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• What's the relationship between meta-circular interpreters, virtual machines and increased performance?

  - by Gomi

  I've read about meta-circular interpreters on the web (including SICP) and I've looked into the code of some implementations (such as PyPy and Narcissus). I've read quite a bit about two languages which made great use of metacircular evaluation, Lisp and Smalltalk. As far as I understood Lisp was the first self-hosting compiler and Smalltalk had the first "true" JIT implementation. One thing I've not fully understood is how can those interpreters/compilers achieve so good performance or, in other words, why is PyPy faster than CPython? Is it because of reflection? And also, my Smalltalk research led me to believe that there's a relationship between JIT, virtual machines and reflection. Virtual Machines such as the JVM and CLR allow a great deal of type introspection and I believe they make great use it in Just-in-Time (and AOT, I suppose?) compilation. But as far as I know, Virtual Machines are kind of like CPUs, in that they have a basic instruction set. Are Virtual Machines efficient because they include type and reference information, which would allow language-agnostic reflection? I ask this because many both interpreted and compiled languages are now using bytecode as a target (LLVM, Parrot, YARV, CPython) and traditional VMs like JVM and CLR have gained incredible boosts in performance. I've been told that it's about JIT, but as far as I know JIT is nothing new since Smalltalk and Sun's own Self have been doing it before Java. I don't remember VMs performing particularly well in the past, there weren't many non-academic ones outside of JVM and .NET and their performance was definitely not as good as it is now (I wish I could source this claim but I speak from personal experience). Then all of a sudden, in the late 2000s something changed and a lot of VMs started to pop up even for established languages, and with very good performance. Was something discovered about the JIT implementation that allowed pretty much every modern VM to skyrocket in performance? A paper or a book maybe?

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

  - by john smith optional

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

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• What's special about currying or partial application?

  - by Vigneshwaran

  I've been reading articles on Functional programming everyday and been trying to apply some practices as much as possible. But I don't understand what is unique in currying or partial application. Take this Groovy code as an example: def mul = { a, b -> a * b } def tripler1 = mul.curry(3) def tripler2 = { mul(3, it) } I do not understand what is the difference between tripler1 and tripler2. Aren't they both the same? The 'currying' is supported in pure or partial functional languages like Groovy, Scala, Haskell etc. But I can do the same thing (left-curry, right-curry, n-curry or partial application) by simply creating another named or anonymous function or closure that will forward the parameters to the original function (like tripler2) in most languages (even C.) Am I missing something here? There are places where I can use currying and partial application in my Grails application but I am hesitating to do so because I'm asking myself "How's that different?" Please enlighten me.

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• Can HTML injection be a security issue?

  - by tkbx

  I recently came across a website that generates a random adjective, surrounded by a prefix and suffix entered by the user. For example, if the user enters "123" for prefix, and "789" for suffix, it might generate "123Productive789". I've been screwing around with it, and I thought I might try something out: I entered this into the prefix field: <a href="javascript:window.close();">Click</a><hr /> And, sure enough, I was given the link, then an <hr>, then a random adjective. What I'm wondering is, could this be dangerous? There must be many more websites out there that have this issue, are all of them vulnerable to some sort of php injection?

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• Organizing ASP.Net Single Page Application with Nancy

  - by OnesimusUnbound

  As a personal project, I'm creating a single page, asp.net web application using Nancy to provide RESTful services to the single page. Due to the complexity of the single page, particularly the JavaScripts used, I've think creating a dedicated project for the client side of web development and another for service side will organize and simplify the development. solution | +-- web / client side (single html page, js, css) | - contains asp.net project, and nancy library | to host the modules in application project folder | +-- application / service (nancy modules, bootstrap for other layer) | . . . and other layers (three tier, domain driven, etc) . Is this a good way of organizing a complex single page application? Am I over-engineering the web app, incurring too much complexity?

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• Save .mov file with applescript

  - by Frost Shadow

  I've installed the Perian addon for Quicktime so it can open .flv files, and then I can save them as .m4v or .mov. I'm trying to make an Applescript to convert from .flv to .m4v automatically by using this tutorial and butchering their example applescript file, which normally converts ChemDraw files (.cdx, .cml, .mol) to .tiff, so that it instead uses Quicktime to save the .flv files as .m4v. When I try to use it, though, I get an error "QuickTime Player got an error: document 1 doesn't understand the save message". My save message is currently: save first document in target_path as ".m4v" which looks like the QuickTime dictionary's instructions: save specifier : The document(s) or window(s) to save. [as saveable file format] : The file format to use. I've also tried "m4v", without the period, and still get the error. Is my Save direction wrong, or is it probably an error from trying to use Quicktime instead of the original ChemDraw? I tried to change references to .cdx, .cml, .mol, .tiff, and ChemDraw to .flv, .m4v, and QuickTime respectively, but maybe it's more complicated than that? I would, in fact, appreciate any example showing how to save an application file (ex: a TextEdit .rtf or .txt), as I can't seem to get any kind of file to save using applescript.

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• How to gain Professional Experience in Java/Java EE Development

  - by Deepak Chandrashekar

  I have been seeing opportunities go past me for just 1 reason: not having professional industry experience. I say to many employers that I'm capable of doing the job and show them the work I've done during the academics and also several personal projects which I took extra time and effort to teach myself the new industry standard technologies. But still, all they want is some 2-3 years experience in an industry. I'm a recent graduate with a Master's Degree in Computer science. I've been applying for quite a few jobs and most of these jobs require 2 years minimum experience. So, I thought somebody here might give me some realistic ideas about getting some experience which can be considered professional. Any kind of constructive comments are welcome.

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• Pythonic use of the isinstance function?

  - by Pace

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

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• is it better to spend my free time mastering a language I work with or learning a new one?

  - by edthethird

  I work full time on an android project and am very comfortable with both java and the android framework. On a good day, I would rate my abilities at an 8, and maybe a 7 on a bad day. I've recently found myself with more free time then I'm used too, so I have been working on a lot of personal projects. I am beginning to wonder what others think about this; is it worth my time to continue experimenting and pushing Android, or would I be better off learning another language? What do you all think about this? What would you do with more free time and energy than you know what to do with?

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• How to depict Import a file action in the Sequence diagram

  - by user970696

  Everyone says sequence diagrams are so easy but I just cannot figure this out. Basically user clicks on an 'Import from temp folder' button, the program opens a window with a list populated with filenames, user clicks on a filename, clicks on OK and the document is imported. I know the order of the actions but how to depict e.g. populating a list, or selecting an item from a list? So I assume the objects would be like: [USER] [ImportDialogWindow] [ListOfFiles:STRING] [?where to go with selected file]

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• Data binding in web UI frameworks, what's the deal?

  - by c-smile

  I believe that most of modern Web frameworks that pretend to be MVC ones also has a notion of data binding in one form or another. Examples: AngularJS, EmberJS, KnockoutJS, etc. I am assuming that "data binding" is a declarative definition (oxymoron, no?) of live link between data (a.k.a. model) and its representation (a.k.a. view). With some transformers in between (a.k.a. controllers). I understand why declarativeness is kind of appealing but also understand that as usual it comes with the price. In particular: 1. Live binding is quite heavy, either with dirty watch (high CPU consumption) or with Object.observe() (high memory consumption with high CPU load in some scenarios). 2. There is a "frame" part in the framework word, means there are some boundaries/limits that can be hard to overcome if you need slightly more than it was designed for. Quite usual time split: 90% of features are made in 10% of project time. But 10% rest take 90% of project time. I suspect (a.k.a. educated guess) that those MVC things are not helping to implement more functionality in less time... If so their usage motivation is not quite clear. As an example: last week wanted to find virtual list idea/solution. Found one in vanilla JavaScript that is 120 LOC. Implementation of the same but in AngualrJS is about 420 LOC. Most of the code there seems like a fight with the framework itself... So is my question: what benefits that MVC stuff or data binding give us? Is it just a buzzword popular among project managers or they give us something useful. If later one then what exactly?

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• PHP rand function (or not so rand)

  - by Badr Hari

  I was testing PHP rand function to write on a image. Of course the output shows that it's not so random. The code I used: <?php header('Content-Type: image/png'); $lenght = 512; $im = imagecreatetruecolor($lenght, $lenght); $blue = imagecolorallocate($im, 0, 255, 255); for ($y = 0; $y < $lenght; $y++) { for ($x = 0; $x < $lenght; $x++) { if (rand(0,1) == 0) { imagesetpixel($im, $x, $y, $blue); } } } imagepng($im); imagedestroy($im); ?> My question is, if I use image width/lenght (variable $lenght in this example) number like 512, 256 or 1024, it is very clear that it's not so random. When I change the variable to 513 for an example, it is so much harder for human eye to detect it. Why is that? What is so special about these numbers? 512: 513: Edit: I'm running xampp on Windows to test it.

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• On-the-fly graphical representation of code

  - by dukeofgaming

  I know about Omondo's plugin for live code-UML synchronization in Eclipse, but I was wondering if there was any other tool/IDE/IDE-extension that has some form of live graphical code representaiton (structural, flow, call-stacks, dependencies, etc.). I'm essentially looking for richer visual feedback on code while programming, not really looking for purely graphical code editors, though round-trips would be nice (edit graphically, code gets modified; edit code, representation gets modified). If you don't know about any graphical live documentation tool for code, maybe someone that can coexist with code, such as MySQL Workbench or Enterprise Architect.

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• Finishing an iteration early

  - by f1dave

  I'd like some input on this on those working with agile methodologies... A current project is finding that development on our planned user stories is finishing some time before the end of the iteration, and that the testing effort and business acceptance is what's actually dragging us out longer towards the end. This means that the devs in question have spare time, and they're essentially going out to the iteration+1 backlog and starting work on cards there before our current iteration cards are 'done'. As iteration manager, I want to put a stop to this - I want a more team-orientated approach where the group takes ownership of getting all the cards done, as opposed to "Well, dev's done so what do I dev next?" The problem I face is convincing the team of this. On one hand, I understand why the devs don't want to test the code they've written (there are unit tests they write of course, but the manual testing to be done could be influenced by their bias). The team sees working ahead as making our next iterations easier, because a lot of the work is done before we start. I see this as screwing with the whole system of planning/actuals - but it's difficult to convince the team as to why this matters. What advice can you guys and girls give? How do we stop devs reaching ahead? What should they be doing instead? How much of a problem is this in the scheme of things, if things are still getting done?

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• What's the best way to create a static utility class in python? Is using metaclasses code smell?

  - by rsimp

  Ok so I need to create a bunch of utility classes in python. Normally I would just use a simple module for this but I need to be able to inherit in order to share common code between them. The common code needs to reference the state of the module using it so simple imports wouldn't work well. I don't like singletons, and classes that use the classmethod decorator do not have proper support for python properties. One pattern I see used a lot is creating an internal python class prefixed with an underscore and creating a single instance which is then explicitly imported or set as the module itself. This is also used by fabric to create a common environment object (fabric.api.env). I've realized another way to accomplish this would be with metaclasses. For example: #util.py class MetaFooBase(type): @property def file_path(cls): raise NotImplementedError def inherited_method(cls): print cls.file_path #foo.py from util import * import env class MetaFoo(MetaFooBase): @property def file_path(cls): return env.base_path + "relative/path" def another_class_method(cls): pass class Foo(object): __metaclass__ = MetaFoo #client.py from foo import Foo file_path = Foo.file_path I like this approach better than the first pattern for a few reasons: First, instantiating Foo would be meaningless as it has no attributes or methods, which insures this class acts like a true single interface utility, unlike the first pattern which relies on the underscore convention to dissuade client code from creating more instances of the internal class. Second, sub-classing MetaFoo in a different module wouldn't be as awkward because I wouldn't be importing a class with an underscore which is inherently going against its private naming convention. Third, this seems to be the closest approximation to a static class that exists in python, as all the meta code applies only to the class and not to its instances. This is shown by the common convention of using cls instead of self in the class methods. As well, the base class inherits from type instead of object which would prevent users from trying to use it as a base for other non-static classes. It's implementation as a static class is also apparent when using it by the naming convention Foo, as opposed to foo, which denotes a static class method is being used. As much as I think this is a good fit, I feel that others might feel its not pythonic because its not a sanctioned use for metaclasses which should be avoided 99% of the time. I also find most python devs tend to shy away from metaclasses which might affect code reuse/maintainability. Is this code considered code smell in the python community? I ask because I'm creating a pypi package, and would like to do everything I can to increase adoption.

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• program logic of printing the prime numbers

  - by Vignesh Vicky

  can any body help to understand this java program it just print prime n.o ,as you enter how many you want and it works good class PrimeNumbers { public static void main(String args[]) { int n, status = 1, num = 3; Scanner in = new Scanner(System.in); System.out.println("Enter the number of prime numbers you want"); n = in.nextInt(); if (n >= 1) { System.out.println("First "+n+" prime numbers are :-"); System.out.println(2); } for ( int count = 2 ; count <=n ; ) { for ( int j = 2 ; j <= Math.sqrt(num) ; j++ ) { if ( num%j == 0 ) { status = 0; break; } } if ( status != 0 ) { System.out.println(num); count++; } status = 1; num++; } } } i dont understand this for loop condition for ( int j = 2 ; j <= Math.sqrt(num) ; j++ ) why we are taking sqrt of num...which is 3....why we assumed it as 3?

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• Complex Release Vehicle Management

  - by Sharon

  I'm looking into improving our build and release system. We are a .Net/Windows shop, and I don't see any really good tools for Windows for generating the files that are to be dropped in patch or hotfix. We are currently using TFSBuild 2010 with Windows Workflows for our continuous integration builds as well as our daily full build which includes an Installshield package for deployment. What is a good way of generating the list of files to be included in a "patch" style release, where one does not redistribute all the files, but only those necessary to accomplish the necessary changes? Are there any open source tools that work well for this, or do teams usually roll their own? I have considered using Beyond Compare but I would prefer something open source. The file "patch" creation must be 100% automatable. Which release vehicles really ought to be patch style? And which releases should replace all system files related to our application? Assume we have a very large amount of resources necessary to maintain. Is there any established material that is trusted within the industry for strategies about this? I realize it is different for "enterprise" rather than with typical websites. I am looking more for "enterprise" strategies due to our product distribution style. tl;dr Looking for info on how to ship more reliable packages?

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• Interviewing someone for general unix skills

  - by Christophe Vanfleteren

  How would you test a developer that claims to have *nix shell experience (just to be clear, we don't want to test if someone can develop on *nix, only that they know their way around the command line). I was thinking about making them solve a problem of getting information out of log files, which would involve some basics like cat, grep, cut, ... combined with piping. What other basic knowledge would you ask for? Once again, this isn't for interviewing someone who will develop for *nix systems, and also not for *nix system admins, but just for regular developers that sometimes need to do some work on a *nix system.

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• User Acceptance Testing Defect Classification when developing for an outside client

  - by DannyC

  I am involved in a large development project in which we (a very small start up) are developing for an outside client (a very large company). We recently received their first output from UAT testing of a fairly small iteration, which listed 12 'defects', triaged into three categories : Low, Medium and High. The issue we have is around whether everything in this list should be recorded as a 'defect' - some of the issues they found would be better described as refinements, or even 'nice-to-haves', and some we think are not defects at all. They client's QA lead says that it is standard for them to label every issues they identify as a defect, however, we are a bit uncomfortable about this. Whilst the relationship is good, we don't see a huge problem with this, but we are concerned that, if the relationship suffers in the future, these lists of 'defects' could prove costly for us. We don't want to come across as being difficult, or taking things too personally here, and we are happy to make all of the changes identified, however we are a bit concerned especially as there is a uneven power balance at play in our relationship. Are we being paranoid here? Or could we be setting ourselves up for problems down the line by agreeing to this classification?

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• [YYYY].[MM].[DD].[hh][mm] vs. [major].[minor].[revision] [closed]

  - by ef2011

  Possible Duplicate: What “version naming convention” do you use? I am currently debating between the traditional versioning convention [major].[minor].[revision] and my own, almost whimsical, [YYYY].[MM].[DD].[hh][mm] for a new project I am starting. I understand that [major].[minor].[revision] is probably the most popular versioning method on the planet and it is indeed pretty straightforward and reasonable, except that determining which changes merit the label "major", "minor" or even "revision" could be... subjective. A versioning system based on a timestamp is purely non-subjective and guarantees uniqueness. Which one would you choose for your project and why?

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• What should one keep in mind when switching from traditional to RESTful routing in Rails?

  - by Brian Holder-Chow

  What should one keep in mind when switching from traditional to RESTful routing in Rails? From a typical Rails routes.rb file: # This is a legacy wild controller route that's not recommended for RESTful applications. # Note: This route will make all actions in every controller accessible via GET requests. match ':controller(/:action(/:id))(.:format)' As switching away from this means that I will have to create routes for each controller individually, does anyone have any advice on the best way to migrate this safely?

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• How to Deal with a Difficult Boss?

  - by Anonymous

  I have some problems with my boss, it's quite a long story :) About one year ago, I'm working as team leader of project X. Everything work fine until one of my fellow (staff) flame me that I have problem with ALL member in our team, that guy also flame me to other staff that I report them with a poor performance. My boss call me and blame me without ask a single question. I try to explain everything to my boss but she doesn't listen to me. One month later, we have a meeting. This is only team leader's meeting, my boss talk about this problem with other team leader. There are two person who have worked with this guy, they all say "This guy cannot trust". That guy had do same thing same problem with his former team leader. Finally, everything's clear and I think I gain some trust from her. I can say that I'm the best team leader in her hand, as only project that archive more than 120% profit. Then I move to new project, this is bigger project and I can manage it quite good. But I have a problem again. One of my staff always leave and does not follow our company rule, I call him to talk and tell him that you cannot do this because that's not allow in our company. He also changed working time record file of himself, then I call him to warn again. This time he ask me to move to another project so I go to talk to my boss. She come to my building when I'm not there (other staff call me) and talk with that guy (who have problem with me); I think she still not trust me. And AGAIN, she believe what that guy said and I got blamed. I want to know how can I deal with this kind of boss, or is it better to find a new job, or any other suggestion about this problem? Thank you :) Additional information: Even my job title is "Team Leader" but it's my responsibility to manage staff working time and their behavior. This responsible is my company's rule.

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• Should library classes be wrapped before using them in unit testing?

  - by Songo

  I'm doing unit testing and in one of my classes I need to send a mail from one of the methods, so using constructor injection I inject an instance of Zend_Mail class which is in Zend framework. Example: class Logger{ private $mailer; function __construct(Zend_Mail $mail){ $this->mail=$mail; } function toBeTestedFunction(){ //Some code $this->mail->setTo('some value'); $this->mail->setSubject('some value'); $this->mail->setBody('some value'); $this->mail->send(); //Some } } However, Unit testing demands that I test one component at a time, so I need to mock the Zend_Mail class. In addition I'm violating the Dependency Inversion principle as my Logger class now depends on concretion not abstraction. Does that mean that I can never use a library class directly and must always wrap it in a class of my own? Example: interface Mailer{ public function setTo($to); public function setSubject($subject); public function setBody($body); public function send(); } class MyMailer implements Mailer{ private $mailer; function __construct(){ $this->mail=new Zend_Mail; //The class isn't injected this time } function setTo($to){ $this->mailer->setTo($to); } //implement the rest of the interface functions similarly } And now my Logger class can be happy :D class Logger{ private $mailer; function __construct(Mailer $mail){ $this->mail=$mail; } //rest of the code unchanged } Questions: Although I solved the mocking problem by introducing an interface, I have created a totally new class Mailer that now needs to be unit tested although it only wraps Zend_Mail which is already unit tested by the Zend team. Is there a better approach to all this? Zend_Mail's send() function could actually have a Zend_Transport object when called (i.e. public function send($transport = null)). Does this make the idea of a wrapper class more appealing? The code is in PHP, but answers doesn't have to be. This is more of a design issue than a language specific feature

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• Javascript Rookie Question: Define Variables Inline

  - by Dylan Kinnett

  I'm proficient with HTML and CSS but I'm still pretty shaky when it comes to Javascript. That said, I've been able to build a site using the Internet Archive Book Reader, which relies on reader.js Here's a copy of one of my versions of reader.js https://gist.github.com/dylan-k/ed4efed2384e221d46cc It's a good site, but I find I have to repeat things a lot. Basically, I have one copy of reader.js for every page/book featured on the site. It seems there must be a better way. I re-use the script, making copies, just so that I can change lines 28, 80, 83, 84. Is there a way I could include just one copy of reader.js and then use a <script> tag to define these 4 lines for the individual pages?

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• What does "context-free" mean in the term "context-free grammar"?

  - by rick

  Given the amount of material that tries to explain what a context-free grammar (CFG) is, I found it surprising that very few (in my sample, less than 1 in 20) give an explanation on why such grammars are called "context-free". And, to my mind, none succeeds in doing so. My question is, why are context-free grammars called context-free? What is "the context"? I had an intuition that the context could be other language constructs surrounding the currently analyzed construct, but that seems not to be the case. Could anyone provide a precise explanation?

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