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  • Is a "factory" method the right pattern?

    - by jdt141
    Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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  • Is it bad practice to make a setter return "this"?

    - by Ken Liu
    Is it a good or bad idea to make setters in java return "this"? public Employee setName(String name){ this.name = name; return this; } This pattern can be useful because then you can chain setters like this: list.add(new Employee().setName("Jack Sparrow").setId(1).setFoo("bacon!")); instead of this: Employee e = new Employee(); e.setName("Jack Sparrow"); ...and so on... list.add(e); ...but it sort of goes against standard convention. I suppose it might be worthwhile just because it can make that setter do something else useful. I've seen this pattern used some places (e.g. JMock, JPA), but it seems uncommon, and only generally used for very well defined APIs where this pattern is used everywhere. Update: What I've described is obviously valid, but what I am really looking for is some thoughts on whether this is generally acceptable, and if there are any pitfalls or related best practices. I know about the Builder pattern but it is a little more involved then what I am describing - as Josh Bloch describes it there is an associated static Builder class for object creation.

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  • How to perform a literal match with regex using wildcard

    - by kashif4u
    I am trying to perform literal match with regular expression using wildcard. string utterance = "Show me customer id 19"; string pattern 1 = "*tom*"; string patter 2 = "*customer id [0-9]*"; Desired results: if (Regex.IsMatch(utterance, pattern 1 )) { MATCH NOT FOUND } if (Regex.IsMatch(utterance, pattern 2 )) { MATCH FOUND } I have tried looking for literal match solution/syntax in wildcard but having difficulty. Could you also enlighten me with with an example on possible Pattern Matching Strength algorithm i.e. if code match 90 select? Note: I have table with 100000 records to perform literal matches from user utterances. Thanks in advance.

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  • Question about design (inheritance, polymorphism)

    - by Dan
    Hi, I have a question about a problem I'm struggling with. Hope you can bear with me. Imagine I have an Object class representing the base class of a hierarchy of physical objects. Later I inherit from it to create an Object1D, Object2D and Object3D classes. Each of these derived classes will have some specific methods and attributes. For example, the 3d object might have functionality to download a 3d model to be used by a renderer. So I'd have something like this: class Object {}; class Object1D : public Object { Point mPos; }; class Object2D : public Object { ... }; class Object3D : public Object { Model mModel; }; Now I'd have a separate class called Renderer, which simply takes an Object as argument and well, renders it :-) In a similar way, I'd like to support different kinds of renderers. For instance, I could have a default one that every object could rely on, and then provide other specific renderers for some kind of objects: class Renderer {}; // Default one class Renderer3D : public Renderer {}; And here comes my problem. A renderer class needs to get an Object as an argument, for example in the constructor in order to retrieve whatever data it needs to render the object. So far so good. But a Renderer3D would need to get an Object3D argument, in order to get not only the basic attributes but also the specific attributes of a 3d object. Constructors would look like this: CRenderer(Object& object); CRenderer3D(Object3D& object); Now how do I specify this in a generic way? Or better yet, is there a better way to design this? I know I could rely on RTTI or similar but I'd like to avoid this if possible as I feel there is probably a better way to deal with this. Thanks in advance!

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  • Implement Exception Handling in ASP.NET C# Project

    - by Shrewd Demon
    hi, I have an application that has many tiers. as in, i have... Presentation Layer (PL) - contains all the html My Codes Layer (CL) - has all my code Entity Layer (EL) - has all the container entities Business Logic Layer (BLL) - has the necessary business logic Data Logic Layer (DLL) - any logic against data Data Access Layer (DAL) - one that accesses data from the database Now i want to provide error handling in my DLL since it is responsible for executing statement like ExecureScalar and all.... And i am confused as to how to go about it...i mean do i catch the error in the DLL and throw it back to the BLL and from there throw it back to my code or what.... can any one please help me how do i implement a clean and easy error handling techinque help you be really appreciated. Thank you.

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  • Separate functionality depending on Role in ASP.NET MVC

    - by Andrew Bullock
    I'm looking for an elegant pattern to solve this problem: I have several user roles in my system, and for many of my controller actions, I need to deal with slightly different data. For example, take /Users/Edit/1 This allows a Moderator to edit a users email address, but Administrators to edit a user's email address and password. I'd like a design for separating the two different bits of action code for the GET and the POST. Solutions I've come up with so far are: Switch inside each method, however this doesn't really help when i want different model arguments on the POST :( Custom controller factory which chooses a UsersController_ForModerators and UsersController_ForAdmins instead of just UsersController from the controller name and current user role Custom action invoker which choose the Edit_ForModerators method in a similar way to above Have an IUsersController and register a different implementation of it in my IoC container as a named instance based on Role Build an implementation of the controller at runtime using Castle DynamicProxy and manipulate the methods to those from role-based implementations Im preferring the named IoC instance route atm as it means all my urls/routing will work seamlessly. Ideas? Suggestions?

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  • Practical rules for premature optimization

    - by DougW
    It seems that the phrase "Premature Optimization" is the buzz-word of the day. For some reason, iphone programmers in particular seem to think of avoiding premature optimization as a pro-active goal, rather than the natural result of simply avoiding distraction. The problem is, the term is beginning to be applied more and more to cases that are completely inappropriate. For example, I've seen a growing number of people say not to worry about the complexity of an algorithm, because that's premature optimization (eg http://stackoverflow.com/questions/2190275/help-sorting-an-nsarray-across-two-properties-with-nssortdescriptor/2191720#2191720). Frankly, I think this is just laziness, and appalling to disciplined computer science. But it has occurred to me that maybe considering the complexity and performance of algorithms is going the way of assembly loop unrolling, and other optimization techniques that are now considered unnecessary. What do you think? Are we at the point now where deciding between an O(n^n) and O(n!) complexity algorithm is irrelevant? What about O(n) vs O(n*n)? What do you consider "premature optimization"? What practical rules do you use to consciously or unconsciously avoid it? This is a bit vague, but I'm curious to hear other peoples' opinions on the topic.

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  • Java library class to handle scheduled execution of "callbacks"?

    - by Hanno Fietz
    My program has a component - dubbed the Scheduler - that lets other components register points in time at which they want to be called back. This should work much like the Unix cron service, i. e. you tell the Scheduler "notify me at ten minutes past every full hour". I realize there are no real callbacks in Java. Here's my approach, is there a library which already does this stuff? Feel free to suggest improvements, too. Register call to Scheduler passes: a time specification containing hour, minute, second, year month, dom, dow, where each item may be unspecified, meaning "execute it every hour / minute etc." (just like crontabs) an object containing data that will tell the calling object what to do when it is notified by the Scheduler. The Scheduler does not process this data, just stores it and passes it back upon notification. a reference to the calling object Upon startup, or after a new registration request, the Scheduler starts with a Calendar object of the current system time and checks if there are any entries in the database that match this point in time. If there are, they are executed and the process starts over. If there aren't, the time in the Calendar object is incremented by one second and the entreis are rechecked. This repeats until there is one entry or more that match(es). (Discrete Event Simulation) The Scheduler will then remember that timestamp, sleep and wake every second to check if it is already there. If it happens to wake up and the time has already passed, it starts over, likewise if the time has come and the jobs have been executed. Edit: Thanks for pointing me to Quartz. I'm looking for something much smaller, however.

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  • Am I abusing Policies?

    - by pmr
    I find myself using policies a lot in my code and usually I'm very happy with that. But from time to time I find myself confronted with using that pattern in situations where the Policies are selected and runtime and I have developed habbits to work around such situations. Usually I start with something like that: class DrawArrays { protected: void sendDraw() const; }; class DrawElements { protected: void sendDraw() const; }; template<class Policy> class Vertices : public Policy { using Policy::sendDraw(); public: void render() const; }; When the policy is picked at runtime I have different choices of working around the situation. Different code paths: if(drawElements) { Vertices<DrawElements> vertices; } else { Vertices<DrawArrays> vertices; } Inheritance and virtual calls: class PureVertices { public: void render()=0; }; template<class Policy> class Vertices : public PureVertices, public Policy { //.. }; Both solutions feel wrong to me. The first creates an umaintainable mess and the second introduces the overhead of virtual calls that I tried to avoid by using policies in the first place. Am I missing the proper solutions or do I use the wrong pattern to solve the problem?

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  • Is there a recommended way to use the Observer pattern in MVP using GWT?

    - by Tomislav Nakic-Alfirevic
    I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed. These are (some of) my goals: - the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*) - the view knows nothing about the model or the presenter - the model knows nothing of the view or the presenter (...obviously) I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified. What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

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  • Is there any reason for an object pool to not be treated as a singleton?

    - by Chris Charabaruk
    I don't necessarily mean implemented using the singleton pattern, but rather, only having and using one instance of a pool. I don't like the idea of having just one pool (or one per pooled type). However, I can't really come up with any concrete situations where there's an advantage to multiple pools for mutable types, at least not any where a single pool can function just as well. What advantages are there to having multiple pools over a singleton pool?

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  • Is It Incorrect to Make Domain Objects Aware of The Data Access Layer?

    - by Noah Goodrich
    I am currently working on rewriting an application to use Data Mappers that completely abstract the database from the Domain layer. However, I am now wondering which is the better approach to handling relationships between Domain objects: Call the necessary find() method from the related data mapper directly within the domain object Write the relationship logic into the native data mapper (which is what the examples tend to do in PoEAA) and then call the native data mapper function within the domain object. Either it seems to me that in order to preserve the 'Fat Model, Skinny Controller' mantra, the domain objects have to be aware of the data mappers (whether it be their own or that they have access to the other mappers in the system). Additionally it seems that Option 2 unnecessarily complicates the data access layer as it creates table access logic across multiple data mappers instead of confining it to a single data mapper. So, is it incorrect to make the domain objects aware of the related data mappers and to call data mapper functions directly from the domain objects? Update: These are the only two solutions that I can envision to handle the issue of relations between domain objects. Any example showing a better method would be welcome.

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  • Silverlight Async Design Pattern Issue

    - by Mike Mengell
    I'm in the middle of a Silverlight application and I have a function which needs to call a webservice and using the result complete the rest of the function. My issue is that I would have normally done a synchronous web service call got the result and using that carried on with the function. As Silverlight doesn't support synchronous web service calls without additional custom classes to mimic it, I figure it would be best to go with the flow of async rather than fight it. So my question relates around whats the best design pattern for working with async calls in program flow. In the following example I want to use the myFunction TypeId parameter depending on the return value of the web service call. But I don't want to call the web service until this function is called. How can I alter my code design to allow for the async call? string _myPath; bool myFunction(Guid TypeId) { WS_WebService1.WS_WebService1SoapClient proxy = new WS_WebService1.WS_WebService1SoapClient(); proxy.GetPathByTypeIdCompleted += new System.EventHandler<WS_WebService1.GetPathByTypeIdCompleted>(proxy_GetPathByTypeIdCompleted); proxy.GetPathByTypeIdAsync(TypeId); // Get return value if (myPath == "\\Server1") { //Use the TypeId parameter in here } } void proxy_GetPathByTypeIdCompleted(object sender, WS_WebService1.GetPathByTypeIdCompletedEventArgs e) { string server = e.Result.Server; myPath = '\\' + server; } Thanks in advance, Mike

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  • Disposing underlying object from finalizer in an immutable object

    - by Juan Luis Soldi
    I'm trying to wrap around Awesomium and make it look to the rest of my code as close as possible to NET's WebBrowser since this is for an existing application that already uses the WebBrowser. In this library, there is a class called JSObject which represents a javascript object. You can get one of this, for instance, by calling the ExecuteJavascriptWithResult method of the WebView class. If you'd call it like myWebView.ExecuteJavascriptWithResult("document", string.Empty).ToObject(), then you'd get a JSObject that represents the document. I'm writing an immutable class (it's only field is a readonly JSObject object) called JSObjectWrap that wraps around JSObject which I want to use as base class for other classes that would emulate .NET classes such as HtmlElement and HtmlDocument. Now, these classes don't implement Dispose, but JSObject does. What I first thought was to call the underlying JSObject's Dispose method in my JSObjectWrap's finalizer (instead of having JSObjectWrap implement Dispose) so that the rest of my code can stay the way it is (instead of having to add using's everywhere and make sure every JSObjectWrap is being properly disposed). But I just realized if more than two JSObjectWrap's have the same underlying JSObject and one of them gets finalized this will mess up the other JSObjectWrap. So now I'm thinking maybe I should keep a static Dictionary of JSObjects and keep count of how many of each of them are being referenced by a JSObjectWrap but this sounds messy and I think could cause major performance issues. Since this sounds to me like a common pattern I wonder if anyone else has a better idea.

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  • Problem implementing Interceptor pattern

    - by ph0enix
    I'm attempting to develop an Interceptor framework (in C#) where I can simply implement some interfaces, and through the use of some static initialization, register all my Interceptors with a common Dispatcher to be invoked at a later time. The problem lies in the fact that my Interceptor implementations are never actually referenced by my application so the static constructors never get called, and as a result, the Interceptors are never registered. If possible, I would like to keep all references to my Interceptor libraries out of my application, as this is my way of (hopefully) enforcing loose coupling across different modules. Hopefully this makes some sense. Let me know if there's anything I can clarify... Does anyone have any ideas, or perhaps a better way to go about implementing my Interceptor pattern? Update: I came across Spring.NET. I've heard of it before, but never really looked into it. It sounds like it has a lot of great features that would be very useful for what I'm trying to do. Does anyone have any experience with Spring.NET? TIA, Jeremy

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  • Can the Singleton be replaced by Factory?

    - by lostiniceland
    Hello Everyone There are already quite some posts about the Singleton-Pattern around, but I would like to start another one on this topic since I would like to know if the Factory-Pattern would be the right approach to remove this "anti-pattern". In the past I used the singleton quite a lot, also did my fellow collegues since it is so easy to use. For example, the Eclipse IDE or better its workbench-model makes heavy usage of singletons as well. It was due to some posts about E4 (the next big Eclipse version) that made me start to rethink the singleton. The bottom line was that due to this singletons the dependecies in Eclipse 3.x are tightly coupled. Lets assume I want to get rid of all singletons completely and instead use factories. My thoughts were as follows: hide complexity less coupling I have control over how many instances are created (just store the reference I a private field of the factory) mock the factory for testing (with Dependency Injection) when it is behind an interface In some cases the factories can make more than one singleton obsolete (depending on business logic/component composition) Does this make sense? If not, please give good reasons for why you think so. An alternative solution is also appreciated. Thanks Marc

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  • Using DTOs and BOs

    - by ryanzec
    One area of question for me about DTOs/BOs is about when to pass/return the DTOs and when to pass/return the BOs. My gut reaction tells me to always map NHibernate to the DTOs, not BOs, and always pass/return the DTOs. Then whenever I needed to perform business logic, I would convert my DTO into a BO. The way I would do this is that my BO would have a have a constructor that takes a parameter that is the type of my interface (that defines the required fields/properties) that both my DTO and BO implement as the only argument. Then I would be able to create my BO by passing it the DTO in the constructor (since both with implement the same interface, they both with have the same properties) and then be able to perform my business logic with that BO. I would then also have a way to convert a BO to a DTO. However, I have also seen where people seem to only work with BOs and only work with DTOs in the background where to the user, it looks like there are no DTOs. What benefits/downfalls are there with this architecture vs always using BO's? Should I always being passing/returning either DTOs or BOs or mix and match (seems like mixing and matching could get confusing)?

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  • How to avoid having very large objects with Domain Driven Design

    - by Pablojim
    We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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  • Has anyone ever encountered a Monad Transformer in the wild?

    - by martingw
    In my area of business - back office IT for a financial institution - it is very common for a software component to carry a global configuration around, to log it's progress, to have some kind of error handling / computation short circuit... Things that can be modelled nicely by Reader-, Writer-, Maybe-monads and the like in Haskell and composed together with monad transformers. But there seem to some drawbacks: The concept behind monad transformers is quite tricky and hard to understand, monad transformers lead to very complex type signatures, and they inflict some performance penalty. So I'm wondering: Are monad transformers best practice when dealing with those common tasks mentioned above?

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  • Is this a well known design pattern? what is it's name

    - by GenEric35
    Hi I have seen this often in code, but when I speak of it i don't know the name of such 'pattern' I have a method with 2 arguments that calls an overloaded method that has 3 arguments and intentionality sets the 3rd one to empty string. public DoWork(string name, string phoneNumber) { CreateContact(name, phoneNumber, string.Empty) } public DoWork(string name, string phoneNumber, string emailAddress) { //do the work } The reason I'm doing this is I to not duplicate code, and allow the existing callers to still call the method that has only 2 parameters. I have associate a few tags to this question, but it probably fit in more categories of questions. Is this a pattern, and does it have a name?

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