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• Procedural object generation and unique identification

  - by 2080

  My question relates to procedural content generation and data management of the emerging objects in a database. I assume a networked game, with a server-client model. Unspecified objects in the game world are generated while the game is running with procedural algorithms (for example perlin noise). The players (/clients) can modify the properties of these objects, but have to notify the server of these changes. How could this communication address unique objects, so that both the server and the client know of which object they are speaking? Not only the inner properties of the objects can differ, but also visible, such as the position. When the player wants to select one of these objects the game has to find out the id - does anyone know which methods or algorithms can accomplish that?

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• How to verify the Liskov substitution principle in an inheritance hierarchy?

  - by Songo

  Inspired by this answer: Liskov Substitution Principle requires that Preconditions cannot be strengthened in a subtype. Postconditions cannot be weakened in a subtype. Invariants of the supertype must be preserved in a subtype. History constraint (the "history rule"). Objects are regarded as being modifiable only through their methods (encapsulation). Since subtypes may introduce methods that are not present in the supertype, the introduction of these methods may allow state changes in the subtype that are not permissible in the supertype. The history constraint prohibits this. I was hoping if someone would post a class hierarchy that violates these 4 points and how to solve them accordingly. I'm looking for an elaborate explanation for educational purposes on how to identify each of the 4 points in the hierarchy and the best way to fix it. Note: I was hoping to post a code sample for people to work on, but the question itself is about how to identify the faulty hierarchies :)

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• Is it a good idea to simplify an character -driven game engine to the point it's unnecessary to learn scripting/programming ?

  - by jokoon

  I remember, and I still think, that one cannot even make a prototyped 3D game to test just simple behaviors without using gigantic tools like unity or knowing extensive C++ programming, design pattern, a decent or basic 3D engine, etc. Now I'm wondering, since I know programming, that I'm still more lucky that the ones who need to learn programming prior to know how to make something: even scripted engines such as unity are not for kids, and to my sense they tend to dictate their ways of doing things, which is not the case with engine like ogre or irrlicht. I remember toying a little with the blender game engine, it was possible to link states or something I don't remember very well. Now I'm thinking that character driven games occupies a big part of the game market. Do you think it is a good idea to make a character-controlled oriented game engine which allows only to build AI instead of anything else ?

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• Is having 'Util' classes a cause for concern? [closed]

  - by Matt Fenwick

  I sometimes create 'Util' classes which primarily serve to hold methods and values that don't really seem to belong elsewhere. But every time I create one of these classes, I think "uh-oh, I'm gonna regret this later ...", because I read somewhere that it's bad. But on the other hand, there seem to be two compelling (at least for me) cases for them: implementation secrets that are used in multiple classes within a package providing useful functionality to augment a class, without cluttering its interface Am I on the way to destruction? What you say !! Should I refactor?

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• To identify the classes for uml diagrams?

  - by user106535

  I want to implement a software engineering project based on "crime management system". The main modules are: visitors, users, administrator. The main events that are taking place are: registration, report complaint, report crime, report most wanted, view status of reported crime. So could you please help me to identify the classes that are to be used in this project and help me to draw the class diagram?

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• How to handle status columns in designing tables

  - by altsyset

  How to handle multiple statuses for a table entry, for example an item table may have an active, inactive, fast moving, and/or batch statuses. And I wanted to handle them in single column with VARCHAR type. Also I might set each of those attributes as a boolean with different columns. But I am not sure what consequences this might lead to. So if you have experienced such situations which one would be the best way to handle it?

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• Semantic coupling vs. large class

  - by user106587

  I have hardware I communicate with via TCP. This hardware accepts ~40 different commands/requests with about 20 different responses. I've created a HardwareProxy class which has a TcpClient to send and receive data. I didn't like the idea of having 40 different methods to send the commands/requests, so I started down the path of having a single SendCommand method which takes an ICommand and returns an IResponse, this results in 40 different SpecificCommand classes. The problem is this requires semantic coupling, i.e. the method that invokes SendCommand receives an IResponse which it has to downcast to SpecificResponse, I use a future map which I believe ensures the appropriate SpecificResponse, but I get the impression this code smells. Besides the semantic coupling, ICommand and IResponse are essentially empty abstract classes (Marker Interfaces) and this seems suspicious to me. If I go with the 40 methods I don't think I have broken the single responisbility principle as the responsibility of the HardwareProxy class is to act as the hardware, which has all of these commands. This route is just ugly, plus I'd like to have Asynchronous versions, so there'd be about 80 methods. Is it better to bite the bullet and have a large class, accept the coupling and MarkerInterfaces for a smaller soultuion, or am I missing a better way? Thanks.

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• Rails: The Law of Demeter [duplicate]

  - by user2158382

  This question already has an answer here: Rails: Law of Demeter Confusion 4 answers I am reading a book called Rails AntiPatterns and they talk about using delegation to to avoid breaking the Law of Demeter. Here is their prime example: They believe that calling something like this in the controller is bad (and I agree) @street = @invoice.customer.address.street Their proposed solution is to do the following: class Customer has_one :address belongs_to :invoice def street address.street end end class Invoice has_one :customer def customer_street customer.street end end @street = @invoice.customer_street They are stating that since you only use one dot, you are not breaking the Law of Demeter here. I think this is incorrect, because you are still going through customer to go through address to get the invoice's street. I primarily got this idea from a blog post I read: http://www.dan-manges.com/blog/37 In the blog post the prime example is class Wallet attr_accessor :cash end class Customer has_one :wallet # attribute delegation def cash @wallet.cash end end class Paperboy def collect_money(customer, due_amount) if customer.cash < due_ammount raise InsufficientFundsError else customer.cash -= due_amount @collected_amount += due_amount end end end The blog post states that although there is only one dot customer.cash instead of customer.wallet.cash, this code still violates the Law of Demeter. Now in the Paperboy collect_money method, we don't have two dots, we just have one in "customer.cash". Has this delegation solved our problem? Not at all. If we look at the behavior, a paperboy is still reaching directly into a customer's wallet to get cash out. EDIT I completely understand and agree that this is still a violation and I need to create a method in Wallet called withdraw that handles the payment for me and that I should call that method inside the Customer class. What I don't get is that according to this process, my first example still violates the Law of Demeter because Invoice is still reaching directly into Customer to get the street. Can somebody help me clear the confusion. I have been searching for the past 2 days trying to let this topic sink in, but it is still confusing.

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• Can the Abstract Factory pattern be considered as a case of polymorphism?

  - by rogcg

  I was looking for a pattern/solution that allows me call a method as a runtime exception in a group of different methods without using Reflection. I've recently become aware of the Abstract Factory Pattern. To me, it looks so much like polymorphism, and I thought it could be a case of polymorphism but without the super class WidgetFactory, as you can see in the example of the link above. Am I correct in this assumption?

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• What books/references are recommended on the subject of planning and developing efficient web sites [closed]

  - by Shakil

  Once I visited a site containing videos; a well-known web developer creating a site from scratch via planning(paper, software), management, designing then development. I bookmarked the site but unable to find it now. My question is : How to do web-development effectively? What books or videos are recommended ???(I tried google but unable to find useful books or videos). I want to learn how people does it. Can you share resources(books, videos, links) about this... Thanks in advance.. Note: I created a job site for my university project. It gave me huge pain. Thats why I want to learn efficient way. I know html, css, javascript, jquery, php[learning(mvc and framework not yet completed)], phpmyadmin.

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• Structuring cascading properties - parent only or parent + entire child graph?

  - by SB2055

  I have a Folder entity that can be Moderated by users. Folders can contain other folders. So I may have a structure like this: Folder 1 Folder 2 Folder 3 Folder 4 I have to decide how to implement Moderation for this entity. I've come up with two options: Option 1 When the user is given moderation privileges to Folder 1, define a moderator relationship between Folder 1 and User 1. No other relationships are added to the db. To determine if the user can moderate Folder 3, I check and see if User 1 is the moderator of any parent folders. This seems to alleviate some of the complexity of handling updates / moved entities / additions under Folder 1 after the relationship has been defined, and reverting the relationship means I only have to deal with one entity. Option 2 When the user is given moderation privileges to Folder 1, define a new relationship between User 1 and Folder 1, and all child entities down to the grandest of grandchildren when the relationship is created, and if it's ever removed, iterate back down the graph to remove the relationship. If I add something under Folder 2 after this relationship has been made, I just copy all Moderators into the new Entity. But when I need to show only the top-level Folders that a user is Moderating, I need to query all folders that have a parent folder that the user does not moderate, as opposed to option 1, where I just query any items that the user is moderating. I think it comes down to determining if users will be querying for all parent items more than they'll be querying child items... if so, then option 1 seems better. But I'm not sure. Is either approach better than the other? Why? Or is there another approach that's better than both? I'm using Entity Framework in case it matters.

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• Earliest use of Comments as Semantically Meaningful Things in a Program?

  - by Alan Storm

  In certain corners of the PHP meta-programming world, it's become fashionable to use PHPDoc comments as a mechanism for providing semantically meaningful information to a program. That is, other code will parse the doc blocks and do something significant with the information encoded in those comments. Doctrine's annotations and code generation are an example of this. What's the earliest (or some early) use of this technique? I have vague memories of some early java Design by Contract implementations doing similar things, but I'm not sure of those folks were inventing the technique, or if they got it from somewhere. Mainly asking so I can provide some historical context for PHP developers who haven't come across the technique before, and are distrustful of it because it seems a little crazy pants.

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• Is it wrong to use a boolean parameter to determine behavior?

  - by Ray

  I have seen a practice from time to time that "feels" wrong, but I can't quite articulate what is wrong about it. Or maybe it's just my prejudice. Here goes: A developer defines a method with a boolean as one of its parameters, and that method calls another, and so on, and eventually that boolean is used, solely to determine whether or not to take a certain action. This might be used, for example, to allow the action only if the user has certain rights, or perhaps if we are (or aren't) in test mode or batch mode or live mode, or perhaps only when the system is in a certain state. Well there is always another way to do it, whether by querying when it is time to take the action (rather than passing the parameter), or by having multiple versions of the method, or multiple implementations of the class, etc. My question isn't so much how to improve this, but rather whether or not it really is wrong (as I suspect), and if it is, what is wrong about it.

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• Implenting ActiveRecord with inheritance?

  - by King

  I recently converted an old application that was using XML files as the data store to use SQL instead. To avoid a lot of changes I basically created ActiveRecord style classes that inherited from the original business objects. For example SomeClassRecord :SomeClass //ID Property //Save method I then used this new class in place of the other one, because of polymorphism I didn't need to change any methods that took SomeClass as a parameter. Would this be considered 'Bad'? What would be a better alternative?

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• Combinatorial explosion of interfaces: How many is too many?

  - by mga

  I'm a relative newcomer to OOP, and I'm having a bit of trouble creating good designs when it comes to interfaces. Consider a class A with N public methods. There are a number of other classes, B, C, ..., each of which interacts with A in a different way, that is, accesses some subset (<= N) of A's methods. The maximum degree of encapsulation is achieved by implementing an interface of A for each other class, i.e. AInterfaceForB, AInterfaceForC, etc. However, if B, C, ... etc. also interact with A and with each other, then there will be a combinatorial explosion of interfaces (a maximum of n(n-1), to be precise), and the benefit of encapsulation becomes outweighed by a code-bloat. What is the best practice in this scenario? Is the whole idea of restricting access to a class's public functions in different ways for other different classes just silly altogether? One could imagine a language that explicitly allows for this sort of encapsulation (e.g. instead of declaring a function public, one could specify exactly which classes it is visible to); Since this is not a feature of C++, maybe it's misguided to try to do it through the back door with interaces?

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• Should I always encapsulate an internal data structure entirely?

  - by Prog

  Please consider this class: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThings(){ return things; } } This class exposes the array it uses to store data, to any client code interested. I did this in an app I'm working on. I had a ChordProgression class that stores a sequence of Chords (and does some other things). It had a Chord[] getChords() method that returned the array of chords. When the data structure had to change (from an array to an ArrayList), all client code broke. This made me think - maybe the following approach is better: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThing(int index){ return things[index]; } public int getDataSize(){ return things.length; } public void setThing(int index, Thing thing){ things[index] = thing; } } Instead of exposing the data structure itself, all of the operations offered by the data structure are now offered directly by the class enclosing it, using public methods that delegate to the data structure. When the data structure changes, only these methods have to change - but after they do, all client code still works. Note that collections more complex than arrays might require the enclosing class to implement even more than three methods just to access the internal data structure. Is this approach common? What do you think of this? What downsides does it have other? Is it reasonable to have the enclosing class implement at least three public methods just to delegate to the inner data structure?

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• Clarify the Single Responsibility Principle.

  - by dsimcha

  The Single Responsibility Principle states that a class should do one and only one thing. Some cases are pretty clear cut. Others, though, are difficult because what looks like "one thing" when viewed at a given level of abstraction may be multiple things when viewed at a lower level. I also fear that if the Single Responsibility Principle is honored at the lower levels, excessively decoupled, verbose ravioli code, where more lines are spent creating tiny classes for everything and plumbing information around than actually solving the problem at hand, can result. How would you describe what "one thing" means? What are some concrete signs that a class really does more than "one thing"?

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• Architecture Question

  - by katie77

  I am writing a rules/eligibility Module. I have 2 sets of data, one is the customer data and the other is the customer products data. Customer data to Customer products data is one to many. Now I have to go through a set of Eligibility rules for each of this Customer product data. For each customer products data, I can say the customer is eligible for that product or decline the eligibility and should move on to the next product record. So in all the rules, I need to have access to customer and customer product data(the particular record that the rules are being executed against). Since all the rules can either approve a product or decline a product, I created an interface with those 2 methods and is implementing the this interface for all the rules. I am passing the Customer data and one product data for all the rules (because rules should be executed on each row of customer product data). An Ideal situation would be having the customer and customer product data available for the rule instead of passing them to each rule. What is the best way of doing this in-terms of architecture?

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• Is this a pattern? Proxy/delegation of interface to existing concrete implementation

  - by Ian Newson

  I occasionally write code like this when I want to replace small parts of an existing implementation: public interface IFoo { void Bar(); } public class Foo : IFoo { public void Bar() { } } public class ProxyFoo : IFoo { private IFoo _Implementation; public ProxyFoo(IFoo implementation) { this._Implementation = implementation; } #region IFoo Members public void Bar() { this._Implementation.Bar(); } #endregion } This is a much smaller example than the real life cases in which I've used this pattern, but if implementing an existing interface or abstract class would require lots of code, most of which is already written, but I need to change a small part of the behaviour, then I will use this pattern. Is this a pattern or an anti pattern? If so, does it have a name and are there any well known pros and cons to this approach? Is there a better way to achieve the same result? Rewriting the interfaces and/or the concrete implementation is not normally an option as it will be provided by a third party library.

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• Use constructor or setter method?

  - by user633600

  I am working on a UI code where I have an Action class, something like this - public class MyAction extends Action { public MyAction() { setText("My Action Text"); setToolTip("My Action Tool tip"); setImage("Some Image"); } } When this Action class was created it was pretty much assumed that the Action class wont be customizable (in a sense- its text, tooltip or image will be not be changed anywhere in the code). Of late, now we are in need of changing the action text at some location in code. So I suggested my co-worker to remove the hardcoded action text from the constructor and accept it as an argument, so that everybody is forced to pass the action text. Something like this code below - public class MyAction extends Action { public MyAction(String actionText) { setText(actionText); setTooltip("My Action tool tip); setImage("My Image"); } } He however thinks that since setText() method belongs to base class. It can be flexibly used to pass the action text wherever action instance is created. That way, there is no need to change the existing MyAction class. So his code would look something like this. MyAction action = new MyAction(); //this creates action instance with the hardcoded text action.setText("User required new action text"); //overwrite the exisitng text. I am not sure if that is a correct way to deal with problem. I think in above mentioned case user is anyway going to change the text, so why not force him while constructing the action. The only benefit I see with the original code is that user can create Action class without much thinking about setting text.

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• Should interface only be used for behavior and not to show logical data grouped together?

  - by jags

  Should an interface only be used to specify certain behavior? Would it be wrong to use interface to group logically related data? To me it looks like we should not use interface to group logically related data as structure seems a better fit. A class may be used but class name should indicate something like DTO so that user gets the impression that class does not have any behavior. Please let me know if my assumption is correct. Also, are there any exceptions where interface can be used to group logically related data?

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• PHP I am pulling my hair out trying to find the best! [closed]

  - by darga33

  PULLING MY HAIR OUT I have heard of Martin Fowler's book PoEAA and the other book Head First OOA OOD but those are not in PHP. I DESPERATELY WANT TO READ THEM, but ONLY in PHP utilizing SOLID principles! Does anyone know of the absolute best, most recent PHP book that utilizes the SOLID principles and GRASP, and all the other best practices? I want to learn from the best possible source! Not beginner books! I already understand OOP. This seems like an almost impossible question to find the answer to and so I thought, hey, might as well post on stackexchange!! Surely someone out there must know!!!!!!!!!! Or if noone knows Maybe they know of an open source application that utilizes these principles that is relatively small that is not a framework. Something that I can go through every single class, and spend time understanding the insides and outs of how the program was developed. Thanks so much in advance! I really really really really appreciate it!

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• Is this a violation of the Liskov Substitution Principle?

  - by Paul T Davies

  Say we have a list of Task entities, and a ProjectTask sub type. Tasks can be closed at any time, except ProjectTasks which cannot be closed once they have a status of Started. The UI should ensure the option to close a started ProjectTask is never available, but some safeguards are present in the domain: public class Task { public Status Status { get; set; } public virtual void Close() { Status = Status.Closed; } } public ProjectTask : Task { public override void Close() { if (Status == Status.Started) throw new Exception("Cannot close a started Project Task"); base.Close(); } } Now when calling Close() on a Task, there is a chance the call will fail if it is a ProjectTask with the started status, when it wouldn't if it was a base Task. But this is the business requirements. It should fail. Can this be regarded as a violation?

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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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• Should single purpose utility app use a class

  - by jmoreno

  When writing a small utility app, that does just one thing, should that one thing be encapsulated in a seperate class, or just let it be part of whatever class/module is used to start the application? I.e. Main would consist of 2 or three lines calling the constructor and then the DoIt methods, nothing else. Or should Main be the DoIt method, with whatever functions it needs added to the main class? Asking because I want to get some alternative perspective, but couldn't find a similar question. If my google-fu is bad and there's a dup, please close.

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