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  • Is there a good design pattern for this messaging class?

    - by salonMonsters
    Is there a good design pattern for this? I want to create a messaging class. The class will be passed: the type of message (eg. signup, signup confirmation, password reminder etc) the client's id The class needs to then look up the client's messaging preferences in the db (whether they want communication by email, sms or both) Then depending on the client's preference it will format the message for the medium (short version for sms, long form for email) and send it through our mail or sms provider's API. Because the fact that we want to be able to change out email and sms providers if need be I wondered if the Command Pattern would be a good choice.

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  • Why should I declare a class as an abstract class?

    - by Pied Piper
    I know the syntax, rules applied to abstract class and I want know usage of an abstract class Abstract class can not be instantiated directly but can be extended by other class What is the advantage of doing so? How it is different from an Interface? I know that one class can implement multiple interfaces but can only extend one abstract class. Is that only difference between an interface and an abstract class? I am aware about usage of an Interface. I have learned that from Event delegation model of AWT in Java. In which situations I should declare class as an abstract class? What is benefits of that?

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  • Where can I learn about every OOP concept?

    - by Mel
    I'm looking for some material that can explain all the concepts related to OOP that doesn't deviate too much from the point. I want something short and understandable for a beginner. I know some of these can be found on wikipedia, but wikipedia is full of minor and sometimes big mistakes and I don't think that is the best choice for learning something. Where should I start ? Also, please don't recommend books of 1000 pages or such.

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  • Share Mulitple Classes as one dll or a lib with Mulitple Projects

    - by JNL
    Currently I have some shared class files(.cpp and .h) which I include them in around 20 Projects. Currently I have to include them in all of the projects. So if I get some business requirments and I change some of the shared(.cpp or .h) files I have to include them in all the 20 Projects which is kind of tedious. Is there a way where I can create a shared dll or library and include it all of my Projects. So if I have to change it, I just have to change it once and then just Add Reference to include that dll or library which contains all the shared(.cpp, .h) files. Any help/recommendations regarding the same, will be highly appreciated. I am using VS2012 for VC++.

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  • Setting up ASP.NET structure for code

    - by user1175327
    I've always coded in C# MVC3 when developing web applications. But now i wanted to learn a bit more about developing web sites with just ASP.NET. But now i'm wondering what a good setup for my code would be. For me, an MVC like pattern seems to be a good way to go. But obviously ASP.NET doesn't have any router and controller classes. So i guess people have a different way of setting up their code when they do ASP.NET. So i'm looking for more information on how to get started with this. So not really the basics of ASP.NET, but something that focuses on a good code setup. Any good tutorials/information about this/?

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  • Using PDO with MVC

    - by mister martin
    I asked this question at stackoverflow and received no response (closed as duplicate with no answer). I'm experimenting with OOP and I have the following basic MVC layout: class Model { // do database stuff } class View { public function load($filename, $data = array()) { if(!empty($data)) { extract($data); } require_once('views/header.php'); require_once("views/$filename"); require_once('views/footer.php'); } } class Controller { public $model; public $view; function __construct() { $this->model = new Model(); $this->view = new View(); // determine what page we're on $page = isset($_GET['view']) ? $_GET['view'] : 'home'; $this->display($page); } public function display($page) { switch($page) { case 'home': $this->view->load('home.php'); break; } } } These classes are brought together in my setup file: // start session session_start(); require_once('Model.php'); require_once('View.php'); require_once('Controller.php'); new Controller(); Now where do I place my database connection code and how do I pass the connection onto the model? try { $db = new PDO('mysql:host='.DB_HOST.';dbname='.DB_DATABASE.'', DB_USERNAME, DB_PASSWORD); $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); } catch(PDOException $err) { die($err->getMessage()); } I've read about Dependency Injection, factories and miscellaneous other design patterns talking about keeping SQL out of the model, but it's all over my head using abstract examples. Can someone please just show me a straight-forward practical example?

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  • Learning OO for a C Programmer

    - by Holysmoke
    I've been programming professionally in C, and only C, for around 10 years in a variety of roles. As would be normal to expect, I understand the idioms of the language fairly well and beyond that also some of the design nuances - which APIs to make public, who calls what, who does what, what is supposed to reentrant and so on. I grew up reading 'Writing Solid Code', it's early C edition, not the one based on C++. However, I've never ever programmed in an OO language. Now, I want to migrate to writing applications for iPhone (maybe android), so want to learn to use Objective-C and use it with a degree of competence fitting a professional programmer. How do I wrap my head around the OO stuff? What would be your smallest reading list suggestion to me. Is there a book that carries some sort of relatively real world example OO design Objective-C? Besides, the reading what source code would you recommend me to go through. How to learn OO paradigm using Objective-C?

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  • Defining formula through user interface in user form

    - by BriskLabs Pakistan
    I am a student and developing a simple assignment - windows form application in visual studio 2010. The application is suppose to construct formulas as per user requirement. The process: It has to pick data from columns of Microsoft Access database and the user should be able to pick the data by column name like we do in a drop down menu. and create reusable formulas in it ( configure it once and can change it again). followings are column titles from database that can be picked for example. e.g Col -1 : Marks in Maths Col -2 : Total Marks in Maths Col -3 : Marks in science Col -4 : Total marks in science Finally we should be able to construct any formula in the UI like (Col 1 + Col 3 ) / ( col 2 + col 4) = Formula 1 once this is formula is set saved and a name is assigned to it by user. he/she can use the formula and results shall appear in a window below. i.e He would be able to calculate his desired figures (formula) by only manipulating underlying data on the UI layer....choose the data for a period and apply the formula and get the answer Problem: It looks like I have to create an app where rules are set through UI....... this means no stored procedures are required in SQL.... please suggest the right approach.

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  • Learning good OOP design & unlearning some bad habits

    - by Nick
    I have been mostly a C programmer so far in my career with knowledge of C++. I rely on C++ mostly for the convenience STL provides and I hardly ever focus on good design practices. As I have started to look for a new job position, this bad habit of mine has come back to haunt me. During the interviews, I have been asked to design a problem (like chess, or some other scenario) using OOP and I doing really badly at that (I came to know this through feedback from one interview). I tried to google stuff and came up with so many opinions and related books that I don't know where to begin. I need a good through introduction to OOP design with which I can learn practical design, not just theory. Can you point me to any book which meets my requirements ? I prefer C++, but any other language is fine as long as I can pick-up good practices. Also, I know that books can only go so far. I would also appreciate any good practice project ideas that helped you learn and improve your OOP concepts. Thanks.

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  • What alternative is better to diagram this scenario?

    - by Mosty Mostacho
    I was creating and discussing a class diagram with a partner of mine. To simplify things, I've modify the real domain we're working on and made up the following diagram: Basically, a company works on constructions that are quite different one from each other but are still constructions. Note I've added one field for each class but there should be many more. Now, I thought this was the way to go but my partner told me that if in the future new construction classes appear we would have to modify the Company class, which is correct. So the new proposed class diagram would be this: Now I've been wondering: Should the fact that in no place of the application will there be mixed lists of planes and bridges affect the design in any way? When we have to list only planes for a company, how are we supposed to distinguish them from the other elements in the list without checking for their class names? Related to the previous question, is it correct to assume that this type of diagram should be high-level and this is something it shouldn't matter at this stage but rather be thought and decided at implementation time? Any comment will be appreciated.

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  • design for supporting entities with images

    - by brainydexter
    I have multiple entities like Hotels, Destination Cities etc which can contain images. The way I have my system setup right now is, I think of all the images belonging to this universal set (a table in the DB contains filePaths to all the images). When I have to add an image to an entity, I see if the entity exists in this universal set of images. If it exists, attach the reference to this image, else create a new image. E.g.: class ImageEntityHibernateDAO { public void addImageToEntity(IContainImage entity, String filePath, String title, String altText) { ImageEntity image = this.getImage(filePath); if (image == null) image = new ImageEntity(filePath, title, altText); getSession().beginTransaction(); entity.getImages().add(image); getSession().getTransaction().commit(); } } My question is: Earlier I had to write this code for each entity (and each entity would have a Set collection). So, instead of re-writing the same code, I created the following interface: public interface IContainImage { Set<ImageEntity> getImages(); } Entities which have image collections also implements IContainImage interface. Now, for any entity that needs to support adding Image functionality, all I have to invoke from the DAO looks something like this: // in DestinationDAO::addImageToDestination { imageDao.addImageToEntity(destination, imageFileName, imageTitle, imageAltText); // in HotelDAO::addImageToHotel { imageDao.addImageToEntity(hotel, imageFileName, imageTitle, imageAltText); It'd be great help if someone can provide me some critique on this design ? Are there any serious flaws that I'm not seeing right away ?

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  • Should I limit my type name suffix vocabulary when using OOP?

    - by Den
    My co-workers tend to think that it is better to limit non-domain type suffixes to a small fixed set of OOP-pattern inspired words, e.g.: *Service *Repository *Factory *Manager *Provider I believe there is no reason to not extend that set with more names, e.g. (some "translation" to the previous vocabulary is given in brackets): *Distributor (= *DistributionManager or *SendingService) *Generator *Browser (= *ReadonlyRepositoryService) *Processor *Manipulator (= *StateMachineManager) *Enricher (= *EnrichmentService) (*) denotes some domain word, e.g. "Order", "Student", "Item" etc. The domain is probably not complex enough to use specialized approaches such as DDD which could drive the naming.

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  • how should I design Objects around this business requirement?

    - by brainydexter
    This is the business requirement: " A Holiday Package (e.g. New York NY Holiday Package) can be offered in different ways based on the Origin city: From New Delhi to NY From Bombay to NY NY itself ( Land package ) (Bold implies default selection) a. and b. User can fly from either New Delhi or Bombay to NY. c. NY is a Land package, where a user can reach NY by himself and is a standalone holidayPackage. " Let's say I have a class that represents HolidayPackage, Destination (aka City). public class HolidayPackage{ Destination holidayCity; ArrayList<BaseHolidayPackageVariant> variants; BaseHolidayPackageVariant defaultVariant; } public abstract class BaseHolidayPackageVariant { private Integer variantId; private HolidayPackage holidayPackage; private String holidayPackageType; } public class LandHolidayPackageVariant extends BaseHolidayPackageVariant{ } public class FlightHolidayPackageVariant extends BaseHolidayPackageVariant{ private Destination originCity; } What data structure/objects should I design to support: options a default within those options Sidenote: A HolidayPackage can also be offered in different ways based on Hotel selections. I'd like to follow a design which I can leverage to support that use case in the future. This is the backend design I have in mind.

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  • Inheritance vs containment while extending a large legacy project

    - by Flot2011
    I have got a legacy Java project with a lot of code. The code uses MVC pattern and is well structured and well written. It also has a lot of unit tests and it is still actively maintained (bug fixing, minor features adding). Therefore I want to preserve the original structure and code style as much as possible. The new feature I am going to add is a conceptual one, so I have to make my changes all over the code. In order to minimize changes I decided not to extend existing classes but to use containment: class ExistingClass { // .... existing code // my code adding new functionality private ExistingClassExtension extension = new ExistingClassExtension(); public ExistingClassExtension getExtension() {return extension;} } ... // somewhere in code ExistingClass instance = new ExistingClass(); ... // when I need a new functionality instance.getExtension().newMethod1(); All functionality that I am adding is inside a new ExistingClassExtension class. Actually I am adding only these 2 lines to each class that needs to be extended. By doing so I also do not need to instantiate new, extended classes all over the code and I may use existing tests to make sure there is no regression. However my colleagues argue that in this situation doing so isn't a proper OOP approach, and I need to inherit from ExistingClass in order to add a new functionality. What do you think? I am aware of numerous inheritance/containment questions here, but I think my question is different.

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  • Fitting an established site into a CI framework

    - by David
    I manage a rather large, feature full nightmare of a site which has no end of feature creep settings/options/etc. Up to now its been coded in a procedural/functional way and would like to move to an OO,MVC setup. I'm quite new to it all but have done alot of research and feel that CodeIgniter is a code choice of framework to use to help quicken the transfer. Before looking at a framework, I started constructing a list of objects to create classes out of: photos users forum topics forums blogs blog posts comments The trouble I have now, is I do understand where these generic/universal objects fall into the CI MVC setup. What is the best way to organise this kind of stuff? These classes can generally be used on multiple models/views/controllers.

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  • Java word scramble game [closed]

    - by Dan
    I'm working on code for a word scramble game in Java. I know the code itself is full of bugs right now, but my main focus is getting a vector of strings broken into two separate vectors containing hints and words. The text file that the strings are taken from has a colon separating them. So here is what I have so far. public WordApp() { inputRow = new TextInputBox(); inputRow.setLocation(200,100); phrases = new Vector <String>(FileUtilities.getStrings()); v_hints = new Vector<String>(); v_words = new Vector<String>(); textBox = new TextBox(200,100); textBox.setLocation(200,200); textBox.setText(scrambled + "\n\n Time Left: \t" + seconds/10 + "\n Score: \t" + score); hintBox = new TextBox(200,200); hintBox.setLocation(300,400); hintBox.hide(); Iterator <String> categorize = phrases.iterator(); while(categorize.hasNext()) { int index = phrases.indexOf(":"); String element = categorize.next(); v_words.add(element.substring(0,index)); v_hints.add(element.substring(index +1)); phrases.remove(index); System.out.print(index); } The FileUtilities file was given to us by the pofessor, here it is. import java.util.*; import java.io.*; public class FileUtilities { private static final String FILE_NAME = "javawords.txt"; //------------------ getStrings ------------------------- // // returns a Vector of Strings // Each string is of the form: word:hint // where word contains no spaces. // The words and hints are read from FILE_NAME // // public static Vector<String> getStrings ( ) { Vector<String> words = new Vector<String>(); File file = new File( FILE_NAME ); Scanner scanFile; try { scanFile = new Scanner( file); } catch ( IOException e) { System.err.println( "LineInput Error: " + e.getMessage() ); return null; } while ( scanFile.hasNextLine() ) { // read the word and follow it by a colon String s = scanFile.nextLine().trim().toUpperCase() + ":"; if( s.length()>1 && scanFile.hasNextLine() ) { // append the hint and add to collection s+= scanFile.nextLine().trim(); words.add(s); } } // shuffle Collections.shuffle(words); return words; } }

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  • nagios3 Error: Could not read object configuration data!

    - by user1493730
    I have a brand new install of nagios3 on ubuntu 12.04. After I log in to the web interface and click any link I get the error: Error: Could not read object configuration data! Here are some things you should check in order to resolve this error: Verify configuration options using the -v command-line option to check for errors. Check the Nagios log file for messages relating to startup or status data errors. I ran it with the -v option and it reported no errors: Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check The nagios log and apache error log and debug log all have nothing regarding this. Does anyone know how to turn on logging that will give me some kind of useful error? Or if anyone knows how to fix this specific problem without additional logging, I guess that's okay too. Thanks!

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  • Paradigms fit for UI programming

    - by Inca
    This is a more specific question (or actually two, but they are related) coming from the comments of OOP technology death where someone stated that OOP is not the right paradigm for GUI programming. Reading the comments there and here I still have the feeling there are things to learn: which programming paradigms are considered good fits and why are they better than others (perhaps with examples to illustrate?) I removed the tk-example from the title and question

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  • Are injectable classes allowed to have constructor parameters in DI?

    - by Songo
    Given the following code: class ClientClass{ public function print(){ //some code to calculate $inputString $parser= new Parser($inputString); $result= $parser->parse(); } } class Parser{ private $inputString; public __construct($inputString){ $this->inputString=$inputString; } public function parse(){ //some code } } Now the ClientClass has dependency on class Parser. However, if I wanted to use Dependency Injection for unit testing it would cause a problem because now I can't send the input string to the parser constructor like before as its calculated inside ClientCalss itself: class ClientClass{ private $parser; public __construct(Parser $parser){ $this->parser=$parser; } public function print(){ //some code to calculate $inputString $result= $this->parser->parse(); //--> will throw an exception since no string was provided } } The only solution I found was to modify all my classes that took parameters in their constructors to utilize Setters instead (example: setInputString()). However, I think there might be a better solution than this because sometimes modifying existing classes can cause much harm than benefit. So, Are injectable classes not allowed to have input parameters? If a class must take input parameters in its constructor, what would be the way to inject it properly? UPDATE Just for clarification, the problem happens when in my production code I decide to do this: $clientClass= new ClientClass(new Parser($inputString));//--->I have no way to predict $inputString as it is calculated inside `ClientClass` itself. UPDATE 2 Again for clarification, I'm trying to find a general solution to the problem not for this example code only because some of my classes have 2, 3 or 4 parameters in their constructors not only one.

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  • Law of Demeter confusion [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. 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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  • Fetching database query through function

    - by Shubham Maurya
    I am sick of connecting database in each script i need a more OOP approach to fetching database results. ex like wordpress use wpdb class to fetch results. This what wordpress does to get data <?php $posts = $wpdb->get_results("SELECT ID, post_title FROM $wpdb->posts WHERE post_status = 'publish' AND post_type='post' ORDER BY comment_count DESC LIMIT 0,4") ?> How can i create the same feature too using any class or function and use it in my script Thank you

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  • Handling Types for Real and Complex Matrices in a BLAS Wrapper

    - by mga
    I come from a C background and I'm now learning OOP with C++. As an exercise (so please don't just say "this already exists"), I want to implement a wrapper for BLAS that will let the user write matrix algebra in an intuitive way (e.g. similar to MATLAB) e.g.: A = B*C*D.Inverse() + E.Transpose(); My problem is how to go about dealing with real (R) and complex (C) matrices, because of C++'s "curse" of letting you do the same thing in N different ways. I do have a clear idea of what it should look like to the user: s/he should be able to define the two separately, but operations would return a type depending on the types of the operands (R*R = R, C*C = C, R*C = C*R = C). Additionally R can be cast into C and vice versa (just by setting the imaginary parts to 0). I have considered the following options: As a real number is a special case of a complex number, inherit CMatrix from RMatrix. I quickly dismissed this as the two would have to return different types for the same getter function. Inherit RMatrix and CMatrix from Matrix. However, I can't really think of any common code that would go into Matrix (because of the different return types). Templates. Declare Matrix<T> and declare the getter function as T Get(int i, int j), and operator functions as Matrix *(Matrix RHS). Then specialize Matrix<double> and Matrix<complex>, and overload the functions. Then I couldn't really see what I would gain with templates, so why not just define RMatrix and CMatrix separately from each other, and then overload functions as necessary? Although this last option makes sense to me, there's an annoying voice inside my head saying this is not elegant, because the two are clearly related. Perhaps I'm missing an appropriate design pattern? So I guess what I'm looking for is either absolution for doing this, or advice on how to do better.

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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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  • 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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  • Does FP mess up your OOP skills?

    - by bonomo
    I've been learning functional programming in Haskell and F# for awhile and now when I got some skills it gets harder for me to think in OOP way and program in C# and JavaScript. Everything seems to be ass-backwards there with classes, interfaces, objects and I often stare at the screen trying to think of a better way around without using them. This is something that scares me, because I didn't have problems like that before (not knowing that the same stuff can be done in a different way). So I am concerned as I don't want to loose myself as a OOP developer, because this is what I do for living. Is it a normal thing? Shall I rather stop doing FP? How did you manage to cope with it?

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