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• Object-Oriented equivalent of LISP's progn function?

  - by Archer

  I'm currently writing a LISP parser that iterates through some AutoLISP code and does its best to make it a little easier to read (changing prefix notation to infix notation, changing setq assignments to "=" assignments, etc.) for those that aren't used to LISP code/only learned object oriented programming. While writing commands that LISP uses to add to a "library" of LISP commands, I came across the LISP command "progn". The only problem is that it looks like progn is simply executing code in a specific order and sometimes (not usually) assigning the last value to a variable. Am I incorrect in assuming that for translating progn to object-oriented understanding that I can simply forgo the progn function and print the statements that it contains? If not, what would be a good equivalent for progn in an object-oriented language?

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• Objected oriented approach to structure inside structure

  - by RishiD

  This is for C++ but should apply to any OO language. Trying to figure out the correct object oriented apporach to do the following (this is what I do in C). struct Container { enum type; union { TypeA a; TypeB b; }; } The type field determines if it TypeA or TypeB object. I am using this to handle responses coming back from a connection, they get parsed and get put into this structure and then based on the message type the appropriate fields get filled in. e.g. struct Container parseResponse(bufferIn, bufferLength); Is there an OO approach for doing this?

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• What is a good design model for my new class?

  - by user66662

  I am a beginning programmer who, after trying to manage over 2000 lines of procedural php code, now has discovered the value of OOP. I have read a few books to get me up to speed on the beginning theory, but would like some advice on practical application. So,for example, let's say there are two types of content objects - an ad and a calendar event. what my application does is scan different websites (a predefined list), and, when it finds an ad or an event, it extracts the data and saves it to a database. All of my objects will share a $title and $description. However, the Ad object will have a $price and the Event object will have $startDate. Should I have two separate classes, one for each object? Should I have a 'superclass' with the $title and $description with two other Ad and Event classes with their own properties? The latter is at least the direction I am on now. My second question about this design is how to handle the logic that extracts the data for $title, $description, $price, and $date. For each website in my predefined list, there is a specific regex that returns the desired value for each property. Currently, I have an extremely large switch statement in my constructor which determines what website I am own, sets the regex variables accordingly, and continues on. Not only that, but now I have to repeat the logic to determine what site I am on in the constructor of each class. This doesn't feel right. Should I create another class Algorithms and store the logic there for each site? Should the functions of to handle that logic be in this class? or specific to the classes whos properties they set? I want to take into account in my design two things: 1) I will add different content objects in the future that share $title and $description, but will have their own properties, so, I want to be able to easily grow these as needed. 2) I will add more websites constantly (each with their own algorithms for data extraction) so I would like to plan efficienty managing and working with these now. I thought about extending the Ad or Event class with 'websiteX' class and store its functions there. But, this didn't feel right either as now I have to manage 100s of little website specific class files. Note, I didn't know if this was the correct site or stackoverflow was the better choice. If so, let me know and I'll post there.

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• Is the "impossible object" possible in computer graphics?

  - by CPP_Person

  This may be a silly question but I want to know the answer to it. I saw this thing called the "impossible object", while they're many different images of this online, it's suppost to be impossible geometry. Here is an example: Now as far as logic goes, I know you don't have to obey it in games, such as a flying cow, or an impossible object. So that's out of the way, but what stands in my way is whether or not there is a way to draw this onto a 3D scene. Like is there a way to represent it as a 3D object? Thanks!

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• Javascript object list sorting by object property

  - by Constructor

  I need to do this: (sorry not in javascript syntax-still learning object language :) ) object=car attibutes:top-speed, brand.... now I want to sort the list of those cars in order by top-speed, brand... How do I do this (please note the solution must be javascript only, no php or other stuff) ?

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• Nhibernate/Hibernate, lookup tables and object design

  - by Simon G

  Hi, I've got two tables. Invoice with columns CustomerID, InvoiceDate, Value, InvoiceTypeID (CustomerID and InvoiceDate make up a composite key) and InvoiceType with InvoiceTypeID and InvoiceTypeName columns. I know I can create my objects like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceType InvoiceType { get; set; } } public class InvoiceType { public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } So the generated sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice WHERE CustomerID = x AND InvoiceDate = y SELECT InvoiceTypeID, InvoiceTypeName FROM InvoiceType WHERE InvoiceTypeID = z But rather that having two select queries executed to retrieve the data I would rather have one. I would also like to avoid using child object for simple lookup lists. So my object would look something like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } And my sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice INNER JOIN InvoiceType ON Invoice.InvoiceTypeID = InvoiceType.InvoiceTypeID WHERE CustomerID = x AND InvoiceDate = y My question is how do I create the mapping for this? I've tried using join but this tried to join using CustomerID and InvoiceDate, am I missing something obvious? Thanks

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• Getting my head around object oriented programing

  - by nLL

  I am entry level .Net developer and using it to develop web sites. I started with classic asp and last year jumped on the ship with a short C# book. As I developed I learned more and started to see that coming from classic asp I always used C# like scripting language. For example in my last project I needed to encode video on the webserver and wrote a code like public class Encoder { Public static bool Encode(string videopath) { ...snip... return true; } } While searching samples related to my project I’ve seen people doing this public class Encoder { Public static Encode(string videopath) { EncodedVideo encoded = new EncodedVideo(); ...snip... encoded.EncodedVideoPath = outputFile; encoded.Success = true; ...snip... } } public class EncodedVideo { public string EncodedVideoPath { get; set; } public bool Success { get; set; } } As I understand second example is more object oriented but I don’t see the point of using EncodedVideo object. Am I doing something wrong? Does it really necessary to use this sort of code in a web app?

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• Designing a class in such a way that it doesn't become a "God object"

  - by devoured elysium

  I'm designing an application that will allow me to draw some functions on a graphic. Each function will be drawn from a set of points that I will pass to this graphic class. There are different kinds of points, all inheriting from a MyPoint class. For some kind of points it will be just printing them on the screen as they are, others can be ignored, others added, so there is some kind of logic associated to them that can get complex. How to actually draw the graphic is not the main issue here. What bothers me is how to make the code logic such that this GraphicMaker class doesn't become the so called God-Object. It would be easy to make something like this: class GraphicMaker { ArrayList<Point> points = new ArrayList<Point>(); public void AddPoint(Point point) { points.add(point); } public void DoDrawing() { foreach (Point point in points) { if (point is PointA) { //some logic here else if (point is PointXYZ) { //...etc } } } } How would you do something like this? I have a feeling the correct way would be to put the drawing logic on each Point object (so each child class from Point would know how to draw itself) but two problems arise: There will be kinds of points that need to know all the other points that exist in the GraphicObject class to know how to draw themselves. I can make a lot of the methods/properties from the Graphic class public, so that all the points have a reference to the Graphic class and can make all their logic as they want, but isn't that a big price to pay for not wanting to have a God class?

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• Javascript Object Database

  - by Narven

  Hi, is there any javascript object database?? Something like http://www.db4o.com/ but for javascript? thanks

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• Is it better to return NULL or empty values from functions/methods where the return value is not present?

  - by P B

  I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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• How to build Object Oriented Skills?

  - by cedar715

  Being a core developer for couple of years, coding applications seeing the class diagrams, sequence diagrams, I decided to improve my self, taking the next step of designing. As I'm an OO developer, I'm interested in improving my design skills. For Example, I had a hard time designing a currency converter. My questions to the SO: Is it by experience the design skills can be acquired? Will learning books/blog/material over internet etc help? Is it that one needs the domain knowledge of the application being developed? Knowing Design patterns, principles? Studying 'Code Complete' book ? Need to have Problem-solving skills? In short, given a problem, I just want to solve it in Object-oriented way??

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• controlling an object through another object ?

  - by Stefano Borini

  Today I've seen the following pattern: you have an object A and an object B. Object B accepts a pointer to A at its constructor. Once B is created, there's a method B.doCalc() that performs a calculation (internally using A's information). The result is obtained with method B.getResult(). In order to perform another calculation, A is modified, and B.doCalc() is called again. What is your opinion on this choice ? I would have designed it differently, but I want to hear your voice. Edit : note that my main objection is to modify A to have a different result from B, without touching B. Although similar, I think that just this discipline expresses a much better feeling of what's going on. Instead of a = new A a.whatever = 5 b = new B(a) b.doCalc() res = b.getResult() a.whatever = 6 b.doCalc() res = b.getResult() You get the a pointer object from b itself. a = new A a.whatever = 5 b = new B(a) b.doCalc() res = b.getResult() a = b.getAPointer() a.whatever = 6 b.doCalc() res = b.getResult() because it makes more explicit the fact that a is taken from b and then modified. I still don't like it, though...

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• C++ Type error with Object versus Object reference

  - by muddybruin

  I have the following function (which worked in Visual Studio): bool Plane::contains(Vector& point){ return normalVector.dotProduct(point - position) < -doubleResolution; } When I compile it using g++ version 4.1.2 , I get the following error: Plane.cpp: In member function âvirtual bool Plane::contains(Vector&)â: Plane.cpp:36: error: no matching function for call to âVector::dotProduct(Vector)â Vector.h:19: note: candidates are: double Vector::dotProduct(Vector&) So as you can see, the compiler thinks (point-position) is a Vector but it's expecting Vector&. What's the best way to fix this? I verified that this works: Vector temp = point-position; return normalVector.dotProduct(temp) < -doubleResolution; But I was hoping for something a little bit cleaner. I heard a suggestion that adding a copy constructor might help. So I added a copy constructor to Vector (see below), but it didn't help. Vector.h: Vector(const Vector& other); Vector.cpp: Vector::Vector(const Vector& other) :x(other.x), y(other.y), z(other.z), homogenous(other.homogenous) { }

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• Uncaught TypeError: Object [object Object] has no method 'onAdded'

  - by user3604227

  I am using ExtJS4 with Java servlets. I am following the MVC architecture for ExtJS. I am trying a simple example of displaying a border layout but it doesnt work and I get the following error in ext-all.js in the javascript console: Uncaught TypeError: Object [object Object] has no method 'onAdded' Here is my code: app.js Ext.Loader.setConfig({ enabled : true }); Ext.application({ name : 'IN', appFolder : 'app', controllers : [ 'Items' ], launch : function() { console.log('in LAUNCH-appjs'); Ext.create('Ext.container.Viewport', { items : [ { xtype : 'borderlyt' } ] }); } }); Items.js (controller) Ext.define('IN.controller.Items', { extend : 'Ext.app.Controller', views : [ 'item.Border' ], init : function() { this.control({ 'viewport > panel' : { render : this.onPanelRendered } }); }, onPanelRendered : function() { console.log('The panel was rendered'); } }); Border.js (view) Ext.define('IN.view.item.Border',{extend : 'Ext.layout.container.Border', alias : 'widget.borderlyt', title : 'Border layout' , autoShow : true, renderTo : Ext.getBody(), defaults : { split : true, layout : 'border', autoScroll : true, height : 800, width : 500 }, items : [ { region : 'north', html : "Header here..", id : 'mainHeader' }, { region : 'west', width : 140, html : "Its West..", }, { region : 'south', html : "This is my temp footer content", height : 30, margins : '0 5 5 5', bodyPadding : 2, id : 'mainFooter' }, { id : 'mainContent', collapsible : false, region : 'center', margins : '5', border : true, } ] }); The folder structure for the Webcontent is as follows: WebContent app controller Items.js model store view item Border.js ext_js resources src ext_all.js index.html app.js Can someone help me resolve this error? Thanks in advance

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• wcf web service in post method, object properties are null, although the object is not null

  - by Abdalhadi Kolayb

  i have this problem in post method when i send object parameter to the method, then the object is not null, but all its properties have the default values. here is data module: [DataContract] public class Products { [DataMember(Order = 1)] public int ProdID { get; set; } [DataMember(Order = 2)] public string ProdName { get; set; } [DataMember(Order = 3)] public float PrpdPrice { get; set; } } and here is the interface: [OperationContract] [WebInvoke( Method = "POST", UriTemplate = "AddProduct", ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.WrappedRequest, RequestFormat = WebMessageFormat.Json)] string AddProduct([MessageParameter(Name = "prod")]Products prod); public string AddProduct(Products prod) { ProductsList.Add(prod); return "return string"; } here is the json request: Content-type:application/json {"prod":[{"ProdID": 111,"ProdName": "P111","PrpdPrice": 111}]} but in the server the object received: {"prod":[{"ProdID": 0,"ProdName": NULL,"PrpdPrice": 0}]}

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• Returning a mock object from a mock object

  - by Songo

  I'm trying to return an object when mocking a parser class. This is the test code using PHPUnit 3.7 //set up the result object that I want to be returned from the call to parse method $parserResult= new ParserResult(); $parserResult->setSegment('some string'); //set up the stub Parser object $stubParser=$this->getMock('Parser'); $stubParser->expects($this->any()) ->method('parse') ->will($this->returnValue($parserResult)); //injecting the stub to my client class $fileHeaderParser= new FileWriter($stubParser); $output=$fileParser->writeStringToFile(); Inside my writeStringToFile() method I'm using $parserResult like this: writeStringToFile(){ //Some code... $parserResult=$parser->parse(); $segment=$parserResult->getSegment();//that's why I set the segment in the test. } Should I mock ParserResult in the first place, so that the mock returns a mock? Is it good design for mocks to return mocks? Is there a better approach to do this all?!

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• Object-Oriented Operating System

  - by nmagerko

  As I thought about writing an operating system, I came across a point that I really couldn't figure out on my own: Can an operating system truly be written in an Object-Oriented Programming (OOP) Language? Being that these types of languages do not allow for direct accessing of memory, wouldn't this make it impossible for a developer to write an entire operating system using only an OOP Language? Take, for example, the Android Operating System that runs many phones and some tablets in use around the world. I believe that this operating system uses only Java, an Object-Oriented language. In Java, I have been unsuccessful in trying to point at and manipulate a specific memory address that the run-time environment (JRE) has not assigned to my program implicitly. In C, C++, and other non-OOP languages, I can do this in a few lines. So this makes me question whether or not an operating system can be written in an OOP, especially Java. Any counterexamples or other information is appreciated.

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• Object Oriented programming on 8-bit MCU Case Study

  - by Calvin Grier

  I see that there's a lot of questions related to OO Programming here. I'm actually trying to find a specific resource related to embedded OO approaches for an 8 bit MCU. Several years back (maybe 6) I was looking for material related to Object Oriented programming for resource constrained 8051 microprocessors. I found an article/website with a case history of a design group that used a very small RAM part, and implemented many Object based constructs during their C design and development. I believe it was an 8051. The project was a success, and managed to stay inside the very small ROM/RAM they had available. I'm attempting to find it again, but Google can't locate it. The article was well written, and recommended a "mixed" approach using C methods for inheritance and encapsulation - if I recall correctly. Can anyone help me locate this article?

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• What is Object Oriented Programming ill-suited for?

  - by Richard JP Le Guen

  In Martin Fowler's book Refactoring, Fowler speaks of how when developers learn something new, they don't consider when it's inappropriate for the job: Ten years ago it was like that with objects. If someone asked me when not to use objects, it was hard to answer. [...] It was just that I didn't know what those limitations were, although I knew what the benefits were. Reading this, it occurred to me I don't know what the limitations or potential disadvantages of Object-Oriented Programming are. What are the limitations of Object Oriented Programming? When should one look at a project and think "OOP is not best suited for this"?

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• Is there really Object-relational impedance mismatch?

  - by user52763

  It is always stated that it is hard to store applications objects in relational databases - the object-relational impedance mismatch - and that is why Document databases are better. However, is there really an impedance mismatch? And object has a key (albeit it may be hidden away by the runtime as a pointer to memory), a set of values, and foreign keys to other objects. Objects are as much made up of tables as it is a document. Neither really fit. I can see a use for databases to model the data into specific shapes for scenarios in the application - e.g. to speed up database lookup and avoid joins, etc., but won't it be better to keep the data as normalized as possible at the core, and transform as required?

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• In which object should I implement wait()/notify()?

  - by Christopher Francisco

  I'm working in an Android project with multithreading. Basically I have to wait to the server to respond before sending more data. The data sending task is delimited by the flag boolean hasServerResponded so the Thread will loop infinitely without doing anything until the flag becomes true. Since this boolean isn't declared as volatile (yet), and also looping without doing anything wastes resources, I thought maybe I should use AtomicBoolean and also implement wait() / notify() mechanism. Should I use the AtomicBoolean object notify() and wait() methods or should I create a lock Object?

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• Representing complex object dependencies

  - by max

  I have several classes with a reasonably complex (but acyclic) dependency graph. All the dependencies are of the form: class X instance contains an attribute of class Y. All such attributes are set during initialization and never changed again. Each class' constructor has just a couple parameters, and each object knows the proper parameters to pass to the constructors of the objects it contains. class Outer is at the top of the dependency hierarchy, i.e., no class depends on it. Currently, the UI layer only creates an Outer instance; the parameters for Outer constructor are derived from the user input. Of course, Outer in the process of initialization, creates the objects it needs, which in turn create the objects they need, and so on. The new development is that the a user who knows the dependency graph may want to reach deep into it, and set the values of some of the arguments passed to constructors of the inner classes (essentially overriding the values used currently). How should I change the design to support this? I could keep the current approach where all the inner classes are created by the classes that need them. In this case, the information about "user overrides" would need to be passed to Outer class' constructor in some complex user_overrides structure. Perhaps user_overrides could be the full logical representation of the dependency graph, with the overrides attached to the appropriate edges. Outer class would pass user_overrides to every object it creates, and they would do the same. Each object, before initializing lower level objects, will find its location in that graph and check if the user requested an override to any of the constructor arguments. Alternatively, I could rewrite all the objects' constructors to take as parameters the full objects they require. Thus, the creation of all the inner objects would be moved outside the whole hierarchy, into a new controller layer that lies between Outer and UI layer. The controller layer would essentially traverse the dependency graph from the bottom, creating all the objects as it goes. The controller layer would have to ask the higher-level objects for parameter values for the lower-level objects whenever the relevant parameter isn't provided by the user. Neither approach looks terribly simple. Is there any other approach? Has this problem come up enough in the past to have a pattern that I can read about? I'm using Python, but I don't think it matters much at the design level.

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• Passing functions into other functions as parameters, bad practice?

  - by BlueHat

  We've been in the process of changing how our AS3 application talks to our back end and we're in the process of implementing a REST system to replace our old one. Sadly the developer who started the work is now on long term sick leave and it's been handed over to me. I've been working with it for the past week or so now and I understand the system, but there's one thing that's been worrying me. There seems to be a lot of passing of functions into functions. For example our class that makes the call to our servers takes in a function that it will then call and pass an object to when the process is complete and errors have been handled etc. It's giving me that "bad feeling" where I feel like it's horrible practice and I can think of some reasons why but I want some confirmation before I propose a re-work to system. I was wondering if anyone had any experience with this possible problem?

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• Sharing object between 2 classes

  - by Justin

  I am struggling to wrap my head around being able to share an object between two classes. I want to be able to create only one instance of the object, commonlib in my main class and then have the classes, foo1 and foo2, to be able to mutually share the properties of the commonlib. commonlib is a 3rd party class which has a property Queries that will be added to in each child class of bar. This is why it is vital that only one instance is created. I create two separate queries in foo1 and foo2. This is my setup: abstract class bar{ //common methods } class foo1 extends bar{ //add query to commonlib } class foo2 extends bar{ //add query to commonlib } class main { public $commonlib = new commonlib(); public function start(){ //goal is to share one instance of $this->commonlib between foo1 and foo2 //so that they can both add to the properites of $this->commonlib (global //between the two) //now execute all of the queries after foo1 and foo2 add their query $this->commonlib->RunQueries(); } }

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• What kind of programs/solutions can only be written with OOP or are too hard to achieve without it?

  - by user1598390

  Paraphrasing a recent question: What is Object Oriented Programming ill-suited for? I would like to ask the opposite question: What kind of programs cannot be written unless you use OOP? What kind of programs are not recommended to be written using non-OOP techniques? What kind of programs need OOP in order to even be written? What kind of programs would be too hard to write without OOP ? The answer to this question can help sell the idea of OOP to project leaders that have no special interest in code quality. At least they could buy the idea if one shows them the kind of things that are not even possible unless you use OOP.

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