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• How to implement or emulate an "abstract" OCUnit test class?

  - by Quinn Taylor

  I have a number of Objective-C classes organized in an inheritance hierarchy. They all share a common parent which implements all the behaviors shared among the children. Each child class defines a few methods that make it work, and the parent class raises an exception for the methods designed to be implemented/overridden by its children. This effectively makes the parent a pseudo-abstract class (since it's useless on its own) even though Objective-C doesn't explicitly support abstract classes. The crux of this problem is that I'm unit testing this class hierarchy using OCUnit, and the tests are structured similarly: one test class that exercises the common behavior, with a subclass corresponding to each of the child classes under test. However, running the test cases on the (effectively abstract) parent class is problematic, since the unit tests will fail in spectacular fashion without the key methods. (The alternative of repeating the common tests across 5 test classes is not really an acceptable option.) The non-ideal solution I've been using is to check (in each test method) whether the instance is the parent test class, and bail out if it is. This leads to repeated code in every test method, a problem that becomes increasingly annoying if one's unit tests are highly granular. In addition, all such tests are still executed and reported as successes, skewing the number of meaningful tests that were actually run. What I'd prefer is a way to signal to OCUnit "Don't run any tests in this class, only run them in its child classes." To my knowledge, there isn't (yet) a way to do that, something similar to a +(BOOL)isAbstractTest method I can implement/override. Any ideas on a better way to solve this problem with minimal repetition? Does OCUnit have any ability to flag a test class in this way, or is it time to file a Radar? Edit: Here's a link to the test code in question. Notice the frequent repetition of if (...) return; to start a method, including use of the NonConcreteClass() macro for brevity.

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• Process arbitrarily large lists without explicit recursion or abstract list functions?

  - by Erica Xu

  This is one of the bonus questions in my assignment. The specific questions is to see the input list as a set and output all subsets of it in a list. We can only use cons, first, rest, empty?, empty, lambda, and cond. And we can only define exactly once. But after a night's thinking I don't see it possible to go through the arbitrarily long list without map or foldr. Is there a way to perform recursion or alternative of recursion with only these functions?

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• When to decide to introduce interfaces (pure abstract base classes) in C++?

  - by Honza Brabec

  Assume that you are developing a functionality and are 90% sure that the implementation class will stay alone. If I was in this position in Java I would probably not use the interface right now to keep the things simple. In Java it is easy to refactor the code and extract the interface later. In C++ the refactoring is not always so easy. It may require replacing values with smart pointers (because of the introduction of polymorphism) and other non-trivial tasks. On the other hand I don't much like the idea of introducing virtual calls when I am 90% sure they won't be needed. After all speed is one of the reasons to prefer C++ over simpler languages.

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• Breaking up a large PHP object used to abstract the database. Best practices?

  - by John Kershaw

  Two years ago it was thought a single object with functions such as $database->get_user_from_id($ID) would be a good idea. The functions return objects (not arrays), and the front-end code never worries about the database. This was great, until we started growing the database. There's now 30+ tables, and around 150 functions in the database object. It's getting impractical and unmanageable and I'm going to be breaking it up. What is a good solution to this problem? The project is large, so there's a limit to the extent I can change things. My current plan is to extend the current object for each table, then have the database object contain these. So, the above example would turn into (assume "user" is a table) $database->user->get_user_from_id($ID). Instead of one large file, we would have a file for every table.

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• What are the methods to estimate source code value?

  - by Antoine

  I've been working on some project on my free time for the past few months. Recently I've been approached by friends to build a startup, and this source code would be very valueable to us. As a co-founder, this code could count for something in the company's capital, and be exchanged for shares. But how can you estimate its value? Do you just multiply industry-standard wqges by the time I spent on it, or are there other methods?

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• Is it dangerous for me to give some of my Model classes Control-like methods?

  - by Pureferret

  In my personal project I have tried to stick to MVC, but I've also been made aware that sticking to MVC too tightly can be a bad thing as it makes writing awkward and forces the flow of the program in odd ways (i.e. some simple functions can be performed by something that normally wouldn't, and avoid MVC related overheads). So I'm beginning to feel justified in this compromise: I have some 'manager programs' that 'own' data and have some way to manipulate it, as such I think they'd count as both part of the model, and part of the control, and to me this feels more natural than keepingthem separate. For instance: One of my Managers is the PlayerCharacterManager that has these methods: void buySkill(PlayerCharacter playerCharacter, Skill skill); void changeName(); void changeRole(); void restatCharacter(); void addCharacterToGame(); void createNewCharacter(); PlayerCharacter getPlayerCharacter(); List<PlayerCharacter> getPlayersCharacter(Player player); List<PlayerCharacter> getAllCharacters(); I hope the mothod names are transparent enough that they don't all need explaining. I've called it a manager because it will help manage all of the PlayerCharacter 'model' objects the code creates, and create and keep a map of these. I may also get it to store other information in the future. I plan to have another two similar classes for this sort of control, but I will orchestrate when and how this happens, and what to do with the returned data via a pure controller class. This splitting up control between informed managers and the controller, as opposed to operating just through a controller seems like it will simplify my code and make it flow more. My question is, is this a dangerous choice, in terms of making the code harder to follow/test/fix? Is this somethign established as good or bad or neutral? I oculdn't find anything similar except the idea of Actors but that's not quite why I'm trying to do. Edit: Perhaps an example is needed; I'm using the Controller to update the view and access the data, so when I click the 'Add new character to a player button' it'll call methods in the controller that then go and tell the PlayerCharacterManager class to create a new character instance, it'll call the PlayerManager class to add that new character to the player-character map, and then it'll add this information to the database, and tell the view to update any GUIs effected. That is the sort of 'control sequence' I'm hoping to create with these manager classes.

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• By what methods can I check information about a DVD video disc?

  - by chobok

  I have some DVD video discs that I am intending to sell. I would like to get information such as region, language, subtitles. Some of the discs are in another language which I cannot read, and some are from small publishers and do not have such information on the disc or the boxes. What methods can I use to access this information? Please list command line options, as well as common GUI based tools (eg VLC player).

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• What Java data structure/design pattern best models this object, considering it would perform these methods?

  - by zundarz

  Methods: 1. getDistance(CityA,CityB) // Returns distance between two cities 2. getCitiesInRadius(CityA,integer) // Returns cities within a given distance of another city 3. getCitiesBeyondRadius(CityA,integer) //Returns cities beyond a given distance of another city 4. getRemoteDestinations(integer) // Returns all city pairs greater than x distance of each other 5. getLocalDestinations(integer) //Returns all city pairs within x distance of each other

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• Is this a good way to expose generic base class methods through an interface?

  - by Nate Heinrich

  I am trying to provide an interface to an abstract generic base class. I want to have a method exposed on the interface that consumes the generic type, but whose implementation is ultimately handled by the classes that inherit from my abstract generic base. However I don't want the subclasses to have to downcast to work with the generic type (as they already know what the type should be). Here is a simple version of the only way I can see to get it to work at the moment. public interface IFoo { void Process(Bar_base bar); } public abstract class FooBase<T> : IFoo where T : Bar_base { abstract void Process(T bar); // Explicit IFoo Implementation void IFoo.Process(Bar_base bar) { if (bar == null) throw new ArgumentNullException(); // Downcast here in base class (less for subclasses to worry about) T downcasted_bar = bar as T; if (downcasted_bar == null) { throw new InvalidOperationException( string.Format("Expected type '{0}', not type '{1}'", T.ToString(), bar.GetType().ToString()); } //Process downcasted object. Process(downcasted_bar); } } Then subclasses of FooBase would look like this... public class Foo_impl1 : FooBase<Bar_impl1> { void override Process(Bar_impl1 bar) { //No need to downcast here! } } Obviously this won't provide me compile time Type Checking, but I think it will get the job done... Questions: 1. Will this function as I think it will? 2. Is this the best way to do this? 3. What are the issues with doing it this way? 4. Can you suggest a different approach? Thanks!

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• What is the most concise, unambiguous syntax for operator associated methods (for overloading etc.) that doesn't pollute the namespace?

  - by Doug Treadwell

  Python tends to add double underscores before its built-in or overloadable operator methods, like __add(), whereas C++ requires declaring overloaded operators as operator + (Thing& thing) { /* code */ } for example. Personally I like the operator syntax because it seems to be more explicit and keeps these operator overloading methods separated from other methods without introducing weird prefix notation. What are your thoughts? Also, what about the case of built-in methods that are needed for the programming language to work properly? Is name mangling (like adding __ prefix or sys or something) the best solution here? What do you think about having another type of method declaration, like ... "system method" for lack of creativity at the moment. So there would be two kinds of declarations: int method_name() { ... } system int method_name() { ... } ... and the call would need to be different to distinguish between them. obj.method_name(); vs obj:method_name(); perhaps, assuming a language where : can be unambiguously used in this situation. obj.method_name() vs obj.(system method_name)() Sure, the latter is ugly, but the idea is to make the common case simple and system stuff should be kept out of the way. Maybe the Objective-C notation of method calls? [obj method_name]? Are there more alternatives? Please make suggestions.

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• Liskov principle: violation by type-hinting

  - by Elias Van Ootegem

  According to the Liskov principle, a construction like the one below is invalid, as it strengthens a pre-condition. I know the example is pointless/nonsense, but when I last asked a question like this, and used a more elaborate code sample, it seemed to distract people too much from the actual question. //Data models abstract class Argument { protected $value = null; public function getValue() { return $this->value; } abstract public function setValue($val); } class Numeric extends Argument { public function setValue($val) { $this->value = $val + 0;//coerce to number return $this; } } //used here: abstract class Output { public function printValue(Argument $arg) { echo $this->format($arg); return $this; } abstract public function format(Argument $arg); } class OutputNumeric extends Output { public function format(Numeric $arg)//<-- VIOLATION! { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } My question is this: Why would this kind of "violation" be considered harmful? So much so that some languages, like the one I used in this example (PHP), don't even allow this? I'm not allowed to strengthen the type-hint of an abstract method but, by overriding the printValue method, I am allowed to write: class OutputNumeric extends Output { final public function printValue(Numeric $arg) { echo $this->format($arg); } public function format(Argument $arg) { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } But this would imply repeating myself for each and every child of Output, and makes my objects harder to reuse. I understand why the Liskov principle exists, don't get me wrong, but I find it somewhat difficult to fathom why the signature of an abstract method in an abstract class has to be adhered to so much stricter than a non-abstract method. Could someone explain to me why I'm not allowed to hind at a child class, in a child class? The way I see it, the child class OutputNumeric is a specific use-case of Output, and thus might need a specific instance of Argument, namely Numeric. Is it really so wrong of me to write code like this?

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• Should I use an interface when methods are only similar?

  - by Joshua Harris

  I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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• Multiple calls to different page methods in same web page are not running in parallel (JQuery/Ajax/A

  - by Tony_Henrich

  I have several page methods defined in the code behind of an aspx page. I have several JS calls (see example below), one after the other, in the ready() method of JQuery to call these page methods. I noticed the javascript calls run asynchronously but the .NET page methods do not run in parallel. Page method 1 finishes first before page method 2 runs. Is there a way to get all the page methods to run all at the same time? My workaround is to put each method in its own aspx page or use iframes but I am looking for better solutions. $.ajax({ type: "POST", url: (page/methodname), data: "{}", contentType: "application/json; charset=utf-8", dataType: "json", success: function(msg) { .... } } });

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• i don't solve "must declare a body because it is not marked abstract, extern, or partial" problem?

  - by programmerist

  How can i solve "must declare a body because it is not marked abstract, extern, or partial". This problem. Can you show me some advices? Full Error message is about Save, Update, Delete, Select events... Full message sample : GenoTip.DAL._AccessorForSQL.Save(string, System.Collections.Specialized.ListDictionary, System.Data.CommandType)' must declare a body because it is not marked abstract, extern, or partial This error also return in Update, Delete, Select... public abstract class _AccessorForSQL { public virtual bool Save(string sp, ListDictionary ld, CommandType cmdType); public virtual bool Update(); public virtual bool Delete(); public virtual DataSet Select(); } class GenAccessor : _AccessorForSQL { DataSet ds; DataTable dt; public override bool Save(string sp, ListDictionary ld, CommandType cmdType) { SqlConnection con = null; SqlCommand cmd = null; SqlDataReader dr = null; try { con = GetConnection(); cmd = new SqlCommand(sp, con); con.Open(); cmd.CommandType = cmdType; foreach (string ky in ld.Keys) { cmd.Parameters.AddWithValue(ky, ld[ky]); } dr = cmd.ExecuteReader(); ds = new DataSet(); dt = new DataTable(); ds.Tables.Add(dt); ds.Load(dr, LoadOption.OverwriteChanges, dt); } catch (Exception exp) { HttpContext.Current.Trace.Warn("Error in GetCustomerByID()", exp.Message, exp); } finally { if (dr != null) dr.Close(); if (con != null) con.Close(); } return (ds.Tables[0].Rows.Count 0) ? true : false; } public override bool Update() { return true; } public override bool Delete() { return true; } public override DataSet Select() { DataSet dst = new DataSet(); return dst; } private static SqlConnection GetConnection() { string connStr = WebConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString; SqlConnection conn = new SqlConnection(connStr); return conn; }

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• How is it that the abstract class XmlWriter can be instantiated using XmlWriter.Create(... ?

  - by Cognize

  Hi, Just looking to clarify my understanding of the workings of the XmlWriter and abstract classes in general. My thinking is (was) that an abstract class can not be instantiated, although it can contain base methods that can be used by an inheriting class. So, while investigating XmlWriter, I find that to instantiate the XmlWriter, you call XmlWriter.Create(.... , which returns an instance of... XmlWriter, which can then be used: FileStream fs = new FileStream("XML.xml", FileMode.Create); XmlWriter w = XmlWriter.Create(fs); XmlSerializer xmlSlr = new XmlSerializer(typeof(TestClass)); xmlSlr.Serialize(fs, tsIn); This clearly works, as tested. Can anyone help me understand what is going on here. As far as I can see there is or should be no 'instance' to work with here??

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• How to mark certain methods in WCF silverlight enabled service?

  - by bgodiy

  I have WCF silverlight enabled service. I have some methods in it. I need to mark certain methods in service and then to determine them when I have get all methods of service by Reflection.

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• How do I prevent JAXB from binding superclass methods of the @XmlRootElement when marshalling?

  - by Matt Fisher

  I have a class that is annotated as the @XmlRootElement with @XmlAccessorType(XmlAccessType.NONE). The problem that I am having is that the superclass's methods are being bound, when I do not want them to be bound, and cannot update the class. I am hoping there is an annotation that I can put on the root element class to prevent this from happening. Example: @XmlRootElement @XmlAccessorType(XmlAccessType.NONE) public class Person extends NamedObject { @XmlElement public String getId() { ... } } I would expect that only the methods annotated @XmlElement on Person would be bound and marshalled, but the superclass's methods are all being bound, as well. The resulting XML then has too much information. How do I prevent the superclass's methods from being bound without having to annotate the superclass, itself?

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• Can the get of a property be abstract and the set be virtual?

  - by K. Georgiev

  I have a base class like this: public class Trajectory{ public int Count { get; set; } public double Initial { get; set { Count = 1; } } public double Current { get; set { Count ++ ; } } } So, I have code in the base class, which makes the set-s virtual, but the get-s must stay abstract. So I need something like this: ... public double Initial { abstract get; virtual set { Count = 1; } } ... But this code gives an error. The whole point is to implement the counter functionality in the base class instead in all the derived classes. So, how can I make the get and set of a property with different modifiers?

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• Can you overload controller methods in ASP.Net MVC?

  - by Eric Brown

  Im curious to see if you can overload controller methods in ASP.Net MVC. Whenever I try, I get the error below. The two methods accept different arguements. Is this something that cannot be done? The current request for action 'MyMethod' on controller type 'MyController' is ambiguous between the following action methods:

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• Is writing comments inside methods not a good practice?

  - by Srini Kandula

  A friend told me that writing comments inside methods is not good. He said that we should have comments only for the method definitions(javadocs) but not inside the method body. It seems he read in a book that having comments inside the code means there is a problem in the code. I don't quite understand his reasoning. I think writing comments inside the method body is good and it helps other developers to understand it better and faster. Please provide your comments.

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• What is the advantage of using static methods in Python?

  - by Curious2learn

  I ran into unbound method error in python with the code class Sample(object): '''This class defines various methods related to the sample''' def drawSample(samplesize,List): sample=random.sample(List,samplesize) return sample Choices=range(100) print Sample.drawSample(5,Choices) After reading many helpful posts here, I figured how I could add @staticmethod above to get the code working. I am python newbie. Can someone please explain why one would want to define static methods? Or, why are not all methods defined as static methods. Thanks in advance.

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• Contract Programming - Deposit % and Payment Methods? Any advice is appreciated

  - by Rick

  I'm pretty new to doing contract work and finally landed a decent paying project. The guy actually offered to put down a deposit and I'm just wondering what percentage I should consider asking for. I was thinking around 25% since its not a terribly large project (only about 20 hours). Also, I can't use PayPal (have had a terrible experience with them freezing funds for no good reason) so I'm wondering if anyone can suggest other methods for the client to send the deposit / payment. I want to make it as easy as possible for them.. thanks for any advice

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• How can I get all the methods in a Protocol?

  - by jdinuncio

  Hello, How can I get a collection of all the (class) methods in a given protocol in smalltalk/squeak/pharo? I'm trying to collect the values returned by a group of methods. I don't want to have to store the methods in an instance or class variable. So I though I could add them to a protocol and in this way to "mark" them. Thanks.

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• Can pydoc/help hide the documentation for inherited class methods and attributes?

  - by EOL

  When declaring a class that inherits from a specific class: class C(dict): added_attribute = 0 the documentation for C lists all the methods of dict (either through help(C) or pydoc). Is there a way to hide the inherited methods from the automatically generated documentation (the documentation string can refer to the base class, for non-overwritten methods)? This would be useful: pydoc lists the functions defined in a module after its classes. Thus, when the classes have a very long documentation, a lot of less than useful information is printed before the new functions provided by the module are presented, which makes the documentation harder to exploit (you have to skip all the documentation for the inherited methods until you reach something specific to the module being documented).

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• Does it make sense to have a model with only static methods?

  - by Jamie Dixon

  Hey everyone, I have an ASP.NET MVC 2 project that I'm working on and I'm wondering where I should place some of my code. I currently have a UsersModel which consists of a bunch of static methods that operate against my data context. These methods include such things as: UserExistsInDatabase, UserIsRegisteredForActivity, GetUserIdFromFacebookId etc etc. Should these methods be inside a UsersModel class or would they be more suited to a user helper class outside of the models context? Cheers for any pointers.

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