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• Does this interface already exist in the standard .NET libraries?

  - by VoidStar

  I found myself needing a simple generic interface, and I wrote it, but it turned out to be pretty much the world's simplest interface. I was wondering if it already exists by some other name. I just want to make sure I'm not reinventing something that is already included with the .NET framework. interface IReceiver<T> { void Receive(T obj); } I can't really find a good list of "standard" interfaces that came with .NET. Does the structure of this interface look familiar to anyone? Have I reinvented something that is already standard? EDIT: I have a data object and a number of objects interested in receiving the data. Objects interested in receiving the data implement the interface, so that 'routing' lists and maps can send the data to them. The idea is full generalization in the routing, the routing will be data-driven.

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• Testing what a String token holds

  - by Yiwei Gao

  I am making a calculator and part of this program takes in user String input and tokenizes it (using my own implementation of a Tokenizer class). So now I have a bunch of Token objects and I would like to test each one of them to see if they hold numbers or operators. Is there a way to test to see if they hold operators (ie. +, -, *, /, =, (, ), etc.) without using if (token.equals("+") || token.equals("-") || ... and so on, for each operator? These Token objects are all of type String.

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• Twin edges - Half edge data structure

  - by Pradeep Kumar

  I have implemented a Half-edge data structure for loading 3d objects. I find that the part of assigning twin/pair edges takes the longest computation time (especially for objects which have hundreds of thousands half edges). The reason is that I use nested loops to accomplish this. Is there a simpler and efficient way of doing this? Below is the code which I've written. HE is the half-edge data structure. hearr is a vector containing all the half edges. vert is the starting vertex and end is the ending vertex. Thanks!! HE *e1,*e2; for(size_t i=0;i<hearr.size();i++){ e1=hearr[i]; for(size_t j=1;j<hearr.size();j++){ e2=hearr[j]; if((e1->vert==e2->end)&&(e2->vert==e1->end)){ e1->twin=e2; e2->twin=e1; } } }

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• How can I duplicate, or copy a Core Data Managed Object?

  - by 106480833665852483906

  I have a managed object ("A") that contains various attributes and types of relationships, and its relationships also have their own attributes & relationships. What I would like to do is to "copy" or "duplicate" the entire object graph rooted at object "A", and thus creating a new object "B" that is very similar to "A". To be more specific, none of the relationships contained by "B" (or its children) should point to objects related to "A". There should be an entirely new object graph with similar relationships intact, and all objects having the same attributes, but of course different id's. There is the obvious manual way to do this, but I was hoping to learn of a simpler means of doing so which was not totally apparent from the Core Data documentation. TIA!

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• Singletons and constants

  - by devoured elysium

  I am making a program which makes use of a couple of constants. At first, each time I needed to use a constant, I'd define it as //C# private static readonly int MyConstant = xxx; //Java private static final int MyConstant = xxx; in the class where I'd need it. After some time, I started to realise that some constants would be needed in more than one class. At this time, I had 3 choises: To define them in the different classes that needed it. This leads to repetition. If by some reason later I need to change one of them, I'd have to check in all classes to replace them everywhere. To define a static class/singleton with all the constants as public. If I needed a constant X in ClassA, ClassB and ClassC, I could just define it in ClassA as public, and then have ClassB and ClassC refer to them. This solution doesn't seem that good to me as it introduces even more dependencies as the classes already have between them. I ended up implementing my code with the second option. Is that the best alternative? I feel I am probably missing some other better alternative. What worries me about using the singleton here is that it is nowhere clear to a user of the class that this class is using the singleton. Maybe I could create a ConstantsClass that held all the constants needed and then I'd pass it in the constructor to the classes that'd need it? Thanks

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• Python: What's a correct and good way to implement __hash__()?

  - by random-name

  What's a correct and good way to implement hash()? I am talking about the function that returns a hashcode that is then used to insert objects into hashtables aka dictionaries. As hash() returns an integer and is used for "binning" objects into hashtables I assume that the values of the returned integer should be uniformly distributed for common data (to minimize collisions). What's a good practice to get such values? Are collisions a problem? In my case I have a small class which acts as a container class holding some ints, some floats and a string.

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• Constructor initialising an array of subobjects?

  - by ojw

  Say I have several objects within a class, each of which needs constructing with a different value. I can write something like this: class b { public: b(int num) { // 1 for a.b1, and 2 for a.b2 } }; class a { public: b b1; b b2; a() : b1(1), b2(2) { } }; However, is it possible to do the same thing if those multiple objects are stored in an array? My first attempt at it doesn't compile: class a { public: b bb[2]; a() : bb[0](1), bb[1](2) { } };

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• FLEX: how to ignore MouseEvents from the container ?

  - by Patrick

  hi, I've some objects on the canvas, and I added eventListeners to these objects for MOUSE_UP event. I'm know checking if it works by tracing e.target.name, and I found out that the event is triggered twice, before on the element container (Canvas) and then the element itself. I read several times the documentation about Capture, Bubbling etc.. but I don't understand how to trigger the events only from the element itself... child.addEventListener(MouseEvent.MOUSE_UP, updateSelectedTags); private function updateSelectedTags(e:MouseEvent):void { Alert.show(e.currentTarget.name); //I have 2 alerts, one for canvas, the other one for the child } } thanks

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• Can I Have Polymorphic Containers With Value Semantics in C++11?

  - by John Dibling

  This is a sequel to a related post which asked the eternal question: Can I have polymorphic containers with value semantics in C++? The question was asked slightly incorrectly. It should have been more like: Can I have STL containers of a base type stored by-value in which the elements exhibit polymorphic behavior? If you are asking the question in terms of C++, the answer is "no." At some point, you will slice objects stored by-value. Now I ask the question again, but strictly in terms of C++11. With the changes to the language and the standard libraries, is it now possible to store polymorphic objects by value in an STL container? I'm well aware of the possibility of storing a smart pointer to the base class in the container -- this is not what I'm looking for, as I'm trying to construct objects on the stack without using new. Consider if you will (from the linked post) as basic C++ example: #include <iostream> using namespace std; class Parent { public: Parent() : parent_mem(1) {} virtual void write() { cout << "Parent: " << parent_mem << endl; } int parent_mem; }; class Child : public Parent { public: Child() : child_mem(2) { parent_mem = 2; } void write() { cout << "Child: " << parent_mem << ", " << child_mem << endl; } int child_mem; }; int main(int, char**) { // I can have a polymorphic container with pointer semantics vector<Parent*> pointerVec; pointerVec.push_back(new Parent()); pointerVec.push_back(new Child()); pointerVec[0]->write(); pointerVec[1]->write(); // Output: // // Parent: 1 // Child: 2, 2 // But I can't do it with value semantics vector<Parent> valueVec; valueVec.push_back(Parent()); valueVec.push_back(Child()); // gets turned into a Parent object :( valueVec[0].write(); valueVec[1].write(); // Output: // // Parent: 1 // Parent: 2 }

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• What Java tools/apis to use for decrypting/encrypting

  - by Java_bear

  I am trying to decrypt (and later encrypt) an email message (ebXML). The message contains a Signature element that contains child elements to specify the SignedInfo, SignatureValue and KeyInfo. Also, the message contains an encrypted attachment. Question: What Java tools/apis should be used for decrypting? I would like to find some tool/api that would (automagically) instantiate objects based on whatever is included with the Signature element, so that the data (message) could be easily validated. And the other way around: Creating objects (specifying methods, signature value and keyinfo) and then outputting the xml to go into the message.

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• Foreign Key Relationships

  - by Yehonathan Quartey

  I have two models class Subject(models.Model): name = models.CharField(max_length=100,choices=COURSE_CHOICES) created = models.DateTimeField('created', auto_now_add=True) modified = models.DateTimeField('modified', auto_now=True) syllabus = models.FileField(upload_to='syllabus') def __unicode__(self): return self.name and class Pastquestion(models.Model): subject=models.ForeignKey(Subject) year =models.PositiveIntegerField() questions = models.FileField(upload_to='pastquestions') def __unicode__(self): return str(self.year) Each Subject can have one or more past questions but a past question can have only one subject. I want to get a subject, and get its related past questions of a particular year. I was thinking of fetching a subject and getting its related past question. Currently am implementing my code such that I rather get the past question whose subject and year correspond to any specified subject like this_subject=Subject.objects.get(name=the_subject) thepastQ=Pastquestion.objects.get(year=2000,subject=this_subject) I was thinking there is a better way to do this. Or is this already a better way? Please Do tell ?

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• The cross-thread usage of "HttpContext.Current" property and related things

  - by smwikipedia

  I read from < Essential ASP.NET with Examples in C# the following statement: Another useful property to know about is the static Current property of the HttpContext class. This property always points to the current instance of the HttpContext class for the request being serviced. This can be convenient if you are writing helper classes that will be used from pages or other pipeline classes and may need to access the context for whatever reason. By using the static Current property to retrieve the context, you can avoid passing a reference to it to helper classes. For example, the class shown in Listing 4-1 uses the Current property of the context to access the QueryString and print something to the current response buffer. Note that for this static property to be correctly initialized, the caller must be executing on the original request thread, so if you have spawned additional threads to perform work during a request, you must take care to provide access to the context class yourself. I am wondering about the root cause of the bold part, and one thing leads to another, here is my thoughts: We know that a process can have multiple threads. Each of these threads have their own stacks, respectively. These threads also have access to a shared memory area, the heap. The stack then, as I understand it, is kind of where all the context for that thread is stored. For a thread to access something in the heap it must use a pointer, and the pointer is stored on its stack. So when we make some cross-thread calls, we must make sure that all the necessary context info is passed from the caller thread's stack to the callee thread's stack. But I am not quite sure if I made any mistake. Any comments will be deeply appreciated. Thanks. ADD Here the stack is limited to user stack.

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• Is it possible to start (and stop) a thread inside a DLL?

  - by Jerry Dodge

  I'm pondering some ideas for building a DLL for some common stuff I do. One thing I'd like to check if it's possible is running a thread inside of a DLL. I'm sure I would be able to at least start it, and have it automatically free on terminate (and make it forcefully terminate its self) - that I can see wouldn't be much of a problem. But once I start it, I don't see how I can continue communicating with it (especially to stop it) mainly because each call to the DLL is unique (as far as my knowledge tells me) but I also know very little of the subject. I've seen how in some occasions, a DLL can be loaded at the beginning and released at the end when it's not needed anymore. I have 0 knowledge or experience with this method, other than just seeing something related to it, couldn't even tell you what or how, I don't remember. But is this even possible? I know about ActiveX/COM but that is not what I want - I'd like just a basic DLL that can be used across languages (specifically C#). Also, if it is possible, then how would I go about doing callbacks from the DLL to the app? For example, when I start the thread, I most probably will assign a function (which is inside the EXE) to be the handler for the events (which are triggered from the DLL). So I guess what I'm asking is - how to load a DLL for continuous work and release it when I'm done - as opposed to the simple method of calling individual functions in the DLL as needed. In the same case - I might assign variables or create objects inside the DLL. How can I assure that once I assign that variable (or create the object), how can I make sure that variable or object will still be available the next time I call the DLL? Obviously it would require a mechanism to Initialize/Finalize the DLL (I.E. create the objects inside the DLL when the DLL is loaded, and free the objects when the DLL is unloaded). EDIT: In the end, I will wrap the DLL inside of a component, so when an instance of the component is created, DLL will be loaded and a corresponding thread will be created inside the DLL, then when the component is free'd, the DLL is unloaded. Also need to make sure that if there are for example 2 of these components, that there will be 2 instances of the DLL loaded for each component. Is this in any way related to the use of an IInterface? Because I also have 0 experience with this. No need to answer it directly with sample source code - a link to a good tutorial would be great.

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• Is there any alternative way of writing this switch statement(C#3.0)

  - by Newbie

  Can it be done in a better way public static EnumFactorType GetFactorEnum(string str) { Standardization e = new Standardization(); switch (str.ToLower()) { case "beta": e.FactorType = EnumFactorType.BETA; break; case "bkp": e.FactorType = EnumFactorType.BOOK_TO_PRICE; break; case "yld": e.FactorType = EnumFactorType.DIVIDEND_YIELD; break; case "growth": e.FactorType = EnumFactorType.GROWTH; break; case "mean": e.FactorType = EnumFactorType.MARKET_CAP; break; case "momentum": e.FactorType = EnumFactorType.MOMENTUM; break; case "size": e.FactorType = EnumFactorType.SIZE; break; case "stat_fact1": e.FactorType = EnumFactorType.STAT_FACT_1; break; case "stat_fact2": e.FactorType = EnumFactorType.STAT_FACT_2; break; case "value": e.FactorType = EnumFactorType.VALUE; break; } return e.FactorType; } If I create a Static class(say Constatant) and declare variable like public static string BETA= "beta"; and then if I try to put that in the Case expression like Case Constants.BETA : e.FactorType = EnumFactorType.BETA; break; then the compiler will report error.(quite expected) So is there any other way?(I canot change the switch statement) Using C#3.0 Thanks

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• How to yield a single element from for loop in scala?

  - by Julio Faerman

  Much like this question: Functional code for looping with early exit Say the code is def findFirst[T](objects: List[T]):T = { for (obj <- objects) { if (expensiveFunc(obj) != null) return /*???*/ Some(obj) } None } How to yield a single element from a for loop like this in scala? I do not want to use find, as proposed in the original question, i am curious about if and how it could be implemented using the for loop. * UPDATE * First, thanks for all the comments, but i guess i was not clear in the question. I am shooting for something like this: val seven = for { x <- 1 to 10 if x == 7 } return x And that does not compile. The two errors are: - return outside method definition - method main has return statement; needs result type I know find() would be better in this case, i am just learning and exploring the language. And in a more complex case with several iterators, i think finding with for can actually be usefull. Thanks commenters, i'll start a bounty to make up for the bad posing of the question :)

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• Dispatching generic tasks in WCF or .Net Remoting

  - by Eric

  Hello all, I've been researching for a couple days on and off, and have yet to figure out the best way to achieve the following goal. I would like to define either an interface or abstract class in C# which has an associated Run method, similar to the Java runnable interface. The goal would be to have a shared queue which contains a list of these objects. Then individual clients would be able to derive their own concrete runnable classes and add them to the queue hosted by the server. Clients would also be able to pop these runnable objects off the queue and execute them arbitrarily. This seems like it should be feasible in a VM based language without needing to place any of the concrete implementations in a shared assembly, but I have thus far had no luck finding a working example of such a system. Does anyone know how this might be achieved?

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• Java PropertyChangeListener

  - by Laphroaig

  Hi, i'm trying to figure out how to listen a property change on another class. this is my code: class with the property to listen: public class ClassWithProperty { private PropertyChangeSupport changes = new PropertyChangeSupport(this); private int usersOnline; public int getUsersOnline() { return usersOnline; } public ClassWithProperty() { usersOnline = 0; while (usersOnline<10) { changes.firePropertyChange("usersOnline", usersOnline, usersOnline++); } } public void addPropertyChangeListener( PropertyChangeListener l) { changes.addPropertyChangeListener(l); } public void removePropertyChangeListener( PropertyChangeListener l) { changes.removePropertyChangeListener(l); } } class where i need to know when the property change: public class Main { private static ClassWithProperty test; public static void main(String[] args) { test = new ClassWithProperty(); test.addPropertyChangeListener(listen()); } private static PropertyChangeListener listen() { System.out.println(test.getUsersOnline()); return null; } } I have the event fired only the last time (usersOnline=10). Sorry if it can be a stupid question, i'm learning now java and can't find a solution.

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• Which way of declaring a variable is fastest?

  - by ADB

  For a variable used in a function that is called very often and for implementation in J2ME on a blackberry (if that changed something, can you explain)? class X { int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { static int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { public void someFunc(int j) { int i = 0; while( i < j ){ [...] i++; } } } I know there is a difference how a static versus non-static class variable is accessed, but I don't know it would affect the speed. I also remember reading somewhere that in-function variables may be accessed faster, but I don't know why and where I read that. Background on the question: some painting function in games are called excessively often and even small difference in access time can affect the overall performance when a variable is used in a largish loop.

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• Android move data between activities

  - by Parhs

  Example I have 4 activities. A B C D A is a list of objects. B C D are used to add a new object. So A calls B then C then D . However C or D have button to 'add the object' When going up from B or C or D to activity A , A should have a List with these objects. Even if user tap back items should be 'saved' However I dont want to start a new Intent at C or D because i dont want user to go back to A and then click again add new item. I have been adviced to keep these data at application object. Is there any other suggestion ?

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• Django: Converting an entire Model into a single dictionary

  - by LarrikJ

  Is there a good way in Django to convert an entire model to a dictionary? I mean, like this: class DictModel(models.Model): key = models.CharField(20) value = models.CharField(200) DictModel.objects.all().to_dict() ... with the result being a dictionary with the key/value pairs made up of records in the Model? Has anyone else seen this as being useful for them? Thanks. Update I just wanted to add is that my ultimate goal is to be able to do a simple variable lookup inside a Template. Something like: {{ DictModel.exampleKey }} With a result of DictModel.objects.get(key__exact=exampleKey).value Overall, though, you guys have really surprised me with how helpful allof your responses are, and how different the ways to approach it can be. Thanks a lot.

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• Data Structure Brushup (Java)

  - by Daddy Warbox

  This should be easy for many of you, but for me it's just another bit of rust needing to be chipped away as I get back into basic Java coding. Using bloody associative arrays for so long in other languages have turned me nice and spoiled. :P My problem is simple: I'm storing a set of objects, each containing a string and a number, in a list. I would like each object inserted into this list to be sorted alphabetically by its string. I would also like to be able to retrieve objects from the list by their string as well. I would like to do this as formally and/or efficiently as possible. Is there something already available in the Java standard libraries for this?

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• Passing enum or object through an intent (the best solution)

  - by jax

  I have an activity that when started needs access to two different ArrayLists. Both Lists are different Objects I have created myself. Basically I need a way to pass these objects to the activity from an Intent. I can use addExtras() but this requires a Parceable compatible class. I could make my classes to be passed serializable but as I understand this slows down the program. What are my options? Can I pass an Enum? As an an aside: is there a way to pass parameters to an Activity Constructor from an Intent?

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• Is it possible to Store Enum value in String?

  - by Narasimham K

  Actally my java progrem like... public class Schedule{ public static enum RepeatType { DAILY, WEEKLY, MONTHLY; } public static enum WeekdayType { MONDAY(Calendar.MONDAY), TUESDAY(Calendar.TUESDAY), WEDNESDAY( Calendar.WEDNESDAY), THURSDAY(Calendar.THURSDAY), FRIDAY( Calendar.FRIDAY), SATURDAY(Calendar.SATURDAY), SUNDAY( Calendar.SUNDAY); private int day; private WeekdayType(int day) { this.day = day; } public static List<Date> generateSchedule(RepeatType repeatType,List<WeekdayType> repeatDays) { ----------------------------- ----------------------------//hear some logic i wrote }//Method } And i'm calling the method into my Business class like following... @RemotingInclude public void createEvent(TimetableVO timetableVO) { if ("repeatDays".equals(timetableVO.getSearchKey())) { List<Date> repeatDaysList=Schedule.generateSchedule(timetableVO.getRepeatType(),timetableVO.getRepeatDays()); } } And Finally TimetableVO is @Entity @Table(name="EC_TIMETABLE") public class TimetableVO extends AbstractVO{ ----- private RepeatType repeatType; private List<WeekdayType> repeatDays;//But in this case the method generateSchedule(-,-) was not calling. ----- } So my Question is Which one is Better Statement in the Following... private List<WeekdayType> repeatDays; (or) private String repeatDays;//if we give like this `How to Convert Enum type to String` because generateSchedule() method taking enum type value....

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• select k th mimimum from array a[0..n-1]

  - by davit-datuashvili

  i have done folloing code from progrmming pearls here is code import java.util.*; public class select { public static int select1(int x[],int l,int u,int k){ //pre l<=k<=u //post x[l..k-1]<=x[k]<=x[k+1..u] Random r=new Random(); int t=r.nextInt(u-1-l)+l; if (l>=u) return -1 ; swap(l,t); int s=x[l]; int i=l; int j=u+1; while (true){ do { i++; }while (i<=u && x[i]<t); do { j--; }while (x[j]>t); if (i>j) break; int temp=x[i]; x[i]=x[j];x[j]=t; swap(l,j); if (j<k){ return select1(x,j+1,u,k); } } return select1(x,l,j-1,k); } public static void main(String[] args) { int x[]=new int[]{4,7,9,3,2,12,13,10,20}; select1(x,0,x.length-1,5); } public static void swap(int i,int j){ int c=i; i=j; j=c; } } but here is mistake Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 at select.select1(select.java:21) at select.main(select.java:36) Java Result: 1 please help

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• Associate two sets of values

  - by PJW

  I have the following code - public static int GetViewLevel(string viewLevelDesc) { try { switch (viewLevelDesc) { case "All": return 0; case "Office": return 10; case "Manager": return 50; default: throw new Exception("Invalid View Level Description"); } } catch (Exception eX) { throw new Exception("Action: GetViewLevel()" + Environment.NewLine + eX.Message); } } public static string GetViewLevelDescription(int viewLevel) { try { switch (viewLevel) { case 0: return "All"; case 10: return "Office"; case 50: return "Manager"; default: throw new Exception("Invalid View Level Description"); } } catch (Exception eX) { throw new Exception("Action: GetViewLevelDescription()" + Environment.NewLine + eX.Message); } } The two static Methods enable me to either get an int ViewLevel from a string ViewLevelDesc or vice versa. I'm sure the way I have done this is far more cumbersome than it needs to be, and I'm looking for some advice how to achieve the same objective but more concisely. The list of int / string pairs will increase significantly. The ones in the above code are just the first three I intend to use.

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