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  • Argument type deduction, references and rvalues

    - by uj2
    Consider the situation where a function template needs to forward an argument while keeping it's lvalue-ness in case it's a non-const lvalue, but is itself agnostic to what the argument actually is, as in: template <typename T> void target(T&) { cout << "non-const lvalue"; } template <typename T> void target(const T&) { cout << "const lvalue or rvalue"; } template <typename T> void forward(T& x) { target(x); } When x is an rvalue, instead of T being deduced to a constant type, it gives an error: int x = 0; const int y = 0; forward(x); // T = int forward(y); // T = const int forward(0); // Hopefully, T = const int, but actually an error forward<const int>(0); // Works, T = const int It seems that for forward to handle rvalues (without calling for explicit template arguments) there needs to be an forward(const T&) overload, even though it's body would be an exact duplicate. Is there any way to avoid this duplication?

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  • Reflection and Operator Overloads in C#

    - by TenshiNoK
    Here's the deal. I've got a program that will load a given assembly, parse through all Types and their Members and compile a TreeView (very similar to old MSDN site) and then build HTML pages for each node in the TreeView. It basically takes a given assembly and allows the user to create their own MSDN-like library for it for documentation purposes. Here's the problem I've run into: whenever an operator overload is encounted in a defined class, reflection returns that as a "MethodInfo" with the name set to something like "op_Assign" or "op_Equality". I want to be able to capture these and list them properly, but I can't find anything in the MethodInfo object that is returned to accurately identify that I'm looking at an operator. I definitely don't want to just capture everything that starts with "op_", since that will most certainly (at some point) will pick up a method it's not supposed to. I know that other methods and properties that are "special cases" like this one have the "IsSpecialName" property set, but appearantly that's not the case with operators. I've been scouring the 'net and wracking my brain to two days trying to figure this one out, so any help will be greatly appreciated.

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  • Factorial function - design and test.

    - by lukas
    I'm trying to nail down some interview questions, so I stared with a simple one. Design the factorial function. This function is a leaf (no dependencies - easly testable), so I made it static inside the helper class. public static class MathHelper { public static int Factorial(int n) { Debug.Assert(n >= 0); if (n < 0) { throw new ArgumentException("n cannot be lower that 0"); } Debug.Assert(n <= 12); if (n > 12) { throw new OverflowException("Overflow occurs above 12 factorial"); } //by definition if (n == 0) { return 1; } int factorialOfN = 1; for (int i = 1; i <= n; ++i) { //checked //{ factorialOfN *= i; //} } return factorialOfN; } } Testing: [TestMethod] [ExpectedException(typeof(OverflowException))] public void Overflow() { int temp = FactorialHelper.MathHelper.Factorial(40); } [TestMethod] public void ZeroTest() { int factorialOfZero = FactorialHelper.MathHelper.Factorial(0); Assert.AreEqual(1, factorialOfZero); } [TestMethod] public void FactorialOf5() { int factOf5 = FactorialHelper.MathHelper.Factorial(5); Assert.AreEqual(120,factOf5); } [TestMethod] [ExpectedException(typeof(ArgumentException))] public void NegativeTest() { int factOfMinus5 = FactorialHelper.MathHelper.Factorial(-5); } I have a few questions: Is it correct? (I hope so ;) ) Does it throw right exceptions? Should I use checked context or this trick ( n 12 ) is ok? Is it better to use uint istead of checking for negative values? Future improving: Overload for long, decimal, BigInteger or maybe generic method? Thank you

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  • Outlook 2010 Crashing Unpredictably

    - by cbkadel
    Very often when I open up Outlook 2010 and start doing actions in it, it will hang and become non responsive. I have tried letting it finish, but it never does come back (up to 20 minutes of letting it try). I generally have to restart Outlook and try again. Usually after about an hour of doing this, Outlook somehow snaps out of it and works for the rest of the day. It's generally in the morning (though I doubt that's the key variable). Generally, the emails that cause problems are HTML/formatted, but not always. What I've done so far to troubleshoot: Install Latest Outlook Hotfix (I think Dec 14, 2010) Start Outlook in Safe Mode Neither of those steps seem to make a difference. Usually - after about 10-15 restarts of Outlook on any given day, then it starts working thereafter. My next step is to uninstall/reinstall Office 2010, but I'm hoping someone has seen this and knows what to do about it - though not sure. My configuration is like this: Microsoft Online Services (using Microsoft's Sign In App) - Connecting to Exchange I have two other Exchange accounts in this profile (new feature in 2010) connected through Outlook Anywhere. Life Meeting Conferencing Add In I've disabled the People tab/add in. I've disabled the "Send to Bluetooth" add-in. Not sure what else to do?

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  • push_back private vectors with 2 methods, one isn't working

    - by jmclem
    I have a class with a private vector of doubles. To access or modify these values, at first I used methods such as void classA::pushVector(double i) { this->vector.push_back(i); } double classA::getVector(int i) { return vector[i]; } This worked for a while until I found I would have to overload a lot of operators for what I needed, so I tried to change it to get and set the vector directly instead of the values, i.e. void classA::setVector(vector<double> vector) { this->vector = vector; } vector<double> classA::getVector() { return vector; } Now, say there is a classB, which has a private classA element, which also has get and set methods to read and write. The problem was when I tried to push back a value to the end vector in classA. void classB::setFirstValue(double first) { this->getClassA().getVector().push_back(first); } This does absolutely nothing to the vector. It remains unchanged and I can't figure out why... Any ideas?

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  • Friends, templates, overloading <<

    - by Crystal
    I'm trying to use friend functions to overload << and templates to get familiar with templates. I do not know what these compile errors are: Point.cpp:11: error: shadows template parm 'class T' Point.cpp:12: error: declaration of 'const Point<T>& T' for this file #include "Point.h" template <class T> Point<T>::Point() : xCoordinate(0), yCoordinate(0) {} template <class T> Point<T>::Point(T xCoordinate, T yCoordinate) : xCoordinate(xCoordinate), yCoordinate(yCoordinate) {} template <class T> std::ostream &operator<<(std::ostream &out, const Point<T> &T) { std::cout << "(" << T.xCoordinate << ", " << T.yCoordinate << ")"; return out; } My header looks like: #ifndef POINT_H #define POINT_H #include <iostream> template <class T> class Point { public: Point(); Point(T xCoordinate, T yCoordinate); friend std::ostream &operator<<(std::ostream &out, const Point<T> &T); private: T xCoordinate; T yCoordinate; }; #endif My header also gives the warning: Point.h:12: warning: friend declaration 'std::ostream& operator<<(std::ostream&, const Point<T>&)' declares a non-template function Which I was also unsure why. Any thoughts? Thanks.

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  • Cast base class object to derived class

    - by Popgalop
    Lets say I have two classes, animal and dog like this. class Animal { }; class Dog : public Animal { }; And I have an animal object named animal, that is actually an instance of dog, how would I cast it back to dog? This may seem like an odd question, but I need it because I am writing a programming language interpreter, and on the stack everything is stored as a BaseObject, and all the other datatypes extend BaseObject. How would I cast the base object from the stack, to a specific data type? I have tried something like this Dog dog = static_cast<Dog>(animal); But it gives me an error 1>------ Build started: Project: StackTests, Configuration: Debug Win32 ------ 1> StackTests.cpp 1>c:\users\owner\documents\visual studio 2012\projects\stacktests\stacktests\stacktests.cpp(173): error C2440: 'static_cast' : cannot convert from 'Animal' to 'Dog' 1> No constructor could take the source type, or constructor overload resolution was ambiguous 1>c:\users\owner\documents\visual studio 2012\projects\stacktests\stacktests\stacktests.cpp(173): error C2512: 'Dog' : no appropriate default constructor available ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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  • How to Implement an Interface that Requires Duplicate Member Names in C#?

    - by Will Marcouiller
    I often have to implement some interfaces such as IEnumerable<T> in my code. Each time, when implementing automatically, I encounter the following: public IEnumerator<T> GetEnumerator() { // Code here... } public IEnumerator GetEnumerator1() { // Code here... } Though I have to implement both GetEnumerator() methods, they impossibly can have the same name, even if we understand that they do the same, somehow. The compiler can't treat them as one being the overload of the other, because only the return type differs. When doing so, I manage to set the GetEnumerator1() accessor to private. This way, the compiler doesn't complaint about not implementing the interface member, and I simply throw a NotImplementedException within the methods body. However, I wonder whether it is a good practice, or if I shall proceed differently, as perhaps a method alias or something like so. What is the best approach while implementing an interface such as IEnumerable<T> that requires the implementation of two different methods with the same name?

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  • Comparing objects and inheritance

    - by ereOn
    Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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  • html in do_GET() method of a simple Python webserver

    - by Meeri_Peeri
    I am relatively new to Python but have been doing a lot of different things with it recently and I am liking it a lot. However, I ran into trouble/block with the following code. import http.server import socketserver import glob import random class Server(http.server.SimpleHTTPRequestHandler): def do_GET(self): self.send_response(200, 'OK') self.send_header('Content-type', 'html') self.end_headers() self.wfile.write(bytes("<html> <head><title> Hello World </title> </head> <body>", 'UTF-8')) images = glob.glob('*.jpg') rand = random.randint(0,len(images)-1) imagestring = "<img src = \"" + images[rand] + "\" height = 1028 width = 786 align = \"right\"/> </body> </html>" self.wfile.write(bytes(imagestring, 'UTF-8')) def serve_forever(port): socketserver.TCPServer(('', port), Server).serve_forever() if __name__ == "__main__": Server.serve_forever(8000) What I am trying to do here is grab a random image from multiple images in the directory and add it into the response to a web request. The code works fine but when I access the server via browser, the image is not displayed. The html of the page is as intended though. The permissions on the files are 755. Also I tried to create an index.html file in the do_GET method. That didn't work either. I mean the index.html was generated fine, but the response in the browser this time did not show anything (not even the hello world in the title). Am I missing anything very simple here? I was thinking should I overload the handle_request of the underlying SocketServer.BaseServer as the documentation says you should never override BaseHTTPServer's handle() method and should rather override the corresponding do_* method?

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  • How to proxy calls to the instance of an object

    - by mr.b
    Edit: Changed question title from "Does C# allow method overloading, PHP style (__call)?" - figured out it doesn't have much to do with actual question. Also edited question text. What I want to accomplish is to proxy calls to a an instance of an object methods, so I could log calls to any of its methods. Right now, I have code similar to this: class ProxyClass { static logger; public AnotherClass inner { get; private set; } public ProxyClass() { inner = new AnotherClass(); } } class AnotherClass { public void A() {} public void B() {} public void C() {} // ... } // meanwhile, in happyCodeLandia... ProxyClass pc = new ProxyClass(); pc.inner.A(); // need to write log message like "method A called" pc.inner.B(); // need to write log message like "method B called" // ... So, how can I proxy calls to an object instance in extensible way? Method overloading would be most obvious solution (if it was supported in PHP way). By extensible, meaning that I don't have to modify ProxyClass whenever AnotherClass changes. In my case, AnotherClass can have any number of methods, so it wouldn't be appropriate to overload or wrap all methods to add logging. I am aware that this might not be the best approach for this kind of problem, so if anyone has idea what approach to use, shoot. Thanks!

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  • Managing a log stream in C++ in a cout-like notation

    - by Andry
    Hello! I have a class in c++ in order to write log files for an application of mine. I have already built the class and it works, it is something like this: class Logger { std::string _filename; public: void print(std::string tobeprinted); } Well, it is intuitive that, in order to print a line in the log file, for an object of Logger, it is simply necessary to do the following: Logger mylogger("myfile.log"); mylogger.print(std::string("This is a log line")); Well. Using a method approach is not the same as using a much better pattern like << is. I would like to do the following: Logger mylogger("myfile.log"); mylogger << "This is a log line"; That's all. I suppose I must overload the << operator... But overloading using this signature (the classic one): ostream& operator<<(ostream& output, const MyObj& o); But I do not have a ostream... So, should I do as follows? Logger& operator<<(Logger& output, const std::string& o); Is this the right way? Thanks

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  • Getting the type of an array of T, without specifying T - Type.GetType("T[]")

    - by Merlyn Morgan-Graham
    I am trying to create a type that refers to an array of a generic type, without specifying the generic type. That is, I would like to do the equivalent of Type.GetType("T[]"). I already know how to do this with a non-array type. E.g. Type.GetType("System.Collections.Generic.IEnumerable`1") // or typeof(IEnumerable<>) Here's some sample code that reproduces the problem. using System; using System.Collections.Generic; public class Program { public static void SomeFunc<T>(IEnumerable<T> collection) { } public static void SomeArrayFunc<T>(T[] collection) { } static void Main(string[] args) { Action<Type> printType = t => Console.WriteLine(t != null ? t.ToString() : "(null)"); Action<string> printFirstParameterType = methodName => printType( typeof(Program).GetMethod(methodName).GetParameters()[0].ParameterType ); printFirstParameterType("SomeFunc"); printFirstParameterType("SomeArrayFunc"); var iEnumerableT = Type.GetType("System.Collections.Generic.IEnumerable`1"); printType(iEnumerableT); var iEnumerableTFromTypeof = typeof(IEnumerable<>); printType(iEnumerableTFromTypeof); var arrayOfT = Type.GetType("T[]"); printType(arrayOfT); // Prints "(null)" // ... not even sure where to start for typeof(T[]) } } The output is: System.Collections.Generic.IEnumerable`1[T] T[] System.Collections.Generic.IEnumerable`1[T] System.Collections.Generic.IEnumerable`1[T] (null) I'd like to correct that last "(null)". This will be used to get an overload of a function via reflections by specifying the method signature: var someMethod = someType.GetMethod("MethodName", new[] { typeOfArrayOfT }); // ... call someMethod.MakeGenericMethod some time later I've already gotten my code mostly working by filtering the result of GetMethods(), so this is more of an exercise in knowledge and understanding.

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  • Ways to make (relatively) safe assumptions about the type of concrete subclasses?

    - by Kylotan
    I have an interface (defined as a abstract base class) that looks like this: class AbstractInterface { public: bool IsRelatedTo(const AbstractInterface& other) const = 0; } And I have an implementation of this (constructors etc omitted): class ConcreteThing { public: bool IsRelatedTo(const AbstractInterface& other) const { return m_ImplObject.has_relationship_to(other.m_ImplObject); } private: ImplementationObject m_ImplObject; } The AbstractInterface forms an interface in Project A, and the ConcreteThing lives in Project B as an implementation of that interface. This is so that code in Project A can access data from Project B without having a direct dependency on it - Project B just has to implement the correct interface. Obviously the line in the body of the IsRelatedTo function cannot compile - that instance of ConcreteThing has an m_ImplObject member, but it can't assume that all AbstractInterfaces do, including the other argument. In my system, I can actually assume that all implementations of AbstractInterface are instances of ConcreteThing (or subclasses thereof), but I'd prefer not to be casting the object to the concrete type in order to get at the private member, or encoding that assumption in a way that will crash without a diagnostic later if this assumption ceases to hold true. I cannot modify ImplementationObject, but I can modify AbstractInterface and ConcreteThing. I also cannot use the standard RTTI mechanism for checking a type prior to casting, or use dynamic_cast for a similar purpose. I have a feeling that I might be able to overload IsRelatedTo with a ConcreteThing argument, but I'm not sure how to call it via the base IsRelatedTo(AbstractInterface) method. It wouldn't get called automatically as it's not a strict reimplementation of that method. Is there a pattern for doing what I want here, allowing me to implement the IsRelatedTo function via ImplementationObject::has_relationship_to(ImplementationObject), without risky casts? (Also, I couldn't think of a good question title - please change it if you have a better one.)

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  • Operator overloading in generic struct: can I create overloads for specific kinds(?) of generic?

    - by Carson Myers
    I'm defining physical units in C#, using generic structs, and it was going okay until I got the error: One of the parameters of a binary operator must be the containing type when trying to overload the mathematical operators so that they convert between different units. So, I have something like this: public interface ScalarUnit { } public class Duration : ScalarUnit { } public struct Scalar<T> where T : ScalarUnit { public readonly double Value; public Scalar(double Value) { this.Value = Value; } public static implicit operator double(Scalar<T> Value) { return Value.Value; } } public interface VectorUnit { } public class Displacement : VectorUnit { } public class Velocity : VectorUnit { } public struct Vector<T> where T : VectorUnit { #... public static Vector<Velocity> operator /(Vector<Displacement> v1, Scalar<Duration> v2) { return new Vector<Velocity>(v1.Magnitude / v2, v1.Direction); } } There aren't any errors for the + and - operators, where I'm just working on a Vector<T>, but when I substitute a unit for T, suddenly it doesn't like it. Is there a way to make this work? I figured it would work, since Displacement implements the VectorUnit interface, and I have where T : VectorUnit in the struct header. Am I at least on the right track here? I'm new to C# so I have difficulty understanding what's going on sometimes.

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  • Is it possible to implement events in C++?

    - by acidzombie24
    I wanted to implement a C# event in C++ just to see if i could do it. I got stuck, i know the bottom is wrong but what i realize my biggest problem is... How do i overload the () operator to be whatever is in T in this case int func(float)? I cant? can i? Can i implement a good alternative? #include <deque> using namespace std; typedef int(*MyFunc)(float); template<class T> class MyEvent { deque<T> ls; public: MyEvent& operator +=(T t) { ls.push_back(t); return *this; } }; static int test(float f){return (int)f; } int main(){ MyEvent<MyFunc> e; e += test; }

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  • C++, overloading std::swap, compiler error, VS 2010

    - by Ian
    I would like to overload std::swap in my template class. In the following code (simplified) #ifndef Point2D_H #define Point2D_H template <class T> class Point2D { protected: T x; T y; public: Point2D () : x ( 0 ), y ( 0 ) {} Point2D( const T &x_, const T &y_ ) : x ( x_ ), y ( y_ ) {} .... public: void swap ( Point2D <T> &p ); }; template <class T> inline void swap ( Point2D <T> &p1, Point2D <T> &p2 ) { p1.swap ( p2 ); } namespace std { template <class T> inline void swap ( Point2D <T> &p1, Point2D <T> &p2 ) { p1.swap ( p2 ); } } template <class T> void Point2D <T>::swap ( Point2D <T> &p ) { using (std::swap); swap ( x, p.x ); swap ( y, p.y ); } #endif there is a compiler error (only in VS 2010): error C2668: 'std::swap' : ambiguous call to overloaded I do not know why, std::swap should be overoaded... Using g ++ code works perfectly. Without templates (i.e. Point2D is not a template class) this code also works.. Thanks for your help.

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  • Emacs - nxhtml-mode - memory full

    - by mbutz
    working with nxhtml-mode in emacs, I get problems since a few weeks. While working emacs pauses unexpectingly until showing a message in the mode line "!MEM FULL!"; obviously nxhtml-mode is filling up the memory until emacs stopps to work. I am working with html, php and css files. I have no idea how I could debug this problem in a meaningfull way. Also I seem to be the only one to have this problem, because googling did not deliver any answers to this question. I am using emacs 2.32 on an Linux Mint 11 system. I can not find out the verson of nxhtml, it says revision 829 downloaded from http://bazaar.launchpad.net/~nxhtml/nxhtml/main/revision/829. I set up a test scenario with a minimal dot-emacs just to test the nxhtml-mode. It seemed to be alright, but it does not reflect my productive set up. It would probably take a week or so to gradually include everything I used to use within emacs (e.g. org-mode) while testing whether nxhtml-mode does not like anything, which is called in my dot-emacs file. Is there another way? Can I find out, what causes the memory overload? Does anyone has similar problems using nxhtml-mode? Greetings Martin

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  • const pod and std::vector

    - by Baz
    To get this code to compile: std::vector<Foo> factory() { std::vector<Foo> data; return data; } I have to define my POD like this: struct Foo { const int i; const int j; Foo(const int _i, const int _j): i(_i), j(_j) {} Foo(Foo& foo): i(foo.i), j(foo.j){} Foo operator=(Foo& foo) { Foo f(foo.i, foo.j); return f; } }; Is this the correct approach for defining a pod where I'm not interested in changing the pod members after creation? Why am I forced to define a copy constructor and overload the assignment operator? Is this compatible for different platform implementations of std::vector? Is it wrong in your opinion to have const PODS like this? Should I just leave them as non-const?

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  • ?Selected node changed

    - by user175084
    I have a tree view like this and i want to navigate to 3 different pages using response .redirect --machine groups (main) ----dept (Parent) ------xyz (child) protected void TreeView2_SelectedNodeChanged(object sender, EventArgs e) { if (TreeView2.SelectedValue == "Machine Groups") { Response.Redirect("~/Gridviewpage.aspx"); } else switch (e.Node.Depth) { case 0: Response.Redirect("~/Machineupdate.aspx?node=" + TreeView2.SelectedNode.Value); break; case 1: Response.Redirect("~/MachineUpdatechild.aspx?node=" + TreeView3.SelectedNode.Value); break; } } } now if i put EventArgs it points to an error on e.Node that system.EventArgs does not contain definition for Node. If i replace EventArgs with TreeNodeEventArgs then that error goes but i get an error on compilation. Compiler Error Message: CS0123: No overload for 'TreeView2_SelectedNodeChanged' matches delegate 'System.EventHandler' <asp:TreeView ID="TreeView2" runat="server" OnUnload="TreeViewMain_Unload" ontreenodepopulate="TreeView2_TreeNodePopulate" onselectednodechanged="TreeView2_SelectedNodeChanged"> <Nodes> <asp:TreeNode PopulateOnDemand="True" Text="Machine Groups" Value="Machine Groups"></asp:TreeNode> </Nodes> </asp:TreeView> Please help me out.... I would also like to kno what is the diff between EventArgs and TreeNodeEventArgs Thanks

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  • Distinctly LINQ &ndash; Getting a Distinct List of Objects

    - by David Totzke
    Let’s say that you have a list of objects that contains duplicate items and you want to extract a subset of distinct items.  This is pretty straight forward in the trivial case where the duplicate objects are considered the same such as in the following example: List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 }; IEnumerable<int> distinctAges = ages.Distinct(); Console.WriteLine("Distinct ages:"); foreach (int age in distinctAges) { Console.WriteLine(age); } /* This code produces the following output: Distinct ages: 21 46 55 17 */ What if you are working with reference types instead?  Imagine a list of search results where items in the results, while unique in and of themselves, also point to a parent.  We’d like to be able to select a bunch of items in the list but then see only a distinct list of parents.  Distinct isn’t going to help us much on its own as all of the items are distinct already.  Perhaps we can create a class with just the information we are interested in like the Id and Name of the parents.  public class SelectedItem { public int ItemID { get; set; } public string DisplayName { get; set; } } We can then use LINQ to populate a list containing objects with just the information we are interested in and then get rid of the duplicates. IEnumerable<SelectedItem> list = (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>() select new SelectedItem { ItemID = item.ParentId, DisplayName = item.ParentName }) .Distinct(); Most of you will have guessed that this didn’t work.  Even though some of our objects are now duplicates, because we are working with reference types, it doesn’t matter that their properties are the same, they’re still considered unique.  What we need is a way to define equality for the Distinct() extension method. IEqualityComparer<T> Looking at the Distinct method we see that there is an overload that accepts an IEqualityComparer<T>.  We can simply create a class that implements this interface and that allows us to define equality for our SelectedItem class. public class SelectedItemComparer : IEqualityComparer<SelectedItem> { public new bool Equals(SelectedItem abc, SelectedItem def) { return abc.ItemID == def.ItemID && abc.DisplayName == def.DisplayName; } public int GetHashCode(SelectedItem obj) { string code = obj.DisplayName + obj.ItemID.ToString(); return code.GetHashCode(); } } In the Equals method we simply do whatever comparisons are necessary to determine equality and then return true or false.  Take note of the implementation of the GetHashCode method.  GetHashCode must return the same value for two different objects if our Equals method says they are equal.  Get this wrong and your comparer won’t work .  Even though the Equals method returns true, mismatched hash codes will cause the comparison to fail.  For our example, we simply build a string from the properties of the object and then call GetHashCode() on that. Now all we have to do is pass an instance of our IEqualitlyComarer<T> to Distinct and all will be well: IEnumerable<SelectedItem> list =     (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>()         select new SelectedItem { ItemID = item.dahfkp, DisplayName = item.document_code })                         .Distinct(new SelectedItemComparer());   Enjoy. Dave Just because I can… Technorati Tags: LINQ,C#

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  • Parallelism in .NET – Part 19, TaskContinuationOptions

    - by Reed
    My introduction to Task continuations demonstrates continuations on the Task class.  In addition, I’ve shown how continuations allow handling of multiple tasks in a clean, concise manner.  Continuations can also be used to handle exceptional situations using a clean, simple syntax. In addition to standard Task continuations , the Task class provides some options for filtering continuations automatically.  This is handled via the TaskContinationOptions enumeration, which provides hints to the TaskScheduler that it should only continue based on the operation of the antecedent task. This is especially useful when dealing with exceptions.  For example, we can extend the sample from our earlier continuation discussion to include support for handling exceptions thrown by the Factorize method: // Get a copy of the UI-thread task scheduler up front to use later var uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); // Start our task var factorize = Task.Factory.StartNew( () => { int primeFactor1 = 0; int primeFactor2 = 0; bool result = Factorize(10298312, ref primeFactor1, ref primeFactor2); return new { Result = result, Factor1 = primeFactor1, Factor2 = primeFactor2 }; }); // When we succeed, report the results to the UI factorize.ContinueWith(task => textBox1.Text = string.Format("{0}/{1} [Succeeded {2}]", task.Result.Factor1, task.Result.Factor2, task.Result.Result), CancellationToken.None, TaskContinuationOptions.NotOnFaulted, uiScheduler); // When we have an exception, report it factorize.ContinueWith(task => textBox1.Text = string.Format("Error: {0}", task.Exception.Message), CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, uiScheduler); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The above code works by using a combination of features.  First, we schedule our task, the same way as in the previous example.  However, in this case, we use a different overload of Task.ContinueWith which allows us to specify both a specific TaskScheduler (in order to have your continuation run on the UI’s synchronization context) as well as a TaskContinuationOption.  In the first continuation, we tell the continuation that we only want it to run when there was not an exception by specifying TaskContinuationOptions.NotOnFaulted.  When our factorize task completes successfully, this continuation will automatically run on the UI thread, and provide the appropriate feedback. However, if the factorize task has an exception – for example, if the Factorize method throws an exception due to an improper input value, the second continuation will run.  This occurs due to the specification of TaskContinuationOptions.OnlyOnFaulted in the options.  In this case, we’ll report the error received to the user. We can use TaskContinuationOptions to filter our continuations by whether or not an exception occurred and whether or not a task was cancelled.  This allows us to handle many situations, and is especially useful when trying to maintain a valid application state without ever blocking the user interface.  The same concepts can be extended even further, and allow you to chain together many tasks based on the success of the previous ones.  Continuations can even be used to create a state machine with full error handling, all without blocking the user interface thread.

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  • Visual Studio 2010 Beta 2 Startup Failures

    - by Rick Strahl
    I’ve been working with VS 2010 Beta 2 for a while now and while it works Ok most of the time it seems the environment is very, very fragile when it comes to crashes and installed packages. Specifically I’ve been working just fine for days, then when VS 2010 crashes it will not re-start. Instead I get the good old Application cannot start dialog: Other failures I’ve seen bring forth other just as useful dialogs with information overload like Operation cannot be performed which for me specifically happens when trying to compile any project. After a bit of digging around and a post to Microsoft Connect the solution boils down to resetting the VS.NET environment. The Application Cannot Start issue stems from a package load failure of some sort, so the work around for this is typically: c:\program files\Visual Studio 2010\Common7\IDE\devenv.exe /ResetSkipPkgs In most cases that should do the trick. If it doesn’t and the error doesn’t go away the more drastic: c:\program files\Visual Studio 2010\Common7\IDE\devenv.exe /ResetSettings is required which resets all settings in VS to its installation defaults. Between these two I’ve always been able to get VS to startup and run properly. BTW it’s handy to keep a list of command line options for Visual Studio around: http://msdn.microsoft.com/en-us/library/xee0c8y7%28VS.100%29.aspx Note that the /? option in VS 2010 doesn’t display all the options available but rather displays the ‘demo version’ message instead, so the above should be helpful. Also note that unless you install Visual C++ the Visual Studio Command Prompt icon is not automatically installed so you may have to navigate manually to the appropriate folder above. Cannot Build Failures If you get the Cannot compile error dialog, there is another thing that have worked for me: Change your project build target from Debug to Release (or whatever – just change it) and compile again. If that doesn’t work doing the reset steps above will do it for me. It appears this failure comes from some sort of interference of other versions of Visual Studio installed on the system and running another version first. Resetting the build target explicitly seems to reset the build providers to a normalized state so that things work in many cases. But not all. Worst case – resetting settings will do it. The bottom line for working in VS 2010 has been – don’t get too attached to your custom settings as they will get blown away quite a bit. I’ve probably been through 20 or more of these VS resets although I’ve been working with it quite a bit on an internal project. It’s kind of frustrating to see this kind of high level instability in a Beta 2 product which is supposedly the last public beta they will put out. On the other hand this beta has been otherwise rather stable and performance is roughly equivalent to VS 2008. Although I mention the crash above – crashes I’ve seen have been relatively rare and no more frequent than in VS 2008 it seems. Given the drastic UI changes in VS 2010 (using WPF for the shell and editor) I’m actually impressed that the product is as stable as it is at this point. Also I was seriously worried about text quality going to a WPF model, but thankfully WPF 4.0 addresses the blurry text issue with native font rendering to render text on non-cleartype enabled systems crisply. Anyway I hope that these notes are helpful to some of you playing around with the beta and running into problems. Hopefully you won’t need them :-}© Rick Strahl, West Wind Technologies, 2005-2010

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  • Throttling in OSB

    - by Knut Vatsendvik
    Technorati Tags: soa,integration,osb,throttling,overload protection A common problem with integration is the risk of overloading a particular web service. When the capacity of a web service is reached and it continues to accept connections, it will most likely start to deteriorate. Fortunately there are 2 techniques, with Oracle Service Bus, that you can apply for protecting this from happening. You can either limit the concurrent number of requests for a Business Service (outbound requests) or you can limit the number of threads processing the requests for a Proxy Service (inbound requests). Limiting the Concurrent Number of Requests Limiting the concurrent requests for a Business Service cannot be set at design time so you have to use the built-in Oracle Service Bus Administration Console to do it (/sbconsole). Follow these steps to enable it: In Change Center, click Create to start a new Session Select Project Explorer, and navigate to the Business Service you want to limit Select the Operational Settings tab of the View a Business Service page In this tab, under Throttling, select the Enable check box. By enabling throttling you Specify a value for Maximum Concurrency Specify a positive integer value for Throttling Queue to backlog messages that has exceeded the message concurrency limit Specify the maximum time in milliseconds for Message Expiration a message can spend in Throttling Queue Click Update Click Active in Change Center to active the new settings If you re-publish the service, it will not overwrite the settings. Only if the resource is renamed or moved, it will. Please note that a throttling queue is an in-memory queue. Messages that are placed in this queue are not recoverable when a server fails or when you restart a server. Limiting the Number of Threads A better approach, in my opinion, is to limit the number of threads that can work with request. Follow these steps to do it: Open the WebLogic Server Console (/console) In Change Center, click Create to start a new Session In the left pane expand Environment and select Work Managers In the Global Work Managers page, click New    Click the Work Manager radio button, then click Next Enter a Name for the new Work Manager, and click Next In the Available Targets list, select server instances or clusters on which you will deploy applications that reference the Work Manager Click Finish. The new Work Manager now appears in the Global Work Managers page. Select the new Work Manager Right next to the Maximum Threads Constraint drop-down box, click New   Click the Maximum Threads Constraint radio button, then click Next Enter a Name and a thread Count to be the maximum size to allocate for requests. Click Next  In the Available Targets list, select server instances or clusters on which you will deploy applications that reference the Work Manager Click Finish Click Save Click Active in Change Center to active your changes.  A restart may be necessary.   Puh! Almost there. Start a new session. Go to the Service Bus Console (/sbconsole) and find your consuming Proxy Service. Click the Edit button of the Transport Configuration tab. Click Next Set the Dispatch Policy to the new Work Manager Click Last Click Save Click Active in Change Center to active your changes. 

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  • Localization with ASP.NET MVC ModelMetadata

    - by kazimanzurrashid
    When using the DisplayFor/EditorFor there has been built-in support in ASP.NET MVC to show localized validation messages, but no support to show the associate label in localized text, unless you are using the .NET 4.0 with Mvc Future. Lets a say you are creating a create form for Product where you have support both English and German like the following. English German I have recently added few helpers for localization in the MvcExtensions, lets see how we can use it to localize the form. As mentioned in the past that I am not a big fan when it comes to decorate class with attributes which is the recommended way in ASP.NET MVC. Instead, we will use the fluent configuration (Similar to FluentNHibernate or EF CodeFirst) of MvcExtensions to configure our View Models. For example for the above we will using: public class ProductEditModelConfiguration : ModelMetadataConfiguration<ProductEditModel> { public ProductEditModelConfiguration() { Configure(model => model.Id).Hide(); Configure(model => model.Name).DisplayName(() => LocalizedTexts.Name) .Required(() => LocalizedTexts.NameCannotBeBlank) .MaximumLength(64, () => LocalizedTexts.NameCannotBeMoreThanSixtyFourCharacters); Configure(model => model.Category).DisplayName(() => LocalizedTexts.Category) .Required(() => LocalizedTexts.CategoryMustBeSelected) .AsDropDownList("categories", () => LocalizedTexts.SelectCategory); Configure(model => model.Supplier).DisplayName(() => LocalizedTexts.Supplier) .Required(() => LocalizedTexts.SupplierMustBeSelected) .AsListBox("suppliers"); Configure(model => model.Price).DisplayName(() => LocalizedTexts.Price) .FormatAsCurrency() .Required(() => LocalizedTexts.PriceCannotBeBlank) .Range(10.00m, 1000.00m, () => LocalizedTexts.PriceMustBeBetweenTenToThousand); } } As you can we are using Func<string> to set the localized text, this is just an overload with the regular string method. There are few more methods in the ModelMetadata which accepts this Func<string> where localization can applied like Description, Watermark, ShortDisplayName etc. The LocalizedTexts is just a regular resource, we have both English and German:   Now lets see the view markup: <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<Demo.Web.ProductEditModel>" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server"> <%= LocalizedTexts.Create %> </asp:Content> <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server"> <h2><%= LocalizedTexts.Create %></h2> <%= Html.ValidationSummary(false, LocalizedTexts.CreateValidationSummary)%> <% Html.EnableClientValidation(); %> <% using (Html.BeginForm()) {%> <fieldset> <%= Html.EditorForModel() %> <p> <input type="submit" value="<%= LocalizedTexts.Create %>" /> </p> </fieldset> <% } %> <div> <%= Html.ActionLink(LocalizedTexts.BackToList, "Index")%> </div> </asp:Content> As we can see that we are using the same LocalizedTexts for the other parts of the view which is not included in the ModelMetadata like the Page title, button text etc. We are also using EditorForModel instead of EditorFor for individual field and both are supported. One of the added benefit of the fluent syntax based configuration is that we will get full compile type checking for our resource as we are not depending upon the string based resource name like the ASP.NET MVC. You will find the complete localized CRUD example in the MvcExtensions sample folder. That’s it for today.

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