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• What is "sentry object" in C++?

  - by Romain Hippeau

  I answered this question, and Potatoswatter answered too as The modern C++ equivalent would be a sentry object: construct it at the beginning of a function, with its constructor implementing call(), and upon return (or abnormal exit), its destructor implements I am not familiar with using sentry objects in C++. I thought they were limited to input and output streams. Could somebody explain to me about C++ sentry objects as well as how to use them as an around interceptor for one or more methods in a class ? i.e. How to do this ? Sentry objects are very similar indeed. On the one hand they require explicit instantiation (and being passed this) but on the other hand you can add to them so that they check not only the invariants of the class but some pre/post conditions for the function at hand.

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• Objects in interface

  - by Peter Kowalchuk

  I created my own object, PKSurvey. In the interface of the View Controller I can define a pointer to it, then in a method I can alloc it and have an instance. How do I keep the instance beyond the method where it was allocated? I assign values in one method and want to be able to use those values in other methods. Should I allocate it in the viewDidLoad method or should I do it somewhere else? @interface DIrectionalDrillerViewController : UIViewController { PKSurvey *Survey=[PKSurvey new]; ---------------- - (void)viewDidLoad { [Survey new];

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• Catching constraint violations in JPA 2.0.

  - by Dennetik

  Consider the following entity class, used with, for example, EclipseLink 2.0.2 - where the link attribute is not the primary key, but unique nontheless. @Entity public class Profile { @Id private Long id; @Column(unique = true) private String link; // Some more attributes and getter and setter methods } When I insert records with a duplicate value for the link attribute, EclipseLink does not throw a EntityExistsException, but throws a DatabaseException, with the message explaining that the unique constraint was violated. This doesn't seem very usefull, as there would not be a simple, database independent, way to catch this exception. What would be the advised way to deal with this? A few things that I have considered are: Checking the error code on the DatabaseException - I fear that this error code, though, is the native error code for the database; Checking the existence of a Profile with the specific value for link beforehand - this obviously would result in an enormous amount of superfluous queries.

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• question about polynomial multiplication

  - by davit-datuashvili

  i know that horners method for polynomial pultiplication is faster but here i dont know what is happening here is code public class horner{ public static final int n=10; public static final int x=7; public static void main(String[] args){ //non fast version int a[]=new int[]{1,2,3,4,5,6,7,8,9,10}; int xi=1; int y=a[0]; for (int i=1;i<n;i++){ xi=x*xi; y=y+a[i]*xi; } System.out.println(y); //fast method int y1=a[n-1]; for (int i=n-2;i>=0;i--){ y1=x*y+a[i]; } System.out.println(y1); } } result of this two methods are not same result of first method is 462945547 and result of second method is -1054348465 please help

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• abstract method signature, inheritance, and "Do" naming convention

  - by T. Webster

  I'm learning about design patterns and in examples of code I've seen a convention where the abstract class declares a method, for example: public abstract class ServiceBase { ... public virtual object GetSomething(); and then protected abstract object DoGetSomething(); My question is on why these two methods exist, since they appear to serve the same purpose. Is this so that the base class GetSomething() method logic cannot be overridden by inherited classes? But then again, the method is marked virtual, so it can be overridden anyway. What is the usefulness here in requiring derived class implementers to implement the abstract method when the virtual method can be called anyway?

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• Better to use constructor or method factory pattern?

  - by devoured elysium

  I have a wrapper class for the Bitmap .NET class called BitmapZone. Assuming we have a WIDTH x HEIGHT bitmap picture, this wrapper class should serve the purpose of allowing me to send to other methods/classes itself instead of the original bitmap. I can then better control what the user is or not allowed to do with the picture (and I don't have to copy the bitmap lots of times to send for each method/class). My question is: knowing that all BitmapZone's are created from a Bitmap, what do you find preferrable? Constructor syntax: something like BitmapZone bitmapZone = new BitmapZone(originalBitmap, x, y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.From(originalBitmap, x , y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.FromBitmap(originalBitmap, x, y, width, height); Other? Why? Thanks

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• Android - Looking for an AOP solution

  - by Serj Lotutovici

  I'm writing an application that on the bottom line uses it's internal API for some manipulations. The problem is that to call any method provided by that class first I (or anybody who uses the API) have to call #prepare() and after that #cleanup(). It all worked fine until the application and the API started to grow. And the risk of not calling one of the supplied methods before or after the API is now to big to be ignored (which makes it a bug risky application). Searching for a solution I found this question. I use Google Guice in my app for other purposes, but Android doesn't support AOP, that's why a use only guice-no_aop-x.jar. So I end-up with two questions: Is there an AOP solution for android to implement the same approach that is shown in the link above? Or may be someone has an idea that will be suitable for my case? Thanks in advice!

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• Home Pages in ASP.NET MVC

  - by Maxim Z.

  I'm trying out ASP.NET MVC, but, after reading a huge tutorial, I'm slightly confused. I understand how Controllers have Actions that URLs are routed to, but how do home pages work? Is the home page its own controller (e.g. "Home") that has no actions? This sounds correct, but how is it functionality implemented without Actions (no Actions means no methods that call the View Engine)? In other words, my question is this: how are home pages implemented (in terms of Controllers and Views)? Could you please provide sample code?

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• Adding DataAnnontations to Generated Partial Classes

  - by Naz

  Hi I have a Subsonic3 Active Record generated partial User class which I've extended on with some methods in a separate partial class. I would like to know if it is possible to add Data Annotations to the member properties on one partial class where it's declared on the other Subsonic Generated one I tried this. public partial class User { [DataType(DataType.EmailAddress, ErrorMessage = "Please enter an email address")] public string Email { get; set; } ... } That examples gives the "Member is already defined" error. I think I might have seen an example a while ago of what I'm trying to do with Dynamic Data and Linq2Sql.

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• Evaluating Django Chained QuerySets Locally

  - by jnadro52

  Hello All: I am hoping someone can help me out with a quick question I have regarding chaining Django querysets. I am noticing a slow down because I am evaluating many data points in the database to create data trends. I was wondering if there was a way to have the chained filters evaluated locally instead of hitting the database. Here is a (crude) example: pastries = Bakery.objects.filter(productType='pastry') # <--- will obviously always hit DB, when evaluated cannoli = pastries.filter(specificType='cannoli') # <--- can this be evaluated locally instead of hitting the DB when evaluated, as long as pastries was evaluated? I have checked the docs and I do not see anything specifying this, so I guess it's not possible, but I wanted to check with the 'braintrust' first ;-). BTW - I know that I can do this myself by implementing some methods to loop through these datapoints and evaluate the criteria, but there are so many datapoints that my deadline does not permit me manually implementing this. Thanks in advance.

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• File Upload in GWT in a Special Case

  - by Maksud

  I am doing a software for a document system. In this system when a user completes a document and want to save it, the document will be uploaded directly to server without the user action. This system uses COM/ActiveX to facilitate user using native editors. Ok, my problem is: suppose I have a file say d:/notepad.txt. Using classical method a user can browse the file and upload it. I can do that with apache commonio and GWT FormPanel and FileUpload. But if I know the filename (d:/notepad.txt), is there any way to upload the file directly to server without the user having to browse the file. I am currently doing this by the ActiveX componenet calling some HttpUpload methods with POST. But that does not maintain session. Thanks

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• NHibernate filters don't work with Session.Get

  - by Khash

  I'm trying to implement a Soft-deletable repository. Usually this can be easily done with a Delete Event listener. To filter out the deleted entities, I can add a Where attribute to my class mapping. However, I also need to implement two more methods in the repository for this entity: Restore and Purge. Restore will "undelete" entities and Purge will hard-delete them. This means I can't use Where attribute (since it block out soft-deleted entities to any access) I tried using filters instead. I can create a filter and enable or disable it within session to achieve the same result. But the problem is filters don't have any effect on Session.Get method (they only affect ICriteria based access). Any ideas as to how solve this problem? Thanks

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• Is it a good idea to "migrate business logic code into our domain model"?

  - by Bytecode Ninja

  I am reading Hibernate in Action and the author suggests to move business logic into our domain models (p. 306). For instance, in the example presented by the book, we have three entities named Item, Bid, and User and the author suggests to add a placeBid(User bidder, BigDecimal amount) method to the Item class. Considering that usually we have a distinct layer for business logic (e.g. Manager or Service classes in Spring) that among other things control transactions, etc. is this really a good advice? Isn't it better not to add business logic methods to our entities? Thanks in advance.

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• logging in scala

  - by IttayD

  In Java, the standard idiom for logging is to create a static variable for a logger object and use that in the various methods. In Scala, it looks like the idiom is to create a Logging trait with a logger member and mixin the trait in concrete classes. This means that each time an object is created it calls the logging framework to get a logger and also the object is bigger due to the additional reference. Is there an alternative that allows the ease of use of "with Logging" while still using a per-class logger instance? EDIT: My question is not about how one can write a logging framework in Scala, but rather how to use an existing one (log4j) without incurring an overhead of performance (getting a reference for each instance) or code complexity. Also, yes, I want to use log4j, simply because I'll use 3rd party libraries written in Java that are likely to use log4j.

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• What are typical server to client communication patterns?

  - by jagse

  What are the usual patterns for bidirectional communication between a client and a server in a wlan environment. How is it possible for the server to push data to a mobile client over wlan after a connection has been established. Lets say I have a webservice running on a server and the moblie cients in the wlan can use this webservice. Now the question is how can the server invoke methods at the client, or directly send data to the client. How is this handled usually? I would apriciate some links to read about this topic. Is this a common problem or is it not that easy to solve? Cheers

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• How does multiple implementing multiple COM interfaces work in C++?

  - by Martin

  I am trying to understand this example code regarding Browser Helper Objects. Inside, the author implements a single class which exposes multiple interfaces (IObjectWithSite, IDispatch). His QueryInterface function performs the following: if(riid == IID_IUnknown) *ppv = static_cast<BHO*>(this); else if(riid == IID_IObjectWithSite) *ppv = static_cast<IObjectWithSite*>(this); else if (riid == IID_IDispatch) *ppv = static_cast<IDispatch*>(this); I have learned that from a C perspective, interface pointers are just pointers to VTables. So I take it to mean that C++ is capable of returning the VTable of any implemented interface using static_cast. Does this mean that a class constructed in this way has a bunch of VTables in memory (IObjectWithSite, IDispatch, etc)? What does C++ do with the name collisions on the different interfaces (they each have a QueryInterface, AddRef and Release function), can I implement different methods for each of these?

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• Android EditText and addTextChangedListener

  - by Alex

  im currently porting a database manager to android and due to performance reasons i like to update only propertys that have been modified. Im trying to do this with the addTextChangedListener in order to add modified entrys to a List, but my Program never enters any of its methods. EditText Et = (EditText) Editors.get(Prop.Name); Et.addTextChangedListener(new TextWatcher() { @Override public void afterTextChanged(Editable s) { // TODO Auto-generated method stub } @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) { // TODO Auto-generated method stub } @Override public void onTextChanged(CharSequence s, int start, int before, int count) { // TODO Auto-generated method stub if(Prop.GetType() == Property.PROPTYPE.num) { float f = Float.parseFloat(s.toString()); Prop.FromString(f); } else { Prop.FromString(s.toString()); } propertiesToUpdate.add(Prop); }); Et.setText(Prop.ToString());

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• How do I throttle my site's API users?

  - by scotts

  The legitimate users of my site occasionally hammer the server with API requests that cause undesirable results. I want to institute a limit of no more than say one API call every 5 seconds or n calls per minute (haven't figured out the exact limit yet). I could obviously log every API call in a DB and do the calculation on every request to see if they're over the limit, but all this extra overhead on EVERY request would be defeating the purpose. What are other less resource-intensive methods I could use to institute a limit? I'm using PHP/Apache/Linux, for what it's worth.

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• Does delegate chaining have to start with a null Delegate?

  - by MCS

  In CLR via C#, Jeffrey Richter gives the following example of delegate chaining (pg. 406): internal delegate void Feedback(Int 32 value); Feedback fb1 = new Feedback(method1); // in the book, these methods Feedback fb2 = new Feedback(method2); // have different names Feedback fb3 = new Feedback(method3); Feedback fbChain = null; fbChain = (Feedback) Delegate.Combine(fbChain, fb1); fbChain = (Feedback) Delegate.Combine(fbChain, fb2); fbChain = (Feedback) Delegate.Combine(fbChain, fb3); Why does the first call to Delegate.Combine have to pass in a null Delegate? Here's how I would have thought it should be written: Feedback fbChain = (Feedback) Delegate.Combine(fb1, fb2); fbChain = (Feedback) Delegate.Combine(fbchain, fb3);

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• delete in tableView..

  - by totato

  I just add this methods in .h file : - (IBAction)EditTable:(id)sender; - (IBAction)DeleteButtonAction:(id)sender; and in .m file : (IBAction)DeleteButtonAction:(id)sender{ [tableList removeLastObject]; [Table reloadData]; } (IBAction) EditTable:(id)sender{ if(self.editing) { [super setEditing:NO animated:NO]; [Table setEditing:NO animated:NO]; [Table reloadData]; [self.navigationItem.leftBarButtonItem setTitle:@"Edit"]; [self.navigationItem.leftBarButtonItem setStyle:UIBarButtonItemStylePlain]; } else { [super setEditing:YES animated:YES]; [Table setEditing:YES animated:YES]; [Table reloadData]; [self.navigationItem.leftBarButtonItem setTitle:@"Done"]; [self.navigationItem.leftBarButtonItem setStyle:UIBarButtonItemStyleDone]; } } when I run the program and click the delete button (red button) the program is stop ! whats the problem ? please any help ?

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• testing .mobile mime format with capybara / rspec

  - by Chris Beck

  For detecting and responding to mobile user agents, I'm using Mime::Type.register_alias "text/html", :mobile and the approach I'm wondering what is the best approach to test with capybara. This article suggests setting up an iphone driver with Capybara.register_driver :iphone do |app| http://blog.plataformatec.com.br/2011/03/configuring-user-agents-with-capybara-selenium-webdriver/ but I'd like a more flexible approach where the mime type is set via the url extension localhost/index.mobile and where I can do this visit user_path( format: :mobile) Rails understands the extension and sets the format in the params hash, but how do I get the url helper methods to add that to all urls as a file extension?

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• Weird use of generics

  - by Karl Trumstedt

  After a bit of programming one of my classes used generics in a way I never seen before. I would like some opinions of this, if it's bad coding or not. abstract class Base<T> : where T : Base<T> { // omitted methods and properties. virtual void CopyTo(T instance) { /*code*/ } } class Derived : Base<Derived> { override void CopyTo(Derived instance) { base.CopyTo(instance); // copy remaining stuff here } } is this an OK use of generics or not? I'm mostly thinking about the constraint to "itself". I sometimes feel like generics can "explode" to other classes where I use the Base class.

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• WCF Service method syncronous/async

  - by Rafal

  Hi I have a problem withi calling WCF Service methods vs Silverlight 3. ` private bool usr_OK = false; clientService.CheckUserMailAsync(this.mailTF.Text); if (usr_OK == true) { isValidationOK = true; } else { isValidationOK = false; MessageBox.Show("User already exists.", "User registered succes!", MessageBoxButton.OK); } ` CheckUserMail should change usr_OK parameter. However it runs in other thread and it does not change the usr_OK param before IF block begins. I've tried thread.join byt the application freezed and i do not know what to do else. Please help me...how can i wait for WCF method to return param usr_OK.

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• Ruby class instance variables and inheritance

  - by rlandster

  I have a Ruby class called LibraryItem. I want to associate with every instance of this class an array of attributes. This array is long and looks something like ['title', 'authors', 'location', ...] Note that these attributes are not really supposed to be methods, just a list of attributes that a LibraryItem has. Next, I want to make a subclass of LibraryItem called LibraryBook that has an array of attributes that includes all the attributes of LibraryItem but will also include many more. Eventually I will want several subclasses of LibraryItem each with their own version of the array @attributes but each adding on to LibraryItem's @attributes (e.g., LibraryBook, LibraryDVD, LibraryMap, etc.). So, here is my attempt: class LibraryItem < Object class << self; attr_accessor :attributes; end @attributes = ['title', 'authors', 'location',] end class LibraryBook < LibraryItem @attributes.push('ISBN', 'pages'] end This does not work. I get the error undefined method `push' for nil:NilClass

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• java - POST vs JDBC

  - by Dan

  OK so here's the code: import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URL; public class Main { public static void main(String[] args) { try { URL my_url = new URL("http://www.viralpatel.net/blogs/"); BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream())); String strTemp = ""; while(null != (strTemp = br.readLine())){ System.out.println(strTemp); } } catch (Exception ex) { ex.printStackTrace(); } } } Using this method I can use POST and GET methods using PHP scripts. I can then use the PHP scripts to the MySQL database which in turn outputs back to the java applet. Is this possible? (and safer?) Thanks.

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