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  • Writing my own implementation of stl-like Iterator in C++.

    - by Negai
    Good evening everybody, I'm currently trying to understand the intrinsics of iterators in various languages i.e. the way they are implemented. For example, there is the following class exposing the list interface. template<class T> class List { public: virtual void Insert( int beforeIndex, const T item ) throw( ListException ) =0 ; virtual void Append( const T item ) =0; virtual T Get( int position ) const throw( ListException ) =0; virtual int GetLength() const =0; virtual void Remove( int position ) throw( ListException ) =0; virtual ~List() =0 {}; }; According to GoF, the best way to implement an iterator that can support different kinds of traversal is to create the base Iterator class (friend of List) with protected methods that can access List's members. The concrete implementations of Iterator will handle the job in different ways and access List's private and protected data through the base interface. From here forth things are getting confusing. Say, I have class LinkedList and ArrayList, both derived from List, and there are also corresponding iterators, each of the classes returns. How can I implement LinkedListIterator? I'm absolutely out of ideas. And what kind of data can the base iterator class retrieve from the List (which is a mere interface, while the implementations of all the derived classes differ significantly) ? Sorry for so much clutter. Thanks.

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  • Is it possible to see the underlying implementation of built in functions of matlab?

    - by user198729
    I'm using this example code to grayscale an image,but the result is not right: I = imread('coins.png'); level = graythresh(I); BW = im2bw(I,level); imshow(BW) Where to see how graythresh is actually implemented? BTW,is there a reason for using matlab feels so alike with python? Or is it known that graythresh doesn't work well for images with little spatial resolution(like 62*21 ones)?

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  • In Castle Windsor, can I register a Interface component and get a proxy of the implementation?

    - by Thiado de Arruda
    Lets consider some cases: _windsor.Register(Component.For<IProductServices>().ImplementedBy<ProductServices>().Interceptors(typeof(SomeInterceptorType)); In this case, when I ask for a IProductServices windsor will proxy the interface to intercept the interface method calls. If instead I do this : _windsor.Register(Component.For<ProductServices>().Interceptors(typeof(SomeInterceptorType)); then I cant ask for windsor to resolve IProductServices, instead I ask for ProductServices and it will return a dynamic subclass that will intercept virtual method calls. Of course the dynamic subclass still implements 'IProductServices' My question is : Can I register the Interface component like the first case, and get the subclass proxy like in the second case?. There are two reasons for me wanting this: 1 - Because the code that is going to resolve cannot know about the ProductServices class, only about the IProductServices interface. 2 - Because some event invocations that pass the sender as a parameter, will pass the ProductServices object, and in the first case this object is a field on the dynamic proxy, not the real object returned by windsor. Let me give an example of how this can complicate things : Lets say I have a custom collection that does something when their items notify a property change: private void ItemChanged(object sender, PropertyChangedEventArgs e) { int senderIndex = IndexOf(sender); SomeActionOnItemIndex(senderIndex); } This code will fail if I added an interface proxy, because the sender will be the field in the interface proxy and the IndexOf(sender) will return -1.

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  • Is my code a correct implementation of insertion sort?

    - by user1657171
    This code sorts correctly. Is this an insertion sort? import java.util.Scanner; public class InsertionSort { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("Enter the number of elements: "); int count; count = sc.nextInt(); int[] a = new int[count]; System.out.println("Enter elements: "); for(int i = 0 ; i<count;i++){ a[i] = sc.nextInt(); } int j,temp; System.out.println("aftr insertion sort :"); for(int i = 1 ; i<count;i++){ j=i; while(j>0 && a[j-1] > a[j] ){ temp = a[j]; a[j] = a[j-1]; a[j-1] = temp; j--; } } for(int i = 0 ; i<count;i++){ System.out.print(a[i]+" "); } } }

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  • What is the best Networking implementation for my application?

    - by CaptainPhil
    I am in the planning phases of a project for myself, it is to be a single and multi-player card game. I would like to track statistics for each person such as world rankings etc... My problem is I do not know the best approach for the client - server architecture and programming. My original goal was to program everything in C# as I want to get proficient in that language. My original idea was to have a back-end database and a back end server run on some sort of hosting on the internet, however that seems costly for such a small project that may or may not make any money. I have tried looking into cloud services however I am unfamiliar with the technology, and I am not sure I can make them suit my needs, especially since most like Google's cloud wants you to use their coding architecture from what I understand. Finally my last problem is that I would like an architecture that can be used for different languages so that I can port it from PC to IPhone, Xbox etc... So does anyone have any advice on the best architecture and language to do this in? Am I worrying about architecture and back-end costs to much and should just concentrate on getting the game running any which way?

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  • Is there any difference in the implementation of these three validation methods?

    - by dontWatchMyProfile
    Core Data is calling these methods in certain situations: - (BOOL)validateForInsert:(NSError **)outError; - (BOOL)validateForUpdate:(NSError **)outError; - (BOOL)validateForDelete:(NSError **)outError; I wonder if they're doing anything different, or if they're essentially doing the exact same things. As far as I know, these methods call the -validateValue:forKey:error: method once for every property. The only difference I can imagine is in the .validateForDelete: method. I see no reason why to validate an object when it shall be deleted, except for applying delete rules, probably only in the case of the DENY rule.

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  • Is it possible to link a method marked with MethodImplOptions.InternalCall to its implementation?

    - by adrianbanks
    In trying to find the possible cause of an exception, I'm following a code path using Reflector. I've got deeper and deeper, but ended up at a method call that looks like: [MethodImpl(MethodImplOptions.InternalCall)] private extern void SomeMethod(int someParameter); This markup on the method tells the framework to call a C++ function somewhere. Is there any way to find out what method actually gets called, and in turn what else is likely to be called? NB: I don't really want to see the source code of this method, I just want to know the possible things that could throw the exception I am seeing that originates out of this method call.

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  • Should I use an interface or factory (and interface) for a cross-platform implementation?

    - by nbolton
    Example A: // pseudo code interface IFoo { void bar(); } class FooPlatformA : IFoo { void bar() { /* ... */ } } class FooPlatformB : IFoo { void bar() { /* ... */ } } class Foo : IFoo { IFoo m_foo; public Foo() { if (detectPlatformA()} { m_foo = new FooPlatformA(); } else { m_foo = new FooPlatformB(); } } // wrapper function - downside is we'd have to create one // of these for each function, which doesn't seem right. void bar() { m_foo.bar(); } } Main() { Foo foo = new Foo(); foo.bar(); } Example B: // pseudo code interface IFoo { void bar(); } class FooPlatformA : IFoo { void bar() { /* ... */ } } class FooPlatformB : IFoo { void bar() { /* ... */ } } class FooFactory { IFoo newFoo() { if (detectPlatformA()} { return new FooPlatformA(); } else { return new FooPlatformB(); } } } Main() { FooFactory factory = new FooFactory(); IFoo foo = factory.newFoo(); foo.bar(); } Which is the better option, example A, B, neither, or "it depends"?

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  • How to implement a tiered "selection tree" in Swing? (Or: is there an existing implementation?)

    - by Sbodd
    I need a Swing component that will let me display a tree-structured list of items, and allow the user to select or de-select an arbitrary subset of those items, with the ability to select or deselect an entire subtree's worth of components by picking that subtree's parent. (Basically, something similar to the Eclipse "Export JAR file's" dialog (an image of the relevant dialog is here - I basically want the "Select resources to export" component, but for a Swing application.) I know I can do this by creating a custom TreeCellRenderer, a custom TreeCellEditor, and a custom TreeModel - but that seems like an awful lot of work. Are there any good off-the-shelf implementations that I can use? Thanks!

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  • Behind ASP.NET MVC Mock Objects

    - by imran_ku07
       Introduction:           I think this sentence now become very familiar to ASP.NET MVC developers that "ASP.NET MVC is designed with testability in mind". But what ASP.NET MVC team did for making applications build with ASP.NET MVC become easily testable? Understanding this is also very important because it gives you some help when designing custom classes. So in this article i will discuss some abstract classes provided by ASP.NET MVC team for the various ASP.NET intrinsic objects, including HttpContext, HttpRequest, and HttpResponse for making these objects as testable. I will also discuss that why it is hard and difficult to test ASP.NET Web Forms.      Description:           Starting from Classic ASP to ASP.NET MVC, ASP.NET Intrinsic objects is extensively used in all form of web application. They provide information about Request, Response, Server, Application and so on. But ASP.NET MVC uses these intrinsic objects in some abstract manner. The reason for this abstraction is to make your application testable. So let see the abstraction.           As we know that ASP.NET MVC uses the same runtime engine as ASP.NET Web Form uses, therefore the first receiver of the request after IIS and aspnet_filter.dll is aspnet_isapi.dll. This will start the application domain. With the application domain up and running, ASP.NET does some initialization and after some initialization it will call Application_Start if it is defined. Then the normal HTTP pipeline event handlers will be executed including both HTTP Modules and global.asax event handlers. One of the HTTP Module is registered by ASP.NET MVC is UrlRoutingModule. The purpose of this module is to match a route defined in global.asax. Every matched route must have IRouteHandler. In default case this is MvcRouteHandler which is responsible for determining the HTTP Handler which returns MvcHandler (which is derived from IHttpHandler). In simple words, Route has MvcRouteHandler which returns MvcHandler which is the IHttpHandler of current request. In between HTTP pipeline events the handler of ASP.NET MVC, MvcHandler.ProcessRequest will be executed and shown as given below,          void IHttpHandler.ProcessRequest(HttpContext context)          {                    this.ProcessRequest(context);          }          protected virtual void ProcessRequest(HttpContext context)          {                    // HttpContextWrapper inherits from HttpContextBase                    HttpContextBase ctxBase = new HttpContextWrapper(context);                    this.ProcessRequest(ctxBase);          }          protected internal virtual void ProcessRequest(HttpContextBase ctxBase)          {                    . . .          }             HttpContextBase is the base class. HttpContextWrapper inherits from HttpContextBase, which is the parent class that include information about a single HTTP request. This is what ASP.NET MVC team did, just wrap old instrinsic HttpContext into HttpContextWrapper object and provide opportunity for other framework to provide their own implementation of HttpContextBase. For example           public class MockHttpContext : HttpContextBase          {                    . . .          }                     As you can see, it is very easy to create your own HttpContext. That's what did the third party mock frameworks like TypeMock, Moq, RhinoMocks, or NMock2 to provide their own implementation of ASP.NET instrinsic objects classes.           The key point to note here is the types of ASP.NET instrinsic objects. In ASP.NET Web Form and ASP.NET MVC. For example in ASP.NET Web Form the type of Request object is HttpRequest (which is sealed) and in ASP.NET MVC the type of Request object is HttpRequestBase. This is one of the reason that makes test in ASP.NET WebForm is difficult. because their is no base class and the HttpRequest class is sealed, therefore it cannot act as a base class to others. On the other side ASP.NET MVC always uses a base class to give a chance to third parties and unit test frameworks to create thier own implementation ASP.NET instrinsic object.           Therefore we can say that in ASP.NET MVC, instrinsic objects are of type base classes (for example HttpContextBase) .Actually these base classes had it's own implementation of same interface as the intrinsic objects it abstracts. It includes only virtual members which simply throws an exception. ASP.NET MVC also provides the corresponding wrapper classes (for example, HttpRequestWrapper) which provides a concrete implementation of the base classes in the form of ASP.NET intrinsic object. Other wrapper classes may be defined by third parties in the form of a mock object for testing purpose.           So we can say that a Request object in ASP.NET MVC may be HttpRequestWrapper or may be MockRequestWrapper(assuming that MockRequestWrapper class is used for testing purpose). Here is list of ASP.NET instrinsic and their implementation in ASP.NET MVC in the form of base and wrapper classes. Base Class Wrapper Class ASP.NET Intrinsic Object Description HttpApplicationStateBase HttpApplicationStateWrapper Application HttpApplicationStateBase abstracts the intrinsic Application object HttpBrowserCapabilitiesBase HttpBrowserCapabilitiesWrapper HttpBrowserCapabilities HttpBrowserCapabilitiesBase abstracts the HttpBrowserCapabilities class HttpCachePolicyBase HttpCachePolicyWrapper HttpCachePolicy HttpCachePolicyBase abstracts the HttpCachePolicy class HttpContextBase HttpContextWrapper HttpContext HttpContextBase abstracts the intrinsic HttpContext object HttpFileCollectionBase HttpFileCollectionWrapper HttpFileCollection HttpFileCollectionBase abstracts the HttpFileCollection class HttpPostedFileBase HttpPostedFileWrapper HttpPostedFile HttpPostedFileBase abstracts the HttpPostedFile class HttpRequestBase HttpRequestWrapper Request HttpRequestBase abstracts the intrinsic Request object HttpResponseBase HttpResponseWrapper Response HttpResponseBase abstracts the intrinsic Response object HttpServerUtilityBase HttpServerUtilityWrapper Server HttpServerUtilityBase abstracts the intrinsic Server object HttpSessionStateBase HttpSessionStateWrapper Session HttpSessionStateBase abstracts the intrinsic Session object HttpStaticObjectsCollectionBase HttpStaticObjectsCollectionWrapper HttpStaticObjectsCollection HttpStaticObjectsCollectionBase abstracts the HttpStaticObjectsCollection class      Summary:           ASP.NET MVC provides a set of abstract classes for ASP.NET instrinsic objects in the form of base classes, allowing someone to create their own implementation. In addition, ASP.NET MVC also provide set of concrete classes in the form of wrapper classes. This design really makes application easier to test and even application may replace concrete implementation with thier own implementation, which makes ASP.NET MVC very flexable.

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  • Making your WCF Web Apis to speak in multiple languages

    - by cibrax
    One of the key aspects of how the web works today is content negotiation. The idea of content negotiation is based on the fact that a single resource can have multiple representations, so user agents (or clients) and servers can work together to chose one of them. The http specification defines several “Accept” headers that a client can use to negotiate content with a server, and among all those, there is one for restricting the set of natural languages that are preferred as a response to a request, “Accept-Language”. For example, a client can specify “es” in this header for specifying that he prefers to receive the content in spanish or “en” in english. However, there are certain scenarios where the “Accept-Language” header is just not enough, and you might want to have a way to pass the “accepted” language as part of the resource url as an extension. For example, http://localhost/ProductCatalog/Products/1.es” returns all the descriptions for the product with id “1” in spanish. This is useful for scenarios in which you want to embed the link somewhere, such a document, an email or a page.  Supporting both scenarios, the header and the url extension, is really simple in the new WCF programming model. You only need to provide a processor implementation for any of them. Let’s say I have a resource implementation as part of a product catalog I want to expose with the WCF web apis. [ServiceContract][Export]public class ProductResource{ IProductRepository repository;  [ImportingConstructor] public ProductResource(IProductRepository repository) { this.repository = repository; }  [WebGet(UriTemplate = "{id}")] public Product Get(string id, HttpResponseMessage response) { var product = repository.GetById(int.Parse(id)); if (product == null) { response.StatusCode = HttpStatusCode.NotFound; response.Content = new StringContent(Messages.OrderNotFound); }  return product; }} The Get method implementation in this resource assumes the desired culture will be attached to the current thread (Thread.CurrentThread.Culture). Another option is to pass the desired culture as an additional argument in the method, so my processor implementation will handle both options. This method is also using an auto-generated class for handling string resources, Messages, which is available in the different cultures that the service implementation supports. For example, Messages.resx contains “OrderNotFound”: “Order Not Found” Messages.es.resx contains “OrderNotFound”: “No se encontro orden” The processor implementation bellow tackles the first scenario, in which the desired language is passed as part of the “Accept-Language” header. public class CultureProcessor : Processor<HttpRequestMessage, CultureInfo>{ string defaultLanguage = null;  public CultureProcessor(string defaultLanguage = "en") { this.defaultLanguage = defaultLanguage; this.InArguments[0].Name = HttpPipelineFormatter.ArgumentHttpRequestMessage; this.OutArguments[0].Name = "culture"; }  public override ProcessorResult<CultureInfo> OnExecute(HttpRequestMessage request) { CultureInfo culture = null; if (request.Headers.AcceptLanguage.Count > 0) { var language = request.Headers.AcceptLanguage.First().Value; culture = new CultureInfo(language); } else { culture = new CultureInfo(defaultLanguage); }  Thread.CurrentThread.CurrentCulture = culture; Messages.Culture = culture;  return new ProcessorResult<CultureInfo> { Output = culture }; }}   As you can see, the processor initializes a new CultureInfo instance with the value provided in the “Accept-Language” header, and set that instance to the current thread and the auto-generated resource class with all the messages. In addition, the CultureInfo instance is returned as an output argument called “culture”, making possible to receive that argument in any method implementation   The following code shows the implementation of the processor for handling languages as url extensions.   public class CultureExtensionProcessor : Processor<HttpRequestMessage, Uri>{ public CultureExtensionProcessor() { this.OutArguments[0].Name = HttpPipelineFormatter.ArgumentUri; }  public override ProcessorResult<Uri> OnExecute(HttpRequestMessage httpRequestMessage) { var requestUri = httpRequestMessage.RequestUri.OriginalString;  var extensionPosition = requestUri.LastIndexOf(".");  if (extensionPosition > -1) { var extension = requestUri.Substring(extensionPosition + 1);  var query = httpRequestMessage.RequestUri.Query;  requestUri = string.Format("{0}?{1}", requestUri.Substring(0, extensionPosition), query); ;  var uri = new Uri(requestUri);  httpRequestMessage.Headers.AcceptLanguage.Clear();  httpRequestMessage.Headers.AcceptLanguage.Add(new StringWithQualityHeaderValue(extension));  var result = new ProcessorResult<Uri>();  result.Output = uri;  return result; }  return new ProcessorResult<Uri>(); }} The last step is to inject both processors as part of the service configuration as it is shown bellow, public void RegisterRequestProcessorsForOperation(HttpOperationDescription operation, IList<Processor> processors, MediaTypeProcessorMode mode){ processors.Insert(0, new CultureExtensionProcessor()); processors.Add(new CultureProcessor());} Once you configured the two processors in the pipeline, your service will start speaking different languages :). Note: Url extensions don’t seem to be working in the current bits when you are using Url extensions in a base address. As far as I could see, ASP.NET intercepts the request first and tries to route the request to a registered ASP.NET Http Handler with that extension. For example, “http://localhost/ProductCatalog/products.es” does not work, but “http://localhost/ProductCatalog/products/1.es” does.

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  • Sharing authentication methods across API and web app

    - by Snixtor
    I'm wanting to share an authentication implementation across a web application, and web API. The web application will be ASP.NET (mostly MVC 4), the API will be mostly ASP.NET WEB API, though I anticipate it will also have a few custom modules or handlers. I want to: Share as much authentication implementation between the app and API as possible. Have the web application behave like forms authentication (attractive log-in page, logout option, redirect to / from login page when a request requires authentication / authorisation). Have API callers use something closer to standard HTTP (401 - Unauthorized, not 302 - Redirect). Provide client and server side logout mechanisms that don't require a change of password (so HTTP basic is out, since clients typically cache their credentials). The way I'm thinking of implementing this is using plain old ASP.NET forms authentication for the web application, and pushing another module into the stack (much like MADAM - Mixed Authentication Disposition ASP.NET Module). This module will look for some HTTP header (implementation specific) which indicates "caller is API". If the header "caller is API" is set, then the service will respond differently than standard ASP.NET forms authentication, it will: 401 instead of 302 on a request lacking authentication. Look for username + pass in a custom "Login" HTTP header, and return a FormsAuthentication ticket in a custom "FormsAuth" header. Look for FormsAuthentication ticket in a custom "FormsAuth" header. My question(s) are: Is there a framework for ASP.NET that already covers this scenario? Are there any glaring holes in this proposed implementation? My primary fear is a security risk that I can't see, but I'm similarly concerned that there may be something about such an implementation that will make it overly restrictive or clumsy to work with.

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  • Should these concerns be separated into separate objects?

    - by Lewis Bassett
    I have objects which implement the interface BroadcastInterface, which represents a message that is to be broadcast to all users of a particular group. It has a setter and getter method for the Subject and Body properties, and an addRecipientRole() method, which takes a given role and finds the contact token (e.g., an email address) for each user in the role and stores it. It then has a getContactTokens() method. BroadcastInterface objects are passed to an object that implements BroadcasterInterface. These objects are responsible for broadcasting a passed BroadcastInterface object. For example, an EmailBroadcaster implementation of the BroadcasterInterface will take EmailBroadcast objects and use the mailer services to email them out. Now, depending on what BroadcasterInterface implementation is used to broadcast, a different implementation of BroadcastInterface is used by client code. The Single Responsibility Principle seems to suggest that I should have a separate BroadcastFactory object, for creating BroadcastInterface objects, depending on what BroadcasterInterface implementation is used, as creating the BroadcastInterface object is a different responsibility to broadcasting them. But the class used for creating BroadcastInterface objects depends on what implementation of BroadcasterInterface is used to broadcast them. I think, because the knowledge of what method is used to send the broadcasts should only be configured once, the BroadcasterInterface object should be responsible for providing new BroadcastInterface objects. Does the responsibility of “creating and broadcasting objects that implement the BroadcastInterface interface” violate the Single Responsibility Principle? (Because the contact token for sending the broadcast out to the users will differ depending on the way it is broadcasted, I need different broadcast classes—though client code will not be able to tell the difference.)

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  • Informed TDD &ndash; Kata &ldquo;To Roman Numerals&rdquo;

    - by Ralf Westphal
    Originally posted on: http://geekswithblogs.net/theArchitectsNapkin/archive/2014/05/28/informed-tdd-ndash-kata-ldquoto-roman-numeralsrdquo.aspxIn a comment on my article on what I call Informed TDD (ITDD) reader gustav asked how this approach would apply to the kata “To Roman Numerals”. And whether ITDD wasn´t a violation of TDD´s principle of leaving out “advanced topics like mocks”. I like to respond with this article to his questions. There´s more to say than fits into a commentary. Mocks and TDD I don´t see in how far TDD is avoiding or opposed to mocks. TDD and mocks are orthogonal. TDD is about pocess, mocks are about structure and costs. Maybe by moving forward in tiny red+green+refactor steps less need arises for mocks. But then… if the functionality you need to implement requires “expensive” resource access you can´t avoid using mocks. Because you don´t want to constantly run all your tests against the real resource. True, in ITDD mocks seem to be in almost inflationary use. That´s not what you usually see in TDD demonstrations. However, there´s a reason for that as I tried to explain. I don´t use mocks as proxies for “expensive” resource. Rather they are stand-ins for functionality not yet implemented. They allow me to get a test green on a high level of abstraction. That way I can move forward in a top-down fashion. But if you think of mocks as “advanced” or if you don´t want to use a tool like JustMock, then you don´t need to use mocks. You just need to stand the sight of red tests for a little longer ;-) Let me show you what I mean by that by doing a kata. ITDD for “To Roman Numerals” gustav asked for the kata “To Roman Numerals”. I won´t explain the requirements again. You can find descriptions and TDD demonstrations all over the internet, like this one from Corey Haines. Now here is, how I would do this kata differently. 1. Analyse A demonstration of TDD should never skip the analysis phase. It should be made explicit. The requirements should be formalized and acceptance test cases should be compiled. “Formalization” in this case to me means describing the API of the required functionality. “[D]esign a program to work with Roman numerals” like written in this “requirement document” is not enough to start software development. Coding should only begin, if the interface between the “system under development” and its context is clear. If this interface is not readily recognizable from the requirements, it has to be developed first. Exploration of interface alternatives might be in order. It might be necessary to show several interface mock-ups to the customer – even if that´s you fellow developer. Designing the interface is a task of it´s own. It should not be mixed with implementing the required functionality behind the interface. Unfortunately, though, this happens quite often in TDD demonstrations. TDD is used to explore the API and implement it at the same time. To me that´s a violation of the Single Responsibility Principle (SRP) which not only should hold for software functional units but also for tasks or activities. In the case of this kata the API fortunately is obvious. Just one function is needed: string ToRoman(int arabic). And it lives in a class ArabicRomanConversions. Now what about acceptance test cases? There are hardly any stated in the kata descriptions. Roman numerals are explained, but no specific test cases from the point of view of a customer. So I just “invent” some acceptance test cases by picking roman numerals from a wikipedia article. They are supposed to be just “typical examples” without special meaning. Given the acceptance test cases I then try to develop an understanding of the problem domain. I´ll spare you that. The domain is trivial and is explain in almost all kata descriptions. How roman numerals are built is not difficult to understand. What´s more difficult, though, might be to find an efficient solution to convert into them automatically. 2. Solve The usual TDD demonstration skips a solution finding phase. Like the interface exploration it´s mixed in with the implementation. But I don´t think this is how it should be done. I even think this is not how it really works for the people demonstrating TDD. They´re simplifying their true software development process because they want to show a streamlined TDD process. I doubt this is helping anybody. Before you code you better have a plan what to code. This does not mean you have to do “Big Design Up-Front”. It just means: Have a clear picture of the logical solution in your head before you start to build a physical solution (code). Evidently such a solution can only be as good as your understanding of the problem. If that´s limited your solution will be limited, too. Fortunately, in the case of this kata your understanding does not need to be limited. Thus the logical solution does not need to be limited or preliminary or tentative. That does not mean you need to know every line of code in advance. It just means you know the rough structure of your implementation beforehand. Because it should mirror the process described by the logical or conceptual solution. Here´s my solution approach: The arabic “encoding” of numbers represents them as an ordered set of powers of 10. Each digit is a factor to multiply a power of ten with. The “encoding” 123 is the short form for a set like this: {1*10^2, 2*10^1, 3*10^0}. And the number is the sum of the set members. The roman “encoding” is different. There is no base (like 10 for arabic numbers), there are just digits of different value, and they have to be written in descending order. The “encoding” XVI is short for [10, 5, 1]. And the number is still the sum of the members of this list. The roman “encoding” thus is simpler than the arabic. Each “digit” can be taken at face value. No multiplication with a base required. But what about IV which looks like a contradiction to the above rule? It is not – if you accept roman “digits” not to be limited to be single characters only. Usually I, V, X, L, C, D, M are viewed as “digits”, and IV, IX etc. are viewed as nuisances preventing a simple solution. All looks different, though, once IV, IX etc. are taken as “digits”. Then MCMLIV is just a sum: M+CM+L+IV which is 1000+900+50+4. Whereas before it would have been understood as M-C+M+L-I+V – which is more difficult because here some “digits” get subtracted. Here´s the list of roman “digits” with their values: {1, I}, {4, IV}, {5, V}, {9, IX}, {10, X}, {40, XL}, {50, L}, {90, XC}, {100, C}, {400, CD}, {500, D}, {900, CM}, {1000, M} Since I take IV, IX etc. as “digits” translating an arabic number becomes trivial. I just need to find the values of the roman “digits” making up the number, e.g. 1954 is made up of 1000, 900, 50, and 4. I call those “digits” factors. If I move from the highest factor (M=1000) to the lowest (I=1) then translation is a two phase process: Find all the factors Translate the factors found Compile the roman representation Translation is just a look-up. Finding, though, needs some calculation: Find the highest remaining factor fitting in the value Remember and subtract it from the value Repeat with remaining value and remaining factors Please note: This is just an algorithm. It´s not code, even though it might be close. Being so close to code in my solution approach is due to the triviality of the problem. In more realistic examples the conceptual solution would be on a higher level of abstraction. With this solution in hand I finally can do what TDD advocates: find and prioritize test cases. As I can see from the small process description above, there are two aspects to test: Test the translation Test the compilation Test finding the factors Testing the translation primarily means to check if the map of factors and digits is comprehensive. That´s simple, even though it might be tedious. Testing the compilation is trivial. Testing factor finding, though, is a tad more complicated. I can think of several steps: First check, if an arabic number equal to a factor is processed correctly (e.g. 1000=M). Then check if an arabic number consisting of two consecutive factors (e.g. 1900=[M,CM]) is processed correctly. Then check, if a number consisting of the same factor twice is processed correctly (e.g. 2000=[M,M]). Finally check, if an arabic number consisting of non-consecutive factors (e.g. 1400=[M,CD]) is processed correctly. I feel I can start an implementation now. If something becomes more complicated than expected I can slow down and repeat this process. 3. Implement First I write a test for the acceptance test cases. It´s red because there´s no implementation even of the API. That´s in conformance with “TDD lore”, I´d say: Next I implement the API: The acceptance test now is formally correct, but still red of course. This will not change even now that I zoom in. Because my goal is not to most quickly satisfy these tests, but to implement my solution in a stepwise manner. That I do by “faking” it: I just “assume” three functions to represent the transformation process of my solution: My hypothesis is that those three functions in conjunction produce correct results on the API-level. I just have to implement them correctly. That´s what I´m trying now – one by one. I start with a simple “detail function”: Translate(). And I start with all the test cases in the obvious equivalence partition: As you can see I dare to test a private method. Yes. That´s a white box test. But as you´ll see it won´t make my tests brittle. It serves a purpose right here and now: it lets me focus on getting one aspect of my solution right. Here´s the implementation to satisfy the test: It´s as simple as possible. Right how TDD wants me to do it: KISS. Now for the second equivalence partition: translating multiple factors. (It´a pattern: if you need to do something repeatedly separate the tests for doing it once and doing it multiple times.) In this partition I just need a single test case, I guess. Stepping up from a single translation to multiple translations is no rocket science: Usually I would have implemented the final code right away. Splitting it in two steps is just for “educational purposes” here. How small your implementation steps are is a matter of your programming competency. Some “see” the final code right away before their mental eye – others need to work their way towards it. Having two tests I find more important. Now for the next low hanging fruit: compilation. It´s even simpler than translation. A single test is enough, I guess. And normally I would not even have bothered to write that one, because the implementation is so simple. I don´t need to test .NET framework functionality. But again: if it serves the educational purpose… Finally the most complicated part of the solution: finding the factors. There are several equivalence partitions. But still I decide to write just a single test, since the structure of the test data is the same for all partitions: Again, I´m faking the implementation first: I focus on just the first test case. No looping yet. Faking lets me stay on a high level of abstraction. I can write down the implementation of the solution without bothering myself with details of how to actually accomplish the feat. That´s left for a drill down with a test of the fake function: There are two main equivalence partitions, I guess: either the first factor is appropriate or some next. The implementation seems easy. Both test cases are green. (Of course this only works on the premise that there´s always a matching factor. Which is the case since the smallest factor is 1.) And the first of the equivalence partitions on the higher level also is satisfied: Great, I can move on. Now for more than a single factor: Interestingly not just one test becomes green now, but all of them. Great! You might say, then I must have done not the simplest thing possible. And I would reply: I don´t care. I did the most obvious thing. But I also find this loop very simple. Even simpler than a recursion of which I had thought briefly during the problem solving phase. And by the way: Also the acceptance tests went green: Mission accomplished. At least functionality wise. Now I´ve to tidy up things a bit. TDD calls for refactoring. Not uch refactoring is needed, because I wrote the code in top-down fashion. I faked it until I made it. I endured red tests on higher levels while lower levels weren´t perfected yet. But this way I saved myself from refactoring tediousness. At the end, though, some refactoring is required. But maybe in a different way than you would expect. That´s why I rather call it “cleanup”. First I remove duplication. There are two places where factors are defined: in Translate() and in Find_factors(). So I factor the map out into a class constant. Which leads to a small conversion in Find_factors(): And now for the big cleanup: I remove all tests of private methods. They are scaffolding tests to me. They only have temporary value. They are brittle. Only acceptance tests need to remain. However, I carry over the single “digit” tests from Translate() to the acceptance test. I find them valuable to keep, since the other acceptance tests only exercise a subset of all roman “digits”. This then is my final test class: And this is the final production code: Test coverage as reported by NCrunch is 100%: Reflexion Is this the smallest possible code base for this kata? Sure not. You´ll find more concise solutions on the internet. But LOC are of relatively little concern – as long as I can understand the code quickly. So called “elegant” code, however, often is not easy to understand. The same goes for KISS code – especially if left unrefactored, as it is often the case. That´s why I progressed from requirements to final code the way I did. I first understood and solved the problem on a conceptual level. Then I implemented it top down according to my design. I also could have implemented it bottom-up, since I knew some bottom of the solution. That´s the leaves of the functional decomposition tree. Where things became fuzzy, since the design did not cover any more details as with Find_factors(), I repeated the process in the small, so to speak: fake some top level, endure red high level tests, while first solving a simpler problem. Using scaffolding tests (to be thrown away at the end) brought two advantages: Encapsulation of the implementation details was not compromised. Naturally private methods could stay private. I did not need to make them internal or public just to be able to test them. I was able to write focused tests for small aspects of the solution. No need to test everything through the solution root, the API. The bottom line thus for me is: Informed TDD produces cleaner code in a systematic way. It conforms to core principles of programming: Single Responsibility Principle and/or Separation of Concerns. Distinct roles in development – being a researcher, being an engineer, being a craftsman – are represented as different phases. First find what, what there is. Then devise a solution. Then code the solution, manifest the solution in code. Writing tests first is a good practice. But it should not be taken dogmatic. And above all it should not be overloaded with purposes. And finally: moving from top to bottom through a design produces refactored code right away. Clean code thus almost is inevitable – and not left to a refactoring step at the end which is skipped often for different reasons.   PS: Yes, I have done this kata several times. But that has only an impact on the time needed for phases 1 and 2. I won´t skip them because of that. And there are no shortcuts during implementation because of that.

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  • Managed Service Architectures Part I

    - by barryoreilly
    Instead of thinking about service oriented architecture, a concept that is continually defined, redefined, abused and mistreated, perhaps it is time to drop the acronym and consider what we actually need to get the job done.   ‘Pure’ SOA involves the modeling of an organisation’s processes, the so called ‘Top Down’ approach, followed by the implementation of these processes as services.     Another approach, more commonly seen in the wild, is the bottom up approach. This usually involves services that simply start popping up in the organization, and SOA in this case is often just an attempt to rein in these services. Such projects, although described as SOA projects for a variety of reasons, have clearly little relation to process driven architecture. Much has been written about these two approaches, with many deciding that a hybrid of both methods is needed to succeed with SOA.   These hybrid methods are a sensible compromise, but one gets the feeling that there is too much focus on ‘Succeeding with SOA’. Organisations who focus too much on bottom up development, or who waste too much time and money on top down approaches that don’t produce results, are often recommended to attempt an ‘agile’(Erl) or ‘middle-out’ (Microsoft) approach in order to succeed with SOA.  The problem with recommending this approach is that, in most cases, succeeding with SOA isn’t the aim of the project. If a project is started with the simple aim of ‘Succeeding with SOA’ then the reasons for the projects existence probably need to be questioned.   There are a number of things we can be sure of: ·         An organisation will have a number of disparate IT systems ·         Some of these systems will have redundant data and functionality ·         Integration will give considerable ROI ·         Integration will already be under way. ·         Services will already exist in the organisation ·         These services will be inconsistent in their implementation and in their governance   So there are three goals here: 1.       Alignment between the business and IT 2.     Integration of disparate systems 3.     Management of services.   2 and 3 are going to happen,  in fact they must happen if any degree of return is expected from the IT department. Ignoring 1 is considered a typical mistake in SOA implementations, as it ignores the business implications. However, the business implication of this approach is the money saved in more efficient IT processes. 2 and 3 are ongoing, and they will continue happening, even if a large project to produce a SOA metamodel is started. The result will then be an unstructured cackle of services, and a metamodel that is already going out of date. So we get stuck in and rebuild our services so that they match the metamodel, with the far reaching consequences that this will have on all our LOB systems are current. Lets imagine that this actually works ( how often do we rip and replace working software because it doesn't fit a certain pattern? Never -that's the point of integration), we will now be working with a metamodel that is out of date, and most likely incomplete if the organisation is large.      Accepting that an object can have more than one model over time, with perhaps more than one model being  at any given time will help us realise the limitations of the top down model. It is entirely normal , and perhaps necessary, for an organisation to be able to view an entity from different perspectives.   So, instead of trying to constantly force these goals in a straight line, why not let them happen in parallel, and manage the changes in each layer.     If  company A has chosen to model their business processes and create a business architecture, there will be a reason behind this. Often the aim is to make the business more flexible and able to cope with change, through alignment between the business and the IT department.   If company B’s IT department recognizes the problem of wild services springing up everywhere, and decides to do something about it, by designing a platform and processes for the introduction of services, is this not a valid approach?   With the hybrid approach, it is recommended that company A begin deploying services as quickly as possible. Based on models that are clearly incomplete, and which will therefore change rapidly and often in the near future. Natural business evolution will also mean that the models can be guaranteed to change in the not so near future. To ‘Succeed with SOA’ Company B needs to go back to the drawing board and start modeling processes and objects. So, in effect, we are telling business analysts to start developing code based on a model they are unsure of, and telling programmers to ignore the obvious and growing problems in their IT department and start drawing lines and boxes.     Could the problem be that there are two different problem domains? And the whole concept of SOA as it being described by clever salespeople today creates an example of oft dreaded ‘tight coupling’ between these two domains?   Could it be that we have taken two large problem areas, and bundled the solution together in order to create a magic bullet? And then convinced ourselves that the bullet actually exists?   Company A wants to have a closer relationship between the business and its IT department, in order to become a more flexible organization. Company B wants to decrease the maintenance costs of its IT infrastructure. If both companies focus on succeeding with SOA, then they aren’t focusing on their actual goals.   If Company A starts building services from incomplete models, without a gameplan, they will end up in the same situation as company B, with wild services. If company B focuses on modeling, they could easily end up with the same problems as company A.   Now we have two companies, who a short while ago had one problem each, that now have two problems each. This has happened because of a focus on ‘Succeeding with SOA’, rather than solving the problem at hand.   This is not to suggest that the two problem domains are unrelated, a strategy that encompasses both will obviously be good for the organization. But only if the organization realizes this and can develop such a strategy. This strategy cannot be bought in a box.       Anyone who has worked with SOA for a while will be used to analyzing the solutions to a problem and judging the solution’s level of coupling. If we have two applications that each perform separate functions, but need to communicate with each other, we create a integration layer between them, perhaps with a service, but we do all we can to reduce the dependency between the two systems. Using the same approach, we can separate the modeling (business architecture) and the service hosting (technical architecture).     The business architecture describes the processes and business objects in the business domain.   The technical architecture describes the hosting and management and implementation of services.   The glue that binds these together, the integration layer in our analogy, is the service contract, where the operations map the processes to their technical implementation, and the messages map business concepts to software objects in the implementation.   If we reduce the coupling between these layers, we should be able to allow developers to develop services, and business analysts to develop models, without the changes rippling through from one side to the other.   This would allow company A to carry on modeling, and company B to develop a service platform, each achieving their intended goal, without necessarily creating the problems seen in pure top down or bottom up approaches. Company B could then at a later date map their service infrastructure to a unified model, and company A could carry on modeling, insulating deployed services from changes in the ongoing modeling.   How do we do this?  The concept of service virtualization has been around for a while, and is instantly realizable in Microsoft’s Managed Services Engine. Here we can create a layer of virtual services, which represent the business analyst’s view, presenting uniform contracts to the outside world. These services can then transform and route messages to the actual service implementations. I like to think of the virtual services with their beautifully modeled interfaces as ‘SOA services’, and the implementations as simple integration ‘adapter’ services providing an interface to a technical implementation. The Managed Services Engine also provides policy based control over services, regardless of where they are deployed, simplifying handling of security, logging, exception handling etc.   This solves a big problem. The pressure to deliver services quickly is always there in projects. It is very important to quickly show value when implementing service architectures. There is also pressure to deliver quality, and you can’t easily do both at the same time. This approach allows quick delivery with quality increasing over time, allowing modeling and service development to occur in parallel and independent of each other. The link between business modeling and service implementation is not one that is obvious to many organizations, and requires a certain maturity to realize and drive forward. It is also completely possible that a company can benefit from one without the other, even if this approach is frowned upon today, there are many companies doing so and seeing ROI.   Of course there are disadvantages to this. The biggest one being the transformations necessary between the virtual interfaces and the service implementations. Bad choices in developing the services in the service implementation could mean that it is impossible to map the modeled processes to the implementation with redevelopment of the service. In many cases the architect will not have a choice here anyway, as proprietary systems are often delivered with predeveloped services. The alternative is to wait until the model is finished and then build the service according the model. However, if that approach worked we wouldn’t be having this discussion! And even when it does work, natural business evolution will mean that the two concepts (model and implementation) will immediately start to drift away from each other, so coupling them tightly together so that they are forever bound to the model that only applies at the time of the modeling work will not really achieve a great deal. Architecture is all about trade offs, and here a choice has to be made. The choice is between something will initially be of low quality but will work, or something that may well be impossible to achieve in most situations.         In conclusion, top-down is a natural approach for business analysts, and bottom-up  is a natural approach for developers. Instead of trying to force something on both that neither want, and which has not shown itself to be successful,  why not let them get on with their jobs, and let an enterprise architect coordinate the processes?

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