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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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  • Help needed with Linq To Sql Query

    - by fearofawhackplanet
    I have the concept of valid/ordered transitions. So for example, it's not possible to move to status In progress from status Complete. Current and Next in table StatusTransition are FK (StatusType.Id). The Linq generator has created the following relations: Child Property Name: StatusTransitions1 Parent Property Name: StatusType1 Participating Properties: StatusType.Id -> StatusTransition.Next Child Property Name: StatusTransitions Parent Property Name: StatusType Participating Properties: StatusType.Id -> StatusTransition.Current I'm normally ok with Linq but I'm having difficulty getting the list of valid Next StatusTypes from the Current status. public List<StatusType> GetValidStatusTransitions(int statusId) { // trying to write something like the following // (obviously not correct) return _statusRepository .Where(s => s.Id == statusId) .Next.StatusTypes; }

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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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  • 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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  • 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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  • To Interface or Not?: Creating a polymorphic model relationship in Ruby on Rails dynamically..

    - by Globalkeith
    Please bear with me for a moment as I try to explain exactly what I would like to achieve. In my Ruby on Rails application I have a model called Page. It represents a web page. I would like to enable the user to arbitrarily attach components to the page. Some examples of "components" would be Picture, PictureCollection, Video, VideoCollection, Background, Audio, Form, Comments. Currently I have a direct relationship between Page and Picture like this: class Page < ActiveRecord::Base has_many :pictures, :as => :imageable, :dependent => :destroy end class Picture < ActiveRecord::Base belongs_to :imageable, :polymorphic => true end This relationship enables the user to associate an arbitrary number of Pictures to the page. Now if I want to provide multiple collections i would need an additional model: class PictureCollection < ActiveRecord::Base belongs_to :collectionable, :polymorphic => true has_many :pictures, :as => :imageable, :dependent => :destroy end And alter Page to reference the new model: class Page < ActiveRecord::Base has_many :picture_collections, :as => :collectionable, :dependent => :destroy end Now it would be possible for the user to add any number of image collections to the page. However this is still very static in term of the :picture_collections reference in the Page model. If I add another "component", for example :video_collections, I would need to declare another reference in page for that component type. So my question is this: Do I need to add a new reference for each component type, or is there some other way? In Actionscript/Java I would declare an interface Component and make all components implement that interface, then I could just have a single attribute :components which contains all of the dynamically associated model objects. This is Rails, and I'm sure there is a great way to achieve this, but its a tricky one to Google. Perhaps you good people have some wise suggestions. Thanks in advance for taking the time to read and answer this.

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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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  • 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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  • 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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  • 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 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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  • 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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  • 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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  • Selecting by ID in Castle ActiveRecord

    - by ripper234
    How can I write a criteria to return all Orders that belong to a specific User? public class User { [PrimaryKey] public virtual int Id { get; set; } } public class Order { [PrimaryKey] public virtual int Id { get; set; } [BelongsTo("UserId")] public virtual User User { get; set; } } return ActiveRecordMediator<Order>.FindAll( // What criteria should I write here ? );

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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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  • 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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  • When should I use a struct instead of a class?

    - by Esteban Araya
    MSDN says that you should use structs when you need lightweight objects. Are there any other scenarios when a struct is preferable over a class? Edit: Some people have forgotten that: 1. structs can have methods! 2. structs have no inheritance capabilites. Another Edit: I understand the technical differences, I just don't have a good feel for WHEN to use a struct.

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  • How to add an additional field to a queryset?

    - by Mark
    I've got a list of affiliates (users who have referred someone to the site): affiliates = User.objects.annotate(referral_count=Count('referrals')).filter(referral_count__gt=0) And a count of the number of users each affiliate has referred within a time frame: new_users = User.objects.filter(date_joined__gt=sd, date_joined__lte=ed) new_referrals = User.objects.filter(referrals__user__in=new_users).annotate(referral_count=Count('referrals')) How can I do something like new_referrals['affiliate.username'].referral_count from within my template? Note that this is not just a syntax issue, I also need to index new_referrals somehow so that I'm able to do this. Either this, or if I can somehow add a new_referral_count to the first query, that'd work too.

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  • Creating relationship between two model instances

    - by Lowgain
    This is probably pretty simple, but here: Say I've got two models, Thing and Tag class Thing < ActiveRecord::Base has_and_belongs_to_many :tags end class Tag < ActiveRecord::Base has_and_belongs_to_many :things end And I have an instance of each. I want to link them. Can I do something like: @thing = Thing.find(1) @tag = Tag.find(1) @thing.tags.add(@tag) If not, what is the best way to do this? Thanks!

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  • Using DAO's or static methods in Domain Object with nHibernate

    - by mickyjtwin
    I am using nHibernate for the first time, and after alot of reading/researching, plus looking at other projects done with nHibernate, have seen a couple of implementation practices. I am looking for opinions about which would be best to use and why. Essentially the two methods are as follows: Using Data Access Objects and a DAO Factory. Example usage: INotificationListDAO nListDAO = NHDaoFactory.GetNotificationListDAO(); NotificationList list = nListDAO.GetByListID(""); Use Static methods in the Domain Object. Example usage: NotificationList list = NotificationList.GetByListID(""); NHHelper.Session.Get(id); NHHelper.Session basically calls the NHibernateSessionManager.Instace.GetSessionFrom(""). While both look similar, it is more to do with best practice. From what I understand, the first option is more so if you are developing enterprise level applications, where my requirements are more for mid-range websites.

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