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• Ruby execute code in class getting inherited to

  - by AdamB

  I'm trying to be able to have a global exception capture where I can add extra information when an error happens. I have two classes, "crawler" and "amazon". What I want to do is be able to call "crawl", execute a function in amazon, and use the exception handling in the crawl function. Here are the two classes I have: require 'mechanize' class Crawler Mechanize.html_parser = Nokogiri::HTML def initialize @agent = Mechanize.new end def crawl puts "crawling" begin #execute code in Amazon class here? rescue Exception => e puts "Exception: #{e.message}" puts "On url: #{@current_url}" puts e.backtrace end end def get(url) @current_url = url @agent.get(url) end end class Amazon < Crawler #some code with errors def stuff page = get("http://www.amazon.com") puts page.parser.xpath("//asldkfjasdlkj").first['href'] end end a = Amazon.new a.crawl Is there a way I can call "stuff" inside of "crawl" so I can use that exception handling over the entire stuff function? Is there a better way to accomplish this?

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• Is there a way to get the list of InnerClasses through Reflection in Java?

  - by kunjaan

  Is there a way to know the inner classes that a Class has through Reflection in Java?

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• How to extend abstract Entity class in RIA Services

  - by Calanus

  I want to add a bool variable and property to the base Entity class in my RIA services project so that it is available throughout all the entity objects but seem unable to work out how to do this. I know that adding properties to actual entities themselves is easy using .shared.cs and partial classes but adding such properties to the Entity class using similar methods doesn't work. For example, the following code doesn't work namespace System.ServiceModel.DomainServices.Client { public abstract partial class Entity { private bool auditRequired; public bool AuditRequired { get { return auditRequired; } set { auditRequired = value; } } } } All that happens is that the existing Entity class gets totally overriden rather than extending the Entity class. How do I extend the base Entity class so that functionality is available thoughout all derived entity classes?

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• How does compiler use lib file ?

  - by Xinus

  I am curious about how c/c++ compiler analyse lib files ? I mean say I create a library containing some classes, I am using that library in my main program. How does compiler know what class names are there in that library. Of course that information is present in binary format, I want to use that functionality in my program, to be specific I have a binary lib file and I want to know all classes and properties/functions present in that lib file. Is it possible ? If compiler can do that why can't some library ? thanks for any clue

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• 'is instanceof' Interface bad design

  - by peterRit

  Say I have a class A class A { Z source; } Now, the context tells me that 'Z' can be an instance of different classes (say, B and C) which doesn't share any common class in their inheritance tree. I guess the naive approach is to make 'Z' an Interface class, and make classes B and C implement it. But something still doesn't convince me because every time an instance of class A is used, I need to know the type of 'source'. So all finishes in multiple 'ifs' making 'is instanceof' which doesn't sound quite nice. Maybe in the future some other class implements Z, and having hardcoded 'ifs' of this type definitely could break something. The escence of the problem is that I cannot resolve the issue by adding functions to Z, because the work done in each instance type of Z is different. I hope someone can give me and advice, maybe about some useful design pattern. Thanks

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• How to deploy a Scala project from Eclipse?

  - by lach

  I have a Scala project in Eclipse that I need to package up so I can deploy it to a server. It's based on Jetty but it runs as a standalone application. It contains Scala classes, Java classes and a number of 3rd party jars. I assumed there would be some kind of deployment option in the Scala Eclipse plugin but I've drawn a blank. What is the simplest way to package the Scala project into a runnable file so it can be deployed? Any help greatly appreciated. Cheers.

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• How to initialize one class from a library?

  - by daemonsvk

  Hi, I have a few classes in the class library (separate assembly). I referenced it to my project and I want to initialize one specific class from that library. I know only its name. All of the classes implements one interface. And here comes the problem. My code so far: using MyLibrary; ... IMyInterface dll = Activator.CreateInstance("MyLibrary", "MyLibrary.NameOfClass") as IMyInterface; But dll is always null. Any ideas? Thanks

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• What to return as an iterator when there is no container?

  - by DaClown

  I have an inheritance structure of objects with begin() and end() as pure virtual member functions in the base class. From this objects I'm planning to build a composite structure. This inner objects have std::vector member the begin() and end() get their data from. But in a leaf class there is no vector. Now I try to find a return value for begin() and end() in the leaf classes. What would be a good way to do that? The easiest way would be to have a vector member in the leaf classes with no elements in it to fuel begin() and end(), but this just doesn't feel right.

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• Is there a way to get the list of InnerClasses throught Reflection in Java?

  - by kunjaan

  Is there a way to know the inner classes that a Class has through Reflection in Java?

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• How can I configure different worker pools using celery?

  - by Chris R

  I need to deploy a queued execution service with (generally) the following three classes of worker: A periodic, low-priority job class that takes a long time and can be processed serially; these jobs should only use 0..2 workers in the system at most. A periodic, deadline-sensitive job class that take a short to medium amount of time (say, topping out at 5 minutes) An ad-hoc job class, that is higher priority than #1, but can interleave with #2. Any workers from class #2 that are inactive when this type of job comes in should handle it, without ever starving the pool of workers for #2 All three job classes are the same task, the only difference between them is how they're requested; they'll take the same input and generate the same output, but each one has different performance guarantees. How can I implement this using celery?

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• Pass Session data to a Class Library without using a bunch of constructors?

  - by sah302

  Hi all, I've got my application here where literally every object has a lastUpdatedBy property. The information I put into here is the person's username, which is retrieved from the session("username") variable. How can I pass this data to my DAL in the class library? At first I was just passing in the value into each method, but this is ridiculous I thought, there should be no reason to do that every time a method is called. Then I thought well if I just put it in a constructor for each of the DAL related classes, that will make it even easier. However, even still on any given page, I've got a plethora of New() declarations, for which every single line I need to pass in the session username casted as a string. Is there an even still more efficient way of doing this so that I could only declare this in one place, and everything will know what it is and I can pass it to classes in a class library?

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• Is it possible to specify a return type of "Derivative(of T)" for a MustOverride sub in VB.NET?

  - by Casey

  VB.NET 2008 .NET 3.5 I have two base classes that are MustInherit (partial). Let's call one class OrderBase and the other OrderItemBase. A specific type of order and order item would inherit from these classes. Let's call these WebOrder (inherits from OrderBase) and WebOrderItem (inherits from OrderItemBase). Now, in the grand scheme of things WebOrder is a composite class containing a WebOrderItem, like so: Public Class WebOrder Inherits OrderBase Public Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class In order to make sure any class that derives from OrderBase has the OrderItem property, I would like to do something like this in the OrderBase class: Public MustInherit Class OrderBase Public MustOverride Property OrderItem() as Derivative(Of OrderItemBase) End Class In other words, I want the derived class to be forced to contain a property that returns a derivative of OrderItemBase. Is this possible, or should I be using an entirely different approach?

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• Questions about my program and Polymorphism

  - by Strobe_

  Ok, so basically I'm creating a program which allows the user to select a shape (triangle, square, circle) and then it takes in a int and calculates the boundary length and area. I have no problem doing this and have a program that's working perfectly. (https://gist.github.com/anonymous/c63a03c129560a7b7434 4 classes) But now I have to implement this with polymorphism concepts and I'm honestly struggling as to how to do it. I have a basic idea of what I want to do when it comes to inheritance Main | Shapes / | \ triangle circle square But I don't understand how I'm supposed to override when all the methods within the triangle/square/circle classes are unique, there are no "abstract" methods as such that I could inherit from the "Shapes" class. If somebody could make look quickly at the code I linked and suggest a way to do this it would be much appreciated. Sorry if I was bad at explaining this. Thanks.

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• Question on a tutorial

  - by hansa

  Hello, i´m trying to get following tutorial to run and understand: http://www.ibm.com/developerworks/web/library/wa-cometjava/index.html In the example code which can be downloaded at the bottom of the page is everything in one class with two inner classes. How can i make the the thread of "MessageSender" (Listing 3) visible to "The Weatherman" (Listing 4) so i can use it in the run method without using inner classes? Thank you hansa Reformulation of Question: How to make the send-method of inner class MessageSender make accessible in ClassThatDoSomething. Example-Code: public class Example extends HttpServlet implements CometProcessor { private MessageSender messageSender = null; @Override public void init() throws ServletException { // starts thread MessageSender } public event(CometEvent) { // Object of ClassThatDoSomething gets created started } private class ClassThatDoSomething { public void start() { Runnable runnable = new Runnable() { public void run(){ messageSender.send(message); } Thread thread = new Thread(runnable); thread.start(); } } private class MessageSender implements Runnable { public void send(String message) { //... } public void run() { //...} } }

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• Do you use another language instead of english ?

  - by Luc M

  Duplicate Should identifiers and comments be always in English or in the native language of the application and developers? For people who are not native English speakers, which language do you use to declare variables, classes, etc. ? I had to continue a project from a Spanish guy. Everything was written in Spanish. Since this time, I have decided to use English identifiers ( variables, classes, file names) and write comments in french. Everything was in french before that. What are the general recommendations about that practice? Do you use English everywhere knowing that no English people will work on your project ? Edit : Here's a post from Jeff Atwood about this subject: The Ugly American Programmer

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• How To Collapse Just One Field in Django Admin?

  - by Apreche

  The django admin allows you to specify fieldsets. You properly structure a tuple that groups different fields together. You can also specify classes for certain groups of fields. One of those classes is collapse, which will hide the field under a collapsable area. This is good for hiding rarely used or advanced fields to keep the UI clean. However, I have a situation where I want to hide just one lonesome field on many different apps. This will be a lot of typing to create a full fieldset specification in every admin.py file just to put one field into the collapsed area. It also creates a difficult maintenance situation because I will have to edit the fieldset every time I edit the associated model. I can easily exclude the field entirely using the exclude option. I want something similar for collapse. Is this possible?

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• WFP Validation & IDataErrorInfo

  - by Jefim

  A note - the classes I have are EntityObject classes! I have the following class: public class Foo { public Bar Bar { get; set; } } public class Bar : IDataErrorInfo { public string Name { get; set; } #region IDataErrorInfo Members string IDataErrorInfo.Error { get { return null; } } string IDataErrorInfo.this[string columnName] { get { if (columnName == "Name") { return "Hello error!"; } Console.WriteLine("Validate: " + columnName); return null; } } #endregion } XAML goes as follows: <StackPanel Orientation="Horizontal" DataContext="{Binding Foo.Bar}"> <TextBox Text="{Binding Path=Name, ValidatesOnDataErrors=true}"/> </StackPanel> I put a breakpoint and a Console.Writeline on the validation there - I get no breaks. The validation is not executed. Can anybody just press me against the place where my error lies?

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• Java Enum Newbie Question

  - by ikurtz

  i have a situation where i need the Checker enum below used in multiple classes: package Sartre.Connect4; public enum Checker { EMPTY, RED, YELLOW } so i put the Checker in a Checker.java file and then from the classes that need it i simply do the following: example: public Cell(){ currentCell = Checker.EMPTY; } example: public Cell(Checker checker){ currentCell = checker; } and the code compiles fine and runs fine also. so what is my question? well being new to Java i am just wondering if the way i use Checker without encapsulating it in a class is a sound implementation? it may be because of The enum declaration defines a class (called an enum type). as noted in Java docs enum tutorial page. thank you for your insight into this matter.

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• Separation of domain and ui layer in a composite

  - by hansmaad

  Hi all, i'm wondering if there is a pattern how to separate the domain logic of a class from the ui responsibilities of the objects in the domain layer. Example: // Domain classes interface MachinePart { CalculateX(in, out) // Where do we put these: // Draw(Screen) ?? // ShowProperties(View) ?? // ... } class Assembly : MachinePart { CalculateX(in, out) subParts } class Pipe : MachinePart { CalculateX(in, out) length, diamater... } There is an application that calculates the value X for machines assembled from many machine parts. The assembly is loaded from a file representation and is designed as a composite. Each concrete part class stores some data to implement the CalculateX(in,out) method to simulate behaviour of the whole assembly. The application runs well but without GUI. To increase the usability a GUi should be developed on top of the existing implementation (changes to the existing code are allowed). The GUI should show a schematic graphical representation of the assembly and provide part specific dialogs to edit several parameters. To achieve these goals the application needs new functionality for each machine part to draw a schematic representation on the screen, show a property dialog and other things not related to the domain of machine simulation. I can think of some different solutions to implement a Draw(Screen) functionality for each part but i am not happy with each of them. First i could add a Draw(Screen) method to the MachinePart interface but this would mix-up domain code with ui code and i had to add a lot of functionality to each machine part class what makes my domain model hard to read and hard to understand. Another "simple" solution is to make all parts visitable and implement ui code in visitors but Visitor does not belong to my favorite patterns. I could derive UI variants from each machine part class to add the UI implementation there but i had to check if each part class is suited for inheritance and had to be careful on changes to the base classes. My currently favorite design is to create a parallel composite hierarchy where each component stores data to define a machine part, has implementation for UI methods and a factory method which creates instances of the corresponding domain classes, so that i can "convert" a UI assembly to a domain assembly. But there are problems to go back from the created domain hierarchy to the UI hierarchy for showing calculation results in the drawing for example (imagine some parts store some values during the calculation i want to show in the schematic representation after the simluation). Maybe there are some proven patterns for such problems?

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• Lazy loading? Better avoiding it?

  - by Charlie Pigarelli

  I just read about this design pattern: Lazy Load. And, since in the application i'm working on i have all the classes in one folder, i was wondering if this pattern could just make me avoiding the include() function for every class. I mean: It's nice to know that if i forgot to include a class, PHP, before falling into an error, trough an __autoload() function try to get it. But is it fine enough to just don't care about including classes and let PHP do it by your own every time? Or we should write __autoload() just in case it is needed?

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• Check if a class is subclass of another class in Java

  - by craesh

  Hi! I'm playing around with Java's reflection API and trying to handle some fields. Now I'm stuck with identifying the type of my fields. Strings are easy, just do myField.getType().equals(String.class). The same applies for other non-derived classes. But how do I check derived classes? E.g. LinkedList as subclass of List. I can't find any isSubclassOf(...) or extends(...) method. Do I need to walk through all getSuperClass() and find my supeclass by my own? Thanks! craesh

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• C++ Multiple Inheritance Question

  - by John

  The scenario generating this is quite complex so I'll strip out a few pieces and give an accurate representation of the classes involved. /* This is inherited using SI by many classes, as normal */ class IBase { virtual string toString()=0; }; /* Base2 can't inherit IBase due to other methods on IBase which aren't appropriate */ class Base2 { string toString() { ... } }; /* a special class, is this valid? */ class Class1 : public IBase, public Base2 { }; So, is this valid? Will there be conflicts on the toString? Or can Class1 use Base2::toString to satisfy IBase? Like I say there are lots of other things not shown, so suggestions for major design changes on this example are probably not that helpful... though any general suggestions/advice are welcome.

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• Refactoring Singleton Overuse

  - by drharris

  Today I had an epiphany, and it was that I was doing everything wrong. Some history: I inherited a C# application, which was really just a collection of static methods, a completely procedural mess of C# code. I refactored this the best I knew at the time, bringing in lots of post-college OOP knowledge. To make a long story short, many of the entities in code have turned out to be Singletons. Today I realized I needed 3 new classes, which would each follow the same Singleton pattern to match the rest of the software. If I keep tumbling down this slippery slope, eventually every class in my application will be Singleton, which will really be no logically different from the original group of static methods. I need help on rethinking this. I know about Dependency Injection, and that would generally be the strategy to use in breaking the Singleton curse. However, I have a few specific questions related to this refactoring, and all about best practices for doing so. How acceptable is the use of static variables to encapsulate configuration information? I have a brain block on using static, and I think it is due to an early OO class in college where the professor said static was bad. But, should I have to reconfigure the class every time I access it? When accessing hardware, is it ok to leave a static pointer to the addresses and variables needed, or should I continually perform Open() and Close() operations? Right now I have a single method acting as the controller. Specifically, I continually poll several external instruments (via hardware drivers) for data. Should this type of controller be the way to go, or should I spawn separate threads for each instrument at the program's startup? If the latter, how do I make this object oriented? Should I create classes called InstrumentAListener and InstrumentBListener? Or is there some standard way to approach this? Is there a better way to do global configuration? Right now I simply have Configuration.Instance.Foo sprinkled liberally throughout the code. Almost every class uses it, so perhaps keeping it as a Singleton makes sense. Any thoughts? A lot of my classes are things like SerialPortWriter or DataFileWriter, which must sit around waiting for this data to stream in. Since they are active the entire time, how should I arrange these in order to listen for the events generated when data comes in? Any other resources, books, or comments about how to get away from Singletons and other pattern overuse would be helpful.

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• Sending object C from class A to class B

  - by user278618

  Hi, I can't figure out how to design classes in my system. In classA I create object selenium (it simulates user actions at website). In this ClassA I create another objects like SearchScreen, Payment_Screen and Summary_Screen. # -*- coding: utf-8 -*- from selenium import selenium import unittest, time, re class OurSiteTestCases(unittest.TestCase): def setUp(self): self.verificationErrors = [] self.selenium = selenium("localhost", 5555, "*chrome", "http://www.someaddress.com/") time.sleep(5) self.selenium.start() def test_buy_coffee(self): sel = self.selenium sel.open('/') sel.window_maximize() search_screen=SearchScreen(self.selenium) search_screen.choose('lavazza') payment_screen=PaymentScreen(self.selenium) payment_screen.fill_test_data() summary_screen=SummaryScreen(selenium) summary_screen.accept() def tearDown(self): self.selenium.stop() self.assertEqual([], self.verificationErrors) if __name__ == "__main__": unittest.main() It's example SearchScreen module: class SearchScreen: def __init__(self,selenium): self.selenium=selenium def search(self): self.selenium.click('css=button.search') I want to know if there is anything ok with a design of those classes?

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• Persistence scheme & state data for low memory situations (iphone)

  - by Robin Jamieson

  What happens to state information held by a class's variable after coming back from a low memory situation? I know that views will get unloaded and then reloaded later but what about some ancillary classes & data held in them that's used by the controller that launched the view? Sample scenario in question: @interface MyCustomController: UIViewController { ServiceAuthenticator *authenticator; } -(id)initWithAuthenticator:(ServiceAuthenticator *)auth; // the user may press a button that will cause the authenticator // to post some data to the service. -(IBAction)doStuffButtonPressed:(id)sender; @end @interface ServiceAuthenticator { BOOL hasValidCredentials; // YES if user's credentials have been validated NSString *username; NSString *password; // password is not stored in plain text } -(id)initWithUserCredentials:(NSString *)username password:(NSString *)aPassword; -(void)postData:(NSString *)data; @end The app delegate creates the ServiceAuthenticator class with some user data (read from plist file) and the class logs the user with the remote service. inside MyAppDelegate's applicationDidFinishLaunching: - (void)applicationDidFinishLaunching:(UIApplication *)application { ServiceAuthenticator *auth = [[ServiceAuthenticator alloc] initWithUserCredentials:username password:userPassword]; MyCustomController *controller = [[MyCustomController alloc] initWithNibName:...]; controller.authenticator = auth; // Configure and show the window [window addSubview:..]; // make everything visible [window makeKeyAndVisible]; } Then whenever the user presses a certain button, 'MyCustomController's doStuffButtonPressed' is invoked. -(IBAction)doStuffButtonPressed:(id)sender { [authenticator postData:someDataFromSender]; } The authenticator in-turn checks to if the user is logged in (BOOL variable indicates login state) and if so, exchanges data with the remote service. The ServiceAuthenticator is the kind of class that validates the user's credentials only once and all subsequent calls to the object will be to postData. Once a low memory scenario occurs and the associated nib & MyCustomController will get unloaded -- when it's reloaded, what's the process for resetting up the 'ServiceAuthenticator' class & its former state? I'm periodically persisting all of the data in my actual model classes. Should I consider also persisting the state data in these utility style classes? Is that the pattern to follow?

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