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  • Question of using static_cast on "this" pointer in a derived object to base class

    - by Johnyy
    Hi, this is an example taken from Effective C++ 3ed, it says that if the static_cast is used this way, the base part of the object is copied, and the call is invoked from that part. I wanted to understand what is happening under the hood, will anyone help? class Window { // base class public: virtual void onResize() { } // base onResize impl }; class SpecialWindow: public Window { // derived class public: virtual void onResize() { // derived onResize impl; static_cast<Window>(*this).onResize(); // cast *this to Window, // then call its onResize; // this doesn't work! // do SpecialWindow- } // specific stuff };

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  • How should I declare default values for instance variables in Python?

    - by int3
    Should I give my class members default values like this: class Foo: num = 1 or like this? class Foo: def __init__(self): self.num = 1 In this question I discovered that in both cases, bar = Foo() bar.num += 1 is a well-defined operation. I understand that the first method will give me a class variable while the second one will not. However, if I do not require a class variable, but only need to set a default value for my instance variables, are both methods equally good? Or one of them more 'pythonic' than the other? One thing I've noticed is that in the Django tutorial, they use the second method to declare Models. Personally I think the second method is more elegant, but I'd like to know what the 'standard' way is.

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  • yet another confusion with multiprocessing error, 'module' object has no attribute 'f'

    - by gatoatigrado
    I know this has been answered before, but it seems that executing the script directly "python filename.py" does not work. I have Python 2.6.2 on SuSE Linux. Code: #!/usr/bin/python # -*- coding: utf-8 -*- from multiprocessing import Pool p = Pool(1) def f(x): return x*x p.map(f, [1, 2, 3]) Command line: > python example.py Process PoolWorker-1: Traceback (most recent call last): File "/usr/lib/python2.6/multiprocessing/process.py", line 231, in _bootstrap self.run() File "/usr/lib/python2.6/multiprocessing/process.py", line 88, in run self._target(*self._args, **self._kwargs) File "/usr/lib/python2.6/multiprocessing/pool.py", line 57, in worker task = get() File "/usr/lib/python2.6/multiprocessing/queues.py", line 339, in get return recv() AttributeError: 'module' object has no attribute 'f'

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  • same flash file (.swf) downloaded multiple times on a page

    - by Gunjan
    I have a page that has a table with each row corresponding to an audio file. The last cell in each row embeds a simple flash audio player. The problem is that the flash file for the player is being downloaded for each row separately and as soon as rows go beyond 40-50 it crashes the browser. I tried using different players (1pixelout, flash-mp3-player) and the problem is still there, so its not a player specific issue. Is there any way to cache the player so that it is only downloaded once?

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  • C# animation - move object from A to B or by angle

    - by Nullstr1ng
    Hi am just doing a little animation which moves an object from point a to point b or by angle/radians. what I currently have is this Point CalcMove(Point pt, double angle, int speed) { Point ret = pt; ret.X = (int)(ret.X + speed * Math.Sin(DegToRad(angle))); ret.Y = (int)(ret.Y + speed * Math.Cos(DegToRad(angle))); return ret; } but it doesn't look what i expected. please help? update: oh and am using NETCF

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  • Objective C Object Functioning & Passing Arrays

    - by Patrick
    I apologise if this has been asked before but I can't find the info I need. Basically I want a UITableView to be populated using info from a server, similar to the SeismicXML example. I have the parser as a separate object, is it correct to alloc, init an instance of that parser & then tell RootViewController to make it's table data source a copy of the parser's array. I can't include code because I haven't written anything yet, I'm just trying to get the design right before I start. Perhaps something like: xmlParser = [[XMLParser alloc] init]; [xmlParser getXMLData]; // Assuming xmlParser stores results in an array called returnedArray self.tableDataSource = xmlParser.returnedArray Is this the best way of doing it?

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  • C# Linq: Restructuring object

    - by Ben
    I'd like to take an object like this: SortedList<string, SortedList<int, SortedList<DateTime, double>>> Data and, for a given 'int' value (key of first nested sorted list), restructure it like this: SortedList<DateTime, SortedList<string, double>> or, better yet, this: SortedList<DateTime, double[]> where each 'double[]' has as many elements as there are KeyValue pairs in the SortedList. I'm guessing Linq is the way to go, but can't figure it out. Thanks for any suggestions.

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  • Initial capacity of collection types, i.e. Dictionary, List

    - by Neil N
    Certain collection types in .Net have an optional "Initial Capacity" constructor param. i.e. Dictionary<string, string> something = new Dictionary<string,string>(20); List<string> anything = new List<string>(50); I can't seem to find what the default initial capacity is for these objects on MSDN. If I know I will only be storing 12 or so items in a dictionary, doesn't it make sense to set the initial capacity to something like 20? My reasoning is, assuming the capacity grows like it does for a StringBuiler, which doubles each time the capacity is hit, and each re-allocation is costly, why not pre-set the size to something you know will hold your data, with some extra room just in case? If the initial capacity is 100, and I know I will only need a dozen or so, it seems as though the rest of that allocated RAM is allocated for nothing. Please spare me the "premature optimization" speil for the O(n^n)th time. I know it won't make my apps any faster or save any meaningful amount of memory, this is mostly out of curiosity.

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  • Using enums or a set of classes when I know I have a finite set of different options?

    - by devoured elysium
    Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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  • How do I serialize/deserialize a NHibernate entity that has references to other objects?

    - by Daniel T.
    I have two NHibernate-managed entities that have a bi-directional one-to-many relationship: public class Storage { public virtual string Name { get; set; } public virtual IList<Box> Boxes { get; set; } } public class Box { public virtual string Box { get; set; } [DoNotSerialize] public virtual Storage ParentStorage { get; set; } } A Storage can contain many Boxes, and a Box always belongs in a Storage. I want to edit a Box's name, so I send it to the client using JSON. Note that I don't serialize ParentStorage because I'm not changing which storage it's in. The client edits the name and sends the Box back as JSON. The server deserializes it back into a Box entity. Problem is, the ParentStorage property is null. When I try to save the Box to the database, it updates the name, but also removes the relationship to the Storage. How do I properly serialize and deserialize an entity like a Box, while keeping the JSON data size to a minimum?

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  • Core Data Predicate To Many

    - by Vikings
    I have a core data model that has a one to many relationship, there is a category, and it can contain many subcategories. Category <---- Subcategory I am trying to perform a fetch that checks if a particular Category contains a Subcategory with a particular name. Let's say I have two categories below, I want to fetch to see if there are any subcategories name "Apple" in the Category named "Fruits". Vetegables - Carrot - Lettuce Fruits - Apple - Orange - Pear Code: - (SubCategory *)searchForSubCategoryWithName:(NSString *)subCategory inCategory:(Category *)category { NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"SubCategory" inManagedObjectContext:self.beer.managedObjectContext]; [fetchRequest setEntity:entity]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == [c] %@", subCategory]; [fetchRequest setPredicate:predicate]; NSError *error; NSArray *fetchedObjects = [self.beer.managedObjectContext executeFetchRequest:fetchRequest error:&error]; if (fetchedObjects != nil && fetchedObjects.count > 0) { return [fetchedObjects objectAtIndex:0]; } else { return nil; } }

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  • Storing Object Types in Variable then Initializing

    - by Jon Mattingly
    Is there a way in Objective-C to store an object/class in a variable to be passed to alloc/init somewhere else? For example: UIViewController = foo foo *bar = [[foo alloc] init] I'm trying to create a system to dynamically create navigation buttons in a separate class based on the current view controller. I can pass 'self' to the method, but the variable that results does not allow me to alloc/init. I could always import the .h file directly, but ideally I would like to make reusing the code as simple as possible. Maybe I'm going about this the wrong way?

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  • How can I define an empty array in a Perl construtor?

    - by Laimoncijus
    I am just beginner with Perl, so if it sounds stupid - sorry for that :) My problem is - I am trying to write a class, which has an empty array, defined in constructor of a class. So I am doing this like this: package MyClass; use strict; sub new { my ($C) = @_; my $self = { items => () }; bless $self, ref $C || $C; } sub get { return $_[0]->{items}; } 1; Later I am testing my class with simple script: use strict; use Data::Dumper; use MyClass; my $o = MyClass->new(); my @items = $o->get(); print "length = ", scalar(@items), "\n", Dumper(@items); And while running the script I get following: $ perl my_test.pl length = 1 $VAR1 = undef; Why am I doing wrong what causes that I get my items array filled with undef? Maybe someone could show me example how the class would need to be defined so I would not get any default values in my array?

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  • UITableView - iPad - Property '' Not Found on Object of type UITableViewCell

    - by user1797508
    I have added a UITableView prototype Cell into a UIView for an iPad application using StoryBoard in Xcode (targeting iOS6). The problem I'm having is that the labels are not being recognized in my viewController when I try to reference them. In my implementation, I have: - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"dashboardMessage"; UITableViewCell *cell = [_tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]; } int row = [indexPath row]; cell.messageSender.text = [_matches valueForKey:@"from"]; } The last line is causing an error: Property 'messageSender' Not Found on Object of type UITableViewCell In the cell's header file I have: @interface DashboardMessageCell : UITableViewCell @property (strong, nonatomic) IBOutlet UILabel *messageSender; @property (strong, nonatomic) IBOutlet UILabel *messageDescr; and the header file is imported into the viewController. I'm lost as to what can be causing the issue, any help would be greatly appreciated. Thanks.

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  • Strange Error - "Object moved to here."

    - by Dkong
    I get the strange error "Object moved to here." on a blank white page when I try to login on a site I created. It works fine locally but not when I deploy it to the test or production server. I am not doing anything odd, just using basic authentication code in a helper function as follows... public static bool AuthenticateUser(string Username, string Password, bool PersistLogin, string RedirectionURL) { if (Membership.ValidateUser(Username, Password)) { FormsAuthentication.SetAuthCookie(Username, PersistLogin); HttpContext.Current.Response.Redirect(RedirectionURL,true); return true; } else return false; }

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  • Cannot access NSDictionary

    - by michael blaize
    I created a JSON using a PHP script. I am reading the JSON and can see that the data has been correctly read. However, when it comes to access the objects I get unrecognized selector sent to instance... Cannot seem to find why that is after too many hours !!!! Any help would be great ! My code looks like that: `NSDictionary *json = [[NSDictionary alloc] init]; json = [NSJSONSerialization JSONObjectWithData:receivedData options:kNilOptions error:&error]; NSLog(@"raw json = %@,%@",json,error); NSMutableArray *name = [[NSMutableArray alloc] init]; [name addObjectsFromArray: [json objectForKey:@"name"]];` The code crashes when reaching the last line above. The output like this: raw json = ( { category = vacancies; link = "http://blablabla.com"; name = "name 111111"; tagline = "tagline 111111"; }, { category = vacancies; link = "http://blobloblo.com"; name = "name 222222222"; tagline = "tagline 222222222"; } ),(null) 2012-06-23 21:46:57.539 Wind expert[4302:15203] -[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0xdcfb970 HELP !!!

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  • C#: why have all static methods/variables in a non-static class?

    - by Craig Johnston
    I have come across a class which is non-static, but all the methods and variables are static. Eg: public class Class1 { private static string String1 = "one"; private static string String2 = "two"; public static void PrintStrings(string str1, string str2) { ... All the variables are static across all instances, so there is no point having separate instances of the class. Is there any reason to create a class such as this?

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  • Events in Classes (VB.NET)

    - by Otaku
    I find that I write a lot of code within my classes to keep properties in sync with each other. I've read about Events in Classes, but have not been able to wrap my head around how to make them work for what I'm looking for. I could use some advice here. For example, in this one I always want to keep myColor up to date with any change whatsoever in any or all of the Red, Green or Blue properties. Class myColors Private Property Red As Byte Private Property Green As Byte Private Property Blue As Byte Private Property myColor As Color Sub New() myColor = Color.FromArgb(0, 0, 0) End Sub Sub ChangeRed(ByVal r As Byte) Red = r myColor = Color.FromArgb(Red, Green, Blue) End Sub Sub ChangeBlue(ByVal b As Byte) Blue = b myColor = Color.FromArgb(Red, Green, Blue) End Sub End Class If one or more of those changes, I want myColor to be updated. Easy enough as above, but is there a way to work with events that would automatically do this so I don't have to put myColor = Color.FromArgb(Red, Green, Blue) in every sub routine?

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  • Observer pattern and violation of Single Responsibility Principle

    - by Devil Jin
    I have an applet which repaints itself once the text has changed Design 1: //MyApplet.java public class MyApplet extends Applet implements Listener{ private DynamicText text = null; public void init(){ text = new DynamicText("Welcome"); } public void paint(Graphics g){ g.drawString(text.getText(), 50, 30); } //implement Listener update() method public void update(){ repaint(); } } //DynamicText.java public class DynamicText implements Publisher{ // implements Publisher interface methods //notify listeners whenever text changes } Isn't this a violation of Single Responsibility Principle where my Applet not only acts as Applet but also has to do Listener job. Same way DynamicText class not only generates the dynamic text but updates the registered listeners. Design 2: //MyApplet.java public class MyApplet extends Applet{ private AppletListener appLstnr = null; public void init(){ appLstnr = new AppletListener(this); // applet stuff } } // AppletListener.java public class AppletListener implements Listener{ private Applet applet = null; public AppletListener(Applet applet){ this.applet = applet; } public void update(){ this.applet.repaint(); } } // DynamicText public class DynamicText{ private TextPublisher textPblshr = null; public DynamicText(TextPublisher txtPblshr){ this.textPblshr = txtPblshr; } // call textPblshr.notifyListeners whenever text changes } public class TextPublisher implments Publisher{ // implements publisher interface methods } Q1. Is design 1 a SPR violation? Q2. Is composition a better choice here to remove SPR violation as in design 2.

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  • failure on creating a Scikits.TimeSeries object

    - by user311906
    Hi All I am trying to create a scikit.timeseries object starting from 2 datetime objects. If I understood correctly it should be possible to create a scikits.timeseries starting from datetime objects. I try the following code but it says that Insufficient parameters. The 2 datetime differs for few microseconds. In this case what should be the value for freq parameter? Is what I am trying allowed? In theory, since timeseries can be based on datetime objects it should be possible to hanlde up to microsecond , is this correct? I think that this is not really clear to me. Regards Eo import datetime import sckilits.timeseries as ts tm1 = datetime.datetime( 2010,1,1, 10,10,2, 123456 ) tm2 = datetime.datetime( 2010,1,1, 10,10,2, 345678 ) d = [ tm1, tm2 ] tseries = ts.time_series( dates=d ) tseries = ts.time_series( d )

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  • jquery split() and indexOf results in "Object doesn't support this property or method"

    - by chris
    I have the following code: var selected = $('#hiddenField').val().split(","); ... if (selected.indexOf(id) > 0) { ... set value ... } I'm dynamically creating a CheckBoxList, and trying to remember the state of the checkboxes by putting the selected IDs into the hidden field. I get an error stating that "Object doesn't support this property or method". My assumption is that selected is an array, which should support indexOf. Is that incorrect?

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