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• Should Equality be commutative within a Class Hierachy?

  - by vossad01

  It is easy to define the Equals operation in ways that are not commutative. When providing equality against other types, there are obviously situations (in most languages) were equality not being commutative is unavoidable. However, within one's own inheritance hierarchy where the root base class defines an equality member, a programmer has more control. Thus you can create situations where (A = B) ? (B = A), where A and B both derive from base class T Substituting the = with the appropriate variation for a given language. (.Equals(_), ==, etc.) That seems wrong to me, however, I recognize I may be biased by background in Mathematics. I have not been in programming long enough to know what is standard/accepted/preferred practice when programming. Do most programmers just accept .Equals(_)may not be commutative and code defensibly. Do they expect commutativity and get annoyed if it is not. In short, when working in a class hierarchy, should effort me made to ensure Equality is commutative?

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• Did Bjarne Stroustrup create the terms constructor/destructor when talking about objects?

  - by user104971

  I was watching this keynote and Bjarne Stroustrup (Creator of C++) claims that he hadn't yet invented the words constructor and destructor yet when he was giving an example of RAII. http://www.youtube.com/watch?v=IYBLXBJr0HU I know the concept of construction and destruction has been around a lot longer (even in C, a function that allocates and returns a struct and then a function that frees it etc.), but was Bjarne really the first to invent the terms?

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• Deleting a game object

  - by Balls

  I tried doing this but it cause an access violation. void GameObjectFactory::Update() { for( std::list<GameObject*>::iterator it=gameObjectList.begin() ..... (*it)->Update(); } void Bomb::Update() { if( time == 2.0f ) { gameObjectFactory->Remove( this ); } } void GameObjectFactory::Remove( ... ) { gameObjectList.remove( ... ); } My thoughts would be to mark the object to be dead then let the factory handle it the on next frame for deletion. Is it the best and fastest way? What do you think?

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• A programmer who doesn't get to program - where to turn? [closed]

  - by Just an Anon

  I'm in my mid 20's, and have been working as a full time programmer / developer for the last ~6 years, with several years of part-time freelancing before this, and three straight years of freelancing in the middle of this short career. I work mostly with PHP and the Drupal framework. By and large, I focus on programming custom pieces of functionality; these, of course, vary greatly from project to project. I've got years of solid experience with OOP (have done some Java & C# years ago, too) including intensive experience with front-end development, and even some design work. I've lead small teams (2-4 people) of developers. And of course, given the large amount of freelancing, I've got decent project- & client-management skills. My problem is staying motivated at any place of employment. In the time mentioned I've worked (full-time) at six local companies. The longest I've stayed at any company was just over a year. I find that I'll get hired and be very excited and motivated for the first few months, but the work quickly gets "stale." By that I mean that the interesting components (ie. the programming) get done, and the rest of the work turns into boring cleanup (move a button, add text, change colours, add a field). I don't get challenged, and I don't feel like I'm learning anything new. This happens repeatedly time and time again, and I always end up leaving for either a new opportunity, or to freelance. I'm wondering if perhaps I've painted myself into a corner with the rather niche work market (although with very high demand and good compensation) and need to explore other career choices. Another possibility is that I may be choosing the wrong places of employment, mostly small agencies, and need to look into working for a larger, more established firm. I find programming, writing code, and architecting solutions very rewarding. When I'm working on an interesting problem I lose all sense of time and 14-16 hours can fly by like minutes. I get the same exciting feeling when I'm doing high-level planning of a complex system, breaking up the work and figuring out how everything will tie-in together. I absolutely hate doing small, "stupid" changes that pose no challenge, yet seem to make up more and more of my work. I want to find a workplace where I will get to work on such tasks, be challenged, and improve in all areas of product development. This maybe a programming job, management, architecture of desktop apps, or may be managing a taco stand on a beach in Mexico - I don't know, and I need some advice and real-world feedback. What are some job areas worth exploring? The requirements are fairly simple: working with computers interacting with others challenging decent pay (I'm making just short of 90k / year with a month of vacation & some benefits, and would like to stay in this range, but am willing to take a temporary cut in pay for a more interesting position) Any advice would be much appreciated!

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• Should the 12-String be in it's own class and why? Java

  - by MayNotBe

  This is my first question here. I will amend it as instructed. This is regarding a homework project in my first Java programming class (online program). The assignment is to create a "stringed instrument" class using (among other things) an array of String names representing instrument string names ("A", "E", etc). The idea for the 12-string is beyond the scope of the assignment (it doesn't have to be included at all) but now that I've thought of it, I want to figure out how to make it work. Part of me feels like the 12-String should have it's own class, but another part of me feels that it should be in the guitar class because it's a guitar. I suppose this will become clear as I progress but I thought I would see what kind of response I get here. Also, why would they ask for a String[] for the instrument string names? Seems like a char[] makes more sense. Thank you for any insight. Here's my code so far (it's a work in progress): public class Guitar { private int numberOfStrings = 6; private static int numberOfGuitars = 0; private String[] stringNotes = {"E", "A", "D", "G", "B", "A"}; private boolean tuned = false; private boolean playing = false; public Guitar(){ numberOfGuitars++; } public Guitar(boolean twelveString){ if(twelveString){ stringNotes[0] = "E, E"; stringNotes[1] = "A, A"; stringNotes[2] = "D, D"; stringNotes[3] = "G, G"; stringNotes[4] = "B, B"; stringNotes[5] = "E, E"; numberOfStrings = 12; } } public int getNumberOfStrings() { return numberOfStrings; } public void setNumberOfStrings(int strings) { if(strings == 12 || strings == 6) { if(strings == 12){ stringNotes[0] = "E, E"; stringNotes[1] = "A, A"; stringNotes[2] = "D, D"; stringNotes[3] = "G, G"; stringNotes[4] = "B, B"; stringNotes[5] = "E, E"; numberOfStrings = strings; } if(strings == 6) numberOfStrings = strings; }//if else System.out.println("***ERROR***Guitar can only have 6 or 12 strings***ERROR***"); } public void getStringNotes() { for(int i = 0; i < stringNotes.length; i++){ if(i == stringNotes.length - 1) System.out.println(stringNotes[i]); else System.out.print(stringNotes[i] + ", "); }//for }

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• Is "If a method is re-used without changes, put the method in a base class, else create an interface" a good rule-of-thumb?

  - by exizt

  A colleague of mine came up with a rule-of-thumb for choosing between creating a base class or an interface. He says: Imagine every new method that you are about to implement. For each of them, consider this: will this method be implemented by more than one class in exactly this form, without any change? If the answer is "yes", create a base class. In every other situation, create an interface. For example: Consider the classes cat and dog, which extend the class mammal and have a single method pet(). We then add the class alligator, which doesn't extend anything and has a single method slither(). Now, we want to add an eat() method to all of them. If the implementation of eat() method will be exactly the same for cat, dog and alligator, we should create a base class (let's say, animal), which implements this method. However, if it's implementation in alligator differs in the slightest way, we should create an IEat interface and make mammal and alligator implement it. He insists that this method covers all cases, but it seems like over-simplification to me. Is it worth following this rule-of-thumb?

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• PHP class data implementation

  - by Bakanyaka

  I'm studying OOP PHP and have watched two tutorials that implement user login\registration system as an example. But implementation varies. Which way will be more correct one to work with data such as this? Load all data retrieved from database as array into a property called something like _data on class creation and further methods operate with this property Create separate properties for each field retrieved from database, on class creation load all data fields into respective properties and operate with that properties separately? Then let's say I want to create a method that returns a list of all users with their data. Which way is better? Method that returns just an array of userdata like this: Array([0]=>array([id] => 1, [username] => 'John', ...), [1]=>array([id] => 2, [username] => 'Jack', ...), ...) Method that creates a new instance of it's class for each user and returns an array of objects

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• Android app, No error message but has stopped unexpectedly [migrated]

  - by user74722

  Does anyone know what is my problem. I do not have any compile error messages however when i run the app it crashes and stops unexpectedly. Here is my codes. Thank you in advance. ListView l ; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_final_project); String arr[]={"Red","Green","Blue","Yellow","Cyan"}; l=(ListView) findViewById(R.id.listView1); ArrayAdapter<String> adapter=new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, arr); l.setAdapter(adapter); Button buttonOne = (Button) findViewById(R.id.button1); buttonOne.setOnClickListener(new OnClickListener(){ @Override public void onClick(View v){ setContentView(R.layout.layout_save); // setContentView(R.layout.activity_final_project); //startActivity(new Intent("com.example.finalproject.layout_save")); } }); }

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• Multiple parameters vs single parameter(object with multiple properties)

  - by Shwetanka

  I have an Entity Student with following properties - (name, joinedOn, birthday, age, batch, etc.) and a function fetchStudents(<params>). I want to fetch students based on multiple filters. In my method I have two ways to pass filters. Pass all filters as params to the method Make a class StudentCriteria with filters as fields and then pass the object of this class While working in java I always go with the second option but recently I'm working in php and I was advised to go with the first way. I am unable to figure out which way is better in maintaining the code, reusability and performance wise. Thanks.

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• IXRepository and test problems

  - by Ridermansb

  Recently had a doubt about how and where to test repository methods. Let the following situation: I have an interface IRepository like this: public interface IRepository<T> where T: class, IEntity { IQueryable<T> Query(Expression<Func<T, bool>> expression); // ... Omitted } And a generic implementation of IRepository public class Repository<T> : IRepository<T> where T : class, IEntity { public IQueryable<T> Query(Expression<Func<T, bool>> expression) { return All().Where(expression).AsQueryable(); } } This is an implementation base that can be used by any repository. It contains the basic implementation of my ORM. Some repositories have specific filters, in which case we will IEmployeeRepository with a specific filter: public interface IEmployeeRepository : IRepository<Employee> { IQueryable<Employee> GetInactiveEmployees(); } And the implementation of IEmployeeRepository: public class EmployeeRepository : Repository<Employee>, IEmployeeRepository // TODO: I have a dependency with ORM at this point in Repository<Employee>. How to solve? How to test the GetInactiveEmployees method { public IQueryable<Employee> GetInactiveEmployees() { return Query(p => p.Status != StatusEmployeeEnum.Active || p.StartDate < DateTime.Now); } } Questions Is right to inherit Repository<Employee>? The goal is to reuse code once all implementing IRepository already been made. If EmployeeRepository inherit only IEmployeeRepository, I have to literally copy and paste the code of Repository<T>. In our example, in EmployeeRepository : Repository<Employee> our Repository lies in our ORM layer. We have a dependency here with our ORM impossible to perform some unit test. How to create a unit test to ensure that the filter GetInactiveEmployees return all Employees in which the Status != Active and StartDate < DateTime.Now. I can not create a Fake/Mock of IEmployeeRepository because I would be testing? Need to test the actual implementation of GetInactiveEmployees. The complete code can be found on Github

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• Vertex Array Object (OpenGL)

  - by user5140

  I've just started out with OpenGL I still haven't really understood what Vertex Array Objects are and how they can be employed. If Vertex Buffer Object are used to store vertex data (such as their positions and texture coordinates) and the VAOs only contain status flags, where can they be used? What's their purpose? As far as I understood from the (very incomplete and unclear) GL Wiki, VAOs are used to set the flags/status for every vertex, following the order described in the Element Array Buffer, but the wiki was really ambiguous about it and I'm not really sure about what VAOs really do and how I could employ them.

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• Where is "open with..." in Nautilus?

  - by perebal

  In Ubuntu 11.04 I usually edit my *.fig files by clicking on the icons. The application (script) which opened the file was texfig. This script was chosen by "open with..." in nautilus. But now there is no possibilities to choose other applications than the predefined ones appropriate to the mimetype. How can I define a default application (or a self made script) in nautilus for the x-xfig mimetype?

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• [PHP] Making a good singleton registry class structure which hold your objects

  - by Saif Bechan

  I am working on a web application in PHP. I have a singleton class called registry. This class will hold all the objects i need throughout my application, such as loader classes, template classes, database, classes, etc. When an object of the registry class is created I send it an array with the classes it need to load: // Create the registry $registry = registry::singleton(); // Store those core objects $registry->storeObjects(Array('session','db','page','template','errors')); In this example I only put some of the classes, to get the basic idea. Now I have some classes in the registry that use each other. For example the 'errors' object uses the 'page' object. Now I was wondering if it is a good practice to make an instance of the registry object in the errors object. Like this; class errors{ private $registry; public function __construct(){ $this->registry = registry::singleton(); } } So there is an instance of the registry object, inside an object of the registry object. This does not sound like a good idea to me. Anyone have a suggestion how to model such a thing?

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• Javascript "this" variable confusion

  - by Assaf M

  Hi I am currently reading the book "Javascript: The Good Parts" and was playing with Functions. I produced a test script to test some properties and I am somewhat confused by the results. Here is the code: <h3>Object</h3> <div style="padding-left: 10px;"> <script type="text/javascript"> function outterF() { document.writeln("outterF.this = " + this + "<br>"); function innerF() { document.writeln("innerF.this = " + this + "<br>"); return this; }; var inner = innerF(); return this; } document.writeln("<b>From Inside:</b><br>"); var outF = outterF(); var inF = outF.inner; document.writeln("<br>"); document.writeln("<b>From Outside:</b><br>"); document.writeln("outterF.this = " + outF + "<br>"); document.writeln("innerF.this = " + inF + "<br>"); </script> </div> Result is: Object From Inside: outterF.this = [object Window] innerF.this = [object Window] From Outside: outterF.this = [object Window] innerF.this = undefined Notice that outF.inner returns "undefined", is that some kind of a language bug? Obviously, outF.inner points to Window object that has nothing to do with my object but shouldn't it be at least pointing to a Function object instead? Thanks -Assaf

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• OO Objective-C design with XML parsing

  - by brainfsck

  Hi, I need to parse an XML record that represents a QuizQuestion. The "type" attribute tells the type of question. I then need to create an appropriate subclass of QuizQuestion based on the question type. The following code works ([auto]release statements omitted for clarity): QuizQuestion *question = [[QuizQuestion alloc] initWithXMLString:xml]; if( [ [question type] isEqualToString:@"multipleChoiceQuestion"] ) { [myQuestions addObject:[[MultipleChoiceQuizQuestion alloc] initWithXMLString:xml]; } //QuizQuestion.m -(id)initWithXMLString:(NSString*)xml { self.type = ...// parse "type" attribute from xml // parse the rest of the xml } //MultipleChoiceQuizQuestion.m -(id)initWithXMLString:(NSString*)xml { if( self= [super initWithXMLString:xml] ) { // multiple-choice stuff } } Of course, this means that the XML is parsed twice: once to find out the type of QuizQuestion, and once when the appropriate QuizQuestion is initialized. To prevent parsing the XML twice, I tried the following approach: // MultipleChoiceQuizQuestion.m -(id)initWithQuizRecord:(QuizQuestion*)record { self=record; // record has already parsed the "type" and other parameters // multiple-choice stuff } However, this fails due to the "self=record" assignment; whenever the MultipleChoiceQuizQuestion tries to call an instance-method, it tries to call the method on the QuizQuestion class instead. Can someone tell me the correct approach for parsing XML into the appropriate subclass when the parent class needs to be initialized to know which subclass is appropriate?

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• How to create a generic list in this wierd case in c#

  - by Marc Bettex

  Hello, In my program, I have a class A which is extended by B, C and many more classes. I have a method GetInstance() which returns a instance of B or C (or of one of the other child), but I don't know which one, so the return type of the method is A. In the method CreateGenericList(), I have a variable v of type A, which is in fact either a B, a C or another child type and I want to create a generic list of the proper type, i.e. List<B> if v is a B or List<C> if v is a C, ... Currently I do it by using reflection, which works, but this is extremely slow. I wanted to know if there is another way to to it, which doesn't use reflection. Here is an example of the code of my problem: class A { } class B : A { } class C : A { } // More childs of A. class Program { static A GetInstance() { // returns an instance of B or C } static void CreateGenericList() { A v = Program.GetInstance(); IList genericList = // Here I want an instance of List<B> or List<C> or ... depending of the real type of v, not a List<A>. } } I tried the following hack. I call the following method, hoping the type inferencer will guess the type of model, but it doesn't work and return a List<A>. I believe that because c# is statically typed, T is resolved as A and not as the real type of model at runtime. static List<T> CreateGenericListFromModel<T>(T model) where T : A { return new List<T> (); } Does anybody have a solution to that problem that doesn't use reflection or that it is impossible to solve that problem without reflection? Thank you very much, Marc

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• How can a static class be resolved by the Unity Framework?

  - by user213988

  I wold like the unity framework to resolve a static class "MyStaticObject" specified in my config file. As my class is static, I am getting an error "The type StaticObject does not have an accessible constructor." My config file looks as below: <unity> <typeAliases> <typeAlias alias="singleton" type="Microsoft.Practices.Unity.ContainerControlledLifetimeManager, Microsoft.Practices.Unity" /> <typeAlias alias="StaticObject" type="MyStaticAssembly.MyStaticObject, MyStaticAssembly, Version=1.0.0.0" /> <typeAlias alias="staticobject" type="MyStaticAssembly.MyStaticObject, MyStaticAssembly" /> </typeAliases> <containers> <container> <types> <type type="StaticObject" mapTo="staticobject" name="My Static Object"> <lifetime type="singleton"/> </type> </types> </container> </containers> </unity> I would highly appreciate any help.

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• Java: Comparing a class with another within that class using a my own .equals

  - by user1670252

  I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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• Smart way to find the corresponding nullable type?

  - by Marc Wittke

  How could I avoid this dictionary (or create it dynamically)? Dictionary<Type,Type> CorrespondingNullableType = new Dictionary<Type, Type> { {typeof(bool), typeof(bool?)}, {typeof(byte), typeof(byte?)}, {typeof(sbyte), typeof(sbyte?)}, {typeof(char), typeof(char?)}, {typeof(decimal), typeof(decimal?)}, {typeof(double), typeof(double?)}, {typeof(float), typeof(float?)}, {typeof(int), typeof(int?)}, {typeof(uint), typeof(uint?)}, {typeof(long), typeof(long?)}, {typeof(ulong), typeof(ulong?)}, {typeof(short), typeof(short?)}, {typeof(ushort), typeof(ushort?)}, {typeof(Guid), typeof(Guid?)}, };

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• Getting the name of a Clojure struct type?

  - by j-g-faustus

  When defining a struct type and instance, I can print the value and get the "struct" implementation type: (defstruct person :name :age) (def p (struct person "peter" 30)) user=> p {:name "peter", :age 30} user=> (type p) clojure.lang.PersistentStructMap But is it possible to tell whether p is an instance of the struct type "person"?

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• Universal Parse Primitive Type on C#

  - by DreamWalker

  I have string value and Type of some variable (For example int and "32" or bool and true). My type is primitive type. Can I parse string to my type in one line?

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• What is the difference between a generic type and a generic type definition?

  - by Micah

  I'm Studying up on .net reflection and am having a hard time figuring out the difference. From what I understand, List is a generic type definition. Does that mean that to .net reflection T is the generic type? Specifically, I guess I'm looking for more background on the Type.IsGenericType and Type.IsGenericTypeDefinition functions. Thanks!

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• Finding out document template type of document library

  - by blade

  Hi, When I make a document library in Sharepoint 2003 and select the document template type etc and come back to edit/administer the document library, how can I find out what document template type I selected at the time of creation? Another way of putting it: If an administrator makes a document library and selects a document template type and he/she leaves without documenting his/her settings for the document library, how could I find out what document template type he selected? Thanks

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• Expecting a LexBuffer<char> but given a LexBuffer<byte> The type 'char' does not match the type 'by

  - by user152518

  Type mismatch. Expecting a LexBuffer but given a LexBuffer The type 'char' does not match the type 'byte' This is the error message that I am getting while using fslex. I have tried manually checking every single occurrence of lexbuf and its type. It's LexBuffer everywhere. But still the compiler is giving me the above error. Can you please tell me why this error occurs and how to go about resolving it. Thanks, chandrasekhar

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• Type problem with Observable.Create from Boo

  - by Tristan

  I'm trying to use Reactive Extensions from Boo and am running into type problems. Here's the basic example: def OnSubscribe(observer as IObservable[of string]) as callable: print "subscribing" def Dispose(): print "disposing" return Dispose observable = System.Linq.Observable.Create[of string](OnSubscribe) observer = System.Linq.Observer.Create[of string]({x as string | print x}) observable.Subscribe(observer) The Subscribe here gives a System.InvalidCastException: Cannot cast from source type to destination type. The issue appears to be with how I'm creating the observable, but I've struggled to see where the type problem arises from. Ideas?

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