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• Is it possible in .NET to achieve event based asynchronous pattern without multithreading?

  - by Jeffrey

  I am amazed by the architectural design of node.js and was wondering if C# is capable of such design: Asynchronous, event based / event loop, non-blocking IO without multithreading.

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• Is this a valid pattern for raising events in C#?

  - by Will Vousden

  Update: For the benefit of anyone reading this, since .NET 4, the lock is unnecessary due to changes in synchronization of auto-generated events, so I just use this now: public static void Raise<T>(this EventHandler<T> handler, object sender, T e) where T : EventArgs { if (handler != null) { handlerCopy(sender, e); } } And to raise it: SomeEvent.Raise(this, new FooEventArgs()); Having been reading one of Jon Skeet's articles on multithreading, I've tried to encapsulate the approach he advocates to raising an event in an extension method like so (with a similar generic version): public static void Raise(this EventHandler handler, object @lock, object sender, EventArgs e) { EventHandler handlerCopy; lock (@lock) { handlerCopy = handler; } if (handlerCopy != null) { handlerCopy(sender, e); } } This can then be called like so: protected virtual void OnSomeEvent(EventArgs e) { this.someEvent.Raise(this.eventLock, this, e); } Are there any problems with doing this? Also, I'm a little confused about the necessity of the lock in the first place. As I understand it, the delegate is copied in the example in the article to avoid the possibility of it changing (and becoming null) between the null check and the delegate call. However, I was under the impression that access/assignment of this kind is atomic, so why is the lock necessary? Update: With regards to Mark Simpson's comment below, I threw together a test: static class Program { private static Action foo; private static Action bar; private static Action test; static void Main(string[] args) { foo = () => Console.WriteLine("Foo"); bar = () => Console.WriteLine("Bar"); test += foo; test += bar; test.Test(); Console.ReadKey(true); } public static void Test(this Action action) { action(); test -= foo; Console.WriteLine(); action(); } } This outputs: Foo Bar Foo Bar This illustrates that the delegate parameter to the method (action) does not mirror the argument that was passed into it (test), which is kind of expected, I guess. My question is will this affect the validity of the lock in the context of my Raise extension method? Update: Here is the code I'm now using. It's not quite as elegant as I'd have liked, but it seems to work: public static void Raise<T>(this object sender, ref EventHandler<T> handler, object eventLock, T e) where T : EventArgs { EventHandler<T> copy; lock (eventLock) { copy = handler; } if (copy != null) { copy(sender, e); } }

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• Which pattern is good for bullets hit test in game that need server validates ?

  - by Konami.Koumura

  I would like to design a PvP game uses flash in client and java socket server, but I do need server validates trajectory and if bullets hit target from cheating. Is there any tutorial or paper provides how to do this ?

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• Qt Creator draws up build issue: "target pattern contains no %. Stop."

  - by Louis93

  The compile output says no% in line 240 of the makefile. Here is an extract of that portion in the Makefile: debug/lv.simplon.class.o: c:/SimplonQt/include/lv.simplon.class.cpp $(CXX) -c $(CXXFLAGS) $(INCPATH) -o debug/lv.simplon.class.o c:/SimplonQt/include/lv.simplon.class.cpp I'm loading a project I have saved in my C drive in Windows, but I am not sure what exactly is the cause of the problem. Thanks in advance!

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• Is it possible in C# to achieve event based asynchronous pattern without multithreading?

  - by Jeffrey

  I am amazed by the architectural design of node.js and was wondering if C# is capable of such design: Aasynchronous, event based / event loop, non-blocking IO without multithreading.

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• Which type of design pattern should be used to create an emulator?

  - by Facon

  I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English. EDITED: Asking for multiple patterns.

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• regEx pattern for checking if sting starts with a certain substring?

  - by kacalapy

  whats the regEx to check if a sting starts with "mailto" or "ftp" or "joe" or... now i am using c# and code like this in a bif if with many OR's: String.StartsWith("mailto:") String.StartsWith("ftp") and looks like regEx would be better for this, or is there a c# way i am missing here?

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• Is There a Good Pattern for Creating a Unique Id based on a Type?

  - by Michael Kelley

  I have a template that creates a unique identifier for each type it is instanced. Here's a streamlined version of the template: template <typename T> class arType { static const arType Id; // this will be unique for every instantiation of arType<>. } // Address of Id is used for identification. #define PA_TYPE_TAG(T) (&arType<T >::Id) This works when you have an executable made purely of static libraries. Unfortunately we're moving to an executable made up of dlls. Each dlls could potentially have its own copy of Id for a type. One obvious solution is to explicitly instantiate all instances of arType. Unfortunately this is cumbersome, and I'd like to ask if anyone can propose a better solution?

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• What OOP pattern to use when only adding new methods, not data?

  - by Jonathon Reinhart

  Hello eveyone... In my app, I have deal with several different "parameters", which derive from IParameter interface, and also ParamBase abstract base class. I currently have two different parameter types, call them FooParameter and BarParameter, which both derive from ParamBase. Obviously, I can treat them both as IParameters when I need to deal with them generically, or detect their specific type when I need to handle their specific functionality. My question lies in specific FooParameters. I currently have a few specific ones with their own classes which derive from FooParameter, we'll call them FP12, FP13, FP14, etc. These all have certain characteristics, which make me treat them differently in the UI. (Most have names associated with the individual bits, or ranges of bits). Note that these specific, derived FP's have no additional data associated with them, only properties (which refer to the same data in different ways) or methods. Now, I'd like to keep all of these parameters in a Dictionary<String, IParameter> for easy generic access. The problem is, if I want to refer to a specific one with the special GUI functions, I can't write: FP12 fp12 = (FP12)paramList["FP12"] because you can't downcast to a derived type (rightfully so). But in my case, I didn't add any data, so the cast would theoretically work. What type of programming model should I be using instead? Thanks!

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• How can I capture a multiline pattern using a regular expressions in java?

  - by lampShade

  I have a text file that I need to parse using regular expressions. The text that I need to capture is in multiline groups like this: truck zDoug Doug's house (123) 456-7890 [email protected] 30 61234.56 8/10/2003 vehicle eRob Rob's house (987) 654-3210 [email protected] For this example I need to capture truck followed by the next seven lines.In other words, in this "block" I have 8 groups. This is what I've tried but it will not capture the next line: (truck)\n(\w). NOTE: I'm using the program RegExr to test my regex before I port it to Java.

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• How to make TwoWay binding on properties of ObservableCollection of custom class using mvvm pattern?

  - by mill

  I have the following class: public class UserGroup { public string GroupName { get; set; } public bool IsIntheGroup{ get; set; } } I want to bind an ObservableCollection of UserGroup items to listbox containing checkbox’s for each item in the collection and the checkbox is cheked based on the IsIntheGroup property of the UserGroup. In my ViewModel I made an ObservableCollection of the UserGroup class: public ObservableCollection Groups { get; set; } and loaded its contents (instances of UserGroup) from my database model I used the following code in my view: ListBox ItemsSource="{Binding Groups, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}" ListBox.ItemTemplate DataTemplate StackPanel Orientation="Horizontal" CheckBox IsChecked="{Binding IsIntheGroup, Mode=TwoWay}"/ TextBlock Text="{Binding GroupName}" / /StackPanel /DataTemplate /ListBox.ItemTemplate /ListBox The problem is I am not notified when the user checks/unchecks a check box in the list so my two way binding failed… How do I do a two way binding in such a case?

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• How might I wrap the FindXFile-style APIs to the STL-style Iterator Pattern in C++?

  - by BillyONeal

  Hello everyone :) I'm working on wrapping up the ugly innards of the FindFirstFile/FindNextFile loop (though my question applies to other similar APIs, such as RegEnumKeyEx or RegEnumValue, etc.) inside iterators that work in a manner similar to the Standard Template Library's istream_iterators. I have two problems here. The first is with the termination condition of most "foreach" style loops. STL style iterators typically use operator!= inside the exit condition of the for, i.e. std::vector<int> test; for(std::vector<int>::iterator it = test.begin(); it != test.end(); it++) { //Do stuff } My problem is I'm unsure how to implement operator!= with such a directory enumeration, because I do not know when the enumeration is complete until I've actually finished with it. I have sort of a hack together solution in place now that enumerates the entire directory at once, where each iterator simply tracks a reference counted vector, but this seems like a kludge which can be done a better way. The second problem I have is that there are multiple pieces of data returned by the FindXFile APIs. For that reason, there's no obvious way to overload operator* as required for iterator semantics. When I overload that item, do I return the file name? The size? The modified date? How might I convey the multiple pieces of data to which such an iterator must refer to later in an ideomatic way? I've tried ripping off the C# style MoveNext design but I'm concerned about not following the standard idioms here. class SomeIterator { public: bool next(); //Advances the iterator and returns true if successful, false if the iterator is at the end. std::wstring fileName() const; //other kinds of data.... }; EDIT: And the caller would look like: SomeIterator x = ??; //Construct somehow while(x.next()) { //Do stuff } Thanks! Billy3

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• How Do I Remove The First 4 Characters From A String If It Matches A Pattern In Ruby

  - by James

  I have the following string: "h3. My Title Goes Here" I basically want to remove the first 4 characters from the string so that I just get back: "My Title Goes Here". The thing is I am iterating over an array of strings and not all have the h3. part in front so I can't just ditch the first 4 characters blindly. I have checked the docs and the closest think I could find was chomp, but that only works for the end of a string. Right now I am doing this: "h3. My Title Goes Here".reverse.chomp(" .3h").reverse This gives me my desired output, but there has to be a better way right? I mean I don't want to reverse a string twice for no reason. I am new to programming so I might have missed something obvious, but I didn't see the opposite of chomp anywhere in the docs. Is there another method that will work? Thanks!

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• What is the difference between the Facade and Addapter Pattern?

  - by devoured elysium

  I've been reading both definitions and they seem quite the same. Could anyone point out what are their differences? Thanks

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• c++ Design pattern for CoW, inherited classes, and variable shared data?

  - by krunk

  I've designed a copy-on-write base class. The class holds the default set of data needed by all children in a shared data model/CoW model. The derived classes also have data that only pertains to them, but should be CoW between other instances of that derived class. I'm looking for a clean way to implement this. If I had a base class FooInterface with shared data FooDataPrivate and a derived object FooDerived. I could create a FooDerivedDataPrivate. The underlying data structure would not effect the exposed getters/setters API, so it's not about how a user interfaces with the objects. I'm just wondering if this is a typical MO for such cases or if there's a better/cleaner way? What peeks my interest, is I see the potential of inheritance between the the private data classes. E.g. FooDerivedDataPrivate : public FooDataPrivate, but I'm not seeing a way to take advantage of that polymorphism in my derived classes. class FooDataPrivate { public: Ref ref; // atomic reference counting object int a; int b; int c; }; class FooInterface { public: // constructors and such // .... // methods are implemented to be copy on write. void setA(int val); void setB(int val); void setC(int val); // copy constructors, destructors, etc. all CoW friendly private: FooDataPrivate *data; }; class FooDerived : public FooInterface { public: FooDerived() : FooInterface() {} private: // need more shared data for FooDerived // this is the ???, how is this best done cleanly? };

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• How can I refactor that code ? (state pattern ?)

  - by alex

  Hello guys, How can I refactor that code ? public enum enum1 { value1 = 0x01, value2 = 0x02, value3 = 0x03, value4 = 0x04, value5 = 0x05, UNKNOWN = 0xFF } class class1 { private const string STR_VALUE1 = "some text description of value1"; private const string STR_VALUE2 = "some text description of value2"; private const string STR_VALUE3 = "some text description of value3"; private const string STR_VALUE4 = "some text description of value4"; private const string STR_VALUE5 = "some text description of value5"; private const string STR_VALUE6 = "some text description of unknown type"; public static string GetStringByTypeCode(enum1 type) { switch(type) { case enum1.value1: return STR_VALUE1; case enum1.value2: return STR_VALUE2; case enum1.value3: return STR_VALUE3; case enum1.value4: return STR_VALUE4; case enum1.value5: return STR_VALUE5; default: return STR_VALUE6; } } } PS: there are many enum1...enumX and GetStringByTypeCode(enum1) ... GetStringByTypeCode(enumX) methods.

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• What's the best practice or design pattern for user registration ?

  - by Space Cracker

  We have a big portal that needs user registration to allow them use its services. It's already done in .NET and SOL Server 2005. we are in the phase now of discovering all the problems of the current registration system to build a new robust flexible one that can be extended easily and can be more usable for all services. Could any help me find best practices and design patterns to help me rebuild this using good architectural practices?

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• Which design pattern should be used to create an emulator?

  - by Facon

  I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English. EDITED - Asking for multiple patterns.

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• JPA: what is the proper pattern for iterating over large result sets?

  - by Caffeine Coma

  Let's say I have a table with millions of rows. Using JPA, what's the proper way to iterate over a query against that table, such that I don't have all an in-memory List with millions of objects? I suspect that the following will blow up if the table is large: List<Model> models = entityManager().createQuery("from Model m", Model.class).getResultList(); for (Model model : models) { // do something with model } Is pagination (looping and manually updating setFirstResult()/setMaxResult()) really the best solution?

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• What is the difference between the Facade and Adapter Pattern?

  - by devoured elysium

  I've been reading both definitions and they seem quite the same. Could anyone point out what are their differences? Thanks

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• What design pattern should be used to create an emulator?

  - by Facon

  I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English.

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• How do I push `sed` matches to the shell call in the replacement pattern?

  - by rassie

  I need to replace several URLs in a text file with some content dependent on the URL itself. Let's say for simplicity it's the first line of the document at the URL. What I'm trying is this: sed "s/^URL=\(.*\)/TITLE=$(curl -s \1 | head -n 1)/" file.txt This doesn't work, since \1 is not set. However, the shell is getting called. Can I somehow push the sed match variables to that subprocess?

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• How do I tell cmake to use Command line pattern?

  - by Runner

  Quoted from this answer: `pkg-config --cflags --libs gtk+-2.0` Suppose FindGTK2() is not working,but pkg-config --cflags --libs gtk+-2.0 is OK,how do I include requires lib/header files?

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• Delegation, is this just opinionated or is there a common pattern?

  - by user1446714

  If I have a java class containing substantial code and I wish to add extra features, am I right in thinking the delegate class would have the additional features added as methods. Then my original class would create the delegate object and just call the extra functionality via the delegate instance? I am being told by somebody else that my original class should become the delegate and that the class containing the new functionality should contain an instance of the original class, to use as a delegate? This seemed a little backward to me, because there would be far more delegate calls because most of the code is now in the delegate.... I was always under the impression the delegate object would contain the additional new behaviour and an instance of it would be in the original class to inboke the new behaviour from?

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• What types of objects should the ViewModel reference in the MVVM pattern?

  - by Blanthor

  I've seen quite a few examples of MVVM. I can see that the View should reference the ViewModel. I've seen recently an example of a ViewModel referencing a View, which seems wrong to me, as it would result in tighter coupling. Given that ViewModel is often described as an intermediary between the View and the Model, is there more to the ViewModel than a facade to domain objects? I hope I used the term "facade" correctly here.

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