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  • What is a useful pattern to maintaining an object state in a one to many relationship?

    - by ahenderson
    I am looking for a design for my application, here are the players(classes) involved. struct Transform { // Uses a matrix to transform the position. // Also acts acts as the state of a Dialog. Position transform(Position p); //other methods. }; struct Dialog { // There are multiple dialog for the user to transform the output. Transform& t; void ChangeTranformation(){t.rotate(360);} } struct Algorithm { //gives us a position based on an implementation. For example this can return points on a circle or line. Transform& t; Position m_p; Dialog& d; Position GetCurrentPosition(){ return t.transform(m_p);} //other methods. } Properties I need: Each algorithms has one dialog and each dialog can have many algorithms associated with it. When the user selects an algorithm a dialog associated with that algorithm is displayed. If the user selects a different algorithm then re-selects back the state is restored in the dialog. Basically I want a good design pattern to maintain the state of the dialog given that many algorithms use it and they can be switched back and forth. Does anyone have any suggestions? Here is a use case: Dialog1 has a single edit box to control the radius. Algorithm1 generates points on a unit circle. Algorithm2 is the same as Algorithm1. The user has selected Algorithm1 and entered 2 into the edit box. This will generate points on a circle of radius 2. The user then selects Algorithm2 and enters 10 into the edit box of Dialog1. This will generate points on a circle of radius 10. Finally Algorithm1 is selected again. The edit box of Dialog1 should show 2 and points on a circle of radius 2 should be generated.

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  • Law of Demeter in MVC regarding Controller-View communication

    - by Antonio MG
    The scenario: Having a Controller that controls a view composed of complex subviews. Each one of those subviews is a separated class in a separate file. For example, one of those subviews is called ButtonsView, and has a bunch of buttons. The Controller has to access those buttons. Would accessing those buttons like this: controllerMainView.buttonsView.firstButton.state(); be a violation of the LOD? On one hand, it could be yes because the controller is accessing the inner hierarchy of the view. On the other, a Controller should be aware of what happens inside the view and how is composed. Any thoughts?

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  • Is this kind of design - a class for Operations On Object - correct?

    - by Mithir
    In our system we have many complex operations which involve many validations and DB activities. One of the main Business functionality could have been designed better. In short, there were no separation of layers, and the code would only work from the scenario in which it was first designed at, and now there were more scenarios (like requests from an API or from other devices) So I had to redesign. I found myself moving all the DB code to objects which acts like Business to DB objects, and I've put all the business logic in an Operator kind of a class, which I've implemented like this: First, I created an object which will hold all the information needed for the operation let's call it InformationObject. Then I created an OperatorObject which will take the InformationObject as a parameter and act on it. The OperatorObject should activate different objects and validate or check for existence or any scenario in which the business logic is compromised and then make the operation according to the information on the InformationObject. So my question is - Is this kind of implementation correct? PS, this Operator only works on a single Business-wise Operation.

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  • Object Design catalog and resources

    - by Tauren
    I'm looking for web sites, books, or other resources that provide a catalog of object designs used in common scenarios. I'm not looking for generic design patterns, but for samples of actual object designs that were used to solve real problems. For instance, I'm about to build an internal messaging system for a web application, similar to Facebook's messaging system. This system will allow administrators to send messages to all members, to selected groups of members, or to individuals. Members can send messages to other members or groups of members. Fairly common stuff and a feature that I'm sure thousands of web applications require. I know each situation is different and there are a million ways to design this solution. Although this scenario isn't really all that complex, I'm sure the basic design of the necessary objects and relationships for a system like this has already been done many times. It would be nice to review other similar designs before building my own. Is there a place where people can share their designs and others can browse/search through the catalog to review and provide feedback on them? StackOverflow could be used to a degree for this, but doesn't really provide a catalog of designs. Any other resources that would relate?

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  • Does this copy the reference or the object?

    - by Water Cooler v2
    Sorry, I am being both thick and lazy, but mostly lazy. Actually, not even that. I am trying to save time so I can do more in less time as there's a lot to be done. Does this copy the reference or the actual object data? public class Foo { private NameValueCollection _nvc = null; public Foo( NameValueCollection nvc) { _nvc = nvc; } } public class Bar { public static void Main() { NameValueCollection toPass = new NameValueCollection(); new Foo( toPass ); // I believe this only copies the reference // so if I ever wanted to compare toPass and // Foo._nvc (assuming I got hold of the private // field using reflection), I would only have to // compare the references and wouldn't have to compare // each string (deep copy compare), right? } I think I know the answer for sure: it only copies the reference. But I am not even sure why I am asking this. I guess my only concern is, if, after instantiating Foo by calling its parameterized ctor with toPass, if I needed to make sure that the NVC I passed as toPass and the NVC private field _nvc had the exact same content, I would just need to compare their references, right?

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  • Design Pattern for Social Game Mission Mechanics

    - by Furkan ÇALISKAN
    When we want to design a mission sub-system like in the The Ville or Sims Social, what kind of design pattern / idea would fit the best? There may be relation between missions (first do this then this etc...) or not. What do you think sims social or the ville or any other social games is using for this? I'm looking for a best-practise method to contruct a mission framework for tha game. How the well-known game firms do this stuff for their large scale social facebook games? Giving missions to the players and wait players to complete them. when they finished the missions, providing a method to catch this mission complete events considering large user database by not using server-side not so much to prevent high-traffic / resource consumption. how should i design the database and server-client communication to achive this design condidering this trade-off.

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  • So, "Are Design Patterns Missing Language Features"?

    - by Eduard Florinescu
    I saw the answer to this question: How does thinking on design patterns and OOP practices change in dynamic and weakly-typed languages? There it is a link to an article with an outspoken title: Are Design Patterns Missing Language Features. But where you can get snippets that seem very objective and factual and that can be verified from experience like: PaulGraham said "Peter Norvig found that 16 of the 23 patterns in Design Patterns were 'invisible or simpler' in Lisp." and a thing that confirms what I recently seen with people trying to simulate classes in javascript: Of course, nobody ever speaks of the "function" pattern, or the "class" pattern, or numerous other things that we take for granted because most languages provide them as built-in features. OTOH, programmers in a purely PrototypeOrientedLanguage? might well find it convenient to simulate classes with prototypes... I am taking into consideration also that design patterns are a communcation tool and because even with my limited experience participating in building applications I can see as an anti-pattern(ineffective and/or counterproductive) for example forcing a small PHP team to learn GoF patterns for small to medium intranet app, I am aware that scale, scope and purpose can determine what is effective and/or productive. I saw small commercial applications that mixed functional with OOP and still be maintainable, and I don't know if many would need for example in python to write a singleton but for me a simple module does the thing. patterns So are there studies or hands on experience shared that takes into consideration, all this, scale and scope of project, dynamics and size of the team, languages and technologies, so that you don't feel that a (difficult for some)design pattern is there just because there isn't a simpler way to do it or that it cannot be done by a language feature?

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  • Design patterns: when to use and when to stop doing everything using patterns

    - by honeybadger
    This question arises due to comment of FredOverflow in my previous post. Design pattern used in projects I am quite confused by the comment. I know design pattern help in making code reusable and readable (may lack in efficiency a bit). But when to use design patterns and most importantly when to stop doing everything using patterns or carried away by it ? Any comments from you will be helpful. tagging programing languages too to cover broader audience.

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  • New book in the style of Advanced Programming Language Design by R. A. Finkel [closed]

    - by mfellner
    I am currently researching visual programming language design for a university paper and came across Advanced Programming Language Design by Raphael A. Finkel from 1996. Other, older discussions in the same vein on Stackoverflow have mentioned Language Implementation Patterns by Terence Parr and Programming Language Pragmatics* by Michael L. Scott. I was wondering if there is even more (and especially up-to-date) literature on the general topic of programming language design. *) http://www.cs.rochester.edu/~scott/pragmatics/

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  • Should pathfinder in A* hold closedSet and openedSet or each object should hold its sets?

    - by Patryk
    I am about to implement A* pathfinding algorithm and I wonder how should I implement this - from the point of view of architecture. I have the pathfinder as a class - I think I will instantiate only one object of this class (or maybe make it a Singleton - this is not so important). The hardest part for me is whether the closedSet and openedSet should be attached to objects that can find the path for them or should be stored in pathfinder class ? I am opened to any hints and critique whatsoever. What is the best practice considering pathfinding in terms of design ?

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  • Does TDD lead to the good design?

    - by Eugen Martynov
    I'm in transition from "writing unit tests" state to TDD. I saw as Johannes Brodwall creates quite acceptable design from avoiding any of architecture phase before. I'll ask him soon if it was real improvisation or he had some thoughts upfront. I also clearly understand that everyone has experience that prevents to write explicit design bad patterns. But after participating in code retreat I hardly believe that writing test first could save us from mistakes. But I also believe that tests after code will lead to mistakes much faster. So this night question is asking for people who is using TDD for a long time share their experience about results of design without upfront thinking. If they really practice it and get mostly suitable design. Or it's my small understanding about TDD and probably agile.

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  • Procedural world generation oriented on gameplay features

    - by Richard Fabian
    In large procedural landscape games, the land seems dull, but that's probably because the real world is largely dull, with only limited places where the scenery is dramatic or tactical. Looking at world generation from this point of view, a landscape generator for a game needs to not follow the rules of landscaping, but instead some rules married to the expectations of the gamer. For example, there could be a choke point / route generator that creates hills ravines, rivers and mountains between cities, rather than cities plotted on the land based on the resources or conditions generated by the mountains and rainfall patterns. Is there any existing work being done like this? Start with cities or population centres and then add in terrain afterwards?

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  • Functional/nonfunctional requirements VS design ideas

    - by Nicholas Chow
    Problem domain Functional requirements defines what a system does. Non-Functional requirements defines quality attributes of what the system does as a whole.(performance, security, reliability, volume, useability, etc.) Constraints limits the design space, they restrict designers to certain types of solutions. Solution domain Design ideas , defines how the system does it. For example a stakeholder need might be we want to increase our sales, therefore we must improve the usability of our webshop so more customers will purchase, a requirement can be written for this. (problem domain) Design takes this further into the solution domain by saying "therefore we want to offer credit card payments in addition to the current prepayment option". My problem is that the transition phase from requirement to design seems really vague, therefore when writing requirements I am often confused whether or not I incorporated design ideas in my requirements, that would make my requirement wrong. Another problem is that I often write functional requirements as what a system does, and then I also specify in what timeframe it must be done. But is this correct? Is it then a still a functional requirement or a non functional one? Is it better to seperate it into two distinct requirements? Here are a few requirements I wrote: FR1 Registration of Organizer FR1 describes the registration of an Organizer on CrowdFundum FR1.1 The system shall display a registration form on the website. FR1.2 The system shall require a Name, Username, Document number passport/ID card, Address, Zip code, City, Email address, Telephone number, Bank account, Captcha code on the registration form when a user registers. FR1.4 The system shall display an error message containing: “Registration could not be completed” to the subscriber within 1 seconds after the system check of the registration form was unsuccessful. FR1.5 The system shall send a verification email containing a verification link to the subscriber within 30 seconds after the system check of the registration form was successful. FR1.6 The system shall add the newly registered Organizer to the user base within 5 seconds after the verification link was accessed. FR2 Organizer submits a Project FR2 describes the submission of a Project by an Organizer on CrowdFundum - FR2 The system shall display a submit Project form to the Organizer accounts on the website.< - FR2.3 The system shall check for completeness the Name of the Project, 1-3 Photo’s, Keywords of the Project, Punch line, Minimum and maximum amount of people, Funding threshold, One or more reward tiers, Schedule of when what will be organized, Budget plan, 300-800 Words of additional information about the Project, Contact details within 1 secondin after an Organizer submits the submit Project form. - FR2.8 The system shall add to the homepage in the new Projects category the Project link within 30 seconds after the system made a Project webpage - FR2.9 The system shall include in the Project link for the homepage : Name of the Project, 1 Photo, Punch line within 30 seconds after the system made a Project webpage. Questions: FR 1.1 : Have I incorporated a design idea here, would " the system shall have a registration form" be a better functional requirement? F1.2 ,2.3 : Is this not singular? Would the conditions be better written for each its own separate requirement FR 1.4: Is this a design idea? Is this a correct functional requirement or have I incorporated non functional(performance) in it? Would it be better if I written it like this: FR1 The system shall display an error message when check is unsuccessful. NFR: The system will respond to unsuccesful registration form checks within 1 seconds. Same question with FR 2.8 and 2.9. FR2.3: The system shall check for "completeness", is completeness here used ambigiously? Should I rephrase it? FR1.2: I added that the system shall require a "Captcha code" is this a functional requirement or does it belong to the "security aspect" of a non functional requirement. I am eagerly waiting for your response. Thanks!

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  • Design Patterns and their most common uses for them [closed]

    - by cable729
    Possible Duplicate: What are some programming design patterns that are useful in game development? As I'm returning to game dev, I've realized that I've lost a lot of the knowledge I had before. So now I'm looking at design patterns that I can use for my next project. One design pattern that I've seen a lot is the 'composition method,' which uses actors and components. Is that the right name for it? I'd like to look more at this and see what the advantages/pitfalls are. So what design patterns are out there, and what are the advantages/disadvantages to them?

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  • Good resources for language design

    - by Aaron Digulla
    There are lots of books about good web design, UI design, etc. With the advent of Xtext, it's very simple to write your own language. What are good books and resources about language design? I'm not looking for a book about compiler building (like the dragon book) but something that answers: How to create a grammar that is forgiving (like adding optional trailing commas)? Which grammar patterns cause problems for users of a language? How create a compact grammar without introducing ambiguities

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  • How to explain why design choices are good?

    - by Telastyn
    As I've become a better developer, I find that much of my design skill comes more from intuition than mechanical analysis. This is great. It lets me read code and get a feel for it quicker. It lets me translate designs between languages and abstractions much easier. And it let's me get stuff done faster. The downside is that I find it harder to explain to teammates (and worse, management) why a particular design is advantageous; especially teammates that are behind the times on best practices. "This design is more testable!" or "You should favor composition over inheritance." go right over their heads, and lead into the rabbit hole of me trying to clue everyone in to the last decade of software engineering advances. I'll get better at it with practice of course, but in the mean time it involves a lot of wasted time and/or bad design (that will lead to wasted time fixing it later). How can I better explain why a certain design is superior, when the benefits aren't completely obvious to the audience?

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  • Are first-class functions a substitute for the Strategy pattern?

    - by Prog
    The Strategy design pattern is often regarded as a substitute for first-class functions in languages that lack them. So for example say you wanted to pass functionality into an object. In Java you'd have to pass in the object another object which encapsulates the desired behavior. In a language such as Ruby, you'd just pass the functionality itself in the form of an annonymous function. However I was thinking about it and decided that maybe Strategy offers more than a plain annonymous function does. This is because an object can hold state that exists independently of the period when it's method runs. However an annonymous function by itself can only hold state that ceases to exist the moment the function finishes execution. So my question is: when using a language that features first-class functions, would you ever use the Strategy pattern (i.e. encapsulate the functionality you want to pass around in an explicit object), or would you always use an annonymous function? When would you decide to use Strategy when you can use a first-class function?

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  • Looking for a better Factory pattern (Java)

    - by Sam Goldberg
    After doing a rough sketch of a high level object model, I am doing iterative TDD, and letting the other objects emerge as a refactoring of the code (as it increases in complexity). (That whole approach may be a discussion/argument for another day.) In any case, I am at the point where I am looking to refactor code blocks currently in an if-else blocks into separate objects. This is because there is another another value combination which creates new set of logical sub-branches. To be more specific, this is a trading system feature, where buy orders have different behavior than sell orders. Responses to the orders have a numeric indicator field which describes some event that occurred (e.g. fill, cancel). The combination of this numeric indicator field plus whether it is a buy or sell, require different processing buy the code. Creating a family of objects to separate the code for the unique handling each of the combinations of the 2 fields seems like a good choice at this point. The way I would normally do this, is to create some Factory object which when called with the 2 relevant parameters (indicator, buysell), would return the correct subclass of the object. Some times I do this pattern with a map, which allows to look up a live instance (or constructor to use via reflection), and sometimes I just hard code the cases in the Factory class. So - for some reason this feels like not good design (e.g. one object which knows all the subclasses of an interface or parent object), and a bit clumsy. Is there a better pattern for solving this kind of problem? And if this factory method approach makes sense, can anyone suggest a nicer design?

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  • Help with MVC design pattern?

    - by user3681240
    I am trying to build a java program for user login but I am not sure if my MVC design is accurate. I have the following classes: LoginControl - servlet LoginBean - data holder java class with private variables getters and setters LoginDAO - concrete java class where I am running my SQL queries and doing rest of the logical work. Connection class - java class just to connect to the database view - jsp to display the results html - used for form Is this how you design a java program based on MVC design pattern? Please provide some suggestions?

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  • Best approach to design a service oriented system

    - by Gustavo Paulillo
    Thinking about service orientation, our team are involved on new application designs. We consist in a group of 4 developers and a manager (that knows something about programming and distributed systems). Each one, having own opinion on service design. It consists in a distributed system: a user interface (web app) accessing the services in a dedicated server (inside the firewall), to obtain the business logic operations. So we got 2 main approachs that I list above : Modular services Having many modules, each one consisting of a service (WCF). Example: namespaces SystemX.DebtService, SystemX.CreditService, SystemX.SimulatorService Unique service All the business logic is centralized in a unique service. Example: SystemX.OperationService. The web app calls the same service for all operations. In your opinion, whats the best? Or having another approach is better for this scenario?

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  • Separation of memory oriented process and CPU oriented process

    - by Jeevan Dongre
    I am develops guy working for an e-commerce company I am running my e-commerce application built using ruby on rails spree commerce. I am presently running 2 medium instances in the production. One is a high memory instance which has 3.8 RAM and single Core CPU and another one is high CPU instance which has Dual Core CPU. Basically AWS calls it has m1.medium and c1.medium instance respectively. My question is it possible to separate the processes according the cpu intense and memory intense? So that all the cpu intense process can be made run in high cpu instance and all the memory intense process can be made to run in the high memory instances. Is any tool available to identify those process. Kindly give me some heads up. Thank you

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  • Object construction design

    - by James
    I recently started to use c# to interface with a database, and there was one part of the process that appeared odd to me. When creating a SqlCommand, the method I was lead to took the form: SqlCommand myCommand = new SqlCommand("Command String", myConnection); Coming from a Java background, I was expecting something more similar to SqlCommand myCommand = myConnection.createCommand("Command String"); I am asking, in terms of design, what is the difference between the two? The phrase "single responsibility" has been used to suggest that a connection should not be responsible for creating SqlCommands, but I would also say that, in my mind, the difference between the two is partly a mental one of the difference between a connection executing a command and a command acting on a connection, the latter of which seems less like what I have been lead to believe OOP should be. There is also a part of me wondering if the two should be completely separate, and should only come together in some sort of connection.execute(command) method. Can anyone help clear up these differences? Are any of these methods "more correct" than the others from an OO point of view? (P.S. the fact that c# is used is completely irrelevant. It just highlighted to me that different approaches were used)

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  • Benefits of classic OOP over Go-like language

    - by tylerl
    I've been thinking a lot about language design and what elements would be necessary for an "ideal" programming language, and studying Google's Go has led me to question a lot of otherwise common knowledge. Specifically, Go seems to have all of the interesting benefits from object oriented programming without actually having any of the structure of an object oriented language. There are no classes, only structures; there is no class/structure inheritance -- only structure embedding. There aren't any hierarchies, no parent classes, no explicit interface implementations. Instead, type casting rules are based on a loose system similar to duck-typing, such that if a struct implements the necessary elements of a "Reader" or a "Request" or an "Encoding", then you can cast it and use it as one. Does such a system obsolete the concept of OOP? Or is there something about OOP as implemented in C++ and Java and C# that is inherently more capable, more maintainable, somehow more powerful that you have to give up when moving to a language like Go? What benefit do you have to give up to gain the simplicity that this new paradigm represents?

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