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• calling a function from a set of overloads depending on the dynamic type of an object

  - by Jasper

  I feel like the answer to this question is really simple, but I really am having trouble finding it. So here goes: Suppose you have the following classes: class Base; class Child : public Base; class Displayer { public: Displayer(Base* element); Displayer(Child* element); } Additionally, I have a Base* object which might point to either an instance of the class Base or an instance of the class Child. Now I want to create a Displayer based on the element pointed to by object, however, I want to pick the right version of the constructor. As I currently have it, this would accomplish just that (I am being a bit fuzzy with my C++ here, but I think this the clearest way) object->createDisplayer(); virtual void Base::createDisplayer() { new Displayer(this); } virtual void Child::createDisplayer() { new Displayer(this); } This works, however, there is a problem with this: Base and Child are part of the application system, while Displayer is part of the GUI system. I want to build the GUI system independently of the Application system, so that it is easy to replace the GUI. This means that Base and Child should not know about Displayer. However, I do not know how I can achieve this without letting the Application classes know about the GUI. Am I missing something very obvious or am I trying something that is not possible?

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• Why timed lock doesnt throws a timeout exception in C++0x?

  - by Vicente Botet Escriba

  C++0x allows to lock on a mutex until a given time is reached, and return a boolean stating if the mutex has been locked or not. template <class Clock, class Duration> bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time); In some contexts, I consider an exceptional situation that the locking fails because of timeout. In this case an exception should be more appropriated. To make the difference a function lock_until could be used to get a timeout exception when the time is reached before locking. template <class Clock, class Duration> void lock_until(const chrono::time_point<Clock, Duration>& abs_time); Do you think that lock_until should be more adequate in some contexts? if yes, on which ones? If no, why try_lock_until will always be a better choice?

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• Include an interface from the same package (Java)

  - by DashRantic

  Hi, I'm new to Java (C++ guy myself) and am trying to compile a simple program (testing different random number algorithms) in Java. I have an interface that I want to use to implement another class with, both of these items are in the same package. So I have two files right now in my "Random" package directory--"RandomInterface.java" and "RandomTest1.java" (which implements RandomInterface). I can use javac to compile RandomInterface.java just fine, but I get the following error when I then try to compile RandomTest1: RandomNew.java:3: cannot find symbol symbol: class RandomClass public class RandomNew implements RandomClass ^ 1 error I declare both files to be part of the same package (Random) as the first line of each file. What do I need to do to include the RandomInterface class into the compile command for RandomTest1? Thanks!

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• frame variable cannot be found

  - by Umzz Mo

  I am making 3 board games, and I have started my coding off in one class. Now that i wanted to move around it is giving me problems. In my view class I just want to have the main frame where users can pick from the games. And in the other views, i.e the childrens of view class i want to have the interface for the actual games. Now that the Jframe frame = new frame was created in the parent class, it cannot find the variable frame in the children classes.

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• Events + Adapter Pattern

  - by Stretto

  I have an adapter pattern on a generic class that essentially adapts between types: class A<T> { event EventHandler e; } class Aadapter<T1, T2> : A<T1> { A<T2> a; Aadapter(A<T2> _a) { a = _a; } } The problem is that A contains an event. I effectively want all event handlers assigned to Adapter to fall through to a. It would be awesome if I could assign the a's event handler to adapter's event handler but this is impossible? The idea here is that A is almost really just A but we need a way to adapt the them. Because of the way event's work I can't how to efficiently do it except manually add two event handlers and when they are called they "relay" the to the other event. This isn't pretty though and it would seem much nicer if I could have something like class A<T> { event EventHandler e; } class Aadapter<T1, T2> : A<T1> { event *e; A<T2> a; Aadapter(A<T2> _a) { a = _a; e = a.e; } } in a sense we have a pointer to the event that we can assign a2's event to. I doubt there is any simple way but maybe someone has some idea to make it work. (BTW, I realize this is possible with virtual events but I'd like to avoid this if at all possible)

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• Java Thread Message Passing

  - by pkulak

  I'm writing an Android app. I have a main method, which creates and runs a new Thread using an anonymous inner Runnable class. The run() method, when it's done, calls a method on it's parent class (in the main thread) that calls notifyDataSetChanged() so that the main thread can redraw the new data. This is causing all kinds of trouble (ViewRoot$CalledFromWrongThreadException). The thing is, this method being called from the worker thread is on the class that's created in the UI thread. Shouldn't that be running on the UI thread? Or am I missing something? Here's some code about what I'm talking about: public class Mealfire extends Activity { @Override public void onCreate(Bundle icicle) { (new Thread() { public void run() { // Do a bunch of slow network stuff. update(); } }).start(); } private void update() { myAdapter.notifyDatasetChanged(); } }

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• jQuery: Getting value from input array

  - by betacar

  We have the following form: <form> ... <table width="100%" cellspacing="0" class="datagrid_ppal"> <tbody> <tr> <th scope="row">Area 1 <input name="config_line" type="hidden" value="0,5,50" /></th> <td class="gantt"> </td> <td class="gantt"> </td> <td class="gantt"> </td> ... </tr> </tbody> </table width="100%" cellspacing="0" class="datagrid_ppal"> ... <form> What we need is to get the first, second or third from the hidden input value. We have tried this and didn't work: var value = $('th').children('input:hidden').val(); Can anyone help us? We would really appreciate it.

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• "error: Expected a type, got 'classname'" in C++

  - by Bay

  Using the following code: template <typename T> class node { [. . .] }; class b_graph { friend istream& operator>> (istream& in, b_graph& ingraph); friend ostream& operator<< (ostream& out, b_graph& outgraph); public: [...] private: vector<node> vertices; //This line I'm getting: error: type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp, class _Alloc> class std::vector’ error: expected a type, got 'node' error: template argument 2 is invalid On the indicated line. Node is clearly defined before b_graph which uses it - what have I done here?

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• Polymorphism and c#

  - by saurabh

  Here one more basic question asked in MS interview recently Class A { public virtual void Method1(){} public void Method2() { Method1(); } } class B:A { public override void Method1() { } } Class main { A obk = new B(); obk.Method2(); } now tell me which function gets called ? sorry for the typos.

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• How to know if a std::list has been modified

  - by Nick

  I have this class: class C { public: C* parent; std::list<C> children; }; I can use this class in this way for example: C root; C child; root.children.push_back(child); // or other method of std::list (es: push_front, insert, ...) // Here child.parent is root // How can I set the parent of child? I want to do this work internally to my class without losing the functionality of std::list, is it possible?

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• jquery next() outside of div

  - by mike

  Hi, I'm trying to use next() to toggle a div. The problem is that the "trigger" is in a different div than the one I want to toggle. An example that works: $("span.trigger").click(function(){ $(this).next("div.task_description").slideToggle("fast"); }); <span class="trigger">The trigger</span> <div class="task_description "> some content </div> But the way I need the html setup is: <div> <span class="trigger">The trigger</span> </div> <div class="task_description "> some content </div> That doesn't work... any suggestions?

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• Vector of objects

  - by Paul

  I've got a abstract class class A { public: virtual void somefunction() = ; }; and some different classes that inherit this class: class Ab { public: void somefunction(); }; etc. I want to make a vector containing some objects of these classes (how many depends on input parameters) so I can access these easily later. However I'm a bit lost on how to do this. My best idea is vector<A> *objectsVector; Ab AbObject; objectsVector.push_back(AbObject); However this gives me a huge amout of errors from various .h files in /usr/include/c++ How should i solve this?

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• Creating a library of classes in php - how to handle the library root location?

  - by jax

  I am about to create a collection of classes in php which are interrelated. Now I would like to include files using their absolute path, ie If I were in '/com/mysite/licences/Generator.class.php' I would like to include files like this: include '/com/mysite/lib/Utils.class.php' I don't want to include like this, I think it is confusing and ugly include '../licenses/Utils.class.php' This works ok, unless 'com' is not in the root of public_html. I assume I will need some sort of prefix to append to each file LIBRARY_ROOT that hold the location of 'com' in the current filesystem. So it might look like this include LIBRARY_ROOT.'com/mysite/lib/Utils.class.php' What is the best way to do this?

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• LINQ - joining multiple lists

  - by kristian

  I've looked at the 101 Linq Samples here but I can't see anything like this in that list. If I'm just not seeing a relevant example there, please link to it. If I have these 3 classes: class Student { int id; string name } class Course { int id, string name } class Enrolment { int studentId; int courseId; } How would I use LINQ to get a list of courses a student is enrolled on? (assume I have an IList of all three classes)

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• Ruby on Rails: create records for multiple models with one form and one submit

  - by notblakeshelton

  I have a 3 models: quote, customer, and item. Each quote has one customer and one item. I would like to create a new quote, a new customer, and a new item in their respective tables when I press the submit button. I have looked at other questions and railscasts and either they don't work for my situation or I don't know how to implement them. I also want my index page to be the page where I can create everything. quote.rb class Quote < ActiveRecord::Base attr_accessible :quote_number has_one :customer has_one :item end customer.rb class Customer < ActiveRecord::Base #unsure of what to put here #a customer can have multiple quotes, so would i use: has_many :quotes #<----? end item.rb class Item < ActiveRecord::Base #also unsure about this #each item can also be in multiple quotes quotes_controller.rb class QuotesController < ApplicationController def index @quote = Quote.new @customer = Customer.new @item = item.new end def create @quote = Quote.new(params[:quote]) @quote.save @customer = Customer.new(params[:customer]) @customer.save @item = Item.new(params[:item]) @item.save end end items_controller.rb class ItemsController < ApplicationController def index end def new @item = Item.new end def create @item = Item.new(params[:item]) @item.save end end customers_controller.rb class CustomersController < ApplicationController def index end def new @customer = Customer.new end def create @customer = Customer.new(params[:customer]) @customer.save end end quotes/index.html.erb <%= form_for @quote do |f| %> <%= f.fields_for @customer do |builder| %> <%= label_tag :firstname %> <%= builder.text_field :firstname %> <%= label_tag :lastname %> <%= builder.text_field :lastname %> <% end %> <%= f.fields_for @item do |builder| %> <%= label_tag :name %> <%= builder.text_field :name %> <%= label_tag :description %> <%= builder.text_field :description %> <% end %> <%= label_tag :quote_number %> <%= f.text_field :quote_number %> <%= f.submit %> <% end %> When I try submitting that I get an error: Can't mass-assign protected attributes: item, customer So to try and fix it I updated the attr_accessible in quote.rb to include :item, :customer but then I get this error: Item(#) expected, got ActiveSupport::HashWithIndifferentAccess(#) Any help would be greatly appreciated.

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• How can I map a String to a function in Java?

  - by Bears will eat you

  Currently, I have a bunch of Java classes that implement a Processor interface, meaning they all have a processRequest(String key) method. The idea is that each class has a few (say, <10) member Strings, and each of those maps to a method in that class via the processRequest method, like so: class FooProcessor implements Processor { String key1 = "abc"; String key2 = "def"; String key3 = "ghi"; // and so on... String processRequest(String key) { String toReturn = null; if (key1.equals(key)) toReturn = method1(); else if (key2.equals(key)) toReturn = method2(); else if (key3.equals(key)) toReturn = method3(); // and so on... return toReturn; } String method1() { // do stuff } String method2() { // do other stuff } String method3() { // do other other stuff } // and so on... } You get the idea. This was working fine for me, but now I need a runtime-accessible mapping from key to function; not every function actually returns a String (some return void) and I need to dynamically access the return type (using reflection) of each function in each class that there's a key for. I already have a manager that knows about all the keys, but not the mapping from key to function. My first instinct was to replace this mapping using if-else statements with a Map<String, Function>, like I could do in Javascript. But, Java doesn't support first-class functions so I'm out of luck there. I could probably dig up a third-party library that lets me work with first-class functions, but I haven't seen any yet, and I doubt that I need an entire new library. I also thought of putting these String keys into an array and using reflection to invoke the methods by name, but I see two downsides to this method: My keys would have to be named the same as the method - or be named in a particular, consistent way so that it's easy to map them to the method name. This seems WAY slower than the if-else statements I have right now. Efficiency is something of a concern because these methods will tend to get called pretty frequently, and I want to minimize unnecessary overhead. TL; DR: I'm looking for a clean, minimal-overhead way to map a String to some sort of a Function object that I can invoke and call (something like) getReturnType() on. I don't especially mind using a 3rd-party library if it really fits my needs. I also don't mind using reflection, though I would strongly prefer to avoid using reflection every single time I do a method lookup - maybe using some caching strategy that combines the Map with reflection. Thoughts on a good way to get what I want? Cheers!

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• Scala : reference is ambiguous (imported twice)

  - by tk

  I want to use a method as a parameter of another method of the same class. I have a class and objects which are companions: class mM(var elem:Matrix){ //apply a function on a dimension rows (1) or cols (2) def app(func:Iterable[Double]=>Double)(dim : Int) : Matrix = { ... } //utility function def logsumexp(): Double = {...} } object mM{ def apply(elem:Matrix):mM={new mM(elem)} def logsumexp(elem:Iterable[Double]): Double ={ this.apply(elem.asInstanceOf[Matrix]).logsumexp() } } Normally I use logsumexp like this mM(matrix).logsumexp but if want to apply it to the rows I can't use mM(matrix).app(mM.logsumexp)(1), I get the error: error: reference to mM is ambiguous; it is imported twice in the same scope by import mM and import mM What is the most elegant solution ? Should I change logsumexp() to another class ? Thanks,=)

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• Adding behaviour to a set of classes

  - by devoured elysium

  I have defined an Event class: Event and all the following classes inherit from Event: SportEventType1 SportEventType2 SportEventType3 SportEventType4 Right now I will only have SportEvents but I don't know if in the future I'll want some other kind of events that doesn't even have anything to do with Sports. Later, I will want to draw some graphics with info taken from Events, and the drawing logic can be a bit complex. But, for the moment, I think I shouldn't think of how the drawing will be done and I believe that maybe it'd be better if that drawing part was not put as an integral part of the Event/SportEventX class chain. I am looking for solutions for this problem. I know I could just make Event have an instance variable(attribute, for the java crowds) pointing to something as an IDrawInterface, but that would make the Event class "assume" it will be later used for drawing. I would like to make the Event class oblivious to this if possible. Thanks!

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• Debug.writeline locks

  - by Carra

  My program frequently stops with a deadlock. When I do a break-all and look at the threads I see that three threads are stuck in our logging function: public class Logging { public static void WriteClientLog(LogLevel logLevel, string message) { #if DEBUG System.Diagnostics.Debug.WriteLine(String.Format("{0} {1}", DateTime.Now.ToString("HH:mm:ss"), message)); //LOCK #endif //...Log4net logging } } If I let the program continue the threads are still stuck on that line. I can't see where this can lock. The debug class, string class & datetime class seem to be thread safe. The error goes away when I remove the "#if DEBUG System... #endif" code but I'm curious why this behavior happens. Thread one: public void CleanCache() { Logging.WriteClientLog(LogLevel.Debug, "Start clean cache.");//Stuck } Thread two: private void AliveThread() { Logging.WriteClientLog(LogLevel.Debug, "Check connection");//Stuck }

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• catching erros and exiting

  - by apple pie

  In python, is there a way to exit a class after testing a condition, without exiting out of python? say i have the class class test(): def __init__(self): self.a = 2 def create_b(self): self.b = 3 def does_b_exist(self): if <self.b doesnt exist>: #terminate self.b += 1 try/except` doesnt work since the rest of the program doesnt terminate after failing. im basically trying to catch an error, and do what python does when it shows you errors, but i cant figure out how to do it

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• How to override [Authorize] attribute in the MVC Web API?

  - by NullReference

  I have a MVC Web Api Controller that uses the [Authorize] attribute at the class level. This makes all of the api methods require authorization but I'd like to create an attribute called [ApiPublic] that overrides the [Authorize] attribute. There is a similar technique described here for normal MVC controllers. I tried creating an AuthorizeAttribute based of the System.Web.Http.AuthorizeAttribute but none of the overridden events are called if I put it on a api method that has the [Authorize] at the class level. Anyone have an idea how to override the authorize for the web api? [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false, Inherited = true)] public class ApiPublicAttribute : AuthorizeAttribute { protected override void HandleUnauthorizedRequest(System.Web.Http.Controllers.HttpActionContext actionContext) { base.HandleUnauthorizedRequest(actionContext); } public override void OnAuthorization(System.Web.Http.Controllers.HttpActionContext actionContext) { base.OnAuthorization(actionContext); } protected override bool IsAuthorized(System.Web.Http.Controllers.HttpActionContext actionContext) { return true; } }

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• How can I get model names from inside my app?

  - by Cameron

  I have a bunch of models in a sub-directory that inherit from a model in the models root directory. I want to be able to set a class variable in another model that lists each inherited model class. i.e @@groups = sub_models.map do { |model| model.class.to_s } Not sure how to get at this info though...

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• STI and accepts_nested_attributes_for in rails

  - by ryanshackintosh

  I have models as follows: class Entity < ActiveRecord::Base has_many :addresses accepts_nested_attributes_for :addresses, :reject_if => lambda { |a| a[:label].blank?} , :allow_destroy => true end class Client < Entity before_save :set_type private def set_type self.type = "Client" end end class Address < ActiveRecord::Base belongs_to :entity end I have recently implemented accepts_nested_attributes_for on the /clients/new form, as follows: <% form_for(@client, :html => {:class => 'form'}) do |f| -%> <%= f.label :name %> <%= f.text_field :name -%> <%= f.label :phone %> <%= f.text_field :phone %> <% f.fields_for :addresses do |a| %> <%= a.label :street %> <%= a.text_field :street%> <%= a.label :city %> <%= a.text_field :city %> <% end %> <% end %> And my controller as follows: class ClientsController < ApplicationController before_filter :load_client , :except => [:index, :new, :create, :render_clients] def new @client = Client.new @client.addresses.build end def create @client = Client.new(params[:client]) if @client.save flash[:notice] = 'Client has been successfully added' redirect_to @client else render :action => 'new' end end The issue is that when the record is saved it gives an error stating: "Entity can't be blank" I assume it is something to do with the fact that a 'Client' and not an 'Entity' is being added. Can anyone point me in the right direction?

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• Parse xml file with same tag multiple times iphone sdk

  - by neha

  Hi all, In my application, I have a tag multiple times. I'm using xml parser. I'm taking a corresponding element with similar name as the one in xml file in my class. So in case of: <photo>abc</photo> <photo>def</photo> What I get in photo element of my class is the second element i.e def, as the first one gets overwritten as there's only one photo element in my class. My question is am I wrong in taking similar elements in class as in case of xml? Is there any better method or a better parser? Or I'm on right path and have to do this manually by setting some flags etc? Thanx in advance.

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• C++ CRTP question

  - by aaa

  following piece of code does not compile, the problem is in T::rank not be inaccessible (I think) or uninitialized in parent template. Can you tell me exactly what the problem is? is passing rank explicitly the only way? or is there a way to query tensor class directly? Thank you #include <boost/utility/enable_if.hpp> template<class T, // size_t N, class enable = void> struct tensor_operator; // template<class T, size_t N> template<class T> struct tensor_operator<T, typename boost::enable_if_c< T::rank == 4>::type > { tensor_operator(T &tensor) : tensor_(tensor) {} T& operator()(int i,int j,int k,int l) { return tensor_.layout.element_at(i, j, k, l); } T &tensor_; }; template<size_t N, typename T = double> // struct tensor : tensor_operator<tensor<N,T>, N> { struct tensor : tensor_operator<tensor<N,T> > { static const size_t rank = N; }; I know the workaround, however am interested in mechanics of template instantiation for self-education

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