuff } } TestObject.prototype = { fC : function { // do stuff } } What is the difference between functions fA and fB? Do they behave exactly the same in scope and potential ability? Is it just convention or is one way technically better or proper? If there is only ever going to be one instance of an object at any given time, would adding a function to the prototype such as fC even be worthwhile? Is there any benefit to doing so? Is the prototype only really useful when dealing with many instances of an object or inheritance? And what is technically the "proper" way to add methods to the prototype the way I have above or calling TestObject.prototype.functionName = function(){} every time? I am looking to keep my JavaScript code as clean and readable as possible but am also very interested in what the proper conventions for Objects are in the language. I come from a Java and PHP background and am trying to not make any assumptions about how JavaScript works since I know it is very different being prototype based. Also are there any definitive JavaScript style guides or documentation about how JavaScript operates at a low level? Thanks!

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