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• Creating a method that is simultaneously an instance and class method

  - by Mike Axiak

  In Python, I'd like to be able to create a function that behaves both as a class function and an instance method, but with the ability to change behaviors. The use case for this is for a set of serializable objects and types. As an example: >>> class Thing(object): #... >>> Thing.to_json() 'A' >>> Thing().to_json() 'B' I know that given the definition of classmethod() in funcobject.c in the Python source, this looks like it'd be simple with a C module. Is there a way to do this from within python? Thanks!

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• Rails: unexpected behavior updating a shared instance

  - by Pascal Lindelauf

  I have a User object, that is related to a Post object via two different association paths: Post --(has_many)-- comments --(belongs to)-- writer (of type User) Post --(belongs to)-- writer (of type User) Say the following hold: user1.name == "Bill" post1.comments[1].writer == user1 post1.writer == user1 Now when I retrieve the post1 and its comments from the database and I update post1.comments[1].writer like so: post1.comments[1].writer.name = "John" I would expect post1.writer to equal "John" too. But it doesn't! It still equals "Bill". So there seems to be some caching going on, but the kind I would not expect. I would expect Rails to be clever enough to load exactly one instance of the user with name "Bill"; instead is appears to load two individual ones: one for each association path. Can someone explain how this works exactly and how I am to handle these types of situations the "Rails way"?

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• Create Generic Class Instance from Static Method in a Derived Class

  - by user343547

  I have a class in C# with a template and static method similar to class BClass<T> { public static BClass<T> Create() { return new BClass<T>(); } } From this I derive a class and specify a template parameter to the base class class DClass : BClass<int> { } A problem occurs when I try to use the static method to create an instance of D class Program { static void Main(string[] args) { DClass d = DClass.Create(); } } Gives a compiler error "Cannot implicitly convert type 'Test.BClass<int ' to 'Test.DClass'." Adding the below cast leads to a runtime casting exception. DClass d = (DClass)DClass.Create(); Is there any succint way to allow the static method to create instances of the derived class? Ideally I would like the equivalent of a c++ typedef and I don't want the below syntax (which does work). BClass<int> d = DClass.Create();

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• Creating Instance of Python Extension Type in C

  - by Brad Zeis

  I am writing a simple Vector implementation as a Python extension module in C that looks mostly like this: typedef struct { PyObject_HEAD double x; double y; } Vector; static PyTypeObject Vector_Type = { ... }; It is very simple to create instances of Vector while calling from Python, but I need to create a Vector instance in the same extension module. I looked in the documentation but I couldn't find a clear answer. What's the best way to do this?

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• Copying blocks (ie: copying them to instance variables) in Objective-C

  - by RyanWilcox

  I'm trying to understand blocks. I get how to use them normally, when passed directly to a method. I'm interested now in taking a block, storing it (say) in an instance variable and calling it later. The blocks programming guide makes it sound like I can do this, by using Block_copy / retain to copy the block away, but when I try to run it I crash my program. - (void) setupStoredBlock { int salt = 42; m_storedBlock = ^(int incoming){ return 2 + incoming + salt; }; [m_storedBlock retain]; } I try to call it later: - (void) runStoredBlock { int outputValue = m_storedBlock(5); NSLog(@"When we ran our stored blockwe got back: %d", outputValue); [m_storedBlock release]; } Anyone have any insights? (Or, is there something I'm not getting with blocks?) Thank you very much!

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• Weblogic server lib VS instance libext

  - by Sebastien Lorber

  Hello, I use weblogic 10. Its provide an Oracle JDBC driver 10.2.0.2 (in the server/lib on weblogic home). Actually someone at work put a long time ago a 10.2.0.3 driver in instance libext folder. But in production we got a jdbc driver stack (nullpointer :O) and by reverse engineering it seems we are using driver 10.2.0.2. We know that we could change the driver in the server/lib of weblogic but i want to understand. Isn't libext supposed to override server libs like META-INF libs override libext? By the way we are in a strange situation: - We have 2 EAR, and for the exact same treatment in those 2, one will sometime throw the oracle driver nullpointer while the other doesn't - I wonder if one ear isn't using 10.2.0.2 while the other is using 10.2.0.3 (i saw a bug fixed that could fit to our problem for this version). - I need to look better but at first sight both ear use the exact same datasource set in weblogic JNDI resources Any idea?

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• unrecognized selector sent to instance

  - by iamsmug

  My app works fine in the simulator but when I run it on my phone I get this error: 2010-04-05 21:32:45.119 Top Banana[119:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[MethodViewController setReferringObject:]: unrecognized selector sent to instance 0x16e930' It happens here: -(void)method { [UIView beginAnimations:@"View Flip" context:nil]; [UIView setAnimationDuration:0.50]; [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut]; [UIView setAnimationTransition: UIViewAnimationTransitionFlipFromRight forView:self.navigationController.view cache:NO]; MethodViewController *methodViewController = [[MethodViewController alloc] initWithNibName:@"MethodViewController" bundle:0]; NSManagedObject *selectedObject = self.referringObject; methodViewController.referringObject = selectedObject; [self.navigationController pushViewController:methodViewController animated:NO]; methodViewController.title = @"Method"; [UIView commitAnimations]; [MethodViewController release]; } It crashes on this line: methodViewController.referringObject = selectedObject; Not sure how to resolve this as it works in the simulator, I'm sure it is fairly basic to fix, any help will be appreciated.

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• Constructor with non-instance variable assistant?

  - by Robert Fischer

  I have a number of classes that look like this: class Foo(val:BasicData) extends Bar(val) { val helper = new Helper(val) val derived1 = helper.getDerived1Value() val derived2 = helper.getDerived2Value() } ...except that I don't want to hold onto an instance of "helper" beyond the end of the constructor. In Java, I'd do something like this: public class Foo { final Derived derived1, derived2; public Foo(BasicData val) { Helper helper = new Helper(val); derived1 = helper.getDerived1Value(); derived2 = helper.getDerived2Value(); } } So how do I do something like that in Scala? I'm aware of creating a helper object of the same name of the class with an apply method: I was hoping for something slightly more succinct.

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• Inherit appenders from calling instance in log4j or logback

  - by Lord.Quackstar

  In my program I have 2 separate streams of logging events (calling them streams for simplicity, in reality its 2 appenders). Stream1 contains client logging and Stream2 contains control logging. Now this might seem easy, except that certain classes can be both in the client logging and server logging, depending on the situation. Complicating this further is the fact that a command that a client wants takes place in 2 separate threads (one being fetched randomly from a thread pool), so any kind of tracking with MDC or NDC isn't possible. What would really simplify this is if the logger could inherit the appenders from the calling instance. That way I can setup 2 appenders for 2 loggers and be done. However I have no idea how to do it cleanly or easily. Can anyone offer any advice on how to do so? Note: If something needs to be passed around, I do have a event bean that gets passed to everything in the chain that can be used if necessary.

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• Installing Skype on Amazon EC2 instance

  - by Adrian

  For my application, I need to have Skype working on my Amazon EC2 Windows instance. I got the application installed and am able to log in, however, I can't make a phone call, since I am getting an 'Can't detect your sound card' error. Since I'm trying to inject audio from an audio file into the phone call, I don't need the sound card on the server. Thus, I need a way to bypass this error message. I have tried installing Virtual Audio Cable, which unfortunately didn't work (even though it worked on my desktop machine).

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• Python 3.0 - Dynamic Class Instance Naming

  - by Jon

  I want to use a while loop to initialize class objects with a simple incremented naming convention. The goal is to be able to scale the number of class objects at will and have the program generate the names automatically. (ex. h1...h100...h1000...) Each h1,h2,h3... being its own instance. Here is my first attempt... have been unable to find a good example. class Korker(object): def __init__(self,ident,roo): self.ident = ident self.roo = roo b = 1 hwinit = 'h' hwstart = 0 while b <= 10: showit = 'h' + str(b) print(showit) #showit seems to generate just fine as demonstrated by print str(showit) == Korker("test",2) #this is the line that fails b += 1 The errors I get range from a string error to a cannot use function type error.... Any help would be greatly appreciated.

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• Setting an instance variable from a block

  - by c00lryguy

  How would I achieve something like below so that when I set the s variable within the block, it also sets the @subject instance variable in my Topic class? class Topic def subject(&blk) blk.call(@subject) if block_given? @subject unless block_given? end end my_topic = Topic.new p my_topic.subject #=> nil my_topic.subject do |s| s = ['one', 'two', 'three'] s.pop p s #=> ['one', 'two'] end p my_topic.subject #=> nil... want it to be ['one, 'two']

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• Unmanaged Struct Instance in Managed Class

  - by HeHasMoments

  Hi, I've got a fairly specific problem i've been struggling with for a couple of days. I'm using a native C++, one of the methods takes a ptr to a struct containing fixed size char arrays. e.g. struct userData { char data1[10]; char data2[10]; }; method: short AddItem(long id, userData* data); I'm trying to call to call this from Managed VC++ but I need to have an instance of userData I can keep hold of in my managed class. Can anyone help with how to achieve this? Thanks

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• Is an ArrayList automaticaly declared static ,if it is an instance variable?(Java)

  - by Alex

  Hy ,what i`m trying to do is something like this: private class aClass { private ArrayList idProd; aClass(ArrayList prd) { this.idProd=new ArrayList(prd); } public ArrayList getIdProd() { return this.idProd; } } So if i have multiple instances of ArrayLIst (st1 ,st2 ,st3) and I want to make new objects of aClass : { aClass obj1,obj2,obj3; obj1=new aClass(st1); obj2=new aClass(st2); obj3=new aClass(st3); }why all of the aClass objects will return st3 if I access the method getIdProd() for each of them(obj1..obj3)? is an arraylist as a instance variable automatically declared static?

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• Two Instances of Sql Server (2005 and 2008)

  - by Felipe

  Hi All, I installed Visual Studio 2008 Professional in my machine and It had installed SQL Server Express 2005 database in machine, and I use it very fine! I installed SQL Managment Studio and works great. So, in this week I Installed Visual Studio 2010 Pro in machine and the setup installed the SQL Server express 2008 and it overwrite the instance of my SQL Server Express 2005. All right, Now, I'd like to know how can I have two instances of the SQL Server Express in my Machine, Express 2005 and Express 2008. I can not access the 2005 , only 2008 :( and my projects uses 2005.. Somebody Help me! thanks Bye

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• Remove only first instance of a character from a list of characters

  - by Luke

  Hi All, Here's what I want to do. I have 2 strings and I want to determine if one string is a permutation of another. I was thinking to simply remove the characters from string A from string B to determine if any characters are left. If no, then it passes. However, I need to make sure that only 1 instance of each letter is removed (not all occurrences) unless there are multiple letters in the word. An example: String A: cant String B: connect Result: -o-nec- Experimenting with NSString and NSScanner has yielded no results so far.

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• C++, create an instance from a static method

  - by Manux

  Hello, let's say I want my users to use only one class, say SpecialData. Now, this data class would have many methods, and depending on the type of data, the methods do different things, internally, but return externally similar results. Therefore my wanting to have one "public" class and other "private", child classes that would change the behavior of methods, etc... It would be amazingly more simple for some types of data that need to be built to do something like this: SpecialData& sm = SpecialData::new_supermatrix(); and new_supermatrix() would return a SuperMatrix instance, which inherits from most behaviors of SpecialData. my header: static SpecialData& new_supermatrix(); my cpp: SpecialData& SpecialData::new_supermatrix()(){ return SuperMatrix(MATRIX_DEFAULT_MAGNITUDE,1000,1239,FLOAT32,etc...); } The problem is, I get this error, which is probably logical due to the circumstances: invalid initialization of non-const reference of type ‘SpecialData&’ from a temporary of type ‘SpecialData’ So, any ideas?

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• SQL Server Error 26 (Error Locating Server/Instance Specified) Only When Debugging

  - by Phsion

  I have a simple asp .net web project I'm working on, and while normally everything is going fine, if I try to debug the site, I get "SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified". I'm not sure if its a weird code issue or a weird SQL Server Issue, but here are the system specs anyway. My dev machine is Windows 7 32-bit, and a Windows Server 2008 VM (on the same Windows 7 Machine) runs both IIS and SQL Server 2008 Express. I haven't had any other problems with the connection string I'm using, and I'm using the simple SA account. Anyhow, thanks for the help.

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• What's the Difference Between These Two Ruby Class Initialaztion Definitions?

  - by michaelmichael

  I'm working through a book on Ruby, and the author used a slightly different form for writing a class initialization definition than he has in previous sections of the book. It looks like this: class Ticket attr_accessor :venue, :date def initialize(venue, date) self.venue = venue self.date = date end end In previous sections of the book, it would've been defined like this: class Ticket attr_accessor :venue, :date def initialize(venue, date) @venue = venue @date = date end end Is there any functional difference between using the setter method, as in the first example vs. using the instance variable in the second? They both seem to work. Even mixing them up seems to work: class Ticket attr_accessor :venue, :date def initialize(venue, date) @venue = venue self.date = date end end

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• How do I dynamically define an instance variable?

  - by Moses

  Hi everyone, I have two classes (class1 and class2) that just store data, no methods. I have a third class that has an instance variable that, depending on some user input, will be set to one of the two classes. So, in the third class I declare the variable generically as NSObject *aClass; and during runtime set it to whatever it should be. aClass = [[Class1 alloc] init]; // or aClass = [[Class2 alloc] init]; However, when I try to access fields from aClass NSString *str = aClass.field1; It gives me the error: request for member 'field1' in something not a structure or a union. Field1 is declared in both class1 and class2. When I try to cast aClass aClass = (Class1 *) aClass; it gives the same error. What am I doing wrong, is there a better way to do this?

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• What's the Difference Between These Two Ruby Class Initialization Definitions?

  - by michaelmichael

  I'm working through a book on Ruby, and the author used a slightly different form for writing a class initialization definition than he has in previous sections of the book. It looks like this: class Ticket attr_accessor :venue, :date def initialize(venue, date) self.venue = venue self.date = date end end In previous sections of the book, it would've been defined like this: class Ticket attr_accessor :venue, :date def initialize(venue, date) @venue = venue @date = date end end Is there any functional difference between using the setter method, as in the first example, vs. using the instance variable as in the second? They both seem to work. Even mixing them up works: class Ticket attr_accessor :venue, :date def initialize(venue, date) @venue = venue self.date = date end end

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• Objective C instance variables - Newbie

  - by Dwayne King

  OK - so I'm sure my confusion here is just a result of being stuck in a "Java mindset" and not understanding how Obj C differs in this case. In Java, I can declare a variable in a class, like this, and each instance of that class will have it's own: MyClass { String myVar; MyClass() { // constructor } } In Obj C I tried to do the same thing by declaring a variable only in the .m file like this: #import "MyClass.h" @implementation MyClass NSString *testVar; @end My expectation here was that this variable has a scope limited to this class. So I created a second class (identical): #import "MySecondClass.h" @implementation MySecondClass NSString *testVar; @end What I'm seeing (and has me baffled) is that changing the variable in one class, affects the value seen in the other class. In fact, if I set a breakpoint, and then "Jump to Definition" of the variable, it takes me to th I've created an extremely small XCode project that demonstrates the problem here Nothing more humbling than moving to a new language :) Thanks in advance.

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• Create instance of generic type in Java?

  - by David Citron

  Is it possible to create an instance of a generic type in Java? I'm thinking based on what I've seen that the answer is "no" (due to type erasure), but I'd be interested if anyone can see something I'm missing: class SomeContainer<E> { E createContents() { return what??? } } EDIT: It turns out that Super Type Tokens could be used to resolve my issue, but it requires a lot of reflection-based code, as some of the answers below have indicated. I'll leave this open for a little while to see if anyone comes up with anything dramatically different than Ian Robertson's Artima Article.

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• Java: Friendlier way to get an instance of FontMetrics

  - by Martijn Courteaux

  Hi people, Is there a friendlier way to get an instance of FontMetrics than FontMetrics fm = Graphics.getFontMetrics(Font); I hate this way because of the following example: If you want to create in a game a menu and you want all the menuitems in the center of the screen you need fontmetrics. But, mostly, menuitems are clickable. So I create an array of Rectangles and all the rectangles fits around the items, so when the mouse is pressed, I can simply use for (int i = 0; i < rects.length; i++) if (rects[i].contains(mouseX, mouseY)) { ... } But to create the rects I also need FontMetrics for their coordinates. So this mean that I have to construct all my rectangles in the paint-method of my menu. So I want a way to get the FontMetrics so I can construct the Rectangles in a method called by the constructor. Hope you understand. Thanks in advance.

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• Jquery scroll to first instance of a class (.error) for jquerytools validator

  - by Tommy Arnold

  I am using jquerytools validator on a clients website but the page using this plugin is very long so I would like to add a custom handler using the folowing code. $("#form").bind("onFail", function(e, errors) { // we are only doing stuff when the form is submitted if (e.originalEvent.type == 'submit') { $(".errormsg").html("Please scroll up and fix the highlighted errors."); //alert("Please fix the highlighted errors to continue"); } }); How would I get it to scroll up to the first instance of .error? Can you recommend any plugins for this?

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