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• Are Java's public fields just a tragic historical design flaw at this point?

  - by Avi Flax

  It seems to be Java orthodoxy at this point that one should basically never use public fields for object state. (I don't necessarily agree, but that's not relevant to my question.) Given that, would it be right to say that from where we are today, it's clear that Java's public fields were a mistake/flaw of the language design? Or is there a rational argument that they're a useful and important part of the language, even today? Thanks! Update: I know about the more elegant approaches, such as in C#, Python, Groovy, etc. I'm not directly looking for those examples. I'm really just wondering if there's still someone deep in a bunker, muttering about how wonderful public fields really are, and how the masses are all just sheep, etc. Update 2: Clearly static final public fields are the standard way to create public constants. I was referring more to using public fields for object state (even immutable state). I'm thinking that it does seem like a design flaw that one should use public fields for constants, but not for state… a language's rules should be enforced naturally, by syntax, not by guidelines.

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• Tail-recursive implementation of take-while

  - by Giorgio

  I am trying to write a tail-recursive implementation of the function take-while in Scheme (but this exercise can be done in another language as well). My first attempt was (define (take-while p xs) (if (or (null? xs) (not (p (car xs)))) '() (cons (car xs) (take-while p (cdr xs))))) which works correctly but is not tail-recursive. My next attempt was (define (take-while-tr p xs) (let loop ((acc '()) (ys xs)) (if (or (null? ys) (not (p (car ys)))) (reverse acc) (loop (cons (car ys) acc) (cdr ys))))) which is tail recursive but needs a call to reverse as a last step in order to return the result list in the proper order. I cannot come up with a solution that is tail-recursive, does not use reverse, only uses lists as data structure (using a functional data structure like a Haskell's sequence which allows to append elements is not an option), has complexity linear in the size of the prefix, or at least does not have quadratic complexity (thanks to delnan for pointing this out). Is there an alternative solution satisfying all the properties above? My intuition tells me that it is impossible to accumulate the prefix of a list in a tail-recursive fashion while maintaining the original order between the elements (i.e. without the need of using reverse to adjust the result) but I am not able to prove this. Note The solution using reverse satisfies conditions 1, 3, 4.

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• Error while installing an application

  - by Bong.Da.City

  So i have installed synaptic package manager.. via it, i have checked once libopencv-highgui-dev and applied complete removal.. after that i installed it... now everytime i try to install an application e.g Format Junkie sudo add-apt-repository ppa:format-junkie-team/release && sudo apt-get update && sudo apt-get install formatjunkie in the command install format junkie it gives me that error everytime: sudo apt-get install formatjunkie Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: libopencv-features2d-dev : Depends: libopencv-highgui-dev (= 2.3.1-11ubuntu2) but it is not going to be installed E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages. What should i do? And 2nd what did i did wrong so it won't happen another time? output of lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 12.10 Release: 12.10 Codename: quantal

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• BoundingSpheres move when they should not

  - by NDraskovic

  I have a XNA 4.0 project in which I load a file that contains type and coordinates of items I need to draw to the screen. Also I need to check if one particular type (the only movable one) is passing in front or trough other items. This is the code I use to load the configuration: if (ks.IsKeyDown(Microsoft.Xna.Framework.Input.Keys.L)) { this.GraphicsDevice.Clear(Color.CornflowerBlue); Otvaranje.ShowDialog(); try { using (StreamReader sr = new StreamReader(Otvaranje.FileName)) { String linija; while ((linija = sr.ReadLine()) != null) { red = linija.Split(','); model = red[0]; x = red[1]; y = red[2]; z = red[3]; elementi.Add(Convert.ToInt32(model)); podatci.Add(new Vector3(Convert.ToSingle(x), Convert.ToSingle(y), Convert.ToSingle(z))); sfere.Add(new BoundingSphere(new Vector3(Convert.ToSingle(x), Convert.ToSingle(y), Convert.ToSingle(z)), 1f)); } } } catch (Exception ex) { Window.Title = ex.ToString(); } } The "Otvaranje" is an OpenFileDialog object, "elementi" is a List (determines the type of item that would be drawn), podatci is a List (determines the location where the items will be drawn) and sfere is a List. Now I solved the picking algorithm (checking for ray and bounding sphere intersection) and it works fine, but the collision detection does not. I noticed, while using picking, that BoundingSphere's move even though the objects that they correspond to do not. The movable object is drawn to the world1 Matrix, and the static objects are drawn into the world2 Matrix (world1 and world2 have the same values, I just separated them so that the static elements would not move when the movable one does). The problem is that when I move the item I want, all boundingSpheres move accordingly. How can I move only the boundingSphere that corresponds to that particular item, and leave the rest where they are?

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• Using Queries with Coherence Write-Behind Caches

  - by jpurdy

  Applications that use write-behind caching and wish to query the logical entity set have the option of querying the NamedCache itself or querying the database. In the former case, no particular restrictions exist beyond the limitations intrinsic to the Coherence query engine itself. In the latter case, queries may see partially committed transactions (e.g. with a parent-child relationship, the version of the parent may be different than the version of the child objects) and/or significant version skew (the query may see the current version of one object and a far older version of another object). This is consistent with "read committed" semantics, but the read skew may be far greater than would ever occur in a non-cached environment. As is usually the case, the application developer may choose to accept these limitations (with the hope that they are sufficiently infrequent), or they may choose to validate the reads (perhaps via a version flag on the objects). This also applies to situations where a third party application (such as a reporting tool) is querying the database. In many cases, the database may only be in a consistent state after the Coherence cluster has been halted.

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• What patterns book for iOS development contains this specific information? [closed]

  - by Brett Ryan

  I've read several books on iOS development and Objective-C, however what a lot of them teach is how to work with interfaces and all contain the model inside the view controller, i.e. a UITableViewController based view will simply have an NSArray as it's model. I'm interested in what the best practices are for designing the structure of an application. Specifically I'm interested in best practices for the following: How to separate a model from the view controller. I think I know how to do this by simply replacing the NSArray style example with a specific model object, however what I do not know how to do is alert the view when the model changes. For example in .NET I would solve this by conforming to INotifyPropertyChanged and databinding, and similarly with Java I would use PropertyChangeListener. How to create a service model for my domain objects. For example I want to learn the best way to create a service for a hypothetical Widget object to manage an internal DB and also services for communicating with remote endpoints. I need to learn the best ways to do this in a way that interface components can subscribe to events such as widgetUpdated. These services should be singleton classes and some how dependency injected into model/controller objects. Books I've read so far are: Programming in Objective-C (4th Edition) Beginning iOS 5 Development: Exploring the iOS SDK The iOS 5 Developer's Cookbook: Expanded Electronic Edition: Essentials and Advanced Recipes for iOS Programmers Learn Objective-C on the Mac: For OS X and iOS I've also purchased the following updated books but not yet read them. The Core iOS 6 Developer's Cookbook (4th edition Programming in Objective-C (5th Edition) I come from a Java and C# background with 15 years experience, I understand that many of the ways I would do things in these languages may not fit to the ObjC way of developing applications. Would someone be able to provide me with the book on this topic containing this specific subject matter?

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• Depending on fixed version of a library and ignore its updates

  - by Moataz Elmasry

  I was talking to a technical boss yesterday. Its about a project in C++ that depends on opencv and he wanted to include a specific opencv version into the svn and keep using this version ignoring any updates which I disagreed with.We had a heated discussion about that. His arguments: Everything has to be delivered into one package and we can't ask the client to install external libraries. We depend on a fixed version so that new updates of opencv won't screw our code. We can't guarantee that within a version update, ex from 3.2.buildx to 3.2.buildy. Buildy the function signatures won't change. My arguments: True everything has to be delivered to the client as one package,but that's what build scripts are for. They download the external libraries and create a bundle. Within updates of the same version 3.2.buildx to 3.2.buildy its impossible that a signature change, unless it is a really crappy framework, which isn't the case with opencv. We deprive ourselves from new updates and features of that library. If there's a bug in the version we took, and even if there's a bug fix later, we won't be able to get that fix. Its simply ineffiecient and anti design to depend on a certain version/build of an external library as it makes our project difficult in the future to adopt to new changes. So I'd like to know what you guys think. Does it really make sense to include a specific version of external library in our svn and keep using it ignoring all updates?

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• Graphics hardware warning when updating to 14.04

  - by pacomet

  As I use Ubuntu at work I just update only LTS versions but now I'm not sure if I can/should. As my computer is now ten years old I would change if was mine but as it is owned by my employer I have to work with it. It's not a bad one, it runs fine (this was not true when still had Windows on it ;-). When updating to 14.04, it warns about possible bad/slow performance with Unity 3D so I stop updating as I am at work, not my own computer. As I understand from http://askubuntu.com/a/438958/25305 Nvidia Geforce FX 5500 graphics card is still supported in 14.04. Now, in 12.04, I have driver version 173 and unity 2d runs fine for me. output of /usr/lib/nux/unity_support_test -p OpenGL vendor string: NVIDIA Corporation OpenGL renderer string: GeForce FX 5500/AGP/SSE2 OpenGL version string: 2.1.2 NVIDIA 173.14.39 Not software rendered: yes Not blacklisted: no GLX fbconfig: yes GLX texture from pixmap: yes GL npot or rect textures: yes GL vertex program: yes GL fragment program: yes GL vertex buffer object: yes GL framebuffer object: yes GL version is 1.4+: yes Unity 3D supported: no Should I update? Is it better to stay with 12.04? Thanks

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• Methods for getting static data from obj-c to Parse (database)

  - by Phil

  I'm starting out thinking out how best to code my latest game on iOS, and I want to use parse.com to store pretty much everything, so I can easily change things. What I'm not sure about is how to get static data into parse, or at least the best method. I've read about using NSMutableDictionary, pLists, JSON, XML files etc. Let's say for example in AS3 I could create a simple data object like so... static var playerData:Object = {position:{startX:200, startY:200}}; Stick it in a static class, and bingo I've got my static data to use how I see fit. Basically I'm looking for the best method to do the same thing in Obj-c, but the data is not to be stored directly in the iOS game, but to be sent to parse.com to be stored on their database there. The game (at least the distribution version) will only load data from the parse database, so however I'm getting the static data into parse I want to be able to remove it from being included in the eventual iOS file. So any ideas on the best methods to sort that? If I had longer on this project, it might be nice to use storyboards and create a simple game editor to send data to parse....actually maybe that's a good idea, it's just I'm new to obj-c and I'm looking for the most straightforward (see quickest) way to achieve things. Thanks for any advice.

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• How do I get HDMI output working on a Dell XPS 15 L502x?

  - by Jones

  Recently I've bought my dream's notebook, a Dell XPS 15 but since then this dream became a kind of endless nightmare. I'm almost getting crazy to make my graphic card driver work properly, but it seems to be just impossible. Yes, I have a 2GB NVIDIA GeForce GT 540m (Optimus) in it! It simply doesn't work. Every time I generate the xorg.conf Ubuntu hangs on while starting up, which forces me to remove this file to be able to start the notebook with the standard graphic settings. Another problem is that the Dell XPS 15 does NOT have a VGA output, but a HDMI. So, to be able to use a second monitor I have to configure it by the NVIDIA X Server Settings, which just works if the driver is properly initialized with the xorg.conf. I've also tried to make it work with the Bumblebee, but unfortunately it didn't help me much with the HDMI output. Do you guys have any idea to solve this deadlock? Is there any way for me to use my second monitor?

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• JiglibX addition to existing project questions

  - by SomeXnaChump

  Got a very simple existing project, that basically contains a lot of cubes. Now I am wanting to add a physics system to it and JiglibX seemed like the simplest one with some tutorials out there. My main problem is that the physics don't seem to be working how I imagined, I expected my tower of cubes to come crashing down, but they dont seem to do anything. I think my problem is that my cubes do not inherit DrawableGameComponent, they are managed by a world object that will update and render them. So they are at no point put into the games component list. I am not sure if this means that JiglibX will not be able to interact with them as in all the tutorials there are no explicit calls to add the Body objects to the physics system, so I can only presume that they are using a static/singleton under the hood which automatically hooks in all things, or they use the game objects component list somehow. I also noticed that in alot of the tutorials they use the following when setting up the physics system: float timeStep = (float)gameTime.ElapsedGameTime.Ticks / TimeSpan.TicksPerSecond; PhysicsSystem.CurrentPhysicsSystem.Integrate(timeStep); Would it not be better to keep a local instance of the created PhysicsSystem object and just call myPhysicsSystem.Integrate(timeStep)?

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• Making a class pseudo-immutable by setting a flag

  - by scott_fakename

  I have a java project that involves building some pretty complex objects. There are quite a lot (dozens) of different ones and some of them have a HUGE number of parameters. They also need to be immutable. So I was thinking the builder pattern would work, but it ends up require a lot of boilerplate. Another potential solution I thought of was to make a mutable class, but give it a "frozen" flag, a-la ruby. Here is a simple example: public class EqualRule extends Rule { private boolean frozen; private int target; public EqualRule() { frozen = false; } public void setTarget(int i) { if (frozen) throw new IllegalStateException( "Can't change frozen rule."); target = i; } public int getTarget() { return target; } public void freeze() { frozen = true; } @Override public boolean checkRule(int i) { return (target == i); } } and "Rule" is just an abstract class that has an abstract "checkRule" method. This cuts way down on the number of objects I need to write, while also giving me an object that becomes immutable for all intents and purposes. This kind of act like the object was its own Builder... But not quite. I'm not too excited, however, about having an immutable being disguised as a bean however. So I had two questions: 1. Before I go too far down this path, are there any huge problems that anyone sees right off the bat? For what it's worth, it is planned that this behavior will be well documented... 2. If so, is there a better solution? Thanks

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• Errors when installing updates

  - by user71613

  I am getting the following errors when installing updates. They started to appear after I upgraded my system to 12.04. Errors were encountered while processing: samba-common samba-common-bin samba grub-pc grub-gfxpayload-lists Setting up samba-common (2:3.6.3-2ubuntu2.2) ... perl: error while loading shared libraries: libperl.so.5.12: cannot open shared object file: No such file or directory dpkg: error processing samba-common (--configure): subprocess installed post-installation script returned error exit status 127 dpkg: dependency problems prevent configuration of samba-common-bin: samba-common-bin depends on samba-common (>= 2:3.4.0~pre1-2); however: Package samba-common is not configured yet. dpkg: error processing samba-common-bin (--configure): dependency problems - leaving unconfigured dpkg: dependency problems prevent configuration of samba: samba depends on samba-common (= 2:3.6.3-2ubuntu2.2); however: Package samba-common is not configured yet. samba depends on samba-common-bin; however: Package samba-common-bin is not configured yet. dpkg: error processing samba (--configure): dependency problems - leaving unconfigured Setting up grub-gfxpayload-lists (0.6) ... Setting up grub-pc (1.99-21ubuntu3.1) ... perl: error while loading shared libraries: libperl.so.5.12: cannot open shared object file: No such file or directory dpkg: error processing grub-pc (--configure): subprocess installed post-installation script returned error exit status 127 Any ideas how to fix this?

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• Android Game Development problem whith size and speed

  - by Charlton Santana

  I have been coding speed for an object. I have made it so the object will move from one end of the screen to another at a speed depending on the screen size, at the monemt I have made it so it will take one second to pass the screen. So i have worked out the speed in code but when I go to assign the speed it tells me to force close and i do not understand why. Here is the code: MainGame Code: @Override protected void onDraw(Canvas canvas) { setBlockSpeed(getWidth()); } private int blockSpeed; private void setBlockSpeed(int screenWidth){ Log.d(TAG, "screenWidth " + screenWidth); blockSpeed = screenWidth / 100; // 100 is the FPS.. i want it to take 1 second to pass the screen Math.round(blockSpeed); // to make it a whole number block.speed = blockSpeed; // if i dont put blockSpeed and put eg 8 it still tells me to force close } Block.java Code: public int speed; public void draw(Canvas canvas) { canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2), y - (bitmap.getHeight() / 2), null); if(dontmove == 0){ this.x -= speed; } }

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• More Tables or More Databases?

  - by BuckWoody

  I got an e-mail from someone that has an interesting situation. He has 15,000 customers, and he asks if he should have a database for their data per customer. Without a LOT more data it’s impossible to say, of course, but there are some general concepts to keep in mind. Whenever you’re segmenting data, it’s all about boundary choices. You have not only boundaries around how big the data will get, but things like how many objects (tables, stored procedures and so on) that will be involved, if there are any cross-sections of data (do they share location or product information) and – very important – what are the security requirements? From the answer to these types of questions, you now have the choice of making multiple tables in a single database, or using multiple databases. A database carries some overhead – it needs a certain amount of memory for locking and so on. But it has a very clean boundary – everything from objects to security can be kept apart. Having multiple users in the same database is possible as well, using things like a Schema. But keeping 15,000 schemas can be challenging as well. My recommendation in complex situations like this is similar to a post on decisions that I did earlier – I lay out the choices on a spreadsheet in rows, and then my requirements at the top in the columns. I  give each choice a number based on how well it meets each requirement. At the end, the highest number wins. And many times it’s a mix – perhaps this person could segment customers into larger regions or districts or products, in a database. Within that database might be multiple schemas for the customers. Of course, he needs to query across all customers, that becomes another requirement. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• How to Install Broadcom Wireless Drivers (BCM43xx)

  - by Fer1805

  I'm having serious problems installing the Broadcom drivers for Ubuntu. It worked perfectly on my previous version, but now, it is impossible. I'm a user with no advance knowledge in Linux, so I would need clear explanations on make, compile, etc. Edit: For the command: "lspci | grep Network", I get the following message: 06:00.0 Network controller: Broadcom Corporation BCM4311 802.11b/g WLAN (rev 01) For the command: iwconfig, i get the following: lo no wireless extensions. eth0 no wireless extensions. When i follow the following steps (from the above link), there are a NO error message at all: open the 'Synaptic Package Manager' and search for bcm uninstall the bcm-kernel-source package make sure that the firmware-b43-installer and the b43-fwcutter packages are installed type into terminal: cat /etc/modprobe.d/* | egrep '8180|acx|at76|ath|b43|bcm|CX|eth|ipw|irmware|isl|lbtf|orinoco|ndiswrapper|NPE|p54|prism|rtl|rt2|rt3|rt6|rt7|witch|wl' (you may want to copy this) and see if the term blacklist bcm43xx is there if it is, type cd /etc/modprobe.d/ and then sudo gedit blacklist.conf put a # in front of the line: blacklist bcm43xx then save the file (I was getting error messages in the terminal about not being able to save, but it actually did save properly). reboot 'End of procedure' Before (not ubuntu 11.04), if i wanted to connect wireles, i just went to the icon at the upper side of the screen, click, showed ALL the wireless network available, and done. Now, the only options i see are: Wired Network Auto Eth0 Disconnect VPN Enable networking Connection information Edit connection. lspci -vnn | grep Network showed: Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b] hope above info is enough for your help.

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• Advertising on personalized pages behind a login

  - by johneth

  I am currently building a web app which requires a user to log in. After they log in, they can see the content they've added to the web app, and things that the web app has done with the content they added. The URL structure won't differentiate different users (e.g. all user's 'homepage' would be example.com/home, not something like example.com/username/home). This is much the same way that Facebook works (all FB user's messages are at facebook.com/messages, for example). This presents a problem with advertising. I know that you can use AdSense behind a login, but as far as I'm aware, that's for things like forums, where everyone sees the same things (which wouldn't be the case in this site). I also know that I could put AdSense on the pages without allowing it to log in, which would produce inferior ads. I'm fairly certain it would be against the Terms of Service to give AdSense a login to a 'dummy' account with typical content, as it would not be seeing the same thing as every other user (which is impossible, as they all see different things). So, my question is: Is there an ad network, or other method, that can serve ads behind a login, maybe based on keywords rather than content?

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• Is there a standard way to track 2d tile positions both locally and on screen?

  - by Magicked

  I'm building a 2D engine based on 32x32 tiles with OpenGL. OpenGL draws from the top left, so Y coordinates go down the screen as they increase. Obviously this is different than a standard graph where Y coordinates move up as they increase. I'm having trouble determining how I want to track positions for both sprites and tile objects (objects that are collections of tiles). My brain wants to set the world position as the bottom left of the object and track every object this way. The problem with this is I would have to translate it to an on screen position on rendering. The positive with this is I could easily visualize (especially in the case of objects made of multiple tiles) how something is structured and needs to be built. Are there standard ways for doing this? Should I just suck it up and get used to positions beginning in the top left? Here are the OpenGL calls to start rendering: // enable textures since we're going to use these for our sprites glEnable(GL_TEXTURE_2D); glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // enable alpha blending glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // disable the OpenGL depth test since we're rendering 2D graphics glDisable(GL_DEPTH_TEST); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(0, WIDTH, HEIGHT, 0, 1, -1); glMatrixMode(GL_MODELVIEW); I assume I need to change: glOrtho(0, WIDTH, HEIGHT, 0, 1, -1); to: glOrtho(0, WIDTH, 0, HEIGHT, 1, -1);

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• What's wrong with this OpenGL model picking code?

  - by openglNewbie

  I am making simple model viewer using OpenGL. When I want to pick an object OpenGL returns nothing or an object that is in another place. This is my code: GLuint buff[1024] = {0}; GLint hits,view[4]; glSelectBuffer(1024,buff); glGetIntegerv(GL_VIEWPORT, view); glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); gluPickMatrix(x,y,1.0,1.0,view); gluPerspective(45,(float)view[2]/(float)view[4],1.0,1500.0); glMatrixMode(GL_MODELVIEW); glRenderMode(GL_SELECT); glLoadIdentity(); //I make the same transformations for normal render glTranslatef(0, 0, -zoom); glMultMatrixf(transform.M); glInitNames(); glPushName(-1); for(int j=0;j<allNodes.size();j++) { glLoadName(allNodes.at(j)->id); allNodes.at(j)->Draw(textures); } glPopName(); glMatrixMode(GL_PROJECTION); glPopMatrix(); hits = glRenderMode(GL_RENDER);

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• Transformation?

  - by Joe G

  I started working at Oracle in 1997.  Since then, we (and most everyone) have been talking about transforming finance operations....but what does that mean exactly?  From my perspective, I thought it meant eliminate waste and menial tasks and giving your finance team more time to work on more strategic things.  That seems logical and simplistic, but how much progress have finance teams (and their IT departments) really made over the past fifteen years? I have yet to talk to a customer that doesn't have one amusing task that makes me chuckle.  Sometimes they still print hard copies of transactions to "file," or sometimes they print 700 pages of data to "analyze," or sometimes they cut and paste from one or more reports into a spreadsheet.  Upon hearing these things, my first question is always, "Why do you do that?" to which their response is rarely the same.    Sometimes it's related to trust (both the employee and the system).  Sometimes, it's habit-based.  And sometimes it is just impossible to accomplish the end result without some manual effort. I will say that I used to print nearly everything that I needed to review.  Partly, because I liked having the ability to scribble notes on the paper, and partly, because it was uncomfortable to read online.  However, I have changed. Rarely do I print anything anymore.  It's easier for me to read and notate online, and well, I guess I've just changed my habits. So where do you think our resistance to change comes from?  Is it truly deficits in our systems, or is it our own personal resistance to change?  What's your most annoying & untransformed task?

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• Returning a flexible datatype from a C++ function

  - by GavinH

  I'm developing for a legacy C++ application which uses ODBC for it's data access. Coming from a C# background, I really miss the ADO style of data access. I'm writing a wrapper (because we can't actually use ADO) to make our data access less painful. This means no char arrays, no manual text blob streaming, and no declaritive column binding. I'm struggling with how to store / return data values. In C# at least, you can declare an object and cast it to whatever (as long as the type is convertable). My current C++ solution is to use boost::any to store the data value in a custom DataColumnValue object. This class has conversion and assignment operators to the various types used in our app (more than 10). There's a bit of complexity here because if you store an int in the boost::any and try to boost::any_cast<long> you get a boost::bad_any_cast. Client objects shouldn't have to know how the value is stored internally. Does anyone have any experience trying to store / return values whose types are only known at runtime? Is there a better / cleaner way?

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• Guidelines for creating referentially transparent callables

  - by max

  In some cases, I want to use referentially transparent callables while coding in Python. My goals are to help with handling concurrency, memoization, unit testing, and verification of code correctness. I want to write down clear rules for myself and other developers to follow that would ensure referential transparency. I don't mind that Python won't enforce any rules - we trust ourselves to follow them. Note that we never modify functions or methods in place (i.e., by hacking into the bytecode). Would the following make sense? A callable object c of class C will be referentially transparent if: Whenever the returned value of c(...) depends on any instance attributes, global variables, or disk files, such attributes, variables, and files must not change for the duration of the program execution; the only exception is that instance attributes may be changed during instance initialization. When c(...) is executed, no modifications to the program state occur that may affect the behavior of any object accessed through its "public interface" (as defined by us). If we don't put any restrictions on what "public interface" includes, then rule #2 becomes: When c(...) is executed, no objects are modified that are visible outside the scope of c.__call__. Note: I unsuccessfully tried to ask this question on SO, but I'm hoping it's more appropriate to this site.

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• Google Chrome with strange behavior

  - by user72274

  I'm former Chromium-browser user, but after not upgrading the PPA for 2 months, I switched to Google Chrome browser yesterday. Everything is okay, except some strange behavior on some pages and crashing after loading "chrome://" configuration pages. The best known website with strange behavior is youtube, there is a picture what I see: When I open user menu in top right corner, it crashes that way and even after closing the menu, some parts of menu stay display. You may say it's Youtube problem, no, I have this problem at least on three other websites, here it is on Imgur: The problem isn't for the whole side, sometimes it happens from the middle of the screen. The interesting part is that it happens everytime in the same distance from the right border. When I check the DOM elements with the Developer tool, the overlay which shows element's position is rendered how it should be. What is more, if there is anchor after the crashed area, it works after clicking on it. Selecting text in crashed page is impossible. I hope there is enough information to give me an advice, thanks in advance. :) EDIT: Here is what the browser posted in "chrome://gpu-internals/": Graphics Feature Status Canvas: Software only, hardware acceleration unavailable Compositing: Hardware accelerated 3D CSS: Hardware accelerated CSS Animation: Software animated. WebGL: Hardware accelerated WebGL multisampling: Hardware accelerated Problems Detected Accelerated CSS animation has been disabled at the command line. Accelerated 2d canvas is unstable in Linux at the moment. Ubuntu 12.04 | Gnome-shell 3.4.1 | ATI Radeon 4550 | Screen resolution 1024*768 | Chrome version 20.0.1132.57 (Official Build 145807)

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• How should I compress a file with multiple bytes that are the same with Huffman coding?

  - by Omega

  On my great quest for compressing/decompressing files with a Java implementation of Huffman coding (http://en.wikipedia.org/wiki/Huffman_coding) for a school assignment, I am now at the point of building a list of prefix codes. Such codes are used when decompressing a file. Basically, the code is made of zeroes and ones, that are used to follow a path in a Huffman tree (left or right) for, ultimately, finding a byte. In this Wikipedia image, to reach the character m the prefix code would be 0111 The idea is that when you compress the file, you will basically convert all the bytes of the file into prefix codes instead (they tend to be smaller than 8 bits, so there's some gain). So every time the character m appears in a file (which in binary is actually 1101101), it will be replaced by 0111 (if we used the tree above). Therefore, 1101101110110111011011101101 becomes 0111011101110111 in the compressed file. I'm okay with that. But what if the following happens: In the file to be compressed there exists only one unique byte, say 1101101. There are 1000 of such byte. Technically, the prefix code of such byte would be... none, because there is no path to follow, right? I mean, there is only one unique byte anyway, so the tree has just one node. Therefore, if the prefix code is none, I would not be able to write the prefix code in the compressed file, because, well, there is nothing to write. Which brings this problem: how would I compress/decompress such file if it is impossible to write a prefix code when compressing? (using Huffman coding, due to the school assignment's rules) This tutorial seems to explain a bit better about prefix codes: http://www.cprogramming.com/tutorial/computersciencetheory/huffman.html but doesn't seem to address this issue either.

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• What do I do for dependencies installing wine1.7 on 14.04

  - by user285207

  user@chrubuntu:~$ sudo apt-get install wine1.7 [sudo] password for user: user Sorry, try again. [sudo] password for user: Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: wine1.7 : Depends: wine1.7-i386 (= 1:1.7.19-0ubuntu2~trusty2) but it is not installable Recommends: gnome-exe-thumbnailer but it is not going to be installed or kde-runtime but it is not going to be installed Recommends: ttf-mscorefonts-installer but it is not going to be installed Recommends: fonts-horai-umefont but it is not going to be installed Recommends: fonts-unfonts-core but it is not going to be installed Recommends: ttf-wqy-microhei Recommends: winetricks but it is not going to be installed E: Unable to correct problems, you have held broken packages. user@chrubuntu:~$ Trying to install wine1.7 on Ubuntu 14.04 64 bit, and i'm not sure what this means, help is greatly appreciated. I already ran sudo apt-get update and get this: Reading package lists... Done W: Duplicate sources.list entry http://dl.google.com/linux/chrome/deb/ stable/main amd64 Packages (/var/lib/apt/lists/dl.google.com_linux_chrome_deb_dists_stable_main_binary-amd64_Packages) W: You may want to run apt-get update to correct these problems So I run apt-get update and: E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied) E: Unable to lock directory /var/lib/apt/lists/ E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root? This is all very stressing because I have been trying to get Wine for the past week and had to reinstall and IT STILL WON'T WORK.

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