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  • Problem bounding name to a class in Django

    - by martinthenext
    Hello! I've got a view function that has to decide which form to use depending on some conditions. The two forms look like that: class OpenExtraForm(forms.ModelForm): class Meta: model = Extra def __init__(self, *args, **kwargs): super(OpenExtraForm, self).__init__(*args, **kwargs) self.fields['opening_challenge'].label = "lame translation" def clean_opening_challenge(self): challenge = self.cleaned_data['opening_challenge'] if challenge is None: raise forms.ValidationError('??????? ???, ??????????? ?????? ???. ???????????') return challenge class HiddenExtraForm(forms.ModelForm): class Meta: model = Extra exclude = ('opening_challenge') def __init__(self, *args, **kwargs): super(HiddenExtraForm, self).__init__(*args, **kwargs) The view code goes like that: @login_required def manage_extra(request, extra_id=None, hidden=False): if not_admin(request.user): raise Http404 if extra_id is None: # Adding a new extra extra = Extra() if hidden: FormClass = HiddenExtraForm else: FormClass = OpenExtraForm else: # Editing an extra extra = get_object_or_404(Extra, pk=extra_id) if extra.is_hidden(): FromClass = HiddenExtraForm else: FormClass = OpenExtraForm if request.POST: form = FormClass(request.POST, instance=extra) if form.is_valid(): form.save() return HttpResponseRedirect(reverse(view_extra, args=[extra.id])) else: form = FormClass(instance=extra) return render_to_response('form.html', { 'form' : form, }, context_instance=RequestContext(request) ) The problem is somehow if extra.is_hidden() returns True, the statement FromClass = HiddenExtraForm doesn't work. I mean, in all other conditions that are used in the code it works fine: the correct Form classes are intantiated and it all works. But if extra.is_hidden(), the debugger shows that the condition is passed and it goes to the next line and does nothing! As a result I get a UnboundLocalVar error which says FormClass hasn't been asssigned at all. Any ideas on what's happening?

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  • Reflecting over classes in .NET produces methods only differing by a modifier

    - by mrjoltcola
    I'm a bit boggled by something, I hope the CLR gearheads can help. Apparently my gears aren't big enough. I have a reflector utility that generates assembly stubs for Cola for .NET, and I find classes have methods that only differ by a modifier, such as virtual. Example below, from Oracle.DataAccess.dll, method GetType(): class OracleTypeException : System.SystemException { virtual string ToString (); virtual System.Exception GetBaseException (); virtual void set_Source (string value); virtual void GetObjectData (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context); virtual System.Type GetType (); // here virtual bool Equals (object obj); virtual int32 GetHashCode (); System.Type GetType (); // and here } What is this? I have not been able to reproduce this with C# and it causes trouble for Cola as it thinks GetType() is a redefinition, since the signature is identical. My method reflector starts like this: static void DisplayMethod(MethodInfo m) { if ( // Filter out things Cola cannot yet import, like generics, pointers, etc. m.IsGenericMethodDefinition || m.ContainsGenericParameters || m.ReturnType.IsGenericType || !m.ReturnType.IsPublic || m.ReturnType.IsArray || m.ReturnType.IsPointer || m.ReturnType.IsByRef || m.ReturnType.IsPointer || m.ReturnType.IsMarshalByRef || m.ReturnType.IsImport ) return; // generate stub signature // [snipped] }

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  • With Google Website Optimizer's multivariate testing, can I vary multiple css classes on a single di

    - by brahn
    I would like to use Google Website Optimizer (GWO)'s multivariate tests to test some different versions of a web page. I can change from version to version just by varying some class tags on a div, i.e. the different versions are of this form: <div id="testing" class="foo1 bar1">content</div> <div id="testing" class="foo1 bar2">content</div> <div id="testing" class="foo2 bar1">content</div> <div id="testing" class="foo2 bar2">content</div> In the ideal, I would be able to use GWO section code in place of each class, and google would just swap in the appropriate tags (foo1 or foo2, bar1 or bar2). However, naively doing this results in horribly malformed code because I would be trying to put <script> tags inside the div's class attribute: <div id="testing" class=" <script>utmx_section("foo-class")</script>foo1</noscript> <script>utmx_section("bar-class")</script>bar1</noscript> "> content </div> And indeed, the browser chokes all over it. My current best approach is just to use a different div for each variable in the test, as follows: <script>utmx_section("foo-class-div")</script> <div class="foo1"> </noscript> <script>utmx_section("bar-class-div")</script> <div class="bar1"> </noscript> content </div> </div> So testing multiple variables requires layer of div-nesting per variable, and it all seems rather awkward. Is there a better approach that I could use in which I just vary the classes on a single div?

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  • Using JSF, PrimeFaces and JPA: Create Basic WebApp without using Generated CRUD Classes, Forms, etc

    - by user2774489
    I am trying to build a basic CRUD application with NetBeans 7.4, JSF, PrimeFaces and JPA using MySQL. I have successfully done this by using the NetBeans wizards. I want to do this from scratch, no wizards. There seems to be a lack of support for the combo of JSF, PrimeFaces and JPA. When I say "lack", I mean a full example (I might be asking too much), without using the CRUD auto-gen templates/classes AND shows actual queries coded and passed to the datatables(primefaces). YouTube is full of non-English speaking examples using Hibernate (not JPA) and other examples that show flashy GUI's with no code. So far I understand you need an @Entity class (provides the physical build of the tables), a Controller (serializable) and the .xhtml web page to show the datatable.. what else? Also, I'm not seeing any posts or examples where queries are using with JPA/JSF and how they are tied together (in one place). I need to connect the dots here so that I can leverage JSF/JPA to create simple queries to populate my PF DataTables. I've read the blogs and I've googled the intranets until I'm blue in the face. Sending me a list of URL's to read to learn about each product is something I've already done. I get what they do independently, but am looking for the "How do they all connect" answer with maybe some basic code examples!! :)

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  • How to use boost normal distribution classes?

    - by David Alfonso
    Hi all, I'm trying to use boost::normal_distribution in order to generate a normal distribution with mean 0 and sigma 1. The following code uses boost normal classes. Am I using them correctly? #include <boost/random.hpp> #include <boost/random/normal_distribution.hpp> int main() { boost::mt19937 rng; // I don't seed it on purpouse (it's not relevant) boost::normal_distribution<> nd(0.0, 1.0); boost::variate_generator<boost::mt19937&, boost::normal_distribution<> > var_nor(rng, nd); int i = 0; for (; i < 10; ++i) { double d = var_nor(); std::cout << d << std::endl; } } The result on my machine is: 0.213436 -0.49558 1.57538 -1.0592 1.83927 1.88577 0.604675 -0.365983 -0.578264 -0.634376 As you can see all values are not between -1 and 1. Thank you all in advance!

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  • java 6 web services share domain specific classes between server and client

    - by user173446
    Hi all, Context: Considering below defined Engine class being parameter of some webservice method. As we have both server and client in java we may have some benefits (???) in sharing Engine class between server and client ( i.e we may put in a common jar file to be added to both client and server classpath ) Some benefits would be : we keep specific operations like 'brushEngine' in same place build is faster as we do not need in our case to generate java code for client classes but to use them from the server build) if we later change server implementation for 'brushEngine' this is reflected automatically in client . Questions: How to share below detailed Engine class using java 6 tools ( i.e wsimport , wsgen etc )? Is there other tools for java that can achieve this sharing ? Is sharing a case that java 6 web services support is missing ? Can this case be reduced to other web service usage patterns? Thanks. Code: public class Engine { private String engineData; public String getData(){ return data; } public setData(String value){ this.data = value; } public void brushEngine(){ engineData = "BrushedEngine"+engineData; } }

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  • Problems finding classes in namespace and testing extend expected parent

    - by Matt
    So I am in the process of building a site in ASP.Net MVC, and in the process I am adding certain things to my Site.Master I want to make sure that all of my model classes extend a certain base class that contains all of the pieces the Site.Master needs to be operable. I want to test to make sure this assumption isn't broken (I believe this will save me time when I forget about it and can't figure out why a new combination isn't working.) I wrote a test that I thought would help with this, but I am running into two problems. First it isn't finding the one example model class I have so far in the LINQ call all of a sudden, I am admittedly still a bit new to LINQ. Second, I had it finding the class earlier, but I couldn't get it to verify that the class inherits from the base class. Here is the example test. [Test] public void AllModelClassesExtendAbstractViewModel() { var abstractViewModelType = typeof (AbstractViewModel); Assembly baseAssembly = Assembly.GetAssembly(abstractViewModelType); var modelTypes = baseAssembly.GetTypes() .Where(assemblyType => (assemblyType.Namespace.EndsWith("Models") && assemblyType.Name != "AbstractViewModel")) .Select(assemblyType => assemblyType); foreach (var modelType in modelTypes) { Assert.That(modelType.IsSubclassOf(abstractViewModelType), Is.True , modelType.Name + " does not extend AbstractViewModel"); } }

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  • Refresher on Java classes in separate files

    - by JohnFaig
    I need a refresher on moving classes from one file into two files. My sample code is in one file called "external_class_file_main". The program runs fine and the code is shown below: Public class external_class_file_main { public static int get_a_random_number (int min, int max) { int n; n = (int)(Math.random() * (max - min +1)) + min; return (n); } public static void main(String[] args) { int r; System.out.println("Program starting..."); r = get_a_random_number (1, 5); System.out.println("random number = " + r); System.out.println("Program ending..."); } } I move the get_a_random_number class to a separate file called "external_class_file". When I do this, I get the following error: Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method get_a_random_number(int, int) is undefined for the type external_class_file_main at external_class_file_main.main(external_class_file_main.java:20) The "external_class_file_main" now contains: public class external_class_file_main { public static void main(String[] args) { int r; System.out.println("Program starting..."); r = get_a_random_number (1, 5); System.out.println("random number = " + r); System.out.println("Program ending..."); } } The "external_class_file" now contains: public class external_class_file { public static int get_a_random_number (int min, int max) { int n; n = (int)(Math.random() * (max - min +1)) + min; return (n); } }

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  • Need help make these classes use Visitor Pattern and generics

    - by Shervin
    Hi. I need help to generify and implement the visitor pattern. We are using tons of instanceof and it is a pain. I am sure it can be modified, but I am not sure how to do it. Basically we have an interface ProcessData public interface ProcessData { public setDelegate(Object delegate); public Object getDelegate(); //I am sure these delegate methods can use generics somehow } Now we have a class ProcessDataGeneric that implements ProcessData public class ProcessDataGeneric implements ProcessData { private Object delegate; public ProcessDataGeneric(Object delegate) { this.delegate = delegate; } } Now a new interface that retrieves the ProcessData interface ProcessDataWrapper { public ProcessData unwrap(); } Now a common abstract class that implements the wrapper so ProcessData can be retrieved @XmlSeeAlso( { ProcessDataMotorferdsel.class,ProcessDataTilskudd.class }) public abstract class ProcessDataCommon implements ProcessDataWrapper { protected ProcessData unwrapped; public ProcessData unwrap() { return unwrapped; } } Now the implementation public class ProcessDataMotorferdsel extends ProcessDataCommon { public ProcessDataMotorferdsel() { unwrapped = new ProcessDataGeneric(this); } } similarly public class ProcessDataTilskudd extends ProcessDataCommon { public ProcessDataTilskudd() { unwrapped = new ProcessDataGeneric(this); } } Now when I use these classes, I always need to do instanceof ProcessDataCommon pdc = null; if(processData.getDelegate() instanceof ProcessDataMotorferdsel) { pdc = (ProcessDataMotorferdsel) processData.getDelegate(); } else if(processData.getDelegate() instanceof ProcessDataTilskudd) { pdc = (ProcessDataTilskudd) processData.getDelegate(); } I know there is a better way to do this, but I have no idea how I can utilize Generics and the Visitor Pattern. Any help is GREATLY appreciated.

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  • Perl - Using hashes in classes

    - by brydgesk
    I have a class with several variables, one of which is a hash (_runs): sub new { my ($class, $name) = @_; my $self = { _name => $name, ... _runs => (), _times => [], ... }; bless ($self, $class); return $self; } Now, all I'm trying to do is create an accessor/mutator, as well as another subroutine that pushes new data into the hash. But I'm having a hell of a time getting all the referencing/dereferencing/$self calls working together. I've about burned my eyes out with "Can't use string ("blah") as a HASH ref etc etc" errors. For the accessor, what is 'best practice' for returning hashes? Which one of these options should I be using (if any)?: return $self->{_runs}; return %{ $self->{_runs} }; return \$self->{_runs}; Further, when I'm using the hash within other subroutines in the class, what syntax do I use to copy it? my @runs = $self->{_runs}; my @runs = %{ $self->{_runs} }; my @runs = $%{ $self->{_runs} }; my @runs = $$self->{_runs}; Same goes for iterating over the keys: foreach my $dt (keys $self->{_runs}) foreach my $dt (keys %{ $self->{_runs} }) And how about actually adding the data? $self->{_runs}{$dt} = $duration; %{ $self->{_runs} }{$dt} = $duration; $$self->{_runs}{$dt} = $duration; You get the point. I've been reading articles about using classes, and articles about referencing and dereferencing, but I can't seem to get my brain to combine the knowledge and use both at the same time. I got my _times array working finally, but mimicking my array syntax over to hashes didn't work.

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  • virtual methods and template classes

    - by soxs060389
    Hi I got over a problem, I think a very specific one. I've got 2 classes, a B aseclass and a D erived class (from B aseclass). B is a template class ( or class template) and has a pure virtual method virutal void work(const T &dummy) = 0; The D erived class is supposed to reimplement this, but as D is Derived from B rather than D being another template class, the compiler spits at me that virtual functions and templates don't work at once. Any ideas how to acomplish what I want? I am thankfull for any thoughts and Ideas, especially if you allready worked out that problem this class is fixed aka AS IS, I can not edit this without breaking existing code base template <typename T> class B { public: ... virtual void work(const T &dummy) = 0; .. }; take int* as an example class D : public B<int*>{ ... virtual void work(const int* &dummy){ /* put work code here */ } .. }; Edit: The compiler tells me, that void B<T>::work(const T&) [with T = int*] is pure virtual within D

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  • Generics vs inheritance (when no collection classes are involved)

    - by Ram
    This is an extension of this questionand probably might even be a duplicate of some other question(If so, please forgive me). I see from MSDN that generics are usually used with collections The most common use for generic classes is with collections like linked lists, hash tables, stacks, queues, trees and so on where operations such as adding and removing items from the collection are performed in much the same way regardless of the type of data being stored. The examples I have seen also validate the above statement. Can someone give a valid use of generics in a real-life scenario which does not involve any collections ? Pedantically, I was thinking about making an example which does not involve collections public class Animal<T> { public void Speak() { Console.WriteLine("I am an Animal and my type is " + typeof(T).ToString()); } public void Eat() { //Eat food } } public class Dog { public void WhoAmI() { Console.WriteLine(this.GetType().ToString()); } } and "An Animal of type Dog" will be Animal<Dog> magic = new Animal<Dog>(); It is entirely possible to have Dog getting inherited from Animal (Assuming a non-generic version of Animal)Dog:Animal Therefore Dog is an Animal Another example I was thinking was a BankAccount. It can be BankAccount<Checking>,BankAccount<Savings>. This can very well be Checking:BankAccount and Savings:BankAccount. Are there any best practices to determine if we should go with generics or with inheritance ?

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  • Flash - can't access classes in another SWF

    - by Ashley Muller
    Hi, I'm trying to load a local SWF file and use the classes in that SWF (its a code only SWF, nothing in library). Here's the code that loads the library: var AD:ApplicationDomain = ApplicationDomain.currentDomain; var context:LoaderContext = new LoaderContext(false, AD); SA_gamecore_loader = new Loader(); SA_gamecore_loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onGameCoreLibraryDataComplete); SA_gamecore_loader.load(new URLRequest("GameCore.swf"), context); Here's the code that tries to instantiate a class from GameCore.swf: var test:Class = GetClassFromDefinition("MenuArt") as Class; var testInstance:Object = new test(); public function GetClassFromDefinition(theStr:String):Object { var theClass:Object; try { theClass = GameCoreLibraryData.applicationDomain.getDefinition(theStr); } catch(e:ReferenceError) { trace(e); return null; } return theClass; } And this is the message that's traced: ReferenceError: Error #1065: Variable MenuArt is not defined. The GameCore.swf is in the same location as the parent swf. I'm using Flash Develop if that helps. Anyone able to point out what I'm doing wrong?

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  • Grails GORM rarely works in domain classes

    - by Vena
    I have many to many relationship between User and Organization. I want to delete user from all his organizations when the user is being deleted, so this is basically what I came up with: class User { ... def beforeDelete() { def user = User.get(id) Organization.all.each { it.removeFromMembers(user) it.save() } } } This surprisingly doesn't work because User.get(id) returns null even though the user with the given id is in the database, when I look at the log, no sql statement is even executed. So I tried to use load() method insted. ObjectNotFoundException is the result then. So I tried this as I was quite desperate: def user = User.find("from User as u where u.id = ?", [1L]) This, for some reason, works. But now, the line with it.removeFromMembers(user) throws NullPointerException. I tried to put this logic in my UserController and it works! Why is this? Why can't I do this in domain classes? This makes beforeDelete hook (and all the others too) pretty useless.

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  • Array passing between classes, gone?

    - by Kenneth
    Hey guys . i have two classes, SelectionScreenTable & GraphView. In the SelectionScreenTable class .h, i declared a NSMutableArray called usagedatas NSMutableArray *usagedatas; } @property (nonatomic, retain) NSMutableArray *usagedatas; In the SelectionScreenTable class.m i remembered to @synthesize. Later on, while processing my methods, i did a NSLog(@"usagedatas count:%i",usagedatas.count); to check whether it has value and it returned 1. so yeah its good up to this point. And in the -(void) dealloc , i remembered to released it . [usagedatas release]; So now comes ME trying to use it in another class. In GraphView.m i imported the "SelectionScreenTable.h". in the -(void)viewDidLoad i did SelectionScreenTable *UD = [SelectionScreenTable alloc]; NSLog(@"GraphView UD.usagedataas.count = :%i",UD.usagedatas.count); it returned 0. Any idea guys?

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  • Using Java classes(whole module with Spring/Hibernate dependency) in Grails

    - by Sitaram
    I have a Java/Spring/Hibernate application with a payment module. Payment module has some domain classes for payment subscription and transactions etc. Corresponding hibernate mapping files are there. This module uses applicationContext.xml for some of the configuration it needs. Also, This module has a PaymentService which uses a paymentDAO to do all database related work. Now, I want to use this module as it is(without any or minimal re-writing) in my other application(Grails application). I want to bring in the payment module as a jar or copy the source files to src/java folder in Grails. With that background, I have following queries: Will the existing applicationContext.xml for Spring configuration in the module will work as it is in Grails? Does it merge with rest of Grails's Spring config? Where do I put the applicationContext.xml? classpath? src/java should work? Can I bundle the applicationContext.xml in Jar(If I use jar option) and can overwrite in Grails if anything needs to be changed? Multiple bean definition problems in that case? PaymentService recognized as regular service? Will it be auto-injected in controllers and/or other services? Will PaymentDAO use the datasource configuration of Grails? Where do I put the hbm files of this module? Can I bundle the hbm files in Jar(If I use jar option) and can overwrite in Grails if anything needs to be changed? Which hbms are picked? or, there will be problems with that? Too many questions! :) All these concerns are actually before trying. I am going to try this in next few days(busy currently). Any help is appreciated. Thanks. Sitaram Meena

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  • Re-usable Obj-C classes with custom values: The right way

    - by Prairiedogg
    I'm trying to reuse a group of Obj-C clases between iPhone applications. The values that differ from app to app have been isolated and I'm trying to figure out the best way to apply these custom values to the classes on an app-to-app basis. Should I hold them in code? // I might have 10 customizable values for each class, that's a long signature! CarController *controller = [[CarController alloc] initWithFontName:@"Vroom" engine:@"Diesel" color:@"Red" number:11]; Should I store them in a big settings.plist? // Wasteful! I sometimes only use 2-3 of 50 settings! AllMyAppSettings *settings = [[AllMyAppSettings alloc] initFromDisk:@"settings.plist"]; MyCustomController *controller = [[MyCustomController alloc] initWithSettings:settings]; [settings release]; Should I have little, optional n_settings.plists for each class? // Sometimes I customize CarControllerSettings *carSettings = [[CarControllerSettings alloc] initFromDisk:@"car_settings.plist"]; CarController *controller = [[CarController alloc] initWithSettings:carSettings]; [carSettings release]; // Sometimes I don't, and CarController falls back to internally stored, reasonable defaults. CarController *controller = [[CarController alloc] initWithSettings:nil]; Or is there an OO solution that I'm not thinking of at all that would be better?

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  • How to create a reference tables for collection classes using fluent nhibernate

    - by Akk
    How can i create a 3 table schema from the following model classes. public class Product { public int Id {get; set;} public string Name {get; set;} public IList<Photo> Photos {get; set;} } public class Photo { public int Id {get; set;} public string Path {get; set;} } I want to create the following table structure in the database: Product ------- Id Name ProductPhotos ------------- ProductId (FK Products.Id) PhotoId (FK Photos.Id) Photos ------ Id Path How i can express the above Database Schema using Fluent NHibernate? I could only manage the following the Mapping but this does not get me the 3rd Photo ref table. public class ProductMap : ClassMap<Product> { public CityMap() { Id(x => x.Id); Map(x => x.Name); Table("Products"); HasMany(x => x.Photos).Table("ProductPhotos").KeyColumn("ProductId"); } }

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  • How can I achieve this kind of relationship (inheritance, composition, something else)?

    - by Tim
    I would like to set up a foundation of classes for an application, two of which are person and student. A person may or may not be a student and a student is always a person. The fact that a student “is a” person led me to try inheritance, but I can't see how to make it work in the case where I have a DAO that returns an instance of person and I then want to determine if that person is a student and call student related methods for it. class Person { private $_firstName; public function isStudent() { // figure out if this person is a student return true; // (or false) } } class Student extends Person { private $_gpa; public function getGpa() { // do something to retrieve this student's gpa return 4.0; // (or whatever it is) } } class SomeDaoThatReturnsPersonInstances { public function find() { return new Person(); } } $myPerson = SomeDaoThatReturnsPersonInstances::find(); if($myPerson->isStudent()) { echo 'My person\'s GPA is: ', $myPerson->getGpa(); } This obviously doesn't work, but what is the best way to achieve this effect? Composition doesn't sond right in my mind because a person does not “have a” student. I'm not looking for a solution necessarily but maybe just a term or phrase to search for. Since I'm not really sure what to call what I'm trying to do, I haven't had much luck. Thank you!

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  • Adding functions to Java class libraries

    - by Eric
    I'm using a Java class library that is in many ways incomplete: there are many classes that I feel ought to have additional member functions built in. However, I am unsure of the best practice of adding these member functions. Lets call the insufficient base class A. class A { public A(/*long arbitrary arguments*/) { //... } public A(/*long even more arbitrary arguments*/) { //... } public int func() { return 1; } } Ideally, I would like to add a function to A. However, I can't do that. My choice is between: class B extends A { //Implement ALL of A's constructors here public int reallyUsefulFunction() { return func()+1; } } and class AddedFuncs { public int reallyUsefulFunction(A a) { return a.func()+1; } } The way I see it, they both have advantages and disadvantages. The first choice gives a cleaner syntax than the second, and is more logical, but has problems: Let's say I have a third class, C, within the class library. class C { public A func() { return new A(/*...*/); } } As I see it, there is no easy way of doing this: C c; int useful = c.func().reallyUsefulFunction(); as the type returned by C.func() is an A, not a B, and you can't down-cast. So what is the best way of adding a member function to a read-only library class?

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  • Using SimpleDB (with SimpleSavant) with POCO / existing entities, not attributes on my classes

    - by alex
    I'm trying to use Simple Savant within my application, to use SimpleDB I currently have (for example) public class Person { public Guid Id { get; set; } public string Name { get; set; } public string Description { get; set; } public DateTime DateOfBirth { get; set; } } To use this with Simple Savant, i'd have to put attributes above the class declaration, and property - [DomainName("Person")] above the class, and [ItemName] above the Id property. I have all my entities in a seperate assembly. I also have my Data access classes an a seperate assembly, and a class factory selects, based on config, the IRepository (in this case, IRepository I want to be able to use my existing simple class - without having attributes on the properties etc.. In case I switch out of simple db, to something else - then I only need to create a different implementation of IRepository. Should I create a "DTO" type class to map the two together? Is there a better way?

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  • Extending abstract classes in c#

    - by ng
    I am a Java developer and I have noticed some differences in extending abstract classes in c# as opposed to Java. I was wondering how a c# developer would achived the following. 1) Covarience public abstract class A { public abstract List<B> List(); } public class BList : List<T> where T : B { } public abstract class C : A { public abstract BList List(); } So in the above hierarchy, there is covarience in C where it returns a type compatible with what A returns. However this gives me an error in Visual Studio. Is there a way to specify a covarient return type in c#? 2) Adding a setter to a property public abstract class A { public abstract String Name { get; } } public abstract class B : A { public abstract String Name { get; set } } Here the compiler complains of hiding. Any suggestions? Please do not suggest using interfaces unless that is the ONLY way to do this.

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  • What are the benefits of a classical structure over a prototyple one?

    - by Rixius
    I have only recently started programming significantly, and being completely self-taught, I unfortunately don't have the benefits of a detailed Computer science course. I've been reading a lot about JavaScript lately, and I'm trying to find the benefit in classes over the prototype nature of JavaScript. The question seems to be drawn down the middle of which one is better, and I want to see the classical side of it. When I look at the prototype example: var inst_a = { "X": 123, "Y": 321, add: function () { return this.X+this.Y; } }; document.write(inst_a.add()); And then the classical version function A(x,y){ this.X = x; this.Y = y; this.add = function(){ return this.X+this.Y; }; }; var inst_a = new A(123,321); document.write(inst_a.add()); I begun thinking about this because I'm looking at the new ecmascript revision 5 and a lot of people seem up in arms that they didn't add a Class system.

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  • Problem with inherited classes in C#

    - by Unniloct
    I have a class called "Entity," with two child classes: "Creature" and "Item." (I'm making a game.) Creature has two functions called "Attack," one for attacking Creatures, and one for attacking Items. So far, everything works well. Now I'm working on the shooting bit, so I have a function called SelectTarget(). It takes all of the Entities (both Creatures and Items) in the player's view that the player can shoot and lets the player choose one. So here lies the problem: SelectTarget() returns an Entity, but I need some code to figure out whether that Entity is a Creature or an Item, and process it appropriately. Since this question looks kind of empty without any code, and I'm not 100% sure my explanation is good enough, here's where I'm at: if (Input.Check(Key.Fire)) { Entity target = Game.State.SelectTarget.Run(); this.Draw(); if (target != null) { //Player.Attack(target); // This won't work, because I have: // Player.Attack((Creature)Target) // Player.Attack((Item)Target) // but nothing for Entity, the parent class to Creature and Item. return true; } } (If the way the game is laid out seems weird, it's a roguelike.)

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  • Trying to instantiate a class member in C++ with a variable name

    - by MarcZero
    Hello. I am writing a program for class that is asking us to create a class of "book". We are then supposed to create new instantiations of that class upon demand from the user. I am new to C++ so I am attempting to code this out but am running into a problem. The main problem is how do I instantiate a class with a variable if I don't know how many I will have to do ahead of time. The user could ask to add 1 book or 1000. I am looking at this basic code: This is the simple code I started with. I wanted to have an index int keep a number and have the book class I create be called by that int (0, 1, 2, etc...) So I attempted to convert the incoming index int into a string, but I'm kind of stuck from here. void addBook(int index){ string bookName; std::stringstream ss; ss << index; book bookName; cout << "Enter the Books Title: "; cin >> bookName.title; } But obviously this doesn't work as "bookName" is a string to the computer and not the class member I tried to create. All of the tutorials I have seen online and in my text show the classes being instantiated with names in the code, but I just don't know how to make it variable so I can create any amount of "books" that the user might want. Any insight on this would be appreciated. Thank you for your time.

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