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  • R: disentangling scopes

    - by rescdsk
    Hi, Right now, in my R project, I have functions1.R with doFoo() and doBar(), functions2.R with other functions, and main.R with the main program in it, which first does source('functions1.R'); source('functions2.R'), and then calls the other functions. I've been starting the program from the R GUI in Mac OS X, with source('main.R'). This is fine the first time, but after that, the variables that were defined the first time through the program are defined for the second time functions*.R are sourced, and so the functions get a whole bunch of extra variables defined. I don't want that! I want an "undefined variable" error when my function uses a variable it shouldn't! Twice this has given me very late nights of debugging! So how do other people deal with this sort of problem? Is there something like source(), but that makes an independent namespace that doesn't fall through to the main one? Making a package seems like one solution, but it seems like a big pain in the butt compared to e.g. Python, where a source file is automatically a separate namespace. Any tips? Thank you!

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  • Why is it preferable to call a static method statically from within an instance of the method's clas

    - by javanix
    If I create an instance of a class in Java, why is it preferable to call a static method of that same class statically, rather than using this.method()? I get a warning from Eclipse when I try to call static method staticMethod() from within the custom class's constructor via this.staticMethod(). public MyClass() { this.staticMethod(); } vs public MyClass() { MyClass.staticMethod(); } Can anyone explain why this is a bad thing to do? It seems to me like the compiler should already have allocated an instance of the object, so statically allocating memory would be unneeded overhead.

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  • How does this code break the Law of Demeter?

    - by Dave Jarvis
    The following code breaks the Law of Demeter: public class Student extends Person { private Grades grades; public Student() { } /** Must never return null; throw an appropriately named exception, instead. */ private synchronized Grades getGrades() throws GradesException { if( this.grades == null ) { this.grades = createGrades(); } return this.grades; } /** Create a new instance of grades for this student. */ protected Grades createGrades() throws GradesException { // Reads the grades from the database, if needed. // return new Grades(); } /** Answers if this student was graded by a teacher with the given name. */ public boolean isTeacher( int year, String name ) throws GradesException, TeacherException { // The method only knows about Teacher instances. // return getTeacher( year ).nameEquals( name ); } private Grades getGradesForYear( int year ) throws GradesException { // The method only knows about Grades instances. // return getGrades().getForYear( year ); } private Teacher getTeacher( int year ) throws GradesException, TeacherException { // This method knows about Grades and Teacher instances. A mistake? // return getGradesForYear( year ).getTeacher(); } } public class Teacher extends Person { public Teacher() { } /** * This method will take into consideration first name, * last name, middle initial, case sensitivity, and * eventually it could answer true to wild cards and * regular expressions. */ public boolean nameEquals( String name ) { return getName().equalsIgnoreCase( name ); } /** Never returns null. */ private synchronized String getName() { if( this.name == null ) { this.name == ""; } return this.name; } } Questions How is the LoD broken? Where is the code breaking the LoD? How should the code be written to uphold the LoD?

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  • When to use "property" builtin: auxiliary functions and generators

    - by Seth Johnson
    I recently discovered Python's property built-in, which disguises class method getters and setters as a class's property. I'm now being tempted to use it in ways that I'm pretty sure are inappropriate. Using the property keyword is clearly the right thing to do if class A has a property _x whose allowable values you want to restrict; i.e., it would replace the getX() and setX() construction one might write in C++. But where else is it appropriate to make a function a property? For example, if you have class Vertex(object): def __init__(self): self.x = 0.0 self.y = 1.0 class Polygon(object): def __init__(self, list_of_vertices): self.vertices = list_of_vertices def get_vertex_positions(self): return zip( *( (v.x,v.y) for v in self.vertices ) ) is it appropriate to add vertex_positions = property( get_vertex_positions ) ? Is it ever ok to make a generator look like a property? Imagine if a change in our code meant that we no longer stored Polygon.vertices the same way. Would it then be ok to add this to Polygon? @property def vertices(self): for v in self._new_v_thing: yield v.calculate_equivalent_vertex()

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  • Should I worry about reigning in namespace number/length/scope?

    - by Jay
    I've recently reorganized a solution-in-progress from 24 projects to 4. To keep the copious files organized in the "main" project, things are in folders in folders in folders. I think I've preserved a logical, discoverable arrangement of the solution content. As a result, of course, I end up with namespaces like AppName.DataAccess.NHibernate.Fluent.Mappings. Is there any compelling reason that I should care about flattening out the namespace hierarchy when my project has a somewhat deeply nested folder structure? (I am not concerned about resolving or managing using directives; I let ReSharper do all the heavy lifting here.)

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  • Can per-user randomized salts be replaced with iterative hashing?

    - by Chas Emerick
    In the process of building what I'd like to hope is a properly-architected authentication mechanism, I've come across a lot of materials that specify that: user passwords must be salted the salt used should be sufficiently random and generated per-user ...therefore, the salt must be stored with the user record in order to support verification of the user password I wholeheartedly agree with the first and second points, but it seems like there's an easy workaround for the latter. Instead of doing the equivalent of (pseudocode here): salt = random(); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword, salt); Why not use the hash of the username as the salt? This yields a domain of salts that is well-distributed, (roughly) random, and each individual salt is as complex as your salt function provides for. Even better, you don't have to store the salt in the database -- just regenerate it at authentication-time. More pseudocode: salt = hash(username); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword); (Of course, hash in the examples above should be something reasonable, like SHA-512, or some other strong hash.) This seems reasonable to me given what (little) I know of crypto, but the fact that it's a simplification over widely-recommended practice makes me wonder whether there's some obvious reason I've gone astray that I'm not aware of.

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  • How to include associative table information and still retain strong typing

    - by mwright
    I am using LINQ to SQL to create strongly typed objects in my project. Let's say I have an object that is represented by a database table. This object has a "Current State" that is kept in an associative table. I would like to make a single db call where I pull back the two tables joined but am unsure how I should be populating that information into some sort of object to preserve strong typing within my model so that the view using the information can just consume the information from the objects. I looked into creating a view model for this but it doesn't seem to quite fit. Am I thinking about this in the wrong way? What information can I include to help clarify my problem? Other details that may or may not be important: It's an MVC project....

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  • How convince other developers not to ignore Exceptions?

    - by Mnementh
    Recently I encountered a bug in an application I took over from another developer. I debugged for the reason and over an hour later I realized, that the problem wasn't the code producing the exception, but some code executed before this returning wrong data. If I dived into this, I encountered the following: try { ... } catch (XYException e){} If the Exception would have been propagated (a change I did), I would have found the reason for the bugs in a few minutes, as the stacktrace had pointed me to the problem. So how can I convince other developers to never catch and ignore exceptions in this way?

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  • Java operator overloading

    - by nimcap
    Not using operators makes my code obscure. (aNumber / aNother) * count is better than aNumber.divideBy(aNother).times(count) After 6 months of not writing a single comment I had to write a comment to the simple operation above. Usually I refactor until I don't need comment. And this made me realize that it is easier to read and perceive math symbols and numbers than their written forms. For example TWENTY_THOUSAND_THIRTEEN.plus(FORTY_TWO.times(TWO_HUNDERED_SIXTY_ONE)) is more obscure than 20013 + 42*261 So do you know a way to get rid of obscurity while not using operator overloading in Java? Update: I did not think my exaggeration on comments would cause such trouble to me. I am admitting that I needed to write comment a couple of times in 6 months. But not more than 10 lines in total. Sorry for that. Update 2: Another example: budget.plus(bonusCoefficient.times(points)) is more obscure than budget + bonusCoefficient * points I have to stop and think on the first one, at first sight it looks like clutter of words, on the other hand, I get the meaning at first look for the second one, it is very clear and neat. I know this cannot be achieved in Java but I wanted to hear some ideas about my alternatives.

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  • Common programming mistakes for Scala developers to avoid

    - by jelovirt
    In the spirit of Common programming mistakes for Java developers to avoid? Common programming mistakes for JavaScript developers to avoid? Common programming mistakes for .NET developers to avoid? Common programming mistakes for Haskell developers to avoid? Common programming mistakes for Python developers to avoid? Common Programming Mistakes for Ruby Developers to Avoid Common programming mistakes for PHP developers to avoid? what are some common mistakes made by Scala developers, and how can we avoid them? Also, as the biggest group of new Scala developers come from Java, what specific pitfalls they have to be aware of? For example, one often cited problem Java programmers moving to Scala make is use a procedural approach when a functional one would be more suitable in Scala. What other mistakes e.g. in API design newcomers should try to avoid.

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  • .Net4 ConcurrentDictionary: Tips & Tricks

    - by SDReyes
    Hi guys, I started to use the new ConcurrentDictionary from .Net4 yesterday to implement a simple caching for a threading project. But I'm wondering what I have to take care of/be careful about when using it? What have been your experiences using it?

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  • HELP!! Ruby & RoR Resources?

    - by aaroninfidel
    Hello, I've been a PHP Developer for a few years now and I've recently been interested in learning Ruby & Rails but I've found a lot of the resources I've found seem to be dated and not for Rails 2.0 or Ruby 1.8.6 etc... can anyone point me in the right direction? I'm running OSX 10.6 with the default ruby & rails installation. Thanks!

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  • controlling if exceptions are swallowed by a static boolean

    - by sandis
    So we are a few guys developing this product that is communicating with a really unstable server. It often returns very strange and corrupt data. During testing we want the resulting crashes to be loud, so we discover them. But every other day we need to demonstrate our product for a potential customer. To the customer the errors will go undiscovered if we just swallow them. I am thinking about implementing something like this around all server communication to quickly switch between swallowing exceptions and crashing: try { apiCall(); } catch (Exception e) { if(!SWALLOW_EXCEPTION) { throw e; } } Is this an awesome idea, or can it be done in a better way?

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  • Managing string resources in a Java application - singleton?

    - by Joe Attardi
    I seek a solution to the age-old problem of managing string resources. My current implementation seems to work well, but it depends on using singletons, and I know how often singletons can be maligned. The resource manager class has a singleton instance that handles lookups in the ResourceBundle, and you use it like so: MessageResources mr = MessageResources.getMessageResources(); // returns singleton instance ... JLabel helloLabel = new JLabel(mr.getString("label.hello")); Is this an appropriate use of a singleton? Is there some better, more universally used approach that I'm not aware of? I understand that this is probably a bit subjective, but any feedback I can get would be appreciated. I'd rather find out early on that I'm doing it wrong than later on in the process. Thanks!

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  • How to create custom javadoc tags

    - by Carlucho
    How to create custom javadoc tags such as @pre / @post... I found some links that explain it but i haven had luck with them, i dont know if that am already tired but i can figure where to put it. these are some of the links http://www.developer.com/java/other/article.php/3085991/Javadoc-Programming.html http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/javadoc.html I'm sorry to ask to be spoon fed but am at the stage where i only see black dots on the screen :\ Thanks a bunch

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  • What is the best area for freelance / small business developer work - and how to find it

    - by Olav
    Most freelance developers are essentially contractors - working full time and often hired through another company. What are the best options for real freelancing or small business built around development skills? (I am only looking for local clients, odesk etc is not interesting) Most options open for small companies are web sites. But most clients don't want to pay much, and there are lots of people that are willing to do it for very little money. Think if you want to do money that way you must be a "web site" business. Think the best option should be to work for companies spending a lot of resources on web and db? How could I get in touch with them? Other ideas? Part of my concept is to use some off-shoring to complement my skillset, so i should be able to do PHP or Drupal even if I am not at expert level.

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  • REST doesn't work with Sever-Client-Client setup

    - by drozzy
    I am having a problem with my current RESTful api design. What I have is a REST api which is consumed by Django web-server, which renders the HTML templates. REST api > Django webserver > HTML The problem I am encountering is that I have to reconstruct all the URLS like mysite.com/main/cities/<id>/streets/ into equivalent rest api urls on my web-server layer: api.com/cities/<id>/streets/ Thus I have a lot of mapping back and forth, but as far as I know REST says that the client (in this case my web-server) should NOT need to know how to re-construct the urls. Can REST be used for such a setup and how? Or is it only viable for Server-Client architecture. Thanks

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