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  • a completely decoupled OO system ?

    - by shrini1000
    To make an OO system as decoupled as possible, I'm thinking of the following approach: 1) we run an RMI/directory like service where objects can register and discover each other. They talk to this service through an interface 2) we run a messaging service to which objects can publish messages, and register subscription callbacks. Again, this happens through interfaces 3) when object A wants to invoke a method on object B, it discovers the target object's unique identity through #1 above, and publishes a message on the message service for object B 4) message services invokes B's callback to give it the message 5) B processes the request and sends the response for A on message service 6) A's callback is called and it gets the response. I feel this system is as decoupled as practically possible, but it has the following problems: 1) communication is typically asynchronous 2) hence it's non real time 3) the system as a whole is less efficient. Are there any other practical problems where this design obviously won't be applicable ? What are your thoughts on this design in general ?

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  • Implementation Details as a "Document" ( In generic terms) - Python, C++

    - by mgj
    Hi..:) For documentation and presentation purposes, we often find professionals/students creating SRS, coding guidelines etc. for these things there is some kind of a checklist which one could use to appropriately match what could relate to a specific case and accordingly one does a documentation for each. On those grounds could you please give me some sort of a checklist( any points/guidelines) one could use for going about Implementation( in the form of Implementation Details) in Python and C++ . Although this might sound specific as the query is "Implementation Details" and is different for different cases as one goes about the REAL implementation, I just want a SET of guidelines one should follow ( Preferably In Python, C++ specific, even for any other language is Welcome) if this( Implementation Details ) has to also be documented or presented. Hope the question is clear, I am sorry if it still sounds ambiguous, I guess this is the best I could do to frame my query. Thank you for your time...:)

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  • Designing a chain of states

    - by devoured elysium
    I want to model a kind of FSM(Finite State Machine). I have a sequence of states (let's say, from StateA to StateZ). This sequence is called a Chain and is implemented internally as a List. I will add states by the order I want them to run. My purpose is to be able to make a sequence of actions in my computer (for example, mouse clicks). (I know this has been done a zillion times). So a state is defined as a: boolean Precondition() <- Checks to see if for this state, some condition is true. For example, if I want to click in the Record button of a program, in this method I would check if the program's process is running or not. If it is, go to the next state in the chain list, otherwise, go to what was defined as the fail state (generally is the first state of them all). IState GetNextState() <- Returns the next state to evaluate. If Precondition() was sucessful, it should yield the next state in the chain otherwise it should yield the fail state. Run() Simply checks the Precondition() and sets the internal data so GetNextState() works as expected. So, a naive approach to this would be something like this: Chain chain = new Chain(); //chain.AddState(new State(Precondition, FailState, NextState) <- Method structure chain.AddState(new State(new WinampIsOpenCondition(), null, new <problem here, I want to referr to a state that still wasn't defined!>); The big problem is that I want to make a reference to a State that at this point still wasn't defined. I could circumvent the problem by using strings when refrering to states and using an internal hashtable, but isn't there a clearer alternative? I could just pass only the pre-condition and failure states in the constructor, having the chain just before execution put in each state the correct next state in a public property but that seems kind of awkward.

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  • Does OOP make sense for small scripts?

    - by Fabian
    I mostly write small scripts in python, about 50 - 250 lines of code. I usually don't use any objects, just straightforward procedural programming. I know OOP basics and I have used object in other programming languages before, but for small scripts I don't see how objects would improve them. But maybe that is just my limited experience with OOP. Am I missing something by not trying harder to use objects, or does OOP just not make a lot of sense for small scripts?

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  • Inheritence and usage of dynamic_cast

    - by Mewzer
    Hello, Suppose I have 3 classes as follows (as this is an example, it will not compile!): class Base { public: Base(){} virtual ~Base(){} virtual void DoSomething() = 0; virtual void DoSomethingElse() = 0; }; class Derived1 { public: Derived1(){} virtual ~Derived1(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD1DoSomething{ ... } }; class Derived2 { public: Derived2(){} virtual ~Derived2(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD2DoSomething{ ... } }; I want to create an instance of Derived1 or Derived2 depending on some setting that is not available until run-time. As I cannot determine the derived type until run-time, then do you think the following is bad practice?... class X { public: .... void GetConfigurationValue() { .... // Get configuration setting, I need a "Derived1" b = new Derived1(); // Now I want to call the special DoSomething for Derived1 (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething(); } private: Base* b; }; I have generally read that usage of dynamic_cast is bad, but as I said, I don't know which type to create until run-time. Please help!

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  • Is it possible to create an enum whose object can't be created but can be used for readonly purpose

    - by Shantanu Gupta
    I created an enum where I stored some table names. I want it to be used to get the name of the table like ds.Tables[BGuestInfo.TableName.L_GUEST_TYPE.ToString()]. public enum TableName : byte { L_GUEST_TYPE = 0 ,L_AGE_GROUP = 1 ,M_COMPANY = 2 ,L_COUNTRY = 3 ,L_EYE_COLOR = 4 ,L_GENDER = 5 ,L_HAIR_COLOR = 6 ,L_STATE_PROVINCE = 7 ,L_STATUS = 8 ,L_TITLE = 9 ,M_TOWER = 10 ,L_CITY = 11 ,L_REGISTER_TYPE = 12 } This is my enum. Now I have not created any object of this enum so that no one can use it for other than read only purpose. For this enum to be accessible in outer classes as well I have to make it public which means some outer class can create its object as well. So what can i do so as to restrict its object creation.

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  • Rails architecture questions

    - by justinbach
    I'm building a Rails site that, among other things, allows users to build their own recipe repository. Recipes are entered either manually or via a link to another site (think epicurious, cooks.com, etc). I'm writing scripts that will scrape a recipe from these sites given a link from a user, and so far (legal issues notwithstanding) that part isn't giving me any trouble. However, I'm not sure where to put the code that I'm writing for these scraper scripts. My first thought was to put it in the recipes model, but it seems a bit too involved to go there; would a library or a helper be more appropriate? Also, as I mentioned, I'm building several different scrapers for different food websites. It seems to me that the elegant way to do this would be to define an interface (or abstract base class) that determines a set of methods for constructing a recipe object given a link, but I'm not sure what the best approach would be here, either. How might I build out these OO relationships, and where should the code go?

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  • PHP string to object name.

    - by Smickie
    Ok I have a string... $a_string = "Product"; and I want to use this string in a call to a object like this: $this->$a_string->some_function(); How the dickens do I dynamically call that object? (don't think Im on php 5 mind)

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  • How do i free objects in C#

    - by assassin
    Hi, Can anyone please tell me how I can free objects in C#? For example, I have an object: Object obj1 = new Object(); //Some code using obj1 //Here I would like to free obj1, after it is no longer required and also more importantly its scope is the full run time of the program. Thanks for all your help

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  • Passing a string when starting a class in PHP

    - by Francesc
    Hi. First I have to say: Happy Christmas to All! I'm starting learning classes in PHP. I coded that: class User { function getFbId($authtoken) { } function getFbFirstName ($authtoken) { } } What I want to do is something like that: $user=new User($authtoken); And pass the $authtoken to the class. It's possible to define that when starting the class. It's possible to retrive that value inside a function of that class?

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  • Stupid java question: Is it a method?

    - by Stefan
    Hello, I'm no Java guy, so I ask myself what this means: public Button(Light light) { this.light = light; } Is Button a method? I ask myself, because it takes an input parameter light. But if it was a method, why would it begin with a capital letter and has no return data type? Here comes the full example: public class Button { private Light light; public Button(Light light) { this.light = light; } public void press() { light.turnOn(); } } I know, this question is really trivial. However, I have nothing to do with Java and haven't found a description for the Button thing above. I'm just interested.

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  • When to define SDD operations System->Actor?

    - by devoured elysium
    I am having some trouble understanding how to make SDDs, as I don't fully grasp why in some cases one should define operations for System - Actor and in others don't. Here is an example: 1) The User tells the System that wants to buy some tickets, stating his client number. 2) The System confirms that the given client number is valid. 3) The User tells the System the movie that wants to see. 4) The System shows the set of available sessions and seats for that movie. 5) The System asks the user which session/seat he wants. 6) The user tells the System the chosen session/seat. This would be converted to: a) -----> tellClientNumber(clientNumber) b) <----- validClientNumber c) -----> tellMovieToSee(movie) d) <----- showsAvailableSeatsHours e) -----> tellSystemChosenSessionSeat(session, seat) I know that when we are dealing with SDD's we are still far away from coding. But I can't help trying to imagine how it how it would have been had I to convert it right away to code: I can understand 1) and 2). It's like if it was a C#/Java method with the following signature: boolean tellClientNumber(clientNumber) so I put both on the SDD. Then, we have the pair 3) 4). I can imagine that as something as: SomeDataStructureThatHoldsAvailableSessionsSeats tellSystemMovieToSee(movie) Now, the problem: From what I've come to understand, my lecturer says that we shouldn't make an operation on the SDD for 5) as we should only show operations from the Actor to the System and when the System is either presenting us data (as in c)) or validating sent data (such as in b)). I find this odd, as if I try to imagine this like a DOS app where you have to put your input sequencially, it makes sense to make an arrow even for 5). Why is this wrong? How should I try to visualize this? Thanks

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  • How to amend return value design in OO manner?

    - by FrontierPsycho
    Hello. I am no newb on OO programming, but I am faced with a puzzling situation. I have been given a program to work on and extend, but the previous developers didn't seem that comfortable with OO, it seems they either had a C background or an unclear understanding of OO. Now, I don't suggest I am a better developer, I just think that I can spot some common OO errors. The difficult task is how to amend them. In my case, I see a lot of this: if (ret == 1) { out.print("yadda yadda"); } else if (ret == 2) { out.print("yadda yadda"); } else if (ret == 3) { out.print("yadda yadda"); } else if (ret == 0) { out.print("yadda yadda"); } else if (ret == 5) { out.print("yadda yadda"); } else if (ret == 6) { out.print("yadda yadda"); } else if (ret == 7) { out.print("yadda yadda"); } ret is a value returned by a function, in which all Exceptions are swallowed, and in the catch blocks, the above values are returned explicitly. Oftentimes, the Exceptions are simply swallowed, with empty catch blocks. It's obvious that swalllowing exceptions is wrong OO design. My question concerns the use of return values. I believe that too is wrong, however I think that using Exceptions for control flow is equally wrong, and I can't think of anything to replace the above in a correct, OO manner. Your input, please?

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  • Pattern for iPhone background loading during init?

    - by Rob S.
    Hi everyone, I'm currently kicking off a background thread to do some REST queries in my app delegate's didFinishLaunchingWithOptions. This thread creates some objects and populates the model as the rest of the app continues to load (because I don't block, and didFinishLaunchingWithOptions returns YES). I also put up a loading UIViewController 'on top' of the main view that I tear down after the background initialization is complete. My problem is that I need to notify the first view (call it the Home view) that the model is ready, and that it should populate itself. The trick is that the background download could have finished before Home.viewDidAppear is called, or any of the other Home.initX methods. I'm having difficulty synchronizing all of this and I've thought about it long enough that it feels like I'm barking up the wrong tree. Are there any patterns here for this sort of thing? I'm sure other apps start by performing lengthy operations with loading screens :) Thanks!

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  • PHP 5 functioning returning an array- interaction without assignment?

    - by Lee
    I'm wondering if this kind of thing will ever be possible in PHP (and whether it already is and I'm just missing something...) <?php function test() { return array( 'id'=>10, 'name'=>'John' ); } echo 'Your name is: '.test()['name']; ?> I'd really like to be able to use returned arrays directly instead of first assigning them to a var... possible?

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  • How to document a Symfony based REST API (similar to enunciate's documentation capabilities)

    - by Dominic
    If I have a REST based service written in the Symfony [symfony-project.org] framework (i.e. PHP), is there any decent tools/frameworks out there that will parse my code and generate API documentation? The Java based framework enunciate has documentation capabilities similar to what I need, you can view an example of this here: http://enunciate.codehaus.org/wannabecool/step1/index.html. I understand the premise of REST based services are supposed to be self evident, however I was after something that would generate this documentation for me without the need to manually write up all my endpoints, supported formats, sample output etc. Thanks

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  • inspect the parameters to "use", and pass on the rest?

    - by JoelFan
    I have a Perl module and I'd like to be able to pick out the parameters that my my module's user passed in the "use" call. Whichever ones I don't recognize I'd like to pass on. I tried to do this by overriding the "import" method but I'm not having much luck. EDIT: To clarify, as it is, I can use my module like this: use MyModule qw/foo bar/; which will import the foo and bar methods of MyModule. But I want to be able to say: use MyModule qw/foo doSpecialStuff bar/; and look for doSpecialStuff to check if I need to do some special stuff at the beginning of the program, then pass qw/foo bar/ to the Exporter's import

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  • How should I handle expected errors? eg. "username already exists"

    - by Pheter
    I am struggling to understand how I should design the error handling parts of my code. I recently asked a similar question about how I should go about returning server error codes to the user, eg. 404 errors. I learnt that I should handle the error from within the current part of the application; seem's simple enough. However, what should I do when I can't handle the error from the current link in the chain? For example, I may have a class that is used to manage authentication. One of it's methods could be createUser($username, $password). Within that function, I need to determine if the username already exists. If this is true, how should I alert the calling code about this? Returning null instead of a user object is one way. But how do I then know what caused the error? How should I handle errors in such a way that calling code can easily find out what caused the error? Is there a design pattern commonly used for this kind of situation?

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  • Recommendation for tool/framework that follows the naked objects pattern?

    - by Marcus Munzert
    I am searching for a tool/framework that follows the naked objects pattern and is written in Java. I know about tools like for instance JMatter, Naked Objects and Domain Object Explorer. That's not exactly what I am searching for, though. Open source would be great, but doesn't need to be. My intention is to use that tool/framework for the purpose of model-driven software development to do the modeling part. Ideally, such a tool/framework would provide the option to use JPA to store/load objects.

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  • Inheritance from static classes? why not?

    - by Sorush Rabiee
    Hi Why inheritance is not provided for static classes in C#? I know C# has a good reason for everything he implements or doesn't implement. I just wondered, what’s that “good reason” here? semantically, what would be happened if I was able to write a static class that inheritances from another static one? is this an ODD issue? or just programming?

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  • What could possibly cause this error(when declaring an object inside a class) ? //noobie question

    - by M4design
    I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info' I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. Thanks. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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  • PHP Access property of a class from within a class instantiated in the original class.

    - by Iain
    I'm not certain how to explain this with the correct terms so maybe an example is the best method... $master = new MasterClass(); $master->doStuff(); class MasterClass { var $a; var $b; var $c; var $eventProccer; function MasterClass() { $this->a = 1; $this->eventProccer = new EventProcess(); } function printCurrent() { echo '<br>'.$this->a.'<br>'; } function doStuff() { $this->printCurrent(); $this->eventProccer->DoSomething(); $this->printCurrent(); } } class EventProcess { function EventProcess() {} function DoSomething() { // trying to access and change the parent class' a,b,c properties } } My problem is i'm not certain how to access the properties of the MasterClass from within the EventProcess-DoSomething() method? I would need to access, perform operations on and update the properties. The a,b,c properties will be quite large arrays and the DoSomething() method would be called many times during the execuction of the script. Any help or pointers would be much appreciated :)

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