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  • What does "static" mean in the context of declaring global template functions?

    - by smf68
    I know what static means in the context of declaring global non-template functions (see e.g. What is a "static" function?), which is useful if you write a helper function in a header that is included from several different locations and want to avoid "duplicate definition" errors. So my question is: What does static mean in the context of declaring global template functions? Please note that I'm specifically asking about global, non-member template functions that do not belong to a class. In other words, what is the difference between the following two: template <typename T> void foo(T t) { /* implementation of foo here */ } template <typename T> static void bar(T t) { /* implementation of bar here */ }

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  • Text replacement for multiple script/config files

    - by user343804
    I am doing some sort of science with a combination of Python, bash scripts and configuration files with weird syntaxes from old C programs. To run different tests, I have to tune (open text file, edit and save) a number of these files, but it is getting harder and harder to remember which files to edit. Also, the tasks are very repetitive and I end having a bunch of comment lines, switching on and off the settings for a specific run. I dream of a tool that can keep a list of files (regardless of the file format) and allow me to centrally choose from a predefined list of "profiles", taking care of editing the script/config files. For example lets say I have a config and script file: config.cfg var1 = 1.0 #var1 = 1.5 script.sct function(200.0) #function(300.0) I would like to instead have auxiliary text files: config.cfg.tem var1 = $$var1$$ script.sct.tem function($$par1$$) and in a central script or even better, a GUI, just switch from profile1 (e.g. var1=1.0,par1=200.0) to profile2 (e.g. var1=1.5,par1=300.0), and the tool to automatically update the text files. Any idea if such a tools exists?

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  • How would I best make this SEO_able?

    - by alex
    I have a search engine that searches albums. For each music album, I have a page. So, the work flow goes like this: People search for music titles The search engine displays a list of albums. People click on an album to go to a details page. I want google to index my front page and the details page. I want the details page to be highly ranked. How can I build a sitemap for this? By the way, I have about 5 million albums (but I want the top 1000 ones to be highly ranked on google)

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  • Why is this span above the text? I want it beside the text.

    - by alex
    <td valign="center" colspan="2"> <a href="" class="table_desc" > <span class="desc_info_butt"></span> </a> text here </td> .desc_info_butt{ background:url(Description_Button.png) top left no-repeat; height:16px; width:16px; display:block; } For some reason, the image and text appear on two different lines!~

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  • Windows Azure Service Bus Scatter-Gather Implementation

    - by Alan Smith
    One of the more challenging enterprise integration patterns that developers may wish to implement is the Scatter-Gather pattern. In this article I will show the basic implementation of a scatter-gather pattern using the topic-subscription model of the windows azure service bus. I’ll be using the implementation in demos, and also as a lab in my training courses, and the pattern will also be included in the next release of my free e-book the “Windows Azure Service Bus Developer Guide”. The Scatter-Gather pattern answers the following scenario. How do you maintain the overall message flow when a message needs to be sent to multiple recipients, each of which may send a reply? Use a Scatter-Gather that broadcasts a message to multiple recipients and re-aggregates the responses back into a single message. The Enterprise Integration Patterns website provides a description of the Scatter-Gather pattern here.   The scatter-gather pattern uses a composite of the publish-subscribe channel pattern and the aggregator pattern. The publish-subscribe channel is used to broadcast messages to a number of receivers, and the aggregator is used to gather the response messages and aggregate them together to form a single message. Scatter-Gather Scenario The scenario for this scatter-gather implementation is an application that allows users to answer questions in a poll based voting scenario. A poll manager application will be used to broadcast questions to users, the users will use a voting application that will receive and display the questions and send the votes back to the poll manager. The poll manager application will receive the users’ votes and aggregate them together to display the results. The scenario should be able to scale to support a large number of users.   Scatter-Gather Implementation The diagram below shows the overall architecture for the scatter-gather implementation.       Messaging Entities Looking at the scatter-gather pattern diagram it can be seen that the topic-subscription architecture is well suited for broadcasting a message to a number of subscribers. The poll manager application can send the question messages to a topic, and each voting application can receive the question message on its own subscription. The static limit of 2,000 subscriptions per topic in the current release means that 2,000 voting applications can receive question messages and take part in voting. The vote messages can then be sent to the poll manager application using a queue. The voting applications will send their vote messages to the queue, and the poll manager will receive and process the vote messages. The questions topic and answer queue are created using the Windows Azure Developer Portal. Each instance of the voting application will create its own subscription in the questions topic when it starts, allowing the question messages to be broadcast to all subscribing voting applications. Data Contracts Two simple data contracts will be used to serialize the questions and votes as brokered messages. The code for these is shown below.   [DataContract] public class Question {     [DataMember]     public string QuestionText { get; set; } }     To keep the implementation of the voting functionality simple and focus on the pattern implementation, the users can only vote yes or no to the questions.   [DataContract] public class Vote {     [DataMember]     public string QuestionText { get; set; }       [DataMember]     public bool IsYes { get; set; } }     Poll Manager Application The poll manager application has been implemented as a simple WPF application; the user interface is shown below. A question can be entered in the text box, and sent to the topic by clicking the Add button. The topic and subscriptions used for broadcasting the messages are shown in a TreeView control. The questions that have been broadcast and the resulting votes are shown in a ListView control. When the application is started any existing subscriptions are cleared form the topic, clients are then created for the questions topic and votes queue, along with background workers for receiving and processing the vote messages, and updating the display of subscriptions.   public MainWindow() {     InitializeComponent();       // Create a new results list and data bind it.     Results = new ObservableCollection<Result>();     lsvResults.ItemsSource = Results;       // Create a token provider with the relevant credentials.     TokenProvider credentials =         TokenProvider.CreateSharedSecretTokenProvider         (AccountDetails.Name, AccountDetails.Key);       // Create a URI for the serivce bus.     Uri serviceBusUri = ServiceBusEnvironment.CreateServiceUri         ("sb", AccountDetails.Namespace, string.Empty);       // Clear out any old subscriptions.     NamespaceManager = new NamespaceManager(serviceBusUri, credentials);     IEnumerable<SubscriptionDescription> subs =         NamespaceManager.GetSubscriptions(AccountDetails.ScatterGatherTopic);     foreach (SubscriptionDescription sub in subs)     {         NamespaceManager.DeleteSubscription(sub.TopicPath, sub.Name);     }       // Create the MessagingFactory     MessagingFactory factory = MessagingFactory.Create(serviceBusUri, credentials);       // Create the topic and queue clients.     ScatterGatherTopicClient =         factory.CreateTopicClient(AccountDetails.ScatterGatherTopic);     ScatterGatherQueueClient =         factory.CreateQueueClient(AccountDetails.ScatterGatherQueue);       // Start the background worker threads.     VotesBackgroundWorker = new BackgroundWorker();     VotesBackgroundWorker.DoWork += new DoWorkEventHandler(ReceiveMessages);     VotesBackgroundWorker.RunWorkerAsync();       SubscriptionsBackgroundWorker = new BackgroundWorker();     SubscriptionsBackgroundWorker.DoWork += new DoWorkEventHandler(UpdateSubscriptions);     SubscriptionsBackgroundWorker.RunWorkerAsync(); }     When the poll manager user nters a question in the text box and clicks the Add button a question message is created and sent to the topic. This message will be broadcast to all the subscribing voting applications. An instance of the Result class is also created to keep track of the votes cast, this is then added to an observable collection named Results, which is data-bound to the ListView control.   private void btnAddQuestion_Click(object sender, RoutedEventArgs e) {     // Create a new result for recording votes.     Result result = new Result()     {         Question = txtQuestion.Text     };     Results.Add(result);       // Send the question to the topic     Question question = new Question()     {         QuestionText = result.Question     };     BrokeredMessage msg = new BrokeredMessage(question);     ScatterGatherTopicClient.Send(msg);       txtQuestion.Text = ""; }     The Results class is implemented as follows.   public class Result : INotifyPropertyChanged {     public string Question { get; set; }       private int m_YesVotes;     private int m_NoVotes;       public event PropertyChangedEventHandler PropertyChanged;       public int YesVotes     {         get { return m_YesVotes; }         set         {             m_YesVotes = value;             NotifyPropertyChanged("YesVotes");         }     }       public int NoVotes     {         get { return m_NoVotes; }         set         {             m_NoVotes = value;             NotifyPropertyChanged("NoVotes");         }     }       private void NotifyPropertyChanged(string prop)     {         if(PropertyChanged != null)         {             PropertyChanged(this, new PropertyChangedEventArgs(prop));         }     } }     The INotifyPropertyChanged interface is implemented so that changes to the number of yes and no votes will be updated in the ListView control. Receiving the vote messages from the voting applications is done asynchronously, using a background worker thread.   // This runs on a background worker. private void ReceiveMessages(object sender, DoWorkEventArgs e) {     while (true)     {         // Receive a vote message from the queue         BrokeredMessage msg = ScatterGatherQueueClient.Receive();         if (msg != null)         {             // Deserialize the message.             Vote vote = msg.GetBody<Vote>();               // Update the results.             foreach (Result result in Results)             {                 if (result.Question.Equals(vote.QuestionText))                 {                     if (vote.IsYes)                     {                         result.YesVotes++;                     }                     else                     {                         result.NoVotes++;                     }                     break;                 }             }               // Mark the message as complete.             msg.Complete();         }       } }     When a vote message is received, the result that matches the vote question is updated with the vote from the user. The message is then marked as complete. A second background thread is used to update the display of subscriptions in the TreeView, with a dispatcher used to update the user interface. // This runs on a background worker. private void UpdateSubscriptions(object sender, DoWorkEventArgs e) {     while (true)     {         // Get a list of subscriptions.         IEnumerable<SubscriptionDescription> subscriptions =             NamespaceManager.GetSubscriptions(AccountDetails.ScatterGatherTopic);           // Update the user interface.         SimpleDelegate setQuestion = delegate()         {             trvSubscriptions.Items.Clear();             TreeViewItem topicItem = new TreeViewItem()             {                 Header = AccountDetails.ScatterGatherTopic             };               foreach (SubscriptionDescription subscription in subscriptions)             {                 TreeViewItem subscriptionItem = new TreeViewItem()                 {                     Header = subscription.Name                 };                 topicItem.Items.Add(subscriptionItem);             }             trvSubscriptions.Items.Add(topicItem);               topicItem.ExpandSubtree();         };         this.Dispatcher.BeginInvoke(DispatcherPriority.Send, setQuestion);           Thread.Sleep(3000);     } }       Voting Application The voting application is implemented as another WPF application. This one is more basic, and allows the user to vote “Yes” or “No” for the questions sent by the poll manager application. The user interface for that application is shown below. When an instance of the voting application is created it will create a subscription in the questions topic using a GUID as the subscription name. The application can then receive copies of every question message that is sent to the topic. Clients for the new subscription and the votes queue are created, along with a background worker to receive the question messages. The voting application is set to receiving mode, meaning it is ready to receive a question message from the subscription.   public MainWindow() {     InitializeComponent();       // Set the mode to receiving.     IsReceiving = true;       // Create a token provider with the relevant credentials.     TokenProvider credentials =         TokenProvider.CreateSharedSecretTokenProvider         (AccountDetails.Name, AccountDetails.Key);       // Create a URI for the serivce bus.     Uri serviceBusUri = ServiceBusEnvironment.CreateServiceUri         ("sb", AccountDetails.Namespace, string.Empty);       // Create the MessagingFactory     MessagingFactory factory = MessagingFactory.Create(serviceBusUri, credentials);       // Create a subcription for this instance     NamespaceManager mgr = new NamespaceManager(serviceBusUri, credentials);     string subscriptionName = Guid.NewGuid().ToString();     mgr.CreateSubscription(AccountDetails.ScatterGatherTopic, subscriptionName);       // Create the subscription and queue clients.     ScatterGatherSubscriptionClient = factory.CreateSubscriptionClient         (AccountDetails.ScatterGatherTopic, subscriptionName);     ScatterGatherQueueClient =         factory.CreateQueueClient(AccountDetails.ScatterGatherQueue);       // Start the background worker thread.     BackgroundWorker = new BackgroundWorker();     BackgroundWorker.DoWork += new DoWorkEventHandler(ReceiveMessages);     BackgroundWorker.RunWorkerAsync(); }     I took the inspiration for creating the subscriptions in the voting application from the chat application that uses topics and subscriptions blogged by Ovais Akhter here. The method that receives the question messages runs on a background thread. If the application is in receive mode, a question message will be received from the subscription, the question will be displayed in the user interface, the voting buttons enabled, and IsReceiving set to false to prevent more questing from being received before the current one is answered.   // This runs on a background worker. private void ReceiveMessages(object sender, DoWorkEventArgs e) {     while (true)     {         if (IsReceiving)         {             // Receive a question message from the topic.             BrokeredMessage msg = ScatterGatherSubscriptionClient.Receive();             if (msg != null)             {                 // Deserialize the message.                 Question question = msg.GetBody<Question>();                   // Update the user interface.                 SimpleDelegate setQuestion = delegate()                 {                     lblQuestion.Content = question.QuestionText;                     btnYes.IsEnabled = true;                     btnNo.IsEnabled = true;                 };                 this.Dispatcher.BeginInvoke(DispatcherPriority.Send, setQuestion);                 IsReceiving = false;                   // Mark the message as complete.                 msg.Complete();             }         }         else         {             Thread.Sleep(1000);         }     } }     When the user clicks on the Yes or No button, the btnVote_Click method is called. This will create a new Vote data contract with the appropriate question and answer and send the message to the poll manager application using the votes queue. The user voting buttons are then disabled, the question text cleared, and the IsReceiving flag set to true to allow a new message to be received.   private void btnVote_Click(object sender, RoutedEventArgs e) {     // Create a new vote.     Vote vote = new Vote()     {         QuestionText = (string)lblQuestion.Content,         IsYes = ((sender as Button).Content as string).Equals("Yes")     };       // Send the vote message.     BrokeredMessage msg = new BrokeredMessage(vote);     ScatterGatherQueueClient.Send(msg);       // Update the user interface.     lblQuestion.Content = "";     btnYes.IsEnabled = false;     btnNo.IsEnabled = false;     IsReceiving = true; }     Testing the Application In order to test the application, an instance of the poll manager application is started; the user interface is shown below. As no instances of the voting application have been created there are no subscriptions present in the topic. When an instance of the voting application is created the subscription will be displayed in the poll manager. Now that a voting application is subscribing, a questing can be sent from the poll manager application. When the message is sent to the topic, the voting application will receive the message and display the question. The voter can then answer the question by clicking on the appropriate button. The results of the vote are updated in the poll manager application. When two more instances of the voting application are created, the poll manager will display the new subscriptions. More questions can then be broadcast to the voting applications. As the question messages are queued up in the subscription for each voting application, the users can answer the questions in their own time. The vote messages will be received by the poll manager application and aggregated to display the results. The screenshots of the applications part way through voting are shown below. The messages for each voting application are queued up in sequence on the voting application subscriptions, allowing the questions to be answered at different speeds by the voters.

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  • Creating an ITemplate from a String

    - by Damon
    I do a lot of work with control templates, and one of the pieces of functionality that I've always wanted is the ability to build a ITemplate from a string.  Throughout the years, the topic has come up from time to time, and I never really found anything about how to do it. though I have run across a number of postings from people who are also wanting the same capability.  As I was messing around with things the other day, I stumbled on how to make it work and I feel really foolish for not figuring it out sooner. ITemplate is an interface that exposes a single method named InstantiateIn.  I've been searching for years for some magical .NET framework component that would take a string and convert it into an ITemplate, when all along I could just build my own.  Here's the code: /// <summary> ///   Allows string-based ITempalte implementations /// </summary> public class StringTemplate : ITemplate {     #region Constructor(s)     ////////////////////////////////////////////////////////////////////////////////////////////     /// <summary>     ///   Constructor     /// </summary>     /// <param name="template">String based version of the control template.</param>     public StringTemplate(string template)     {         Template = template;     }     /// <summary>     ///   Constructor     /// </summary>     /// <param name="template">String based version of the control template.</param>     /// <param name="copyToContainer">True to copy intermediate container contents to the instantiation container, False to leave the intermediate container in place.</param>     public StringTemplate(string template, bool copyToContainer)     {         Template = template;         CopyToContainer = copyToContainer;     }     ////////////////////////////////////////////////////////////////////////////////////////////     #endregion     #region Properties     ////////////////////////////////////////////////////////////////////////////////////////////     /// <summary>     ///   String based template     /// </summary>     public string Template     {         get;         set;     }     /// <summary>     ///   When a StringTemplate is instantiated it is created inside an intermediate control     ///   due to limitations of the .NET Framework.  Specifying True for the CopyToContainer     ///   property copies all the controls from the intermediate container into instantiation     ///   container passed to the InstantiateIn method.     /// </summary>     public bool CopyToContainer     {         get;         set;     }     ////////////////////////////////////////////////////////////////////////////////////////////     #endregion     #region ITemplate Members     ////////////////////////////////////////////////////////////////////////////////////////////     /// <summary>     ///   Creates the template in the specified control.     /// </summary>     /// <param name="container">Control in which to make the template</param>     public void InstantiateIn(Control container)     {         Control tempContainer = container.Page.ParseControl(Template);         if (CopyToContainer)         {             for (int i = tempContainer.Controls.Count - 1; i >= 0; i--)             {                 Control tempControl = tempContainer.Controls[i];                 tempContainer.Controls.RemoveAt(i);                 container.Controls.AddAt(0, tempControl);             }                         }         else         {             container.Controls.Add(tempContainer);         }     }     ////////////////////////////////////////////////////////////////////////////////////////////     #endregion } //class Converting a string into a user control is fairly easy using the ParseControl method from a Page object.  Fortunately, the container passed into the InstantiateIn method has a Page property.  One caveat, however, is that the Page property only has a reference to a Page if the container is located ON the page.  If you run into this problem, you may have to find a creative way to get the Page reference (you can add it to the constructor, store it in the request context, etc).  Another issue that I ran into is that the ParseControl creates a new control, parses the string template, places any controls defined in the template onto the new control it created, and returns that new control with the template on it.  You cannot pass in your own container. Adding this directly to the container provided as a parameter in the InstantiateIn means that you end up with an additional "level" in the control hierarchy.  To avoid this, I added code in that removes each control from the intermediate container and places it into the actual container.  I am not, however, sure about the performance penalty associated with moving a bunch of control from one place to another, nor am I completely sure if doing such a move completely screws something up if you have a code behind, etc.  It seems to work when it's just a template, but my testing was ever-so-slightly shy of thorough when it comes to other crazy scenarios.  As a catch-all, I added a Boolean property called CopyToContainer that allows you to turn the copying on or off depending on your desires and needs. Technorati Tags: .NET,ASP.NET,ITemplate,Development,C#,Custom Controls,Server Controls

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  • Am I wrong to disagree with A Gentle Introduction to symfony's template best practices?

    - by AndrewKS
    I am currently learning symfony and going through the book A Gentle Introduction to symfony and came across this section in "Chapter 4: The Basics of Page Creation" on creating templates (or views): "If you need to execute some PHP code in the template, you should avoid using the usual PHP syntax, as shown in Listing 4-4. Instead, write your templates using the PHP alternative syntax, as shown in Listing 4-5, to keep the code understandable for non-PHP programmers." Listing 4-4 - The Usual PHP Syntax, Good for Actions, But Bad for Templates <p>Hello, world!</p> <?php if ($test) { echo "<p>".time()."</p>"; } ?> (The ironic thing about this is that echo statement would look even better if time was variable declared in the controller, because then you could just embed the variable in the string instead of concatenating) Listing 4-5 - The Alternative PHP Syntax, Good for Templates <p>Hello, world!</p> <?php if ($test): ?> <p><?php echo time(); ?> </p><?php endif; ?> I fail to see how listing 4-5 makes the code "understandable for non-PHP programmers", and its readability is shaky at best. 4-4 looks much more readable to me. Are there any programmers who are using symfony that write their templates like those in 4-4 rather than 4-5? Are there reasons I should use one over the other? There is the very slim chance that somewhere down the road someone less technical could be editing it the template, but how does 4-5 actually make it more understandable to them?

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  • Am I wrong to disagree with A Gentle Introduction to symfony's template best practices?

    - by AndrewKS
    I am currently learning symfony and going through the book A Gentle Introduction to symfony and came across this section in "Chapter 4: The Basics of Page Creation" on creating templates (or views): "If you need to execute some PHP code in the template, you should avoid using the usual PHP syntax, as shown in Listing 4-4. Instead, write your templates using the PHP alternative syntax, as shown in Listing 4-5, to keep the code understandable for non-PHP programmers." Listing 4-4 - The Usual PHP Syntax, Good for Actions, But Bad for Templates <p>Hello, world!</p> <?php if ($test) { echo "<p>".time()."</p>"; } ?> (The ironic thing about this is that the echo statement would look even better if time was a variable declared in the controller because then you could just embed the variable in the string instead of concatenating) Listing 4-5 - The Alternative PHP Syntax, Good for Templates <p>Hello, world!</p> <?php if ($test): ?> <p><?php echo time(); ?> </p><?php endif; ?> I fail to see how listing 4-5 makes the code "understandable for non-PHP programmers", and its readability is shaky at best. 4-4 looks much more readable to me. Are there any programmers who are using symfony that write their templates like those in 4-4 rather than 4-5? Are there reasons I should use one over the other? There is the very slim chance that somewhere down the road someone less technical could be editing it the template, but how does 4-5 actually make it more understandable to them?

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  • C++ template member specialization - is this a compiler limitation?

    - by LoudNPossiblyRight
    Is it possible to do this kind of specialization? If so, how? The specialization in question is marked //THIS SPECIALIZATION WILL NOT COMPILE I have used VS2008, VS2010, gcc 4.4.3 and neither can compile this. #include<iostream> #include<string> using namespace std; template <typename ALPHA> class klass{ public: template <typename BETA> void func(BETA B); }; template <typename ALPHA> template <typename BETA> void klass<ALPHA>::func(BETA B){ cout << "I AM A BETA FUNC: " << B <<endl; } //THIS SPECIALIZATION WILL NOT COMPILE template <typename ALPHA> template <> void klass<ALPHA>::func(string B){ cout << "I AM A SPECIAL BETA FUNC: " << B <<endl; } int main(){ klass<string> k; k.func(1); k.func("hello"); return 0; }

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  • Can a custom MFC window/dialog be a template class?

    - by John
    There's a bunch of special macros that MFC uses when creating dialogs, and in my quick tests I'm getting weird errors trying to compile a template dialog class. Is this likely to be a big pain to achieve? Here's what I tried: MyDlg.h template <class W> class CMyDlg : public CDialog { typedef CDialog super; DECLARE_DYNAMIC(CMyDlg <W>) public: CMyDlg (CWnd* pParent); // standard constructor virtual ~CMyDlg (); // Dialog Data enum { IDD = IDD_MYDLG }; protected: virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support DECLARE_MESSAGE_MAP() private: W *m_pWidget; //W will always be a CDialog }; IMPLEMENT_DYNAMIC(CMyDlg<W>, super) <------------------- template <class W> CMyDlg<W>::CMyDlg(CWnd* pParent) : super(CMyDlg::IDD, pParent) { m_pWidget = new W(this); } I get a whole bunch of errors but main one appears to be: error C2955: 'CMyDlg' : use of class template requires template argument list I tried using some specialised template versions of macros but it doesn't help much, other errors change but this one remains. Note my code is all in one file, since C++ templates don't like .h/.cpp like normal.

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  • Dynamic Code for type casting Generic Types 'generically' in C#

    - by Rick Strahl
    C# is a strongly typed language and while that's a fundamental feature of the language there are more and more situations where dynamic types make a lot of sense. I've written quite a bit about how I use dynamic for creating new type extensions: Dynamic Types and DynamicObject References in C# Creating a dynamic, extensible C# Expando Object Creating a dynamic DataReader for dynamic Property Access Today I want to point out an example of a much simpler usage for dynamic that I use occasionally to get around potential static typing issues in C# code especially those concerning generic types. TypeCasting Generics Generic types have been around since .NET 2.0 I've run into a number of situations in the past - especially with generic types that don't implement specific interfaces that can be cast to - where I've been unable to properly cast an object when it's passed to a method or assigned to a property. Granted often this can be a sign of bad design, but in at least some situations the code that needs to be integrated is not under my control so I have to make due with what's available or the parent object is too complex or intermingled to be easily refactored to a new usage scenario. Here's an example that I ran into in my own RazorHosting library - so I have really no excuse, but I also don't see another clean way around it in this case. A Generic Example Imagine I've implemented a generic type like this: public class RazorEngine<TBaseTemplateType> where TBaseTemplateType : RazorTemplateBase, new() You can now happily instantiate new generic versions of this type with custom template bases or even a non-generic version which is implemented like this: public class RazorEngine : RazorEngine<RazorTemplateBase> { public RazorEngine() : base() { } } To instantiate one: var engine = new RazorEngine<MyCustomRazorTemplate>(); Now imagine that the template class receives a reference to the engine when it's instantiated. This code is fired as part of the Engine pipeline when it gets ready to execute the template. It instantiates the template and assigns itself to the template: var template = new TBaseTemplateType() { Engine = this } The problem here is that possibly many variations of RazorEngine<T> can be passed. I can have RazorTemplateBase, RazorFolderHostTemplateBase, CustomRazorTemplateBase etc. as generic parameters and the Engine property has to reflect that somehow. So, how would I cast that? My first inclination was to use an interface on the engine class and then cast to the interface.  Generally that works, but unfortunately here the engine class is generic and has a few members that require the template type in the member signatures. So while I certainly can implement an interface: public interface IRazorEngine<TBaseTemplateType> it doesn't really help for passing this generically templated object to the template class - I still can't cast it if multiple differently typed versions of the generic type could be passed. I have the exact same issue in that I can't specify a 'generic' generic parameter, since there's no underlying base type that's common. In light of this I decided on using object and the following syntax for the property (and the same would be true for a method parameter): public class RazorTemplateBase :MarshalByRefObject,IDisposable { public object Engine {get;set; } } Now because the Engine property is a non-typed object, when I need to do something with this value, I still have no way to cast it explicitly. What I really would need is: public RazorEngine<> Engine { get; set; } but that's not possible. Dynamic to the Rescue Luckily with the dynamic type this sort of thing can be mitigated fairly easily. For example here's a method that uses the Engine property and uses the well known class interface by simply casting the plain object reference to dynamic and then firing away on the properties and methods of the base template class that are common to all templates:/// <summary> /// Allows rendering a dynamic template from a string template /// passing in a model. This is like rendering a partial /// but providing the input as a /// </summary> public virtual string RenderTemplate(string template,object model) { if (template == null) return string.Empty; // if there's no template markup if(!template.Contains("@")) return template; // use dynamic to get around generic type casting dynamic engine = Engine; string result = engine.RenderTemplate(template, model); if (result == null) throw new ApplicationException("RenderTemplate failed: " + engine.ErrorMessage); return result; } Prior to .NET 4.0  I would have had to use Reflection for this sort of thing which would have a been a heck of a lot more verbose, but dynamic makes this so much easier and cleaner and in this case at least the overhead is negliable since it's a single dynamic operation on an otherwise very complex operation call. Dynamic as  a Bailout Sometimes this sort of thing often reeks of a design flaw, and I agree that in hindsight this could have been designed differently. But as is often the case this particular scenario wasn't planned for originally and removing the generic signatures from the base type would break a ton of other code in the framework. Given the existing fairly complex engine design, refactoring an interface to remove generic types just to make this particular code work would have been overkill. Instead dynamic provides a nice and simple and relatively clean solution. Now if there were many other places where this occurs I would probably consider reworking the code to make this cleaner but given this isolated instance and relatively low profile operation use of dynamic seems a valid choice for me. This solution really works anywhere where you might end up with an inheritance structure that doesn't have a common base or interface that is sufficient. In the example above I know what I'm getting but there's no common base type that I can cast to. All that said, it's a good idea to think about use of dynamic before you rush in. In many situations there are alternatives that can still work with static typing. Dynamic definitely has some overhead compared to direct static access of objects, so if possible we should definitely stick to static typing. In the example above the application already uses dynamics extensively for dynamic page page templating and passing models around so introducing dynamics here has very little additional overhead. The operation itself also fires of a fairly resource heavy operation where the overhead of a couple of dynamic member accesses are not a performance issue. So, what's your experience with dynamic as a bailout mechanism? © Rick Strahl, West Wind Technologies, 2005-2012Posted in CSharp   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Metro: Grouping Items in a ListView Control

    - by Stephen.Walther
    The purpose of this blog entry is to explain how you can group list items when displaying the items in a WinJS ListView control. In particular, you learn how to group a list of products by product category. Displaying a grouped list of items in a ListView control requires completing the following steps: Create a Grouped data source from a List data source Create a Grouped Header Template Declare the ListView control so it groups the list items Creating the Grouped Data Source Normally, you bind a ListView control to a WinJS.Binding.List object. If you want to render list items in groups, then you need to bind the ListView to a grouped data source instead. The following code – contained in a file named products.js — illustrates how you can create a standard WinJS.Binding.List object from a JavaScript array and then return a grouped data source from the WinJS.Binding.List object by calling its createGrouped() method: (function () { "use strict"; // Create List data source var products = new WinJS.Binding.List([ { name: "Milk", price: 2.44, category: "Beverages" }, { name: "Oranges", price: 1.99, category: "Fruit" }, { name: "Wine", price: 8.55, category: "Beverages" }, { name: "Apples", price: 2.44, category: "Fruit" }, { name: "Steak", price: 1.99, category: "Other" }, { name: "Eggs", price: 2.44, category: "Other" }, { name: "Mushrooms", price: 1.99, category: "Other" }, { name: "Yogurt", price: 2.44, category: "Other" }, { name: "Soup", price: 1.99, category: "Other" }, { name: "Cereal", price: 2.44, category: "Other" }, { name: "Pepsi", price: 1.99, category: "Beverages" } ]); // Create grouped data source var groupedProducts = products.createGrouped( function (dataItem) { return dataItem.category; }, function (dataItem) { return { title: dataItem.category }; }, function (group1, group2) { return group1.charCodeAt(0) - group2.charCodeAt(0); } ); // Expose the grouped data source WinJS.Namespace.define("ListViewDemos", { products: groupedProducts }); })(); Notice that the createGrouped() method requires three functions as arguments: groupKey – This function associates each list item with a group. The function accepts a data item and returns a key which represents a group. In the code above, we return the value of the category property for each product. groupData – This function returns the data item displayed by the group header template. For example, in the code above, the function returns a title for the group which is displayed in the group header template. groupSorter – This function determines the order in which the groups are displayed. The code above displays the groups in alphabetical order: Beverages, Fruit, Other. Creating the Group Header Template Whenever you create a ListView control, you need to create an item template which you use to control how each list item is rendered. When grouping items in a ListView control, you also need to create a group header template. The group header template is used to render the header for each group of list items. Here’s the markup for both the item template and the group header template: <div id="productTemplate" data-win-control="WinJS.Binding.Template"> <div class="product"> <span data-win-bind="innerText:name"></span> <span data-win-bind="innerText:price"></span> </div> </div> <div id="productGroupHeaderTemplate" data-win-control="WinJS.Binding.Template"> <div class="productGroupHeader"> <h1 data-win-bind="innerText: title"></h1> </div> </div> You should declare the two templates in the same file as you declare the ListView control – for example, the default.html file. Declaring the ListView Control The final step is to declare the ListView control. Here’s the required markup: <div data-win-control="WinJS.UI.ListView" data-win-options="{ itemDataSource:ListViewDemos.products.dataSource, itemTemplate:select('#productTemplate'), groupDataSource:ListViewDemos.products.groups.dataSource, groupHeaderTemplate:select('#productGroupHeaderTemplate'), layout: {type: WinJS.UI.GridLayout} }"> </div> In the markup above, six properties of the ListView control are set when the control is declared. First the itemDataSource and itemTemplate are specified. Nothing new here. Next, the group data source and group header template are specified. Notice that the group data source is represented by the ListViewDemos.products.groups.dataSource property of the grouped data source. Finally, notice that the layout of the ListView is changed to Grid Layout. You are required to use Grid Layout (instead of the default List Layout) when displaying grouped items in a ListView. Here’s the entire contents of the default.html page: <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>ListViewDemos</title> <!-- WinJS references --> <link href="//Microsoft.WinJS.0.6/css/ui-dark.css" rel="stylesheet"> <script src="//Microsoft.WinJS.0.6/js/base.js"></script> <script src="//Microsoft.WinJS.0.6/js/ui.js"></script> <!-- ListViewDemos references --> <link href="/css/default.css" rel="stylesheet"> <script src="/js/default.js"></script> <script src="/js/products.js" type="text/javascript"></script> <style type="text/css"> .product { width: 200px; height: 100px; border: white solid 1px; font-size: x-large; } </style> </head> <body> <div id="productTemplate" data-win-control="WinJS.Binding.Template"> <div class="product"> <span data-win-bind="innerText:name"></span> <span data-win-bind="innerText:price"></span> </div> </div> <div id="productGroupHeaderTemplate" data-win-control="WinJS.Binding.Template"> <div class="productGroupHeader"> <h1 data-win-bind="innerText: title"></h1> </div> </div> <div data-win-control="WinJS.UI.ListView" data-win-options="{ itemDataSource:ListViewDemos.products.dataSource, itemTemplate:select('#productTemplate'), groupDataSource:ListViewDemos.products.groups.dataSource, groupHeaderTemplate:select('#productGroupHeaderTemplate'), layout: {type: WinJS.UI.GridLayout} }"> </div> </body> </html> Notice that the default.html page includes a reference to the products.js file: <script src=”/js/products.js” type=”text/javascript”></script> The default.html page also contains the declarations of the item template, group header template, and ListView control. Summary The goal of this blog entry was to explain how you can group items in a ListView control. You learned how to create a grouped data source, a group header template, and declare a ListView so that it groups its list items.

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  • Metro: Grouping Items in a ListView Control

    - by Stephen.Walther
    The purpose of this blog entry is to explain how you can group list items when displaying the items in a WinJS ListView control. In particular, you learn how to group a list of products by product category. Displaying a grouped list of items in a ListView control requires completing the following steps: Create a Grouped data source from a List data source Create a Grouped Header Template Declare the ListView control so it groups the list items Creating the Grouped Data Source Normally, you bind a ListView control to a WinJS.Binding.List object. If you want to render list items in groups, then you need to bind the ListView to a grouped data source instead. The following code – contained in a file named products.js — illustrates how you can create a standard WinJS.Binding.List object from a JavaScript array and then return a grouped data source from the WinJS.Binding.List object by calling its createGrouped() method: (function () { "use strict"; // Create List data source var products = new WinJS.Binding.List([ { name: "Milk", price: 2.44, category: "Beverages" }, { name: "Oranges", price: 1.99, category: "Fruit" }, { name: "Wine", price: 8.55, category: "Beverages" }, { name: "Apples", price: 2.44, category: "Fruit" }, { name: "Steak", price: 1.99, category: "Other" }, { name: "Eggs", price: 2.44, category: "Other" }, { name: "Mushrooms", price: 1.99, category: "Other" }, { name: "Yogurt", price: 2.44, category: "Other" }, { name: "Soup", price: 1.99, category: "Other" }, { name: "Cereal", price: 2.44, category: "Other" }, { name: "Pepsi", price: 1.99, category: "Beverages" } ]); // Create grouped data source var groupedProducts = products.createGrouped( function (dataItem) { return dataItem.category; }, function (dataItem) { return { title: dataItem.category }; }, function (group1, group2) { return group1.charCodeAt(0) - group2.charCodeAt(0); } ); // Expose the grouped data source WinJS.Namespace.define("ListViewDemos", { products: groupedProducts }); })(); Notice that the createGrouped() method requires three functions as arguments: groupKey – This function associates each list item with a group. The function accepts a data item and returns a key which represents a group. In the code above, we return the value of the category property for each product. groupData – This function returns the data item displayed by the group header template. For example, in the code above, the function returns a title for the group which is displayed in the group header template. groupSorter – This function determines the order in which the groups are displayed. The code above displays the groups in alphabetical order: Beverages, Fruit, Other. Creating the Group Header Template Whenever you create a ListView control, you need to create an item template which you use to control how each list item is rendered. When grouping items in a ListView control, you also need to create a group header template. The group header template is used to render the header for each group of list items. Here’s the markup for both the item template and the group header template: <div id="productTemplate" data-win-control="WinJS.Binding.Template"> <div class="product"> <span data-win-bind="innerText:name"></span> <span data-win-bind="innerText:price"></span> </div> </div> <div id="productGroupHeaderTemplate" data-win-control="WinJS.Binding.Template"> <div class="productGroupHeader"> <h1 data-win-bind="innerText: title"></h1> </div> </div> You should declare the two templates in the same file as you declare the ListView control – for example, the default.html file. Declaring the ListView Control The final step is to declare the ListView control. Here’s the required markup: <div data-win-control="WinJS.UI.ListView" data-win-options="{ itemDataSource:ListViewDemos.products.dataSource, itemTemplate:select('#productTemplate'), groupDataSource:ListViewDemos.products.groups.dataSource, groupHeaderTemplate:select('#productGroupHeaderTemplate'), layout: {type: WinJS.UI.GridLayout} }"> </div> In the markup above, six properties of the ListView control are set when the control is declared. First the itemDataSource and itemTemplate are specified. Nothing new here. Next, the group data source and group header template are specified. Notice that the group data source is represented by the ListViewDemos.products.groups.dataSource property of the grouped data source. Finally, notice that the layout of the ListView is changed to Grid Layout. You are required to use Grid Layout (instead of the default List Layout) when displaying grouped items in a ListView. Here’s the entire contents of the default.html page: <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>ListViewDemos</title> <!-- WinJS references --> <link href="//Microsoft.WinJS.0.6/css/ui-dark.css" rel="stylesheet"> <script src="//Microsoft.WinJS.0.6/js/base.js"></script> <script src="//Microsoft.WinJS.0.6/js/ui.js"></script> <!-- ListViewDemos references --> <link href="/css/default.css" rel="stylesheet"> <script src="/js/default.js"></script> <script src="/js/products.js" type="text/javascript"></script> <style type="text/css"> .product { width: 200px; height: 100px; border: white solid 1px; font-size: x-large; } </style> </head> <body> <div id="productTemplate" data-win-control="WinJS.Binding.Template"> <div class="product"> <span data-win-bind="innerText:name"></span> <span data-win-bind="innerText:price"></span> </div> </div> <div id="productGroupHeaderTemplate" data-win-control="WinJS.Binding.Template"> <div class="productGroupHeader"> <h1 data-win-bind="innerText: title"></h1> </div> </div> <div data-win-control="WinJS.UI.ListView" data-win-options="{ itemDataSource:ListViewDemos.products.dataSource, itemTemplate:select('#productTemplate'), groupDataSource:ListViewDemos.products.groups.dataSource, groupHeaderTemplate:select('#productGroupHeaderTemplate'), layout: {type: WinJS.UI.GridLayout} }"> </div> </body> </html> Notice that the default.html page includes a reference to the products.js file: <script src=”/js/products.js” type=”text/javascript”></script> The default.html page also contains the declarations of the item template, group header template, and ListView control. Summary The goal of this blog entry was to explain how you can group items in a ListView control. You learned how to create a grouped data source, a group header template, and declare a ListView so that it groups its list items.

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  • How do I define a template class and divide it into multiple files?

    - by hkBattousai
    I have written a simple template class for test purpose. It compiles without any errors, but when I try to use it in main(), it give some linker errors. main.cpp #include <iostream> #include "MyNumber.h" int wmain(int argc, wchar_t * argv[]) { MyNumber<float> num; num.SetValue(3.14); std::cout << "My number is " << num.GetValue() << "." << std::endl; system("pause"); return 0; } MyNumber.h #pragma once template <class T> class MyNumber { public: MyNumber(); ~MyNumber(); void SetValue(T val); T GetValue(); private: T m_Number; }; MyNumber.cpp #include "MyNumber.h" template <class T> MyNumber<T>::MyNumber() { m_Number = static_cast<T>(0); } template <class T> MyNumber<T>::~MyNumber() { } template <class T> void MyNumber<T>::SetValue(T val) { m_Number = val; } template <class T> T MyNumber<T>::GetValue() { return m_Number; } When I build this code, I get the following linker errors: Error 7 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\X64\Debug\Console Demo.exe 1 error LNK1120: 4 unresolved externals Error 3 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: __cdecl MyNumber::~MyNumber(void)" (??1?$MyNumber@M@@QEAA@XZ) referenced in function wmain Error 6 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: __cdecl MyNumber::MyNumber(void)" (??0?$MyNumber@M@@QEAA@XZ) referenced in function wmain Error 4 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: float __cdecl MyNumber::GetValue(void)" (?GetValue@?$MyNumber@M@@QEAAMXZ) referenced in function wmain Error 5 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: void __cdecl MyNumber::SetValue(float)" (?SetValue@?$MyNumber@M@@QEAAXM@Z) referenced in function wmain But, if I leave main() empty, I don't get any linker errors. What is wrong with my template class? What am I doing wrong?

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  • Specify a base classes template parameters while instantiating a derived class?

    - by DaClown
    Hi, I have no idea if the title makes any sense but I can't find the right words to descibe my "problem" in one line. Anyway, here is my problem. There is an interface for a search: template <typename InputType, typename ResultType> class Search { public: virtual void search (InputType) = 0; virtual void getResult(ResultType&) = 0; }; and several derived classes like: template <typename InputType, typename ResultType> class XMLSearch : public Search<InputType, ResultType> { public: void search (InputType) { ... }; void getResult(ResultType&) { ... }; }; The derived classes shall be used in the source code later on. I would like to hold a simple pointer to a Search without specifying the template parameters, then assign a new XMLSearch and thereby define the template parameters of Search and XMLSearch Search *s = new XMLSearch<int, int>(); I found a way that works syntactically like what I'm trying to do, but it seems a bit odd to really use it: template <typename T> class Derived; class Base { public: template <typename T> bool GetValue(T &value) { Derived<T> *castedThis=dynamic_cast<Derived<T>* >(this); if(castedThis) return castedThis->GetValue(value); return false; } virtual void Dummy() {} }; template <typename T> class Derived : public Base { public: Derived<T>() { mValue=17; } bool GetValue(T &value) { value=mValue; return true; } T mValue; }; int main(int argc, char* argv[]) { Base *v=new Derived<int>; int i=0; if(!v->GetValue(i)) std::cout<<"Wrong type int."<<std::endl; float f=0.0; if(!v->GetValue(f)) std::cout<<"Wrong type float."<<std::endl; std::cout<<i<<std::endl<<f; char c; std::cin>>c; return 0; } Is there a better way to accomplish this?

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  • In XSLT is it possible to use the value of an xpath expression in a call to a template using an par

    - by Cell
    I am performing an xsl transform and in it I call a template with a param using the following code <xsl:call-template name="GenerateColumns"> <xsl:with-param name="curRow" select="$curRow"/> <xsl:with-param name="curCol" select="$curCol + 1"/> </xsl:call-template> This calls a template function which outputs part of a table element in HTML. The curRow and curCol are used to determine which row and column we are in the table. gbl_maxCols is set to the number of columns in an html table <xsl:template name="GenerateColumns"> <xsl:when test="$curCol &lt;= $gbl_maxCols"> <td> <xsl:attribute="colspan"> <xsl:value-of select="/page/column/@skipColumns"/> </xsl:attribute> </xsl:when> </xsl:template> The result of this function is a set of td elements, however some of these elements (those with a skipColumn attribute greater than 1 span more than 1 column, I need to skip this many columns with the next call to generateColumns. this works just like I would expect in the case where I simply increment the curCol param but I have a case where I need to use the value from the xml attribute skipColumns in the math to calculate the value for curCol. In the above case I iterate through all the columns and this works for the majority of my use cases. However in same cases I need to skip over some of the columns and need to pass in that value from the xml attribute to calculate how many columns I need to skip. My naive first attempt was something like this <xsl:call-template name="GenerateColumns"> <xsl:with-param name="curRow" select="$curRow"/> <xsl:with-param name="curCol" select="$curCol + /page/column/@skipColumns"/> </xsl:call-template> But unforutnately this does not seem to work. Is there any way to use an attribute from an xml page in the calculation for the value of a param in xsl. My xml page is something like this (edited heavily since the xml file is rather large) <page> <column name="blank" skipColumns="1"/> <column name="blank" skipColumns="1"/> <column name="test" skipColumns="3"/> <column name="blank" skipColumns="1"/> <column name="test2" skipColumns="6"/> </page> after all of this I would like to have a set of td elements like the following <td></td><td></td><td colSpan="3"></td><td></td><td colSpan="6"></td> if I just iterate through the columns I instead end up with something like this which gives me more td elements than I should have <td></td><td></td><td colSpan="3"></td><td></td><td colSpan="6"></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td> Edited to provide more information

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