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• How to create a dynamic array of an Abstract class?

  - by outsyncof

  Lets say I have an abstract class Cat that has a few concrete subclasses Wildcat, Housecat, etc. I want my array to be able to store pointers to a type of cat without knowing which kind it really is. When I try to dynamically allocate an array of Cat, it doesn't seem to be working. Please help? Cat* catArray = new Cat[200];

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• Is it possible to make a subclass of NSObject which support subnodes in IB for iPhone project?

  - by Eonil

  I'm making a custom UI element class for iPhone. It'll cool to edit my class on Interface Builder with hierarchy. Some of my class is management class like UINavigationController, but they're not one of them, subclasses from NSObject. Of course, I can place a NSObject instance on IB, but it cannot have a child node. Is there a way to enable adding child node to subclass of NSObject?

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• Rails STI - Prevent base class from instantiation

  - by Jake

  Is there any way in a Rails STI situation to through an error when the base class is Instantiated? Overriding initialize will do it but then that gets trickled down to the subclasses. Thanks

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• Scala: how to specify varargs as type?

  - by IttayD

  Instead of def foo(configuration: (String, String)*) I'd like to be able to write: type Configuration = (String, String)* def foo(configuration: Configuration) The main use case is to provide an easy method signature when overriding in subclasses

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• 'Auto' option missing for TreeView subclass

  - by Jared

  I've created a custom control that subclasses TreeView. Right now it's completely empty, doesn't override anything. However when I place an instance in the designer the 'Auto' value for the Width and Height fields is no longer available as it is with the default TreeView. What am I missing?

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• Passing parameter to base class constructor or using instance variable?

  - by deamon

  All classes derived from a certain base class have to define an attribute called "path". In the sense of duck typing I could rely upon definition in the subclasses: class Base: pass # no "path" variable here def Sub(Base): def __init__(self): self.path = "something/" Another possiblity would be to use the base class constructor: class Base: def __init__(self, path): self.path = path def Sub(Base): def __init__(self): super().__init__("something/") What would you prefer and why? Is there a better way?

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• What is the purpose of subclassing the class "object" in Python?

  - by ignoramus

  All the Python built-ins are subclasses of object and I come across many user-defined classes which are too. Why? What is the purpose of the class object? It's just an empty class, right?

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• nonatomic property in model class when using NSOperationQueue (iPhone)?

  - by Andrew B.

  I have a custom model class with an NSMutableData ivar that will be accessed by custom NSOperation subclasses (using an NSOperationQueue). I think I can guarantee thread-safe access to the ivar from multiple NSOperations by using dependencies, and I can guarantee that I don't access the ivar from other code (say my main app thread) by waiting until the Q has finished all operations. Should I use a nonatomic property specification, or leave it atomic? Is there a significant impact on performance?

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• Collection, which method is used to authorize an add of an element ?

  - by Duke Vador

  We find a lot of concrete subclasses under Collection. While trying to add an element in a concrete collection, this collection will use a method to determine if it can accept to store the element (and eventually that this element is not already in the collection). It could use equals(), hashCode() or compareTo() of the element. Is it possible to find a summary about which method is used by each implementation of Collection ? Thanks a lot for your answers.

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• interact with an interface?

  - by ajsie

  from what i've read it seems that one can interact with an interface? eg. lets say that i've got an interface with an empty method "eat()" then 2 subclasses are implementing this interface. can my controller interact with only the interface and use it's eat() method? have a look at the picture in this link strategy

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• What's the Flash equivalent of FlexEvent.CREATION_COMPLETE

  - by John

  I'm moving some Flex classes to pure Flash/AS3 to be part of a shared library. I have an event listener on FlexEvent.CREATION_COMPLETE to create and add display-objects once things are running, but I don't know the right way to do this in Flash? edit: Maybe if my class subclasses Sprite rather than a Flex class, I can add children in the constructor, I don't need to wait for a "construction complete" event?

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• Creating an instance of a subclass extending an abstract class (Java)

  - by dacay

  In Java, is there any way to create an instance of any class that extends abstract class A, inside a member method of class A? Classes that extends abstract class A will return their instances with this method, but i don't want to implement same method in all subclasses with a "return this();" kind line.

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• [[alloc] init] as a factory method

  - by iter

  I want to initialize an instance of one of the subclasses of a superclass depending on the arguments to init: [[Vehicle alloc] initWithItinerary: shortWay]; // returns a bicycle [[Vehicle alloc] initWithItinerary: longWay]; // returns a car I can't find examples of code like this. I wonder if this is not idiomatic in Objective C, or I simply am not looking in the right places.

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• How to handle error in this case? By Exceptions or boolean or something else

  - by TP

  I am trying to create a Response class in Java which has a method void setResponse(String response); Different response subclasses will have different requirements for the response. The string that is passed to the function is received from the user. What is the correct way of handling a wrong response? Should the function throw an exception like IllegalResponseException Should the function be declared like boolean setResponse(String response, String errorMsg) and return false if the response is wrong and set the error message to the appropriate value

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• Why abstract classes necessary?

  - by bala3569

  1.What is the point of creating a class that can't be instantiated? Most commonly to serve as a base-class or interface (some languages have a separate interface construct, some don't) - it doesn't know the implementation (that is to be provided by the subclasses / implementing classes) 2.Why would anybody want such a class? For abstraction and re-use 3.What is the situation in which abstract classes become NECESSARY?can anyone brief it with an example?

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• Android : How to get the dirty(changed) properties

  - by con_9

  How to get the dirty(changed) properties(any controls subclasses of view) amongst a number of properties on a layout. Does android has a dirty flag to mark if the layout has any field that has a changed content??

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• spring component scan for classes

  - by awk

  I want to scan all the classes in a package that that are subclasses of the particular class. Then I want to take these classes and for each of them instantiate a bean of same type, using the class as a property. Then I want to gather all these anonymous beans and put them into collection. Is it possible to configure spring context in XML like this? Thx

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• How do I restrict the creation of an anonymous subclass (Java)

  - by Ad

  Hi I have an abstract class A in a package P with subclasses B and C. I don't want it to be possible to create an anonymous subclass to the class A from outside the package P.

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• Writing A Good C# Equals Method

  - by ChloeRadshaw

  Does anyone have a template for writing a decent equals method - I remember in Effective Java there was problems around handling equals when dealing with subclasses. I dont have the book with me and I cannot remember if it was practical advice - So how do you write a solid robust equals method implementation?

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• Are there any data-binding solution that works in C++ and GWT and supports structures polymorphism?

  - by user116854

  I expect it should share a common description, like XmlSchema or IDL and should generate classes for target language. I found Thrift and it's really nice solution, but it doesn't support structures polymorphism. I would like to have collections of base class objects, where I could place instances of subclasses, serialize this and deserialize at the opposite side. Some mechanism of polymorphic behavior support, like Visitor, would be a perfect. Does anybody know something suitable for these requirements?

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• How to extend a file definition from an existing module in the node?

  - by c33s

  I use an older version of the example42 mysql module, which defines the mysql.conf file but not its content. Mmy goal is to just include the mysql module and add a content definition in the node. class mysql { ... file { "mysql.conf": path => "${mysql::params::configfile}", mode => "${mysql::params::configfile_mode}", owner => "${mysql::params::configfile_owner}", group => "${mysql::params::configfile_group}", ensure => present, require => Package["mysql"], notify => Service["mysql"], } ... } node xyz { include mysql File["mysql.conf"] { content => template("mymodule/mysql.conf.erb")} } The above code produces a "Only subclasses can override parameters" What is the correct way to just add a content definition to an existing file definition?

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• HUGE EF4 Inheritance Bug

  - by djsolid

  Well maybe not for everyone but for me is definitely really important. That is why I get straight into the point. We have the following model: Which maps to the following database: We are using EF4.0 and we want to load all Burgers including BurgerDetails. So we write the following query: But it fails. The error is : “The ResultType of the specified expression is not compatible with the required type. The expression ResultType is 'Transient.reference[SampleEFDBModel.Food]' but the required type is 'Transient.reference[SampleEFDBModel.Burger]'.Parameter name: arguments[0]”   So in the new version of EF there is no way to eager load data through Navigation Properties with 1-1 relationships defined in subclasses. Here is the relevant Microsoft Connect Issue. It is described through an other example but the result is the same.  Please if you think this is important vote up on Microsoft Connect.   EF 4.0 has many improvements. I am using it since v1 in large-scale projects and this version is faster,produces cleaner sql, more reliable and can be used for complicated business scenarios. That is why I believe this issue should be solved as soon as possible. I understand that release cycles are slow but I am hoping atleast for a hotfix. I also have uploaded the example project so you can test it. Download it from here. If anyone has found any workarounds please post it in the comments section. Thanks!

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• Designing javascript chart library

  - by coolscitist

  I started coding a chart library on top of d3js: My chart library. I read Javascript API reusability and Towards reusable charts. However, I am NOT really following the suggestions because I am not really convinced about them. This is how my library can be used to create a bubble chart: var chart = new XYBubbleChart(); chart.data = [{"xValue":200,"yValue":300},{"xValue":400,"yValue":200},{"xValue":100,"yValue":310}]; //set data chart.dataKey.x = "xValue"; chart.dataKey.y = "yValue"; chart.elementId = "#chart"; chart.createChart(); Here are my questions: It does not use chaining. Is it a big issue? Every property and function is exposed publicly. (Example: width, height are exposed in Chart.js). OOP is all about abstraction and hiding, but I don't really see the point right now. I think exposing everything gives flexibility to change property and functionality inside subclasses and objects without writing a lot of code. What could be pitfalls of such exposure? I have implemented functions like: zooming, "showing info boxes when data point is clicked" as "abilities". (example: XYZoomingAbility.js). Basically, such "abilities" accept "chart" object, play around with public variables of "chart" to add functionality. What this allows me to do is to add an ability by writing: activateZoomAbility(chartObject); My goal is to separate "visualization" from "interactivity". I want "interactivity" like: zooming to be plugged into the chart rather than built inside the chart. Like, I don't want my bubble chart to know anything about "zooming". However, I do want zoomable bubble chart. What is the best way to do this? How to test and what to test? I have written mixed tests: jasmine and actual html files so that I can test manually on browser.

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• How to build MVC Views that work with polymorphic domain model design?

  - by Johann de Swardt

  This is more of a "how would you do it" type of question. The application I'm working on is an ASP.NET MVC4 app using Razor syntax. I've got a nice domain model which has a few polymorphic classes, awesome to work with in the code, but I have a few questions regarding the MVC front-end. Views are easy to build for normal classes, but when it comes to the polymorphic ones I'm stuck on deciding how to implement them. The one (ugly) option is to build a page which handles the base type (eg. IContract) and has a bunch of if statements to check if we passed in a IServiceContract or ISupplyContract instance. Not pretty and very nasty to maintain. The other option is to build a view for each of these IContract child classes, breaking DRY principles completely. Don't like doing this for obvious reasons. Another option (also not great) is to split the view into chunks with partials and build partial views for each of the child types that are loaded into the main view for the base type, then deciding to show or hide the partial in a single if statement in the partial. Also messy. I've also been thinking about building a master page with sections for the fields that only occur in subclasses and to build views for each subclass referencing the master page. This looks like the least problematic solution? It will allow for fairly simple maintenance and it doesn't involve code duplication. What are your thoughts? Am I missing something obvious that will make our lives easier? Suggestions?

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• Organising data access for dependency injection

  - by IanAWP

  In our company we have a relatively long history of database backed applications, but have only just begun experimenting with dependency injection. I am looking for advice about how to convert our existing data access pattern into one more suited for dependency injection. Some specific questions: Do you create one access object per table (Given that a table represents an entity collection)? One interface per table? All of these would need the low level Data Access object to be injected, right? What about if there are dozens of tables, wouldn't that make the composition root into a nightmare? Would you instead have a single interface that defines things like GetCustomer(), GetOrder(), etc? If I took the example of EntityFramework, then I would have one Container that exposes an object for each table, but that container doesn't conform to any interface itself, so doesn't seem like it's compatible with DI. What we do now, in case it helps: The way we normally manage data access is through a generic data layer which exposes CRUD/Transaction capabilities and has provider specific subclasses which handle the creation of IDbConnection, IDbCommand, etc. Actual table access uses Table classes that perform the CRUD operations associated with a particular table and accept/return domain objects that the rest of the system deals with. These table classes expose only static methods, and utilise a static DataAccess singleton instantiated from a config file.

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