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• Algorithms or patterns for a linked question and answer cost calculator

  - by kmc

  I've been asked to build an online calculator in PHP (and the Laravel framework). It will take the answers to a series of questions to estimate the cost of a home extension. For example, a couple of questions may be: What is the lie of your property? Flat, slightly inclined, heavily inclined. (these suggestive values could have specific values in the underlying calculator like, 0 degrees, 5 degrees, 10 degrees. What is your current flooring system? Wooden, or concrete? These would then impact the results of other questions. Once the size of the extension has been input, the lie of the land will affect how much site works will cost, and how much rubbish collection will cost. The second question will impact the cost of the extensions flooring, as stumping and laying floorboards is a different cost to laying foundations and a concrete slab. It will also influence what heating and cooling systems are available in the calculator. So it's VERY interlinked. The answer to any question can influence the options of other questions, and the end result. I'm having trouble figuring out an approach to this that will allow new options and questions to be plugged in at a later stage without having things too coupled. The Observer pattern, or Laravel's events may be handy, but currently the sheer breadth of the calculator has me struggling to gather my thoughts and see a sensible implementation. Are there any patterns or OO approaches that may help? Thanks!

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• Pipe an infinite stream to internal loop?

  - by Sh3ljohn

  I've seen a lot of things about redirecting stdout to a TCP socket, but no real example of how to do it in practice, specifically when the output stream generated by the first "command" never ends. To talk about something concrete, let's take programs like servers that typically output their log endlessly to stdout (well, as long as they run). If you redirect the output to a log file on the disk, then this file is always open (therefore not readable by others?) and grows infinitely, which eventually is going to cause problems. This might be a nood question, but I don't know what it does or how to do it so. How to redirect the output of a command to the internal loop? I want to make sure that data is sent EVERY time something is written to stdout, and that the pipe won't wait for the command to end (never happens ideally!). Is that right? If 2 is true, is there a buffer system to send chunks of data once it reaches a certain size only? Could you give me concrete command line examples to do the above? Thanks in advance

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• Using C++ but not using the language's specific features, should switch to C?

  - by Petruza

  I'm developing a NES emulator as a hobby, in my free time. I use C++ because is the language I use mostly, know mostly and like mostly. But now that I made some advance into the project I realize I'm not using almost any specific features of C++, and could have done it in plain C and getting the same result. I don't use templates, operator overloading, polymorphism, inheritance. So what would you say? should I stay in C++ or rewrite it in C? I won't do this to gain in performance, it could come as a side effect, but the idea is why should I use C++ if I don't need it? The only features of C++ I'm using is classes to encapsulate data and methods, but that can be done as well with structs and functions, I'm using new and delete, but could as well use malloc and free, and I'm using inheritance just for callbacks, which could be achieved with pointers to functions. Remember, it's a hobby project, I have no deadlines, so the overhead time and work that would require a re-write are not a problem, might be fun as well. So, the question is C or C++?

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• Use decorator and factory together to extend objects?

  - by TheClue

  I'm new to OOP and design pattern. I've a simple app that handles the generation of Tables, Columns (that belong to Table), Rows (that belong to Column) and Values (that belong to Rows). Each of these object can have a collection of Property, which is in turn defined as an enum. They are all interfaces: I used factories to get concrete instances of these products, depending on circumnstances. Now I'm facing the problem of extending these classes. Let's say I need another product called "SpecialTable" which in turn has some special properties or new methods like 'getSomethingSpecial' or an extended set of Property. The only way is to extend/specialize all my elements (ie. build a SpecialTableFactory, a SpecialTable interface and a SpecialTableImpl concrete)? What to do if, let's say, I plan to use standard methods like addRow(Column column, String name) that doesn't need to be specialized? I don't like the idea to inherit factories and interfaces, but since SpecialTable has more methods than Table i guess it cannot share the same factory. Am I wrong? Another question: if I need to define product properties at run time (a Table that is upgraded to SpecialTable at runtime), i guess i should use a decorator. Is it possible (and how) to combine both factory and decorator design? Is it better to use a State or Strategy pattern, instead?

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• Avoiding bloated Domain Objects

  - by djcredo

  We're trying to move data from our bloated Service layer into our Domain layer using a DDD approach. We currently have a lot of business logic in our services, which is spread out all over the place and doesn't benefit from inheritance. We have a central Domain class which is the focus of most of our work - a Trade. The Trade object will know how to price itself, how to estimate risk, validate itself, etc. We can then replace conditionals with polymorphism. Eg: SimpleTrade will price itself one way, but ComplexTrade will price itself another. However, we are worried that this will bloat the Trade class(s). It really should be in charge of its own processing but the class size is going to increase exponentially as more features are added. So we have choices: Put processing logic in Trade class. Processing logic is now polymorphic based on the type of the trade, but Trade class is now has multiple responsibilites (pricing, risk, etc) and is large Put processing logic into other class such as TradePricingService. No longer polymorphic with the Trade inheritance tree, but classes are smaller and easier to test. What would be the suggested approach?

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• Working Qt controls in a 3d environment

  - by Jay

  I need some advice from a Qt expert. The background: I have a 3D engine (ogre3d) working in concert with Qt. The 3D Content is displayed in a widget (using a custom OS window in the client area). I'm able to overlay arbitrary Qt widgets onto the 3d world using the widget render() method and a shared bitmap. This makes a great "heads up display". I can use the standard Qt style sheets and animation using this technique. My goal I'd like to go a step further and allow the user to move these rendered widgets using the mouse. I'd like some advice on the best way to implement this. Possible solutions: The widgets in the HUD are not part of the inheritance chain. I render them manually. They don't get events though. I could add them to the inheritance chain so they get events in the usual way. Then I would need to change them to render to my shared bitmap instead of to the operating system. I looked at this once but couldn't find enough information to implement it. Capture mouse events in the 3D display widget and EMIT them to child controls. I basically create my own event handling chain. Any suggestions on how to implement this? I'm also considering switching to Qt5. I'm not sure how that might affect this decision.

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• When to use an IOC container?

  - by nivlam

  I'm trying to understand when I should use a container versus manually injecting dependencies. If I have an application that uses a 1-2 interfaces and only has 1-2 concrete implementations for each interface, I would lean towards just handling that myself. If I have a small application that uses 2-3 interfaces and each interface has 2-3 concrete implementations, should I use a full-blown container? Would something something simple like this suffice? Basically I'm trying to understand when it's appropriate to manually handle these dependencies, when (or if) I should use something simple like the above, and when to use an IOC container like Ninject, Windsor, etc....

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• Access Control Lists basics

  - by vtortola

  Hi, I'm gonna add authorization, user and groups management to my application, basically... you will can define a set of permissions for a concrete user or group. For example, you could specify whom can use a concrete resource. So I want to ensure that my assumptions about ACLs are right: A basic rule could be "Grant", "Deny", "NoSet". User permissions have priority over group permissions. "Deny" statement has priority over "Grant". For example, user "u1" belongs to group "A", the resource "X" has this ACL "u1:grant,A:deny" user "u1" should be able to access the resource, shouldn't it? If a resource has no ACL set... does it means that anyone can access it? should I provide a default ACL? Any document about ACL in a general way? Cheers.

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• Metalanguage like BNF or XML-Schema to validate a tree-instance against a tree-model

  - by Stefan

  Hi! I'm implementing a new machine learning algorithm in Java that extracts a prototype datastructure from a set of structured datasets (tree-structure). As im developing a generic library for that purpose, i kept my design independent from concrete data-representations like XML. My problem now is that I need a way to define a data model, which is basically a ruleset describing valid trees, against which a set of trees is being matched. I thought of using BNF or a similar dialect. Basically I need a way to iterate through the space of all valid TreeNodes defined by the ModelTree (Like a search through the search space for algorithms like A*) so that i can compare my set of concrete trees with the model. I know that I'll have to deal with infinite spaces there but first things first. I know, it's rather tricky (and my sentences are pretty bumpy) but I would appreciate any clues. Thanks in advance, Stefan

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• Hibernate MappingException

  - by Marcus

  I'm getting this Hibernate error: org.hibernate.MappingException: Could not determine type for: a.b.c.Results$BusinessDate, for columns: [org.hibernate.mapping.Column(businessDate)] The class is below. Does anyone know why I'm getting this error?? @XmlAccessorType(XmlAccessType.FIELD) @XmlType(name = "", propOrder = { "businessDate" }) @XmlRootElement(name = "Results") @Entity(name = "Results") @Table(name = "RESULT") @Inheritance(strategy = InheritanceType.JOINED) @Cache(usage = CacheConcurrencyStrategy.READ_ONLY) public class Results implements Equals, HashCode { @XmlElement(name = "BusinessDate", required = true) protected Results.BusinessDate businessDate; public Results.BusinessDate getBusinessDate() { return businessDate; } public void setBusinessDate(Results.BusinessDate value) { this.businessDate = value; } @XmlAccessorType(XmlAccessType.FIELD) @XmlType(name = "", propOrder = { "raw", "display" }) @Entity(name = "Results$BusinessDate") @Table(name = "BUSINESSDATE") @Inheritance(strategy = InheritanceType.JOINED) public static class BusinessDate implements Equals, HashCode { ....

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• Storing Interface type in ASP.NET Profile

  - by NathanD

  In my ASP.NET website all calls into the data layer return entities as interfaces and the website does not need to know what the concrete type is. This works fine, but I have run into a problem when trying to store one of those types into the user Profile. My interface implements ISerializable, like the following: public interface IInsured : IPerson, IEntity, ISerializable and the concrete type in the datalayer does implement ISerializable. My Profile property in web.config is: <add name="ActiveInsured" type="FacadeInterfaces.IInsured" serializeAs="Binary" defaultValue="[null]"/> It compiles just fine, but I get a runtime error on Profile.Save() saying that the interface cannot be serialized. I have also tried it with serializeAs="Xml". I thought that if my interface implemented ISerializable it would work. Anybody had this problem before or know of a workaround?

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• DDD and IOC Containers

  - by MegaByte

  Hi Im fairly new with DDD and Im trying to use IOC in order to loosen up my tightly coupled layers :) My C# web application consists of a UI, domain and persistence layer. My persistence layer references my domain layer and contains my concrete repository implementations and nhibernate mappings. Currently my UI references my domain layer. My question : How do I use an IOC container to inject my concrete classes, in my persistence layer, into my domain layer? Does this meen that my UI should also reference my persistence layer?

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• Is Opacity is INHERITED in a div

  - by Jean

  Hello, Is it possible to remove the opacity inheritance from a parent to a child div? Thanks Jean

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• Inherit a parent class docstring as __doc__ attribute

  - by Reinout van Rees

  There is a question about Inherit docstrings in Python class inheritance, but the answers there deal with method docstrings. My question is how to inherit a docstring of a parent class as the __doc__ attribute. The usecase is that Django rest framework generates nice documentation in the html version of your API based on your view classes' docstrings. But when inheriting a base class (with a docstring) in a class without a docstring, the API doesn't show the docstring. It might very well be that sphinx and other tools do the right thing and handle the docstring inheritance for me, but django rest framework looks at the (empty) .__doc__ attribute. class ParentWithDocstring(object): """Parent docstring""" pass class SubClassWithoutDoctring(ParentWithDocstring): pass parent = ParentWithDocstring() print parent.__doc__ # Prints "Parent docstring". subclass = SubClassWithoutDoctring() print subclass.__doc__ # Prints "None" I've tried something like super(SubClassWithoutDocstring, self).__doc__, but that also only got me a None.

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• Which OOD approach should I take?

  - by Sorush Rabiee

  According to Niklaus Wirth, Algorithms + Data Structures = Programs. So I use this as a start point to object-oriented modeling and inheritance design: in a way that I separate the 'Objects' from 'Operations'. then look for patterns and inheritance hierarchy. But now after practice I guess it's not a good idea for every modeling problem, because sometimes it's not effective. (I mean there is no possibility of developing (or is very hard to develop) codes of Turing-Completed languages based on this paradigm.) What is your viewpoint for designing an OOD structure as an experienced programmer?

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• interfaces in java

  - by abson

  Java doesn't allow multiple inheritance but it allows implementing multiple interfaces. Why?

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• dotnetnuke iis 6 problem

  - by user311166

  i went to the root dir of my website in iis 6. right clicked properties and went the documents tab. i wanted to add a document extension to the list. when i clicked apply i received an inheritance override (UNCPassword and DefaultDoc) pop up showing many dnn files. i clicked cancel in both pop ups and then okay to apply the new document extension. now all my pages only pull up the home page information in dotnetnuke. the url changes in the address bar but only home page information is displayed. what could i have done to break dotnetnuke? are there some inheritance parameters needed? if so can i revert? thanks in advance.

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• Hidden Features of Visual Studio winforms designer

  - by CodingBarfield

  One of the most loved and hated feautures of visual studio must be the form designer. Creating a simple form/user control layout usually is a breeze. Setting properties and adding events is easy. Setting up the toolbox to use you own controls can be a bit harder and getting the ToolBoxIcons to show up can be a pain. Using third party components by visual inheritance can throw of the designer. And using multiple inheritance on designerables can be really hard. So what are your favorite 'hidden' and or obvious visual studio designer features.

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• ASP.NET MVC IoC usability

  - by Andrew Florko

  Hello everybody, How often do you use IoC for controllers/DAL in real projects? IoC allows to abstract application from concrete implementation with additional layer of interfaces that should be implemented. But how often concrete implementation changes? Should we really have to do job twice adding method to interface then the implementation if implementation hardly will ever be changed? I took part in about 10 asp.net projects and DAL (ORM-like and not) was never rewritten completely. Watching lots of videos I clearly understand that IoC "is cool" and the really nice way to program, but does it really needed?

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• Best practice Unit testing abstract classes?

  - by Paul Whelan

  Hello I was wondering what the best practice is for unit testing abstract classes and classes that extend abstract classes. Should I test the abstract class by extending it and stubbing out the abstract methods and then test all the concrete methods? Then only test the methods I override and the abstract methods in the unit tests for objects that extend my abstract class. Should I have an abstract test case that can be used to test the methods of the abstract class and extend this class in my test case for objects that extend the abstract class? EDIT: My abstract class has some concrete methods. I would be interested to see what people are using. Thanks Paul

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• identifying the type

  - by Gokul

  Hi, In my application, there is a inheritance hierarchy in which only the classes that are at the end of the inheritance chain are non-abstract classes. Also there is some usage of boost::variant. I want to write a function which takes a pointer and a Type and says whether the object belongs to that type. For example template< typename Type, bool TypeisAbstract, typename ptrType > bool checkType( ptrType* t) { return ( typeid(*t) == typeid(Type) ); } template< typename Type, typename ptrType > bool checkType<Type, true, ptrType>( ptrType* t) { return ( dynamic_cast<Type*>(t) != NULL ); } Now if there is a boost variant, i want to find out whether the boost variant stores that particular type. Can someone help me with that? Thanks, Gokul.

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• Self-type mismatch in Scala

  - by Alexey Romanov

  Given this: abstract class ViewPresenterPair { type V <: View type P <: Presenter trait View {self: V => val presenter: P } trait Presenter {self: P => var view: V } } I am trying to define an implementation in this way: case class SensorViewPresenter[T] extends ViewPresenterPair { type V = SensorView[T] type P = SensorPresenter[T] trait SensorView[T] extends View { } class SensorViewImpl[T](val presenter: P) extends SensorView[T] { presenter.view = this } class SensorPresenter[T] extends Presenter { var view: V } } Which gives me the following errors: error: illegal inheritance; self-type SensorViewPresenter.this.SensorView[T] does not conform to SensorViewPresenter.this.View's selftype SensorViewPresenter.this.V trait SensorView[T] extends View { ^ <console>:13: error: type mismatch; found : SensorViewPresenter.this.SensorViewImpl[T] required: SensorViewPresenter.this.V presenter.view = this ^ <console>:16: error: illegal inheritance; self-type SensorViewPresenter.this.SensorPresenter[T] does not conform to SensorViewPresenter.this.Presenter's selftype SensorViewPresenter.this.P class SensorPresenter[T] extends Presenter { ^ I don't understand why. After all, V is just an alias for SensorView[T], and the paths are the same, so how can it not conform?

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• NoSql Crash Course/Tutorial

  - by Chris Thompson

  Hi all, I've seen NoSQL pop up quite a bit on SO and I have a solid understanding of why you would use it (from here, Wikipedia, etc). This could be due to the lack of concrete and uniform definition of what it is (more of a paradigm than concrete implementation), but I'm struggling to wrap my head around how I would go about designing a system that would use it or how I would implement it in my system. I'm really stuck in a relational-db mindset thinking of things in terms of tables and joins... At any rate, does anybody know of a crash course/tutorial on a system that would use it (kind of a "hello world" for a NoSQL-based system) or a tutorial that takes an existing "Hello World" app based on SQL and converts it to NoSQL (not necessarily in code, but just a high-level explanation). I see this having one solid answer, but if you guys feel like it should be community wiki, I'll be happy to change it. Thanks! Chris

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• Is removing unused functionality a bad thing?

  - by Andrew Grimm

  Is it possible for YAGNI to apply in the past tense? You created some functionality, it was used a little bit a while ago, but you aren't using it any more, and you don't want to maintain it, so you'd rather delete it. Is getting rid of unused or rarely-used functionality neccessarily a bad thing? Background: I use source control, so if I need the functionality again, I can get it. I'm the only user of my software (I'm a bioinformatician analyzing a data set). One scenario where I came across this was that I was using inheritance, with a parent class, and two child classes. One was handling files generated by 454 sequencing (next-generation sequencing), and the other was handling files generated by Sanger sequencing (previous-generation sequencing). I was actively maintaining the latter, but not the former. Maybe my mistake was using inheritance rather than composition, but that's a slightly different story.

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• What is a practical, real world example of the Linked List?

  - by JStims

  I understand the definition of a Linked List, but how can it be represented and related to a common concept or item? For example, inheritance in OOP can be related to automobiles. All (most) automobiles in real life are the essentially same thing; an automobile has an Engine, you can start() it, you can make the car go(), stop() and so on. An automobile would typically have a maximum passenger capacity but it would differ between a Bus and a SportsCar, which are both automobiles. Is there some real life, intuitive example of the plain ole' singly Linked List like we have with inheritance? The typical textbook Linked List example shows a node with an integer and a pointer to the next, and it just doesn't seem very useful. Your input is appreciated.

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