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  • Query something and return the reason if nothing has been found

    - by Daniel Hilgarth
    Assume I have a Query - as in CQS that is supposed to return a single value. Let's assume that the case that no value is found is not exceptional, so no exception will be thrown in this case. Instead, null is returned. However, if no value has been found, I need to act according to the reason why no value has been found. Assuming that the Query knows the reason, how would I communicate it to the caller of the Query? A simple solution would be not return the value directly but a container object that contains the value and the reason: public class QueryResult { public TValue Value { get; private set; } public TReason ReasonForNoValue { get; private set; } } But that feels clumsy, because if a value is found, ReasonForNoValue makes no sense and if no value has been found, Value makes no sense. What other options do I have to communicate the reason? What do you think of one event per reason? For reference: This is going to be implemented in C#.

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  • DDD / Layers and legacy systems

    - by CSM
    I have to refactor a complex C# app (many dialogs, mixed logic and so on). There is a part managing the communication with special hardware equipments (sending commands and receive data via asynchronous c# callbacks). The code is "spaghetti" with mixed UI/Logic/Communication/etc and my task is to split the layers in a DDD sense. So, to which layer belongs a callback driver routine? The callbacks are creating "bubbles" in the system, up to the UI layer and because of this I cannot enforce the essential principle that any element of a layer depends only on other elements in the same layer or on elements of the layers "beneath" it. Thank you in advance.

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  • What programming concept is used in Nokia Lumina City Lens application [closed]

    - by gowri
    I am totally impressed about the Nokia City Lens application. How does the Nokia Lumia City Lens app work? Nokia Lumia City Lens app detects shops, restaurants, etc. by scanning the visual environment. But how can it detect shops or anything by only scanning visual information? Because we need a 360 degree view to detect a location. Because we can't simply match visual information and get that data. The visuals will change proportionally with distance and angle. So how does this app match the location and retrieve the information? Can anyone explain the concept What technology or algorithm is used in this app?

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  • Mobile Multiplayer games and coping with high latency

    - by spaceOwl
    I'm currently researching regarding a design for an online (realtime) mobile multiplayer game. As such, i'm taking into consideration that latencies (lag) is going to be high (perhaps higher than PC/consoles). I'd like to know if there are ways to overcome this or minimize the issues of high latency? The model i'll be using is peer-to-peer (using Photon cloud to broadcast messages to all other players). How do i deal with a scenario where a message about a local object's state at time t will only get to other players at *t + HUGE_LAG* ?

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  • Writing Game Engine from scratch with OpenGL [on hold]

    - by Wazery
    I want to start writing my game engine from scratch for learning purpose, what is the prerequisites and how to do that, what programming languages and things you recommend me? Also if you have good articles and books on that it will be great. Thanks in advance! My Programming languages and tools are: C/C++ is it good to use only C? Python OpenGL Git GDB What I want to learn from it: Core Game Engine Rendering / Graphics Game Play/Rules Input (keyboard/mouse/controllers, etc) In Rendering/Graphics: 3D Shading Lighting Texturing

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  • Do you leverage the benefits of the open-closed principle?

    - by Kaleb Pederson
    The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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  • Service Layer - how broad should it be, and should it also be on the local application?

    - by BornToCode
    Background: I need to build a desktop application with some operations (CRUD and more) (=winforms), I need to make another application which will re-use some of the functions of the main application (=webforms). I understood that using service layer is the best approach here. If I understood correctly the service should be calling the function on the BL layer (correct me if I'm wrong) The dilemma: In my main winform UI - should I call the functions from the BL, or from the service? (please explain why) Should I create a service for every single function on the BL even if I need some of the functions only in one UI? for example - should I create services for all the CRUD operations, even though I need to re-use only update operation in the webform? YOUR HELP IS MUCH APPRECIATED

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  • Entity system in Lua, communication with C++ and level editor. Need advice.

    - by Notbad
    Hi!, I know this is a really difficult subject. I have been reading a lot this days about Entity systems, etc... And now I'm ready to ask some questions (if you don't mind answering them) because I'm really messed. First of all, I have a 2D basic editor written in Qt, and I'm in the process of adding entitiy edition. I want the editor to be able to receive RTTI information from entities to change properties, create some logic being able to link published events to published actions (Ex:A level activate event throws a door open action), etc... Because all of this I guess my entity system should be written in scripting, in my case Lua. In the other hand I want to use a component based design for my entities, and here starts my questions: 1) Should I define my componentes en C++? If I do this en C++ won't I loose all the RTTI information I want for my editor?. In the other hand, I use box2d for physics, if I define all my components in script won't it be a lot of work to expose third party libs to lua? 2) Where should I place the messa system for my game engine? Lua? C++?. I'm tempted to just have C++ object to behave as servers, offering services to lua business logic. Things like physics system, rendering system, input system, World class, etc... And for all the other things, lua. Creation/Composition of entities based on components, game logic, etc... Could anyone give any insight on how to accomplish this? And what aproach is better?. Thanks in advance, HexDump.

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  • What common interface would be appropriate for these game object classes?

    - by Jefffrey
    Question A component based system's goal is to solve the problems that derives from inheritance: for example the fact that some parts of the code (that are called components) are reused by very different classes that, hypothetically, would lie in a very different branch of the inheritance tree. That's a very nice concept, but I've found out that CBS is often hard to accomplish without using ugly hacks. Implementations of this system are often far from clean. But I don't want to discuss this any further. My question is: how can I solve the same problems a CBS try to solve with a very clean interface? (possibly with examples, there are a lot of abstract talks about the "perfect" design already). Context Here's an example I was going for before realizing I was just reinventing inheritance again: class Human { public: Position position; Movement movement; Sprite sprite; // other human specific components }; class Zombie { Position position; Movement movement; Sprite sprite; // other zombie specific components }; After writing that I realized I needed an interface, otherwise I would have needed N containers for N different types of objects (or to use boost::variant to gather them all together). So I've thought of polymorphism (move what systems do in a CBS design into class specific functions): class Entity { public: virtual void on_event(Event) {} // not pure virtual on purpose virtual void on_update(World) {} virtual void on_draw(Window) {} }; class Human : public Entity { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; class Zombie : public Entity { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; Which was nice, except for the fact that now the outside world would not even be able to know where a Human is positioned (it does not have access to its position member). That would be useful to track the player position for collision detection or if on_update the Zombie would want to track down its nearest human to move towards him. So I added const Position& get_position() const; to both the Zombie and Human classes. And then I realized that both functionality were shared, so it should have gone to the common base class: Entity. Do you notice anything? Yes, with that methodology I would have a god Entity class full of common functionality (which is the thing I was trying to avoid in the first place). Meaning of "hacks" in the implementation I'm referring to I'm talking about the implementations that defines Entities as simple IDs to which components are dynamically attached. Their implementation can vary from C-stylish: int last_id; Position* positions[MAX_ENTITIES]; Movement* movements[MAX_ENTITIES]; Where positions[i], movements[i], component[i], ... make up the entity. Or to more C++-style: int last_id; std::map<int, Position> positions; std::map<int, Movement> movements; From which systems can detect if an entity/id can have attached components.

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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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  • prism and multiple screens

    - by Avi
    OK - I am studying Prism a little because of a "free weekend" offer on Pluralsight. As this is proving too complex for me, I went to the Prism book and looked at the forward, and this is what it said: What comes after “Hello, World?” WPF and Silverlight developers are blessed with an abundance of excellent books... There’s no lack of tutorials on Model-View-ViewModel ... But they stop short of the guidance you need to deliver a non-trivial application in full. Your first screen goes well. You add a second screen and a third. Because you started your solution with the built-in “Navigation Application Template,” adding new screens feels like hanging shirts on a closet rod. You are on a roll. Until the harsh reality of real application requirements sets in. As it happens, your application has 30 screens not three. There’s no room on that closet rod for 30 screens. Some screens are modal pop-ups; you don’t navigate to a pop-up. Screens become interdependent such that user activity in one screen triggers changes that propagate throughout the UI. Some screens are optional; others are visible only to authorized users. Some screens are permanent, while other screens can be opened and closed at will. You discover that navigating back to a previously displayed screen creates a new instance. That’s not what you expected and, to your horror, the prior instance is gone along with the user’s unsaved changes. Now the issue is, I don't relate to this description. I've never been a UI programmer, but same as everyone else I'm using Windows apps such as MS-Office, and web sites such as Amazon, Facebook and StackExchange. And I look at these and I don't see many "so many screens" issues! Indeed, the only applications having many windows I can think of is Visual Studio. Maybe also Visio, a little. But take Word - You have a ribbon and a main window. Or take Facebook: You have those lists on the left (Favorites, Lists, Groups etc.), the status middle, the adds and then the Contacts sidebar. But it's only one page. Of course, I understand that in enterprise scenarios there are dashboad applications where multiple segments of the screen are updated from multiple non-related services. This I dig. But other scenarios? So - What am I missing? What is the "multiple screens" monster Pirsm is supposed to be the silver bullet solution for? Shoud I invest in studying Prism in addition to learning WPF or ASP.NET MVC?

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  • Multiple objects listening for the same key press

    - by xiaohouzi79
    I want to learn the best way to implement this: I have a hero and an enemy on the screen. Say the hero presses "k" to get out a knife, I want the enemy to react in a certain way. Now, if in my game loop I have a listener for the key press event and I identify a "k" was pressed, the quick and easy way would be to do: // If K pressed // hero.getOoutKnife() // enemy.getAngry() But what is commonly done in more complex games, where say I have 10 types of character on screen and they all need to react in a unique way when the letter "k" is pressed? I can think of a bunch of hacky ways to do this, but would love to know how it should be done properly. I am using C++, but I'm not looking for a code implementation, just some ideas on how it should be done the right way.

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  • How should I architect a personal schedule manager that runs 24/7?

    - by Crawford Comeaux
    I've developed an ADHD management system for myself that's attempting to change multiple habits at once. I know this is counter to conventional wisdom, but I've tried the conventional for years & am now trying it my way. (just wanted to say that to try and prevent it from distracting people from the actual question) Anyway, I'd like to write something to run on a remote server that monitors me, helps me build/avoid certain habits, etc. What this amounts to is a system that: runs 24/7 may have multiple independent tasks to run at once may have tasks that require other tasks to run first lets tasks be scheduled by specific time, recurrence (ie. "run every 5 mins"), or interval (ie. "run from 2pm to 3pm") My first naive attempt at this was just a single PHP script scheduled to run every minute by cron (language was chosen in order to use a certain library, but no longer necessary). The logic behind when to run this or that portion of code got hairy pretty quick. So my question is how should I approach this from here? I'm not tied to any one language, though I'm partial to python/javascript. Thoughts: Could be done as a set of scripts that include a scheduling mechanism with one script per bit of logic...but the idea just feels wrong to me. Building it as a daemon could be helpful, but still unsure what to do about dozens of if-else statements for detecting the current time

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  • How should I structure moving from overworld to menu system / combat?

    - by persepolis
    I'm making a text-based "Arena" game where the player is the owner of 5 creatures that battle other teams for loot, experience and glory. The game is very simple, using Python and a curses emulator. I have a static ASCII map of an "overworld" of sorts. My character, represented by a glyph, can move about this static map. There are locations all over the map that the character can visit, that break down into two types: 1) Towns, which are a series of menus that will allow the player to buy equipment for his team, hire new recruits or do other things. 2) Arenas, where the player's team will have a "battle" interface with actions he can perform, messages about the fight, etc. Maybe later, an ASCII representation of the fight but for now, just screens of information with action prompts. My main problem is what kind of design or structure I should use to implement this? Right now, the game goes through a master loop which waits for keyboard input and then moves the player about the screen. My current thinking is this: 1) Upon keyboard input, the Player coordinates are checked against a list of Location objects and if the Player coords match the Location coords then... 2) ??? I'm not sure if I should then call a seperate function to initiate a "menu" or "combat" mode. Or should I create some kind of new GameMode object that contains a method itself for drawing the screen, printing the necessary info? How do I pass my player's team data into this object? My main concern is passing around the program flow into all these objects. Should I be calling straight functions for different parts of my game, and objects to represent "things" within my game? I was reading about the MVC pattern and how this kind of problem might benefit - decouple the GUI from the game logic and user input but I have no idea how this applies to my game.

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  • How should I organise classes for a space simulator?

    - by Peteyslatts
    I have pretty much taught myself everything I know about programming, so while I know how to teach myself (books, internet and reading API's), I'm finding that there hasn't been a whole lot in the way of good programming. I am finishing up learning the basics of XNA and I want to create a space simulator to test my knowledge. This isn't a full scale simulator, but just something that covers everything I learned. It's also going to be modular so I can build on it, after I get the basics down. One of the early features I want to implement is AI. And I want to take this into account as I'm designing my classes so I can minimize rewriting code. So my question: How should I design ship classes so that both the player and AI can use them? The only idea I have so far is: Create a ship class that contains stats, models, textures, collision data etc. The player and AI would then have the data for position, rotation, health, etc and would base their status off of the ship stats.

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  • Store VOD wmi data in a database directly or use CQRS?

    - by JD01
    I need to collect Video on demand bandwidth usage every few minutes (or maybe ever few seconds) and store this in a database so users can produce graphs on bandwidth usage over a period of time (few hours, days, weeks or even possibly months). So the sort of data that will be stored will be the number of users watching videos, current server bandwidth (Mb/s), multicast bit rate etc. I am wondering whether using CQRS would be a good approach with Event sourcing as I can then rebuild my objects to create different projections (I.e. different graphs/reports etc) but then again it seems like I am introducing complexity which might not be needed. Or would it be best to just put the data directly in a database (currently using PostGres) directly and query off that? Having thought about it, my table is a form of audit log anyway, so I don't think I need event sourcing at all. Any thoughts?

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  • Digital "Post It" notes for organizing content of sites/pages

    - by Alex
    We're restructuring our old intranet into a new one and are going through each site to find content and use our new standard structure/look-and-feel. Do you recommend a tool where you can do "digital Post-It" notes? It would provide a way to type some items on a "card" and be able to move it around and organize it quickly. Also, if you know of tools in general for this kind of task, please advise. Thank you.

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  • Profiling and containing memory per system

    - by chadb
    I have been interesting in profiling and keeping a managed memory pool for each subsystem, so I could get statistic on how much memory was being used in something such as sounds or graphics. However, what is the best design for doing this? I was thinking of using multiple allocators and just using one per subsystem, however, that would result in global variables for my allocators (or so it would seem to me). Another approach I have seen/been suggested is to just overload new and pass in an allocator for a parameter. I had a similar question over on stackoverflow here with a bounty, however, it seems as if perhaps I was too vague or just there is not enough people with knowledge in the subject.

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  • Any frameworks or library allow me to run large amount of concurrent jobs schedully?

    - by Yoga
    Are there any high level programming frameworks that allow me to run large amount of concurrent jobs schedully? e.g. I have 100K of urls need to check their uptime every 5 minutes Definitely I can write a program to handle this, but then I need to handle concurrency, queuing, error handling, system throttling, job distribution etc. Will there be a framework that I only focus on a particular job (i.e. the ping task) and the system will take care of the scaling and error handling for me? I am open to any language.

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  • Assessing Relative Maintainability

    - by João Bragança
    We (a contractor, actually) are implementing an off the shelf system to replace a legacy homegrown system for the core domain of the company (designing widgets). Unfortunately both systems will have to run concurrently for some time, as the product just isn't ready yet. Also, the decision was made to only migrate some of the widgets from the legacy system, based on date of last sale activity. Later on a new requirement came down: certain people in the company, most of them outside of the widget development context, want to search all widgets. The search results screen has 3 pieces of data: a GUID, a human readable id that is searchable, and a brief description (may need to be searchable in the future). In the widget details, there will be multiple screens. These screens align very well along SOA / bounded context lines - a screen for marketing data, a screen for sales history, etc. UML ahead! I am probably using the wrong kind of arrows here so please forgive me. The current solution - which is not in production yet - is something like the following: Both systems will be queried and the controller will merge the results. The new system has its own proprietary query language (we've alleviated this a bit with a LINQ provider). It also puts a lot of data on the wire. 15 search results typically run about 60k of unintelligible SOAP-wrapped xml. So I would prefer to avoid querying this system directly. These two systems publish events to help us integrate with other systems, mainly an ERP system. One of these events contains all the data necessary for the search screen. I proposed the following alternative: However I am being told that 'adding another database' will create more maintenance down the road. However, I believe this to be false, as I had to add a relatively simple feature that took several hours longer than anticipated because of this merging code. I want to get a feel for which system is more maintainable in the long run. I personally have not had the burden of maintaining any large system. I want something more than my gut. Specifically I'd like to know if having more, specialized physical databases is more or less maintainable than having less larger physical databases.

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  • OOP implementation of BUFFS and Stats. Suggestion

    - by Mattia Manzo Manzati
    I am developing an MMORPG server using NodeJS. I am not sure how to implement Buffs, i mean, equipped objects or used skills have effects on the Player() which has many Stats(), some of them have a max cap... Effects can change the Stat value, increasing or decreasing it by a value, a percentage or completly rewrite the value of the stat. After a while I have decided to create a base class for buffs, which can be hidden (if they are casted from an equipped object) or shown if they came from an ability (Spell). Anyway I need suggestion how to implement it, use an array for all active buffs for a stat and have a function calculate the value of the stat affected by buffs each time I need the value of the stat or...? Other more OOP's ways to do it? I have read this What's a way to implement a flexible buff/debuff system? but this implements only a percentage system, which buffs can only say "+10%, +20%, etc...", but I would love to have an hybrid system, which can have percentage values or static values (like WoW does), and using modifiers it's hard to implement, because modifiers refers to the current value of stat :/ Thanks for suggestions :)

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  • Is premature optimization really the root of all evil?

    - by Craig Day
    A colleague of mine today committed a class called ThreadLocalFormat, which basically moved instances of Java Format classes into a thread local, since they are not thread safe and "relatively expensive" to create. I wrote a quick test and calculated that I could create 200,000 instances a second, asked him was he creating that many, to which he answered "nowhere near that many". He's a great programmer and everyone on the team is highly skilled so we have no problem understanding the resulting code, but it was clearly a case of optimizing where there is no real need. He backed the code out at my request. What do you think? Is this a case of "premature optimization" and how bad is it really?

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  • Real Time Monitoring System using .net [closed]

    - by sameer
    I need to develop the application which display the dashboard where data from various SQL DB is fetched from different servers and displayed. Now this need to happen real time we can have refresh time say 5 min. Here is my thought, suggest if anything is wrong. 1) To Develop the Windows Service to accumulate the data from various SQL Server Instance. 2) Then Persist those details into SQL DB from which Dashboard will displayed on the web page. 3) Fetch of data from Windows service will be trigger every x minutes. 4) SQL Server Instance details will be stored in SQL DB which Windows Service will be referring. Thus this approach make sense. Thanks..

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  • How to manage many mobile device users at server side?

    - by Rami
    I built a social Android application in which users can see other users around them by GPS location. At the beginning thing went well as I had low number of users, but now that I have increasing number of users (about 1500 +100 every day) it has revealed a major problem in my design. In my Google App Engine servlet I have static HashMap that holds all the users profiles objects, currently 1500 and this number will increase as more users register. Why I'm doing it? Every user that requests for the users around him compares his GPS with other users and checks if they are in his 10km radius. This happens every five minutes on average. Consequently, I can't get the users from db every time because GAE read/write operation quota will tear me apart. The problem with this design is? As the number of users increases, the Hashmap turns to null every 4-6 hours, I think that this time is getting shorter, but I'm not sure. I'm fixing this by reloading the users from the db every time I detect that it becomes null, but this causes DOS to my users for 30 sec, so I'm looking for better solution. I'm guessing that it happens because the size of the hashmap. Am I right? I have been advised to use a spatial database, but that means that I can't work with GAE any more and it means that I need to build my big server all over again and lose my existing DB. Is there something I can do with the existing tools? Thanks.

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  • How do I separate model positions from view positions in MVC?

    - by tieTYT
    Using MVC in games (as opposed to web apps) always confuses me when it comes to the view. How am I supposed to keep the model agnostic of how the view is presenting things? I always end up giving the Model a position that holds x and y but invariably, these values end up being in units of pixels and that feels wrong. I can see the advantage* of avoiding that but how am I supposed to? This idea was suggested: Don't think of it in units of pixels, think of them in arbitrary distance units that just happen map to pixels at a 1:1 ratio. Oh, the resolution is half of what it was? We are now taking the x/y coordinates at 50% value for screen display, and your spells casting range is still 300 units long, which now is 150 pixels. But those numbers conveniently work out. What do I do if the numbers divide in such a way that I get decimal places? Floating points are unsafe. I think allowing decimal places would eventually cause really weird bugs in my game. *It'd let me write the model once and write different views depending on the device.

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