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What is the meaning of method class in the class definition in Ruby?

- by Steven Xu

I'm familiar with function definitions and variable declarations being in class definitions: public class MyClass { public int myvar; public void doSomething() { } } But what does it "mean" in Ruby when a method is actually called in the class definition? This happens amply in Rails, for instance: class User < ActiveRecord::Base has_many :posts end What exactly does this do (at a lower level than "it adds some methods to the class")? How would I implement such a function (e.g., one that mixes in some additional methods)?

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Compare class objects

- by reto

I have to compare a class object against a list of pre defined classes. Is it safe to use == or should I use equals()? if (klass == KlassA.class) { } else if (klass == KlassB.class) { } else if (klass == KlassC.class) { } else { } Note: I cannot use instanceof, I don't have an object, I just have the class object. I (mis)use it like an enum in this situation! Thanks!

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Why can't create object of an abstract class?

- by Gaurav

Here is a scenario in my mind and I have googled, Binged it a lot but got the answer like "Abstract class has not implemented method so, we cant create the object" "The word 'Abstract' instruct the clr that not to create object of the class" But in a simple class where we have all virtual method, able to create an object??? Also, we can define different access modified to Abstract class constructor like private, protected or public. My search terminated to this question ; Why we can't create object of an Abstract class?

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sizeof(class) c++

- by badkya

How is it possible for sizeof(class) to return two different values depending on context? The class itself should have the same size right irrespective of where I ask this question? I see a smaller value when querying class size from main() and another when I query class size from an extended class.

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assignment not working in a dll exported C++ class

- by Jim Jones

Using VS 2008 Have a C++ class in which I'm calling functions from a 3rd party dll. The definition in the header file is as follows: namespace OITImageExport { class ImageExport { private: SCCERR seResult; /* Error code returned. */ VTHDOC hDoc; /* Input doc handle returned by DAOpenDocument(). */ VTHEXPORT hExport; /* Handle to the export returned by EXOpenExport(). */ VTDWORD dwFIFlags; /* Used in setting the SCCOPT_FIFLAGS option. */ VTCHAR szError[256]; /* Error string buffer. */ VTDWORD dwOutputId; /* Output Format. */ VTDWORD dwSpecType; public: ImageExport(const char* outputId, const char* specType); void ProcessDocument(const char* inputPath, const char* outputPath); ~ImageExport(); }; } In the constructor I initialize two of the class fields having values which come from enumerations in the 3rd party dll: ImageExport::ImageExport(const char* outputId, const char* specType) { if(outputId == "jpeg") { dwOutputId = FI_JPEGFIF; } if(specType == "ansi") { dwSpecType = IOTYPE_ANSIPATH; } seResult = DAInit(); if (seResult != SCCERR_OK) { DAGetErrorString(seResult, szError, sizeof(szError)); fprintf(stderr, "DAInit() failed: %s (0x%04X)\n", szError, seResult); exit(seResult); } } When I use this class inside of a console app, with a main method in another file (all in the same namespace), instantiating the class object and calling the methods, it works like a champ. So, now that I know the basic code works, I open a dll project using the class header and code file. Course I have to add the dll macro, namely: #ifdef IMAGEDLL_EXPORTS #define DLL __declspec(dllexport) #else #define DLL __declspec(dllimport) #endif and changed the class definition to "class DLL ImageExport". Compiled nicely to a dll and .lib file (No errors, No warnings). Now to test this dll I open another console project using the same main method as before and linking to the (dll) lib file. Had problems, which when tracked down were the result of the two fields not being set; both had values of 0. Went back to the first console app and printed out the values: dwOutputId was 1535 (#define FI_JPEGFIF 1535) and dwSpecType was 2 (#define IOTYPE_ANSIPATH 2). Now if I was assigning these values outside of the class, I can see how the visibility could be different, but why is the assignment in the dll not working? Is it something about having a class in the dll?

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Nhibernate Common columns in base class

- by sukh

I want to design following scenario Base class (Id, Name, order, Value) 3 Derived classes derive1, derive2, derive3 inheriting properties from base There is no table for base class. And 1 table for each derived class. 3 tables have same columns. How can I create mapping file ignoring base class? Do I need to create 1 mapping file for each derived class? can I achieve this using only 1 mapping file?

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Calling private event handler from outside class

- by Azodious

i've two classes. One class (say A) takes a textbox in c'tor. and registers TextChanged event with private event-handler method. 2nd class (say B) creates the object of class A by providing a textbox. how to invoke the private event handler of class A from class B? it also registers the MouseClick event. is there any way to invoke private eventhandlers?

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Is null a class in java?

- by Somerandomeguy

According to, http://www.freshvanilla.org:8080/display/www/Java+Interview+Questions Under, Which class is the superclass of every class? null seems to be the answer. I found that new Object().getClass().getSuperClass() verifies the answer as correct. But can null be considered a class? I see all primitive data types are represented as Class objects from java[dot]sun.com/j2se/1.4.2/docs/api/java/lang/Class.html

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Can we instantiate abstract class?

- by satheesh.droid

I don't understand whether we can instantiate abstract class by any means because I have read we can inherit the abstract class but in have found we can create an object by calling method of other class.For example LocationProvider is an abstract class but we can create object for the same by calling getProvider() function in LocationManager class. By the following code LocationManager lm=getSystemService(Context.LOCATION_PROVIDER) LocationProvider lp=lm.getProvider("gps");

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call a python function in another class from a class?

- by user3527697

hi i'am begginer in pYthon and openerp , i want to call a function exists in another class for example: i have 2 class : class a: def notif_personne_event(self, cr, uid,ids,context=None): and import a class b: notifier(self, cr, uid,ids,context=None): self.notifiernotif_personne_event() but when i do this an error is displayed telling me that class b have not an attribute notifiernotif_personne_event() someone help me please

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Hibernate not Loading a class

- by Noor

Hi, I have a class Auction that contains a Class Item and Users but when I am getting the class, the class item and Users are not being loaded. Auction Class Mapping File: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">  <hibernate-mapping> <class name="com.BiddingSystem.Models.Auction" table="AUCTION"> <id name="AuctionId" type="long"> <column name="AUCTIONID" /> <generator class="native" /> </id> <property name="StartTime" type="java.util.Date"> <column name="STARTTIME" /> </property> <property name="EndTime" type="java.util.Date"> <column name="ENDTIME" /> </property> <property name="StartingBid" type="long"> <column name="STARTINGBID" /> </property> <property name="MinIncrement" type="long"> <column name="MININCREMENT" /> </property> <many-to-one name="CurrentItem" class="com.BiddingSystem.Models.Item" fetch="join" cascade="all"> <column name="ItemId" /> </many-to-one> <property name="AuctionStatus" type="java.lang.String"> <column name="AUCTIONSTATUS" /> </property> <property name="BestBid" type="long"> <column name="BESTBID" /> </property> <many-to-one name="User" class="com.BiddingSystem.Models.Users" fetch="join"> <column name="UserId" /> </many-to-one> </class> </hibernate-mapping> When I am doing this: Query query=session.createQuery("from Auction where UserId="+UserId); List <Auction> AllAuctions= new LinkedList<Auction>(query.list()); The Users and Item are null

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Asp.net mvc class reference in session

- by Billy

Hi, if I put a custom class in session, then in an action method I get an instance of that class from session, and populate some fields, I noticed that when a different controller gets that class from session, those fields are populated. Even though after the first call didn't save the updated class back in session. is this typical behavior for session objects? I thought I had to use keyword 'static' on the class in session for this to happen thanks

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Php dynamic class construction

- by pistacchio

Hi to all, I'm trying to avoid the use of eval. I can dynamically instantiate a class like this: class myclass {} $my_class_name = 'myclass'; $obj = new $myclass(); If the constructor is like follows: class myclass { public function __construct( $argument1, $argument2 ) {} } and i have the values of the arguments in an array, how can i dynamically instantiate the class and pass it dynamic arguments? Mind that I have no way to modify the class, so I have to work on the way of using it. Thanks

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Grails many to many using a third 'join' class

- by andy mccullough

I read that a m:m relationship often means there is a third class that isn't yet required. So I have m:m on User and Project, and I created a third domain class, ProjectMembership The three domains are as follows (minimized for illustration purposes): User class User { String name static hasMany = [projectMemberships : ProjectMembership] } Project Membership class ProjectMembership { static constraints = { } static belongsTo = [user:User, project:Project] } Project: class Project { String name static hasMany = [projectMemberships : ProjectMembership] static constraints = { } } If I have the ID of the user, how can I get a list of Project objects that they are assigned to?

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Jquery remove class from image

- by user1269625

Hey ya'll I have these 3 images thumbnails here... <div class="wpcart_gallery" style="text-align:center; padding-top:5px;"> <a class="thickbox cboxElement" title="DSC_0118" href="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/DSC_0118.jpg" rel="Teardrop Druzy Amethyst Ring" rev="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/DSC_0118.jpg"> <img class="attachment-gold-thumbnails colorbox-736" width="50" height="50" title="DSC_0118" alt="DSC_0118" src="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/DSC_0118-50x50.jpg"> </a> <a class="thickbox cboxElement" title="P7230376" href="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/P7230376.jpg" rel="Teardrop Druzy Amethyst Ring" rev="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/P7230376.jpg"> <img class="attachment-gold-thumbnails colorbox-736" width="50" height="50" title="P7230376" alt="P7230376" src="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/P7230376-50x50.jpg"> </a> <a class="thickbox cboxElement" title="P7230378" href="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/P7230378.jpg" rel="Teardrop Druzy Amethyst Ring" rev="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/P7230378.jpg"> <img class="attachment-gold-thumbnails colorbox-736" width="50" height="50" title="P7230378" alt="P7230378" src="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/P7230378-50x50.jpg"> </a> </div> What I am trying to do is come up with a jquery code that would remove the cboxElement from the first image and if I click on one of the images to remove cboxElement and place cboxElement to the other images... I also have this big image and when you click on one of the thumbnails, the image is replaced by the thumbnail and thats really the thumbnail I want to exclude...Could I possible just say if one of the 3 images src = this one image = src remove the class from this thumbnail? Which way would be better? I am very new at jquery :( I hope this makes sense. Here is the code for the big image... <a class="preview_link cboxElement" style="text-decoration:none;" href="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/DSC_0118.jpg" rel="Teardrop Druzy Amethyst Ring"> <img id="product_image_736" class="product_image colorbox-736" width="400" src="http://www.taranmarlowjewelry.com/wp-content/uploads/2012/07/DSC_0118.jpg" title="Teardrop Druzy Amethyst Ring" alt="Teardrop Druzy Amethyst Ring"> <br> <div style="text-align:center; color:#F39B91;">Click To Enlarge</div> </a> Any help or a point in the right direction would be awesome!!

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C++0x class factory with variadic templates problem

- by randomenglishbloke

I have a class factory where I'm using variadic templates for the c'tor parameters (code below). However, when I attempt to use it, I get compile errors; when I originally wrote it without parameters, it worked fine. Here is the class: template< class Base, typename KeyType, class... Args > class GenericFactory { public: GenericFactory(const GenericFactory&) = delete; GenericFactory &operator=(const GenericFactory&) = delete; typedef Base* (*FactFunType)(Args...); template <class Derived> static void Register(const KeyType &key, FactFunType fn) { FnList[key] = fn; } static Base* Create(const KeyType &key, Args... args) { auto iter = FnList.find(key); if (iter == FnList.end()) return 0; else return (iter->second)(args...); } static GenericFactory &Instance() { static GenericFactory gf; return gf; } private: GenericFactory() = default; typedef std::unordered_map<KeyType, FactFunType> FnMap; static FnMap FnList; }; template <class B, class D, typename KeyType, class... Args> class RegisterClass { public: RegisterClass(const KeyType &key) { GenericFactory<B, KeyType, Args...>::Instance().Register(key, FactFn); } static B *FactFn(Args... args) { return new D(args...); } }; Here is the error: when calling (e.g.) // Tucked out of the way RegisterClass<DataMap, PDColumnMap, int, void *> RC_CT_PD(0); GCC 4.5.0 gives me: In constructor 'RegisterClass<B, D, KeyType, Args>::RegisterClass(const KeyType&) [with B = DataMap, D = PDColumnMap, KeyType = int, Args = {void*}]': no matching function for call to 'GenericFactory<DataMap, int, void*>::Register(const int&, DataMap* (&)(void*))' I can't see why it won't compile and after extensive googling I couldn't find the answer. Can anyone tell me what I'm doing wrong (aside from the strange variable name, which makes sense in context)?

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Detect if class has overloaded function fails on Comeau compiler

- by Frank

Hi Everyone, I'm trying to use SFINAE to detect if a class has an overloaded member function that takes a certain type. The code I have seems to work correctly in Visual Studio and GCC, but does not compile using the Comeau online compiler. Here is the code I'm using: #include <stdio.h> //Comeau doesnt' have boost, so define our own enable_if_c template<bool value> struct enable_if_c { typedef void type; }; template<> struct enable_if_c< false > {}; //Class that has the overloaded member function class TestClass { public: void Func(float value) { printf( "%f\n", value ); } void Func(int value) { printf( "%i\n", value ); } }; //Struct to detect if TestClass has an overloaded member function for type T template<typename T> struct HasFunc { template<typename U, void (TestClass::*)( U )> struct SFINAE {}; template<typename U> static char Test(SFINAE<U, &TestClass::Func>*); template<typename U> static int Test(...); static const bool Has = sizeof(Test<T>(0)) == sizeof(char); }; //Use enable_if_c to only allow the function call if TestClass has a valid overload for T template<typename T> typename enable_if_c<HasFunc<T>::Has>::type CallFunc(TestClass &test, T value) { test.Func( value ); } int main() { float value1 = 0.0f; int value2 = 0; TestClass testClass; CallFunc( testClass, value1 ); //Should call TestClass::Func( float ) CallFunc( testClass, value2 ); //Should call TestClass::Func( int ) } The error message is: no instance of function template "CallFunc" matches the argument list. It seems that HasFunc::Has is false for int and float when it should be true. Is this a bug in the Comeau compiler? Am I doing something that's not standard? And if so, what do I need to do to fix it?

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A question about making a C# class persistant during a file load

- by Adam

Apologies for the indescriptive title, however it's the best I could think of for the moment. Basically, I've written a singleton class that loads files into a database. These files are typically large, and take hours to process. What I am looking for is to make a method where I can have this class running, and be able to call methods from within it, even if it's calling class is shut down. The singleton class is simple. It starts a thread that loads the file into the database, while having methods to report on the current status. In a nutshell it's al little like this: public sealed class BulkFileLoader { static BulkFileLoader instance = null; int currentCount = 0; BulkFileLoader() public static BulkFileLoader Instance { // Instanciate the instance class if necessary, and return it } public void Go() { // kick of 'ProcessFile' thread } public void GetCurrentCount() { return currentCount; } private void ProcessFile() { while (more rows in the import file) { // insert the row into the database currentCount++; } } } The idea is that you can get an instance of BulkFileLoader to execute, which will process a file to load, while at any time you can get realtime updates on the number of rows its done so far using the GetCurrentCount() method. This works fine, except the calling class needs to stay open the whole time for the processing to continue. As soon as I stop the calling class, the BulkFileLoader instance is removed, and it stops processing the file. What I am after is a solution where it will continue to run independently, regardless of what happens to the calling class. I then tried another approach. I created a simple console application that kicks off the BulkFileLoader, and then wrapped it around as a process. This fixes one problem, since now when I kick off the process, the file will continue to load even if I close the class that called the process. However, now the problem I have is that cannot get updates on the current count, since if I try and get the instance of BulkFileLoader (which, as mentioned before is a singleton), it creates a new instance, rather than returning the instance that is currently in the executing process. It would appear that singletons don't extend into the scope of other processes running on the machine. In the end, I want to be able to kick off the BulkFileLoader, and at any time be able to find out how many rows it's processed. However, that is even if I close the application I used to start it. Can anyone see a solution to my problem?

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Accessing initialized variable on different class C++

- by d0pe

I'm having some difficulties with this problem. The main idea is, I initialized a variable of class type B in class A, class A.h has the variable Z declared as public, like B *Z; In class A.cpp, I initialized it as Z = new B(); Now, I want to access that variable from class C and I'm unable to do so. C.h includes A.h and B.h

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What's the difference between calling MyClass.class and MyClass.getClass()

- by Mocha

MyClass.class and MyClass.getClass() both seem to return a java.lang.Class. Is there a subtle distinction or can they be used interchangeably? Also, is MyClass.class a public property of the superclass Class class? (I know this exists but can't seem to find any mention of it in the javadocs)

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dhcpd: varying vendor-class-identifier

- by jessicah

I'm having trouble selectively sending parameters in response to a DHCP Inform packet using groups (or even without, just using host declarations) for bootp stuff. My configuration file right now looks like: subnet 130.123.131.128 netmask 255.255.255.128 { allow unknown-clients; } host dev-mac-09 { option vendor-class-identifier "example-identifier"; hardware ethernet 10:9a:dd:51:ff:83; } If I put vendor-class-identifier in the global scope, using tcpdump I can see that the client receives the vendor class option successfully. If I take it out, and just keep it in the host scope (or group scope), the client never receives the option. Specifying option dhcp-parameter-request list 60 doesn't help either. I did try using a class definition inside a group, but then it applied even if the host wasn't a part of the group. As an aside, how do I get detailed logging? At least something to indicate what groups and things got used to generate the response to the client.

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rJava - how to call an abstract class method?

- by Sarah

I am trying to create an R function that taps into my JAVA code. I have an abstract class, let's say StudentGroup, that has abstract methods, and one method "getAppropriateStudentGroup" which returns (based on config) a class which extends StudentGroup. This allows calling classes to behave the same regardless of which StudentGroups is actually appropriate. 1) How can I use rJava to call getAppropriateStudentGroup? and 2) How can I call the methods on the returned class? Thank you!

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Puppet class inheritance confusion

- by EMiller

I've read the documentation on scope, but I'm still having trouble working this out. I've got two environments that are very similar - so I've got: modules/django-env/manifests/init.pp class django-env { package { "python26": ensure => installed } # etc ... } import "er.pp" modules/django-env/manifests/er.pp $venvname = "er" $venvpath = "/home/django/virtualenvs" class er { file { "$venvpath/$venvname" : ensure => directory } # etc ... } class er-dev { include er } class er-bce-dev { $venvname = "er-bce" include er } manifests/modules.pp import "django-env" manifests/nodes.pp node default { # etc ... } node 'centos-dev' imports default { include django-env include er-bce-dev include er-dev } The result here is that the "inheritance" works - but only the first "er-" item under the 'centos-dev' node is acted upon, I either get er-bce-dev or er-dev, but not both. There must be some basic thing I'm misunderstanding here. Is it the difference between import and include ? (not sure I understand that)

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Why should I use a puppet parameterized class?

- by robbyt

Generally when working with complex puppet modules, I will set variables at the node level or inside a class. e.g., node 'foo.com' { $file_owner = "larry" include bar } class bar { $file_name = "larry.txt" include do_stuff } class do_stuff { file { $file_name: ensure => file, owner => $file_owner, } } How/when/why does parametrized classes help when this situation? How are you using parametrized classes to structure your puppet modules?

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Why should I use a puppet parametrized class?

- by robbyt

Generally when working with complex puppet modules, I will set variables at the node level or inside a class. e.g., node 'foo.com' { $file_owner = "larry" include bar } class bar { $file_name = "larry.txt" include do_stuff } class do_stuff { file { $file_name: ensure => file, owner => $file_owner, } } How/when/why does parametrized classes help when this situation? How are you using parametrized classes to structure your puppet modules?

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