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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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  • C++ inheritance and member function pointers

    - by smh
    In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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  • java protected method accessibility

    - by JavaUser
    In the below code the Consumer class can access the protected method of Parent class.How is it possible since there is no relation between Parent and Consumer class.Please explain class Parent { public void method1(){ System.out.println("PUBLIC METHOD"); } private void method2(){ System.out.println("PRIVATE METHOD"); } protected void method3(){ System.out.println("PROTECTED METHOD"); } } public class Consumer { public static void main(String[] args){ Parent parentObj = new Parent(); parentObj.method1(); //parentObj.method2(); parentObj.method3(); } } Thanks

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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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  • Improve this generic abstract class

    - by Keivan
    I have the following abstract class design, I was wondering if anyone can suggest any improvements in terms of stronger enforcement of our requirements or simplifying implementing of the ControllerBase. //Dependency Provider base public abstract class ControllerBase<TContract, TType> where TType : TContract, class { public static TContract Instance { get { return ComponentFactory.GetComponent<TContract, TType>(); } } public TContract GetComponent<TContract, TType>() where TType : TContract, class { component = (TType)Activator.CreateInstance(typeof(TType), true); RegisterComponentInstance<TContract>(component); } } //Contract public interface IController { void DoThing(); } //Actual Class Logic public class Controller: ControllerBase<IController,Controller> { public void DoThing(); //internal constructor internal Controller(){} } //Usage public static void Main() { Controller.Instance.DoThing(); } The following facts should always be true, TType should always implement TContract (Enforced using a generic constraint) TContract must be an interface (Can't find a way to enforce it) TType shouldn't have public constructor, just an internal one, is there any way to Enforce that using ControllerBase? TType must be an concrete class (Didn't include New() as a generic constrain since the constructors should be marked as Internal)

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  • How to profile object creation in Java?

    - by gooli
    The system I work with is creating a whole lot of objects and garbage collecting them all the time which results in a very steeply jagged graph of heap consumption. I would like to know which objects are being generated to tune the code, but I can't figure out a way to dump the heap at the moment the garbage collection starts. When I tried to initiate dumpHeap via JConsole manually at random times, I always got results after GC finished its run, and didn't get any useful data. Any notes on how to track down excessive temporary object creation are welcome.

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  • Define an empty array in Perl class new()

    - by Laimoncijus
    Hi, 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? Thanks!

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  • Opening IProject properties when another (adaptable to IProject) object is selected

    - by Stan
    I have a custom view displaying a hierarchy model of the current project. The root element is of class MyProject which is my own class, but it represents one Eclipse IProject, and it's adaptable to IProject. I have a "properties" menu option in the popup menu for that view, and I'd like to open up IProject's properties when a MyProject object is selected. PropertyDialogAction only looks for property pages registered for MyProject and doesn't give me a chance to offer an adapter -- or, at least, I don't know how to offer one. What's the proper solution for this? In the meantime, I've overridden PropertyDialogAction to handle my class in the special way I require, but that seems like quite a kludge to get this done.

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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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  • php how to serialize array of objects?

    - by hequ
    Hello, I have small class called 'Call' and I need to store these calls into a flat file. I've made another class called 'CallStorage' which contains an array where I put these calls into. My problem is that I would like to store this array to disk so I could later read it back and get the calls from that array. I've tried to achieve this using serialize() and unserialize() but these seems to act somehow strange and part of the information gets lost. This is what I'm doing: //write array to disk $filename = $path . 'calls-' . $today; $serialized = serialize($this->array); $fp = fopen($filename, 'a'); fwrite($fp, $serialized); fclose($fp); //read array from serialized file $filename = $path . 'calls-' . $today; if (file_exists($filename)) { $handle = fopen($filename, 'r'); $contents = fread($handle, filesize($filename)); fclose($handle); $unserialized = unserialize($contents); $this->setArray($unserialized); } Can someone see what I'm doing wrong, or what. I've also tried to serialize and write arrays that contains plain strings. I didn't manage to get that working either.. I have a Java background so I just can't see why I couldn't just write an array to disk if it's serialized. :)

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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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  • Binding to a List<object> in silverlight problem.

    - by cw
    Hello, Can someone suggest what I am doing wrong? Basically I have a List Items, when an item gets added to the list I am resetting the collection to the viewmodel property. The only way I can get it to work is if I null the member object out before reassigning the binding. Any suggestions on how to go about updating a UI when an item gets added to a List? public List<Item> RegisteredItems { get { return m_vRegisteredItems; } set { m_vRegisteredItems= null; NotifyPropertyChanged("RegisteredItems"); m_vRegisteredItems= value; NotifyPropertyChanged("RegisteredItems"); } }

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  • Make Java parent class not part of the interface

    - by Bart van Heukelom
    (This is a hypothetical question for discussion, I have no actual problem). Say that I'm making an implementation of SortedSet by extending LinkedHashMap: class LinkedHashSortedMapThing extends LinkedHashMap implements SortedSet { ... } Now programmers who use this class may do LinkedHashMap x = new LinkedHashSortedMapThing(); But what if I consider the extending of LinkedHashMap an implementation detail, and do not want it to be a part of the class' contract? If people use the line above, I can no longer freely change this detail without worrying about breaking existing code. Is there any way to prevent this sort of thing, other than favouring composition over inheritance (which is not always possible due to private/protected members)?

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  • In Drools Rules, how to use two different ArrayList objects,obj1 is used in rule 1 and obj2 used in rule2?

    - by Jenn
    I am doing ksession.insert(list) and after that I have to fire rule 1 in the drl file, then ksession.insert(list) and fire rule 2 in the drl. Could someone tell me how to achieve this. I read about agenda filters and facthandles but do not really know how to get this to work Below is some code: ArrayList list = new ArrayList(); list.add(product1); list.add(product2); list.add(product3); ksession.insert(list); ksession.fireAllRules("fire rule 1 in drl"); //remove list? ArrayList list2 = new ArrayList(); list2.add(str1); list2.add(str2); list2.add(str3); ksession.insert(list2); ksession.fireAllRules("fire rule 2 in drl");

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  • How do I correct feature envy in this case?

    - by RMorrisey
    I have some code that looks like: class Parent { private Intermediate intermediateContainer; public Intermediate getIntermediate(); } class Intermediate { private Child child; public Child getChild() {...} public void intermediateOp(); } class Child { public void something(); public void somethingElse(); } class Client { private Parent parent; public void something() { parent.getIntermediate().getChild().something(); } public void somethingElse() { parent.getIntermediate().getChild().somethingElse(); } public void intermediate() { parent.getIntermediate().intermediateOp(); } } I understand that is an example of the "feature envy" code smell. The question is, what's the best way to fix it? My first instinct is to put the three methods on parent: parent.something(); parent.somethingElse(); parent.intermediateOp(); ...but I feel like this duplicates code, and clutters the API of the Parent class (which is already rather busy). Do I want to store the result of getIntermediate(), and/or getChild(), and keep my own references to these objects?

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  • Compromising design & code quality to integrate with existing modules

    - by filip-fku
    Greetings! I inherited a C#.NET application I have been extending and improving for a while now. Overall it was obviously a rush-job (or whoever wrote it was seemingly less competent than myself). The app pulls some data from an embedded device & displays and manipulates it. At the core is a communications thread in the main application form which executes a 600+ lines of code method which calls functions all over the place, implementing a state machine - lots of if-state-then-do type code. Interaction with the device is done by setting the state/mode globally and letting the thread do it's thing. (This is just one example of the badness of the code - overall it is not very OO-like, it reminds of the style of embedded C code the device firmware is written in). My problem is that this piece of code is central to the application. The software, communications protocol or device firmware are not documented at all. Obviously to carry on with my work I have to interact with this code. What I would like some guidance on, is whether it is worth scrapping this code & trying to piece together something more reasonable from the information I can reverse engineer? I can't decide! The reason I don't want to refactor is because the code already works, and changing it will surely be a long, laborious and unpleasant task. On the flip side, not refactoring means I have to sometimes compromise the design of other modules so that I may call my code from this state machine! I've heard of "If it ain't broke don't fix it!", so I am wondering if it should apply when "it" is influencing the design of future code! Any advice would be appreciated! Thanks!

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  • Create facebook object each and every time?

    - by oshirowanen
    I have a login page which will log a user into my webapp based on their facebook login details. I then create a session to remember who they are. What I want to know is, should I be creating and/or checking the facebook credential on every single page of my webapp, or should I simply use the session I create at the beginning to login? For example, once they have logged in, I would like to allow them to post a message onto their own facebook wall from my app. Should I check the login credentials before they can post by recreating the facebook object, or should I simply use the stored login details already in my session and use that to post to their facebook wall?

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  • Where to start when doing a Domain Model?

    - by devoured elysium
    Let's say I've made a list of concepts I'll use to draw my Domain Model. Furthermore, I have a couple of Use Cases from which I did a couple of System Sequence Diagrams. When drawing the Domain Model, I never know where to start from: Designing the model as I believe the system to be. This is, if I am modelling a the human body, I start by adding the class concepts of Heart, Brain, Bowels, Stomach, Eyes, Head, etc. Start by designing what the Use Cases need to get done. This is, if I have a Use Case which is about making the human body swallow something, I'd first draw the class concepts for Mouth, Throat, Stomatch, Bowels, etc. The order in which I do things is irrelevant? I'd say probably it'd be best to try to design from the Use Case concepts, as they are generally what you want to work with, not other kind of concepts that although help describe the whole system well, much of the time might not even be needed for the current project. Is there any other approach that I am not taking in consideration here? How do you usually approach this? Thanks

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  • Custom link on embedded youtube video

    - by 0plus1
    I'm looking to direct the user on the channell webpage instead of the video url that I'm embedding. I've read the api and I didn't see any way to achieve this. I tried enclosing the embedded video in a and I added this code: $('#youtube').click(function() { document.write('http://www.youtube.com/user/trasportareoggi'); return false; }); And surprise it won't work. How, if it's even possible I can do this?

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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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  • Modules vs. Classes and their influence on descendants of ActiveRecord::Base

    - by Chris
    Here's a Ruby OO head scratcher for ya, brought about by this Rails scenario: class Product < ActiveRecord::Base has_many(:prices) # define private helper methods end module PrintProduct attr_accessor(:isbn) # override methods in ActiveRecord::Base end class Book < Product include PrintProduct end Product is the base class of all products. Books are kept in the products table via STI. The PrintProduct module brings some common behavior and state to descendants of Product. Book is used inside fields_for blocks in views. This works for me, but I found some odd behavior: After form submission, inside my controller, if I call a method on a book that is defined in PrintProduct, and that method calls a helper method defined in Product, which in turn calls the prices method defined by has_many, I'll get an error complaining that Book#prices is not found. Why is that? Book is a direct descendant of Product! More interesting is the following.. As I developed this hierarchy PrintProduct started to become more of an abstract ActiveRecord::Base, so I thought it prudent to redefine everything as such: class Product < ActiveRecord::Base end class PrintProduct < Product end class Book < PrintProduct end All method definitions, etc. are the same. In this case, however, my web form won't load because the attributes defined by attr_accessor (which are "virtual attributes" referenced by the form but not persisted in the DB) aren't found. I'll get an error saying that there is no method Book#isbn. Why is that?? I can't see a reason why the attr_accessor attributes are not found inside my form's fields_for block when PrintProduct is a class, but they are found when PrintProduct is a Module. Any insight would be appreciated. I'm dying to know why these errors are occurring!

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