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• What is a good design pattern / lib for iOS 5 to synchronize with a web service?

  - by Junto

  We are developing an iOS application that needs to synchronize with a remote server using web services. The existing web services have an "operations" style rather than REST (implemented in WCF but exposing JSON HTTP endpoints). We are unsure of how to structure the web services to best fit with iOS and would love some advice. We are also interested in how to manage the synchronization process within iOS. Without going into detailed specifics, the application allows the user to estimate repair costs at a remote site. These costs are broken down by room and item. If the user has an internet connection this data can be sent back to the server. Multiple photographs can be taken of each item, but they will be held in a separate queue, which sends when the connection is optimal (ideally wifi). Our backend application controls the unique ids for each room and item. Thus, each time we send these costs to the server, the server echoes the central database ids back, thus, that they can be synchronized in the mobile app. I have simplified this a little, since the operations contract is actually much larger, but I just want to illustrate the basic requirements without complicating matters. Firstly, the web service architecture: We currently have two operations: GetCosts and UpdateCosts. My assumption is that if we used a strict REST architecture we would need to break our single web service operations into multiple smaller services. This would make the services much more chatty and we would also have to guarantee a delivery order from the app. For example, we need to make sure that containing rooms are added before the item. Although this seems much more RESTful, our perception is that these extra calls are expensive connections (security checks, database calls, etc). Does the type of web api (operation over service focus) determine chunky vs chatty? Since this is mobile (3G), are we better handling lots of smaller messages, or a few large ones? Secondly, the iOS side. What is the current advice on how to manage data synchronization within the iOS (5) app itself. We need multiple queues and we need to guarantee delivery order in each queue (and technically, ordering between queues). The server needs to control unique ids and other properties and echo them back to the application. The application then needs to update an internal database and when re-updating, make sure the correct ids are available in the update message (essentially multiple inserts and updates in one call). Our backend has a ton of business logic operating on these cost estimates. We don't want any of this in the app itself. Currently the iOS app sends the cost data, and then the server echoes that data back with populated ids (and other data). The existing cost data is deleted and the echoed response data is added to the client database on the device. This is causing us problems, because any photos might not have been sent, but the original entity tree has been removed and replaced. Obviously updating the costs tree rather than replacing it would remove this problem, but I'm not sure if there are any nice xcode libraries out there to do such things. I welcome any advice you might have.

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• Questioning one of the arguments for dependency injection: Why is creating an object graph hard?

  - by oberlies

  Dependency injection frameworks like Google Guice give the following motivation for their usage (source): To construct an object, you first build its dependencies. But to build each dependency, you need its dependencies, and so on. So when you build an object, you really need to build an object graph. Building object graphs by hand is labour intensive (...) and makes testing difficult. But I don't buy this argument: Even without dependency injection, I can write classes which are both easy to instantiate and convenient to test. E.g. the example from the Guice motivation page could be rewritten in the following way: class BillingService { private final CreditCardProcessor processor; private final TransactionLog transactionLog; // constructor for tests, taking all collaborators as parameters BillingService(CreditCardProcessor processor, TransactionLog transactionLog) { this.processor = processor; this.transactionLog = transactionLog; } // constructor for production, calling the (productive) constructors of the collaborators public BillingService() { this(new PaypalCreditCardProcessor(), new DatabaseTransactionLog()); } public Receipt chargeOrder(PizzaOrder order, CreditCard creditCard) { ... } } So there may be other arguments for dependency injection (which are out of scope for this question!), but easy creation of testable object graphs is not one of them, is it?

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• Is there really anything to gain with complex design? [duplicate]

  - by SB2055

  This question already has an answer here: What is enterprise software, exactly? 8 answers I've been working for a consulting firm for some time, with clients of various sizes, and I've seen web applications ranging in complexity from really simple: MVC Service Layer EF DB To really complex: MVC UoW DI / IoC Repository Service UI Tests Unit Tests Integration Tests But on both ends of the spectrum, the quality requirements are about the same. In simple projects, new devs / consultants can hop on, make changes, and contribute immediately, without having to wade through 6 layers of abstraction to understand what's going on, or risking misunderstanding some complex abstraction and costing down the line. In all cases, there was never a need to actually make code swappable or reusable - and the tests were never actually maintained past the first iteration because requirements changed, it was too time-consuming, deadlines, business pressure, etc etc. So if - in the end - testing and interfaces aren't used rapid development (read: cost-savings) is a priority the project's requirements will be changing a lot while in development ...would it be wrong to recommend a super-simple architecture, even to solve a complex problem, for an enterprise client? Is it complexity that defines enterprise solutions, or is it the reliability, # concurrent users, ease-of-maintenance, or all of the above? I know this is a very vague question, and any answer wouldn't apply to all cases, but I'm interested in hearing from devs / consultants that have been in the business for a while and that have worked with these varying degrees of complexity, to hear if the cool-but-expensive abstractions are worth the overall cost, at least while the project is in development.

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• Making a class pseudo-immutable by setting a flag

  - by scott_fakename

  I have a java project that involves building some pretty complex objects. There are quite a lot (dozens) of different ones and some of them have a HUGE number of parameters. They also need to be immutable. So I was thinking the builder pattern would work, but it ends up require a lot of boilerplate. Another potential solution I thought of was to make a mutable class, but give it a "frozen" flag, a-la ruby. Here is a simple example: public class EqualRule extends Rule { private boolean frozen; private int target; public EqualRule() { frozen = false; } public void setTarget(int i) { if (frozen) throw new IllegalStateException( "Can't change frozen rule."); target = i; } public int getTarget() { return target; } public void freeze() { frozen = true; } @Override public boolean checkRule(int i) { return (target == i); } } and "Rule" is just an abstract class that has an abstract "checkRule" method. This cuts way down on the number of objects I need to write, while also giving me an object that becomes immutable for all intents and purposes. This kind of act like the object was its own Builder... But not quite. I'm not too excited, however, about having an immutable being disguised as a bean however. So I had two questions: 1. Before I go too far down this path, are there any huge problems that anyone sees right off the bat? For what it's worth, it is planned that this behavior will be well documented... 2. If so, is there a better solution? Thanks

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• How to play many sounds at once in OpenAL

  - by Krom Stern

  I'm developing an RTS game and I would like to add sounds to it. My choice has landed on OpenAL. I have plenty of units which from time to time make sounds: fSound.Play(sfx_shoot, location). Sounds often repeat, e.g. when squad of archers shoots arrows, but they are not synced with each other. My questions are: What is the common design pattern to play multiple sounds in OpenAL, when some of them are duplicate? What are the hardware limitations on sounds count and tricks to overcome them?

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• How to determine if class meets single responsibility principle ?

  - by user1483278

  Single Responsibility Principle is based on high cohesion principle. The difference between the two is that highly cohesive classes feature a set of responsibilities that are strongly related, while classes adhering to SRP have just one responsibility. But how do we determine whether particular class features a set of responsibilities and is thus just highly cohesive, or whether it has only one responsibility and is thus adhering to SRP? Namely, isn't it more or less subjective, since some may find class very granular ( and as such will consider a class as adhering to SRP ), while others may find it not granular enough?

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• How to handle sorting of complex objects?

  - by AedonEtLIRA

  How would one sort a list of objects that have more than one sortable element? Suppose you have a simple object Car and car is a defined as such: class Car { public String make; public String model; public int year; public String color; // ... No methods, just a structure / container } I designed a simple framework that would allow for multiple SortOptions to be provided to a Sorter that would then sort the list. interface ISorter<T> { List<T> sort(List<T> items); void addSortOption(ISortOption<T> option); ISortOption<T>[] getSortOptions(); void setSortOption(ISortOption<T> option); } interface ISortOption<T> { String getLabel(); int compare(T t1, T t2); } Example use class SimpleStringSorter extends MergeSorter<String> { { addSorter(new AlphaSorter()); } private static final class AlphaSorter implements ISortOption<String> { // ... implementation of alpha compare and get label } } The issue with this solution is that it is not easily expandable. If car was to ever receive a new field, say, currentOwner. I would need to add the field, then track down the sorter class file, implement a new sort option class then recompile the application for redistribution. Is there an easier more expandable/practical way to sort data like this?

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• Design pattern: static function call with input/output containers?

  - by Pavlo Dyban

  I work for a company in software research department. We use algorithms from our real software and wrap them so that we can use them for prototyping. Every time an algorithm interface changes, we need to adapt our wrappers respectively. Recently all algorithms have been refactored in such a manner that instead of accepting many different inputs and returning outputs via referenced parameters, they now accept one input data container and one output data container (the latter is passed by reference). Algorithm interface is limited to a static function call like that: class MyAlgorithm{ static bool calculate(MyAlgorithmInput input, MyAlgorithmOutput &output); } This is actually a very powerful design, though I have never seen it in a C++ programming environment before. Changes in the number of parameters and their data types are now encapsulated and they don't change the algorithm callback. In the latest algorithm which I have developed I used the same scheme. Now I want to know if this is a popular design pattern and what it is called.

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• Callbacks: when to return value, and when to modify parameter?

  - by MarkN

  When writing a callback, when is best to have the callback return a value, and when is it best to have the callback modify a parameter? Is there a difference? For example, if we wanted to grab a list of dependencies, when would you do this: function GetDependencies(){ return [{"Dep1" : 1.1}, {"Dept2": 1.2}, {"Dep3" : 1.3}]; } And when would you do this? function RegisterDependencies(register){ register.add("Dep1", 1.1); register.add("Dep2", 1.2); register.add("Dep3", 1.3); }

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• ASP.NET design not SOLID

  - by w0051977

  SOLID principles are described here: http://en.wikipedia.org/wiki/SOLID_%28object-oriented_design%29 I am developing a large ASP.NET app. The previous developer created a few very large classes each with lots of different purposes. It is very difficult to maintain and extend. The classes are deployed to the web server along with the code behind files etc. I want to share a small amount of the app with another application. I am considering moving all of the classes of the ASP.NET web app to a DLL, so the small subset of functionality can be shared. I realise it would be better to only share the classes which contain code to be shared but because of the dependencies this is proving to be very difficult e.g. class A contains code that should be shared, however class A contains references to classes B, C, D, E, F, G etc, so class A cannot be shared on its own. I am planning to refactor the code in the future. As a temporary solution I am planning to convert all the classes into a single class library. Is this a bad idea and if so, is there an alternative? as I don't have time to refactor at the moment.

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• What to do as a new team lead on a project with maintainability problems?

  - by Mr_E

  I have just been put in charge of a code project with maintainability problems. What things can I do to get the project on a stable footing? I find myself in a place where we are working with a very large multi-tiered .NET system that is missing a lot of the important things such as unit tests, IOC, MEF, too many static classes, pure datasets etc. I'm only 24 but I've been here for almost three years (this app has been in development for 5) and mostly due to time constraints we've been just adding in more crap to fit the other crap. After doing a number of projects in my free time I have begun to understand just how important all those concepts are. Also due to employee shifting I find myself to now be the team lead on this project and I really want to come up with some smart ways to improve this app. Ways where the value can be explained to management. I have ideas of what I would like to do but they all seem so overwhelming without much upfront gain. Any stories of how people have or would have dealt with this would be a very interesting read. Thanks.

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• A better alternative to incompatible implementations for the same interface?

  - by glenatron

  I am working on a piece of code which performs a set task in several parallel environments where the behaviour of the different components in the task are similar but quite different. This means that my implementations are quite different but they are all based on the relationships between the same interfaces, something like this: IDataReader -> ContinuousDataReader -> ChunkedDataReader IDataProcessor -> ContinuousDataProcessor -> ChunkedDataProcessor IDataWriter -> ContinuousDataWriter -> ChunkedDataWriter So that in either environment we have an IDataReader, IDataProcessor and IDataWriter and then we can use Dependency Injection to ensure that we have the correct one of each for the current environment, so if we are working with data in chunks we use the ChunkedDataReader, ChunkedDataProcessor and ChunkedDataWriter and if we have continuous data we have the continuous versions. However the behaviour of these classes is quite different internally and one could certainly not go from a ContinuousDataReader to the ChunkedDataReader even though they are both IDataProcessors. This feels to me as though it is incorrect ( possibly an LSP violation? ) and certainly not a theoretically correct way of working. It is almost as though the "real" interface here is the combination of all three classes. Unfortunately in the project I am working on with the deadlines we are working to, we're pretty much stuck with this design, but if we had a little more elbow room, what would be a better design approach in this kind of scenario?

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• best way to send messages to all subscribers with multiple subscriptions and multiple providers

  - by coding_idiot

  I'm writing an application in which - Many users can subsribe to posts made by another users. So for a single publisher there can be many subscribers. When a message is posted by an user X, all users who have subscribed to messages of User X will be sent an email. How to achieve this ? I'm thinking of using publish-subscribe pattern. And then I came through JMS. Which is the best JMS implementation to use according to your experience ? Or else what else solution do you propose to the given problem ? Shall I go for a straight-forward solution ?: User x posts a message, I find all users (from database) who subscribe to user x and then for every user, I call the sendEmail() method. [EDIT] My intention here is not to send-emails. I'm really sorry if it wasn't clear. I also have to send kind of system-notifications apart from Email to all subscribers. Right now, I've implemented the email-sending as a threadPool

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• What is MVC, really?

  - by NickC

  As a serious programmer, how do you answer the question What is MVC? In my mind, MVC is sort of a nebulous topic — and because of that, if your audience is a learner, then you're free to describe it in general terms that are unlikely to be controversial. However, if you are speaking to a knowledgeable audience, especially an interviewer, I have a hard time thinking of a direction to take that doesn't risk a reaction of "well that's not right!...". We all have different real-world experience, and I haven't truly met the same MVC implementation pattern twice. Specifically, there seem to be disagreements regarding strictness, component definition, separation of parts (what piece fits where), etc. So, how should I explain MVC in a way that is correct, concise, and uncontroversial?

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• "Best fit" to avoid reuse of object instances in a collection

  - by Simon

  Imagine I have a collection of object instances which represent activities for a user to undertake. Dependent on user attributes, I have to randomly select instances to present activities to the user. For some users, I need to present more activities to them than there are available activities in which case, I want to use the following algorithm. If all available activities have already been presented to the user, then re-select a "used" activity, selecting the earliest presented activity ordered by frequency of use. In other words, try to reduce repetition and where repetition is unavoidable, use the instances which have been repeated less often and were presented furthest back in time. Before I go on to code that algorithm, I wondered if there is some existing pattern I can re-use? [EDIT] "Furthest back in time" is not relevant as I will pass the algorithm an ordered collection of used instances where the first entry is the first presented.

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• Failure Driven Development

  - by DevSolo

  At our shop, we strive to be agile. And I'd say we are making great strides. That said, a few of us have spotted a pattern we have started calling "Failure Driven Development". Failure Driven Development can basically be desribed as an agile release/iteration cycle where the bugs/features are guided not by tasks and stories with acceptance criteria, but with defects entered in the defect tracking software. Our team has a great Project Manager who strives to get the acceptance criteria from the customer(s), but it's not always possible. From my development chair, this is due to the customer either not knowing exactly what they want or (and this is the kicker) two different "camps" at the customer's main office conflict with how a story should be implemented. Camp A will losely dictate that Feature X works like this, then Camp B will fail it due not functioning like that. Hence, the term "FDD". The process is driven by "failures". This leads to my question: Has anyone else encountered this and if so, any tips/suggestions for dealing with it? We have, of course, tried to get Camp A and B to agree prior, but everyone knows this isn't always the case. Thanks

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• Is OOP hard because it is not natural?

  - by zvrba

  One can often hear that OOP naturally corresponds to the way people think about the world. But I would strongly disagree with this statement: We (or at least I) conceptualize the world in terms of relationships between things we encounter, but the focus of OOP is designing individual classes and their hierarchies. Note that, in everyday life, relationships and actions exist mostly between objects that would have been instances of unrelated classes in OOP. Examples of such relationships are: "my screen is on top of the table"; "I (a human being) am sitting on a chair"; "a car is on the road"; "I am typing on the keyboard"; "the coffee machine boils water", "the text is shown in the terminal window." We think in terms of bivalent (sometimes trivalent, as, for example in, "I gave you flowers") verbs where the verb is the action (relation) that operates on two objects to produce some result/action. The focus is on action, and the two (or three) [grammatical] objects have equal importance. Contrast that with OOP where you first have to find one object (noun) and tell it to perform some action on another object. The way of thinking is shifted from actions/verbs operating on nouns to nouns operating on nouns -- it is as if everything is being said in passive or reflexive voice, e.g., "the text is being shown by the terminal window". Or maybe "the text draws itself on the terminal window". Not only is the focus shifted to nouns, but one of the nouns (let's call it grammatical subject) is given higher "importance" than the other (grammatical object). Thus one must decide whether one will say terminalWindow.show(someText) or someText.show(terminalWindow). But why burden people with such trivial decisions with no operational consequences when one really means show(terminalWindow, someText)? [Consequences are operationally insignificant -- in both cases the text is shown on the terminal window -- but can be very serious in the design of class hierarchies and a "wrong" choice can lead to convoluted and hard to maintain code.] I would therefore argue that the mainstream way of doing OOP (class-based, single-dispatch) is hard because it IS UNNATURAL and does not correspond to how humans think about the world. Generic methods from CLOS are closer to my way of thinking, but, alas, this is not widespread approach. Given these problems, how/why did it happen that the currently mainstream way of doing OOP became so popular? And what, if anything, can be done to dethrone it?

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• Strategies for avoiding SQL in your Controllers... or how many methods should I have in my Models?

  - by Keith Palmer

  So a situation I run into reasonably often is one where my models start to either: Grow into monsters with tons and tons of methods OR Allow you to pass pieces of SQL to them, so that they are flexible enough to not require a million different methods For example, say we have a "widget" model. We start with some basic methods: get($id) insert($record) update($id, $record) delete($id) getList() // get a list of Widgets That's all fine and dandy, but then we need some reporting: listCreatedBetween($start_date, $end_date) listPurchasedBetween($start_date, $end_date) listOfPending() And then the reporting starts to get complex: listPendingCreatedBetween($start_date, $end_date) listForCustomer($customer_id) listPendingCreatedBetweenForCustomer($customer_id, $start_date, $end_date) You can see where this is growing... eventually we have so many specific query requirements that I either need to implement tons and tons of methods, or some sort of "query" object that I can pass to a single -query(query $query) method... ... or just bite the bullet, and start doing something like this: list = MyModel-query(" start_date X AND end_date < Y AND pending = 1 AND customer_id = Z ") There's a certain appeal to just having one method like that instead of 50 million other more specific methods... but it feels "wrong" sometimes to stuff a pile of what's basically SQL into the controller. Is there a "right" way to handle situations like this? Does it seem acceptable to be stuffing queries like that into a generic -query() method? Are there better strategies?

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• Who can change the View in MVC?

  - by Luke

  I'm working on a thick client graph displaying and manipulation application. I'm trying to apply the MVC pattern to our 3D visualization component. Here is what I have for the Model, View, and Controller: Model - The graph and it's metadata. This includes vertices, edges, and the attributes of each. It does not contain position information, icons, colors, or anything display related. View - This would commonly be called a scene graph. It includes the 3D display information, texture information, color information, and anything else that is related specifically to the visualization of the model. Controller - The controller takes the view and displays it in a Window using OpenGL (but it could potentially be any 3D graphics package). The application has various "layouts" that change the position of the vertices in the display. For instance, one layout may arrange the vertices in a circle. Is it common for these layouts to access and change the view directly? Should they go through the Controller to access the View? If they go through the Controller, should they just ask for direct access to the View or should each change go through the controller? I realize this is a bit different from the standard MVC example where there a finite number of Views. In this case, the View can change in an infinite number of ways. Perhaps I'm shattering some basic principle of MVC here. Thanks in advance!

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• Does MVC apply only to web

  - by Deeptechtons

  It is almost and instantaneous whenever I talk to developers about Model View Controller (MVC) they say you make a request to a url the server builds a entity (MODEL) and provides you with visual representation of that model. So does this mean MVC is only for the web or have I been meeting people who are just developers who employ MVC for writing web applications? Are there usages for MVC on desktop style applications? I for one am new to paradigm and would like to know of any super-set to MVC

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• How do I reuse a state machine in a slightly different way?

  - by JoJo

  Problem I have a big state machine. The design requirements of the project have changed such that I need to re-use this state machine in another place. All the states remain the same in this new place, but a few states run slightly different stuff. What design pattern allows me to reuse this state machine? Motivation I am building a video player. It is modeled by a state machine with these states: stopped, loading, playing, paused, crashed, and some more... This video player needs to be used on two web pages. When the player crashes on the first page, it should show an error message below. If the player crashes on the second page, the error message should appear in the center of the video and pulsate a few times.

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• When designing a job queue, what should determine the scope of a job?

  - by Stuart Pegg

  We've got a job queue system that'll cheerfully process any kind of job given to it. We intend to use it to process jobs that each contain 2 tasks: Job (Pass information from one server to another) Fetch task (get the data, slowly) Send task (send the data, comparatively quickly) The difficulty we're having is that we don't know whether to break the tasks into separate jobs, or process the job in one go. Are there any best practices or useful references on this subject? Is there some obvious benefit to a method that we're missing? So far we can see these benefits for each method: Split Job lease length reflects job length: Rather than total of two Finer granularity on recovery: If we lose outgoing connectivity we can tell them all to retry The starting state of the second task is saved to job history: Helps with debugging (although similar logging could be added in single task method) Single Single job to be scheduled: Less processing overhead Data not stale on recovery: If the outgoing downtime is quite long, the pending Send jobs could be outdated

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• How to layer if statements when order of logic is irrelevant?

  - by jimmyjimmy

  Basically I have a series of logic in my website that can lead to 5 total outcomes. Basically two different if tests and then a catch all else statement. For example: if cond1: if mod1: #do things elif mod2: #do things elif cond2: if mod1: #do things elif mod2 #do things else: #do things I was thinking about rewriting it like this: if cond1 and mod1: #do things elif cond1 and mod2: #do things elif cond2 and mod1: #do things elif cond2 and mod2: #do things else: #do things Is there any real difference in these two coding options/a better choice for this kind of logic testing?

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• Is the structure used for these web pages a design pattern?

  - by aspdotnetuser

  I want to know if the structure for an ASP.NET website I'm working on uses a design pattern for it's web pages. If it is a design pattern, what is it called? The web pages have the following structure: UserDetails page (UserDetails.aspx) - includes UserDetailsController.ascx user control. UserDetailsController.ascx includes sub user controls like UserAccountDetails.ascx and UserLoginDetails.ascx etc Each sub user control contains a small amount of code/logic, the 'controller' user controls that host these sub user controls (i.e UserDetailsController.ascx) appear to call the business rules code and pass the data to the sub user controls. Is this a design pattern? What is it called?

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• Using allocators for different systems

  - by chadb

  I am going over the memory architecture for my game and even though I know my memory budgets may not be final, I at the point where I can start using them in a general sense. I know that I will need several allocators (for systems such as audio, rendering, etc) but I am unsure of how they will be accessed. I do not use singletons, so I can't just have something such as AudioManager::GetInstance().get_allocator(). Instead, I need to find a different method of usage but I am not sure of how. How can I store and call my allocators needed for several different systems over engine in an efficient manner?

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