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  • C# specifying generic delegate type param at runtime

    - by smerlin
    following setup, i have several generic functions, and i need to choose the type and the function identified by two strings at runtime. my first try looked like this: public static class FOOBAR { public delegate void MyDelegateType(int param); public static void foo<T>(int param){...} public static void bar<T>(int param){...} public static void someMethod(string methodstr, string typestr) { MyDelegateType mydel; Type mytype; switch(typestr) { case "int": mytype = typeof(int); break; case "double": mytype = typeof(double); break; default: throw new InvalidTypeException(typestr); } switch(methodstr) { case "foo": mydel = foo<mytype>; //error break; case "bar": mydel = bar<mytype>; //error break; default: throw new InvalidTypeException(methodstr); } for(int i=0; i<1000; ++i) mydel(i); } } since this didnt work, i nested those switchs (a methodstr switch inside the typestr switch or viceversa), but that solution is really ugly and unmaintainable. The number of types is pretty much fixed, but the number of functions like foo or bar will increase by high numbers, so i dont want nested switchs. So how can i make this working without using nested switchs ?

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  • Copy values from one object to another.

    - by BrokeMyLegBiking
    Anyone have a suggestion for a good utility class that maps values from one object to another? I want a utility class that uses reflection and takes two objects and copies values from the 1st object to the second if there is a public property with the same name. I have two entities that are generated from a web service proxy, so I can't change the parent class or impliment an interface or anything like that. But I know that the two objects have the same public properties.

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  • difference between -> and . for member selection operator.

    - by TimothyTech
    in this book i have I'm learning pointers, and i just got done with the chapter about OOP (spits on ground) anyways its telling me i can use a member selection operator like this ( - ). it sayd that is is like the "." except points to objects rather than member objects. whats the difference, it looks like it is used the same way...

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  • .net - invoke methods from classes from a certain namespace via reflection

    - by Kristian Hildebrandt
    SPL and PHP allows you to create objects on the fly from classes, that fulfill certain conditions, such as implementing certain interfaces and stuff like that. However, I would like to do something similar in c# and automatically create objects from all classes in a namespace and invoke a particular method from those classes that implement a certain interface. My experience developing desktop apps is very limited. I am not quite sure if I should use delegates to archive this or if reflection is really the way to go.

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  • Using a Hash table

    - by Maria Attard
    I have 2 lists in my program one that store objects of type student and another one which stores objects of type marks. I have 3 methods one that inputs the details of the students, one that inputs the marks and one to view student details and their marks. My question is how I can use a hash table to get the Id of a student and then use it to input the marks and then how to retrieve both the student details and their marks altogether. Please help me if you can.

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  • Interview question : What is the fastest way to generate prime number recursively ?

    - by hilal
    Generation of prime number is simple but what is the fastest way to find it and generate( prime numbers) it recursively ? Here is my solution. However, it is not the best way. I think it is O(N*sqrt(N)). Please correct me, if I am wrong. public static boolean isPrime(int n) { if (n < 2) { return false; } else if (n % 2 == 0 & n != 2) { return false; } else { return isPrime(n, (int) Math.sqrt(n)); } } private static boolean isPrime(int n, int i) { if (i < 2) { return true; } else if (n % i == 0) { return false; } else { return isPrime(n, --i); } } public static void generatePrimes(int n){ if(n < 2) { return ; } else if(isPrime(n)) { System.out.println(n); } generatePrimes(--n); } public static void main(String[] args) { generatePrimes(200); }

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  • What's does "cardinality of an relationship" mean in Core Data?

    - by dontWatchMyProfile
    From the docs: If all of a managed object's relationship delete rules are Nullify, then for that object at least there is no additional work to do (you may have to consider other objects that were at the destination of the relationship—if the inverse relationship was either mandatory or had a lower limit on cardinality, then the destination object or objects might be in an invalid state). Does someone have an example of this cardinality thing? What's this good for and what's important to know about this? (sounds very important...)

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  • Is there a better way to format this Python/Django code as valid PEP8?

    - by Ryan Detzel
    I have code written both ways and I see flaws in both of them. Is there another way to write this or is one approach more "correct" than the other? def functionOne(subscriber): try: results = MyModelObject.objects.filter( project__id=1, status=MyModelObject.STATUS.accepted, subscriber=subscriber).values_list( 'project_id', flat=True).order_by('-created_on') except: pass def functionOne(subscriber): try: results = MyModelObject.objects.filter( project__id=1, status=MyModelObject.STATUS.accepted, subscriber=subscriber) results = results.values_list('project_id', flat=True) results = results.order_by('-created_on') except: pass

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  • @Unique doesn't have any effect in DataNucleus w/ NeoDatis

    - by David Parks
    Using JDO / DataNucleus / NeoDatis datastore I added @Unique to a field of a persistable object, however I am allowed to create multiple objects which violate the unique constraint. The docs for DataNucleus/NeoDatis suggest that Unique fields are supported. @PersistenceCapable public class User { @Persistent @Unique private String username; //... } If I add multiple objects to the DB with the same username there's no problem doing so. :(

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  • Threads syncronization with ThreadPoolExecutor

    - by justme1
    I'm trying to implement some logic when I create main(father) thread witch executes several other threads. Then it waits for some condition which child threads creates. After condition is meet the father executes some more child threads. The problem that when I use wait/notify I have java.lang.IllegalMonitorStateException exception. Here is the code: public class MyExecutor { final static ArrayBlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(10); final static ExecutorService svc = Executors.newFixedThreadPool(1); static final ThreadPoolExecutor threadPool = new ThreadPoolExecutor(5, 8, 10, TimeUnit.SECONDS, queue); public static void main(String[] args) throws InterruptedException { final MyExecutor me = new MyExecutor(); svc.execute(new Runnable() { public void run() { try { System.out.println("Main Thread"); me.execute(threadPool, 1); System.out.println("Main Thread waiting"); wait(); System.out.println("Main Thread notified"); me.execute(threadPool, 2); Thread.sleep(100); threadPool.shutdown(); threadPool.awaitTermination(20000, TimeUnit.SECONDS); } catch (InterruptedException e) { e.printStackTrace(); } } }); svc.shutdown(); svc.awaitTermination(10000, TimeUnit.SECONDS); System.out.println("Main Thread finished"); } public void execute(ThreadPoolExecutor tpe, final int id) { tpe.execute(new Runnable() { public void run() { try { System.out.println("Child Thread " + id); Thread.sleep(2000); System.out.println("Child Thread " + id + " finished"); notify(); } catch (InterruptedException e) { e.printStackTrace(); } } }); } } When I comment wait and notify line I have the following output: Main Thread Main Thread waiting Main Thread notified Child Thread 1 Child Thread 2 Child Thread 1 finished Child Thread 2 finished Main Thread finished

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  • binary quicksort

    - by davit-datuashvili
    hi i want implement Binary quicksort algorithm from robert sedgewick book it looks like this public class quickb{ public static final int bitsword=32; public static void quicksortB(int a[],int l,int r,int d){ int i=l; int j=r-1; if (r<=l || d>bitsword) return ; while (j!=i) { while (digit(a[i],d)==0 && (i<j)) i++; while (digit(a[j],d)==1 && (j>i)) j++; int t=a[i]; a[i]=a[j]; a[j]=t; } if (digit(a[r-1],d)== 0) j++; quicksortB(a,l,j-1,d+1); quicksortB(a,j,r,d+1); } public static void main(String[]args){ int a[]=new int[]{4,7,3,9,8,2}; quicksortB(a,0,a.length-1,0); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static int digit(int m,int d){ return (m>>d)&1; } } but it show me error: java.lang.ArrayIndexOutOfBoundsException: 6 at quickb.quicksortB(quickb.java:13) at quickb.main(quickb.java:32) what is wrong?

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  • Hibernate - how to create list of pojos?

    - by AspNewbie
    I am very new to Hibernate. I have MySQL database and mapped pojos. What should I do next? I know little bit LINQ to SQL from .NET, and it generates me List of mapped objects. So basically, what are my next steps after creating POJOS if I want to have List of them and do CRUD operations upon them and data will be also saved in DB not only in java objects ? kthx

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  • Resource allocation and automatic deallocation

    - by nabulke
    In my application I got many instances of class CDbaOciNotifier. They all share a pointer to only one instance of class OCIEnv. What I like to achieve is that allocation and deallocation of the resource class OCIEnv will be handled automatically inside class CDbaOciNotifier. The desired behaviour is, with the first instance of class CDbaOciNotifier the environment will be created, after that all following notifiers use that same environment. With the destruction of the last notifier, the environment will be destroyed too (call to custom deleter). What I've got so far (using a static factory method to create notifiers): #pragma once #include <string> #include <memory> #include "boost\noncopyable.hpp" class CDbaOciNotifier : private boost::noncopyable { public: virtual ~CDbaOciNotifier(void); static std::auto_ptr<CDbaOciNotifier> createNotifier(const std::string &tnsName, const std::string &user, const std::string &password); private: CDbaOciNotifier(OCIEnv* envhp); // All notifiers share one environment static OCIEnv* m_ENVHP; // Custom deleter static void freeEnvironment(OCIEnv *env); OCIEnv* m_envhp; }; CPP: #include "DbaOciNotifier.h" using namespace std; OCIEnv* CDbaOciNotifier::m_ENVHP = 0; CDbaOciNotifier::~CDbaOciNotifier(void) { } CDbaOciNotifier::CDbaOciNotifier(OCIEnv* envhp) :m_envhp(envhp) { } void CDbaOciNotifier::freeEnvironment(OCIEnv *env) { OCIHandleFree((dvoid *) env, (ub4) OCI_HTYPE_ENV); *env = null; } auto_ptr<CDbaOciNotifier> CDbaOciNotifier::createNotifier(const string &tnsName, const string &user, const string &password) { if(!m_ENVHP) { OCIEnvCreate( (OCIEnv **) &m_ENVHP, OCI_EVENTS|OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *)) 0, (size_t) 0, (dvoid **) 0 ); } //shared_ptr<OCIEnv> spEnvhp(m_ENVHP, freeEnvironment); ...got so far... return auto_ptr<CDbaOciNotifier>(new CDbaOciNotifier(m_ENVHP)); } I'd like to avoid counting references (notifiers) myself, and use something like shared_ptr. Do you see an easy solution to my problem?

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  • Input In Java- How does it work?

    - by Nir Avnon
    Hey guys, with a lot of help from you i was managed to write this nice code (I'm new in it, so kind of exciting.. :) ) And still I have not understand how can I input this code. first of all, I get an this error in the console line (I'm using Eclipse): Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at NumberConverter.main(NumberConverter.java:5). What does that mean? I just want to chack whether it works, and I can't call the function/program any how. I used to call in an "old fashion way", like in scheme, to the function that I wrote and see if something happens. How does it work in java? Do we call the program itself? function? what and where do we write? -I want to chack if it works, doesn't matter how, and I'll be glad to know how can I plugin input. Thank you so much! public class NumberConverter{ public static void main(String[] args) { int i = Integer.parseInt(args[0]); toBinary(i); toOctal(i); toHex(i); } public static void toBinary(int int1){ System.out.println(int1 + " in binary is"); System.out.println(Integer.toBinaryString(int1)); } public static void toOctal(int int1){ System.out.println(int1 + " in octal is"); System.out.println(Integer.toOctalString(int1)); } public static void toHex(int int1){ System.out.println(int1 + " in hex is"); System.out.println(Integer.toHexString(int1)); } }

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  • Force calling the derived class implementation within a generic function in C#?

    - by Adam Hardy
    Ok so I'm currently working with a set of classes that I don't have control over in some pretty generic functions using these objects. Instead of writing literally tens of functions that essentially do the same thing for each class I decided to use a generic function instead. Now the classes I'm dealing with are a little weird in that the derived classes share many of the same properties but the base class that they are derived from doesn't. One such property example is .Parent which exists on a huge number of derived classes but not on the base class and it is this property that I need to use. For ease of understanding I've created a small example as follows: class StandardBaseClass {} // These are simulating the SMO objects class StandardDerivedClass : StandardBaseClass { public object Parent { get; set; } } static class Extensions { public static object GetParent(this StandardDerivedClass sdc) { return sdc.Parent; } public static object GetParent(this StandardBaseClass sbc) { throw new NotImplementedException("StandardBaseClass does not contain a property Parent"); } // This is the Generic function I'm trying to write and need the Parent property. public static void DoSomething<T>(T foo) where T : StandardBaseClass { object Parent = ((T)foo).GetParent(); } } In the above example calling DoSomething() will throw the NotImplemented Exception in the base class's implementation of GetParent(), even though I'm forcing the cast to T which is a StandardDerivedClass. This is contrary to other casting behaviour where by downcasting will force the use of the base class's implementation. I see this behaviour as a bug. Has anyone else out there encountered this?

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  • Maximize/Minimize is causing Close Button to be re-enabled after disabling it -- Why?

    - by Brainsick
    I have used P/Invoke to call GetSystemMenu and EnableMenuItem (win32api) to disable the close functionality. However, after minimizing or maximizing my Windows Forms application the button is re-enabled. Obviously minimizing or maximizing is causing the behavior, but how? I'm not sure where to look to prevent this behavior. Should I be preventing the maximize and minimize behavior or is there something particularly wrong with the way in which I P/Invoked the calls? Once the application (main form) has loaded, I call the static method from a button click. class PInvoke { // P/Invoke signatures [DllImport("user32.dll")] static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert); [DllImport("user32.dll")] static extern bool EnableMenuItem(IntPtr hMenu, uint uIDEnableItem, uint uEnable); // SysCommand (WM_SYSCOMMAND) constant internal const UInt32 SC_CLOSE = 0xF060; // Constants used with Add/Check/EnableMenuItem internal const UInt32 MF_BYCOMMAND = 0x00000000; internal const UInt32 MF_ENABLED = 0x00000000; internal const UInt32 MF_GRAYED = 0x00000001; internal const UInt32 MF_DISABLED = 0x00000002; /// <summary> /// Sets the state of the Close (X) button and the System Menu close functionality. /// </summary> /// <param name="window">Window or Form</param> /// <param name="bEnabled">Enabled state</param> public static void EnableCloseButton(IWin32Window window, bool bEnabled) { IntPtr hSystemMenu = GetSystemMenu(window.Handle, false); EnableMenuItem(hSystemMenu, SC_CLOSE, MF_BYCOMMAND | (bEnabled ? MF_ENABLED : MF_GRAYED)); } }

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  • how to get memory address

    - by levirg
    hey Folks, Is there any way in ruby to get the memory address of objects.. say.. (i = 5) is that possible to get the mem address of that object 5.. 'object_id_' is not that satisfying.. I just wanted to know how referencing to objects work on ruby, so i thought address will be useful, to get things done plugin memprof doesnt work on x_32bit, so is there any better way pls help me..., Any answer would be really appreciated... thanks, Regards levirg

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  • C#: How to implement a smart cache

    - by Svish
    I have some places where implementing some sort of cache might be useful. For example in cases of doing resource lookups based on custom strings, finding names of properties using reflection, or to have only one PropertyChangedEventArgs per property name. A simple example of the last one: public static class Cache { private static Dictionary<string, PropertyChangedEventArgs> cache; static Cache() { cache = new Dictionary<string, PropertyChangedEventArgs>(); } public static PropertyChangedEventArgs GetPropertyChangedEventArgsa(string propertyName) { if (cache.ContainsKey(propertyName)) return cache[propertyName]; return cache[propertyName] = new PropertyChangedEventArgs(propertyName); } } But, will this work well? For example if we had a whole load of different propertyNames, that would mean we would end up with a huge cache sitting there never being garbage collected or anything. I'm imagining if what is cached are larger values and if the application is a long-running one, this might end up as kind of a problem... or what do you think? How should a good cache be implemented? Is this one good enough for most purposes? Any examples of some nice cache implementations that are not too hard to understand or way too complex to implement?

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  • How can I access the "through" object of a Django ManyToManyField?

    - by Macha
    I have the following models in my Django app. How can I from the Team model find all the User objects who have accepted as True in the Membership model? I know I need to use Team.objects.filter(), but I'm not sure how to check the value of the accepted field. from django.contrib.auth.models import User class Team(models.Model): members = models.ManyToManyField(User, through="Membership") class Membership(models.Model): user = models.ForeignKey(User) team = models.ForeignKey(Team) accepted = models.BooleanField(default=False)

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  • Returning the size of available virtual memory at run-time in C++

    - by Greenhouse Gases
    In C++ is there a predefined library function that will return the size of RAM currently available on a computer a program is being run on, at run-time? For instance, if an object is 4bytes, then can we divide the available virtual memory by 4 bytes to give an estimate of how many more objects could be stored by the program safely? I have used the sizeof() function to return the size of objects within my program. Thanks

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  • What good programming practices will change with C++0x?

    - by Jon
    For example, "Don't return objects by value if they are expensive to copy" (RVO can't always be used). This advice might change because of rvalue references. The same might be said about storing collections of pointers to objects, because copying them by value into the collection was too expensive; this reason might no longer be valid. Or the use of enums might be discouraged in favour of "enum class". What other practices or tips will change?

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