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• prolog recursion

  - by AhmadAssaf

  am making a function that will send me a list of all possible elemnts .. in each iteration its giving me the last answer .. but after the recursion am only getting the last answer back .. how can i make it give back every single answer .. thank you the problem is that am trying to find all possible distributions for a list into other lists .. the code test :- bp(3,12,[7, 3, 5, 4, 6, 4, 5, 2], Answer), format("Answer = ~w\n",[Answer]). bp(NB,C,OL,A):- addIn(C,OL,[[],[],[]],A); bp(NB,C,_,A). addIn(_,[],Result,Result). addIn(C,[Element|Rest],[F|R],Result):- member( Members , [F|R]), sumlist( Members, Sum), sumlist([Element],ElementLength), Cap is Sum + ElementLength, (Cap =< C, append([Element], Members,New), insert( Members, New, [F|R], PartialResult), addIn(C,Rest,PartialResult,Result)). by calling test .. am getting back all the list of possible answers .. now if i tried to do something that will fail like bp(3,11,[8,2,4,6,1,8,4],Answer). it will just enter a while loop .. more over if i changed the bp(NB,C,OL,A):- addIn(C,OL,[[],[],[]],A); bp(NB,C,_,A). to and instead of Or .. i get error : ERROR: is/2: Arguments are not sufficiently instantiated appreciate the help .. Thanks alot @hardmath

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• Refining Search Results [PHP/MySQL]

  - by Dae

  I'm creating a set of search panes that allow users to tweak their results set after submitting a query. We pull commonly occurring values in certain fields from the results and display them in order of their popularity - you've all seen this sort of thing on eBay. So, if a lot of rows in our results were created in 2009, we'll be able to click "2009" and see only rows created in that year. What in your opinion is the most efficient way of applying these filters? My working solution was to discard entries from the results that didn't match the extra arguments, like: while($row = mysql_fetch_assoc($query)) { foreach($_GET as $key => $val) { if($val !== $row[$key]) { continue 2; } } // Output... } This method should hopefully only query the database once in effect, as adding filters doesn't change the query - MySQL can cache and reuse one data set. On the downside it makes pagination a bit of a headache. The obvious alternative would be to build any additional criteria into the initial query, something like: $sql = "SELECT * FROM tbl MATCH (title, description) AGAINST ('$search_term')"; foreach($_GET as $key => $var) { $sql .= " AND ".$key." = ".$var; } Are there good reasons to do this instead? Or are there better options altogether? Maybe a temporary table? Any thoughts much appreciated!

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• Are there equivalents to Ruby's method_missing in other languages?

  - by Justin Ethier

  In Ruby, objects have a handy method called method_missing which allows one to handle method calls for methods that have not even been (explicitly) defined: Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. The example below creates a class Roman, which responds to methods with names consisting of roman numerals, returning the corresponding integer values. class Roman def romanToInt(str) # ... end def method_missing(methId) str = methId.id2name romanToInt(str) end end r = Roman.new r.iv #=> 4 r.xxiii #=> 23 r.mm #=> 2000 For example, Ruby on Rails uses this to allow calls to methods such as find_by_my_column_name. My question is, what other languages support an equivalent to method_missing, and how do you implement the equivalent in your code?

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• What C++ templates issue is going on with this error?

  - by WilliamKF

  Running gcc v3.4.6 on the Botan v1.8.8 I get the following compile time error building my application after successfully building Botan and running its self test: ../../src/Botan-1.8.8/build/include/botan/secmem.h: In member function `Botan::MemoryVector<T>& Botan::MemoryVector<T>::operator=(const Botan::MemoryRegion<T>&)': ../../src/Botan-1.8.8/build/include/botan/secmem.h:310: error: missing template arguments before '(' token What is this compiler error telling me? Here is a snippet of secmem.h that includes line 130: [...] /** * This class represents variable length buffers that do not * make use of memory locking. */ template<typename T> class MemoryVector : public MemoryRegion<T> { public: /** * Copy the contents of another buffer into this buffer. * @param in the buffer to copy the contents from * @return a reference to *this */ MemoryVector<T>& operator=(const MemoryRegion<T>& in) { if(this != &in) set(in); return (*this); } // This is line 130! [...]

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• Generic Class Vb.net

  - by KoolKabin

  hi guys, I am stuck with a problem about generic classes. I am confused how I call the constructor with parameters. My interface: Public Interface IDBObject Sub [Get](ByRef DataRow As DataRow) Property UIN() As Integer End Interface My Child Class: Public Class User Implements IDBObject Public Sub [Get](ByRef DataRow As System.Data.DataRow) Implements IDBObject.Get End Sub Public Property UIN() As Integer Implements IDBObject.UIN Get End Get Set(ByVal value As Integer) End Set End Property End Class My Next Class: Public Class Users Inherits DBLayer(Of User) #Region " Standard Methods " #End Region End Class My DBObject Class: Public Class DBLayer(Of DBObject As {New, IDBObject}) Public Shared Function GetData() As List(Of DBObject) Dim QueryString As String = "SELECT * ***;" Dim Dataset As DataSet = New DataSet() Dim DataList As List(Of DBObject) = New List(Of DBObject) Try Dataset = Query(QueryString) For Each DataRow As DataRow In Dataset.Tables(0).Rows **DataList.Add(New DBObject(DataRow))** Next Catch ex As Exception DataList = Nothing End Try Return DataList End Function End Class I get error in the starred area of the DBLayer Object. What might be the possible reason? what can I do to fix it? I even want to add New(byval someval as datatype) in IDBObject interface for overloading construction. but it also gives an error? how can i do it? Adding Sub New(ByVal DataRow As DataRow) in IDBObject producess following error 'Sub New' cannot be declared in an interface. Error Produced in DBLayer Object line: DataList.Add(New DBObject(DataRow)) Msg: Arguments cannot be passed to a 'New' used on a type parameter.

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• Convincing why testing is good

  - by FireAphis

  Hello, In my team of real-time-embedded C/C++ developers, most people don't have any culture of testing their code beyond the casual manual sanity checks. I personally strongly believe in advantages of autonomous automatic tests, but when I try to convince I get some reappearing arguments like: We will spend more time on writing the tests than writing the code. It takes a lot of effort to maintain the tests. Our code is spaghetti; no way we can unit-test it. Our requirement are not sealed – we’ll have to rewrite all the tests every time the requirements are changed. Now, I'd gladly hear any convincing tips and advises, but what I am really looking for are references to researches, articles, books or serious surveys that show (preferably in numbers) how testing is worth the effort. Something like "We in IBM/Microsoft/Google, surveying 3475 active projects, found out that putting 50% more development time into testing decreased by 75% the time spent on fixing bugs" or "after half a year, the time needed to write code with test was only marginally longer than what used to take without tests". Any ideas? P.S.: I'm adding C++ tag too in case someone has a specific experience with convincing this, usually elitist, type of developers :-)

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• How to buffer an IPoint or IGeometry? (How to do buffered intersection checks on an IPoint?)

  - by Quigrim

  How would I buffer an IPoint to do an intersection check using IRelationalOperator? I have, for arguments sake: IPoint p1 = xxx; IPoint p2 = yyy; IRelationalOperator rel1 = (IRelationalOperator)p1; if (rel.Intersects (p2)) // Do something But now I want to add a tolerance to my check, so I assume the right way to do that is by either buffering p1 or p2. Right? How do I add such a buffer? Note: the Intersects method I am using is an extension method I wrote to simplify my code. Here it is: /// <summary> /// Returns true if the IGeometry is intersected. /// This method negates the Disjoint method. /// </summary> /// <param name="relOp">The rel op.</param> /// <param name="other">The other.</param> /// <returns></returns> public static bool Intersects ( this IRelationalOperator relOp, IGeometry other) { return (!relOp.Disjoint (other)); }

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• WPF Binding to variable / DependencyProperty

  - by Peter

  I'm playing around with WPF Binding and variables. Apparently one can only bind DependencyProperties. I have come up with the following, which works perfectly fine: The code-behind file: public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } public string Test { get { return (string)this.GetValue(TestProperty); } set { this.SetValue(TestProperty, value); } //set { this.SetValue(TestProperty, "BBB"); } } public static readonly DependencyProperty TestProperty = DependencyProperty.Register( "Test", typeof(string), typeof(MainWindow), new PropertyMetadata("CCC")); private void button1_Click(object sender, RoutedEventArgs e) { MessageBox.Show(Test); Test = "AAA"; MessageBox.Show(Test); } } XAML: <Window x:Class="WpfApplication3.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase" Title="MainWindow" Height="350" Width="525" DataContext="{Binding RelativeSource={RelativeSource Self}}"> <Grid> <TextBox Height="31" HorizontalAlignment="Left" Margin="84,86,0,0" Name="textBox1" VerticalAlignment="Top" Width="152" Text="{Binding Test, Mode=TwoWay, diag:PresentationTraceSources.TraceLevel=High}"/> <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="320,85,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" /> <TextBox Height="31" HorizontalAlignment="Left" Margin="84,138,0,0" Name="textBox2" Text="{Binding Test, Mode=TwoWay}" VerticalAlignment="Top" Width="152" /> </Grid> The two TextBoxes update one an other. And the Button sets them to "AAA". But now I replaced the Setter function with the one that is commented out (simulating some manipulation of the given value). I would expect that whenever the property value is changed it will be reset to "BBB". It does so when you press the button, that is when you set the property in code. But it does for some reason not affect the WPF Bindings, that is you can change the TextBox contents and thus the property, but apparently the Setter is never called. I wonder why that is so, and how one would go about to achive the expected behaviour.

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• What is the fastest way to find duplicates in multiple BIG txt files?

  - by user2950750

  I am really in deep water here and I need a lifeline. I have 10 txt files. Each file has up to 100.000.000 lines of data. Each line is simply a number representing something else. Numbers go up to 9 digits. I need to (somehow) scan these 10 files and find the numbers that appear in all 10 files. And here comes the tricky part. I have to do it in less than 2 seconds. I am not a developer, so I need an explanation for dummies. I have done enough research to learn that hash tables and map reduce might be something that I can make use of. But can it really be used to make it this fast, or do I need more advanced solutions? I have also been thinking about cutting up the files into smaller files. To that 1 file with 100.000.000 lines is transformed into 100 files with 1.000.000 lines. But I do not know what is best: 10 files with 100 million lines or 1000 files with 1 million lines? When I try to open the 100 million line file, it takes forever. So I think, maybe, it is just too big to be used. But I don't know if you can write code that will scan it without opening. Speed is the most important factor in this, and I need to know if it can be done as fast as I need it, or if I have to store my data in another way, for example, in a database like mysql or something. Thank you in advance to anybody that can give some good feedback.

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• How to treat Base* pointer as Derived<T>* pointer?

  - by dehmann

  I would like to store pointers to a Base class in a vector, but then use them as function arguments where they act as a specific class, see here: #include <iostream> #include <vector> class Base {}; template<class T> class Derived : public Base {}; void Foo(Derived<int>* d) { std::cerr << "Processing int" << std::endl; } void Foo(Derived<double>* d) { std::cerr << "Processing double" << std::endl; } int main() { std::vector<Base*> vec; vec.push_back(new Derived<int>()); vec.push_back(new Derived<double>()); Foo(vec[0]); Foo(vec[1]); delete vec[0]; delete vec[1]; return 0; } This doesn't compile: error: call of overloaded 'Foo(Base*&)' is ambiguous Is it possible to make it work? I need to process the elements of the vector differently, according to their int, double, etc. types.

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• Stuck trying to get Log4Net to work with Dependency Injection

  - by Pure.Krome

  I've got a simple winform test app i'm using to try some Log4Net Dependency Injection stuff. I've made a simple interface in my Services project :- public interface ILogging { void Debug(string message); // snip the other's. } Then my concrete type will be using Log4Net... public class Log4NetLogging : ILogging { private static ILog Log4Net { get { return LogManager.GetLogger( MethodBase.GetCurrentMethod().DeclaringType); } } public void Debug(string message) { if (Log4Net.IsDebugEnabled) { Log4Net.Debug(message); } } } So far so good. Nothing too hard there. Now, in a different project (and therefore namesapce), I try and use this ... public partial class Form1 : Form { public Form1() { FileInfo fileInfo = new FileInfo("Log4Net.config"); log4net.Config.XmlConfigurator.Configure(fileInfo); } private void Foo() { // This would be handled with DI, but i've not set it up // (on the constructor, in this code example). ILogging logging = new Log4NetLogging(); logging.Debug("Test message"); } } Ok .. also pretty simple. I've hardcoded the ILogging instance but that is usually dependency injected via the constructor. Anyways, when i check this line of code... return LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType); the DeclaringType type value is of the Service namespace, not the type of the Form (ie. X.Y.Z.Form1) which actually called the method. Without passing the type INTO method as another argument, is there anyway using reflection to figure out the real method that called it?

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• ASP.NET MVC Unit Testing Controllers - Repositories

  - by Brian McCord

  This is more of an opinion seeking question, so there may not be a "right" answer, but I would welcome arguments as to why your answer is the "right" one. Given an MVC application that is using Entity Framework for the persistence engine, a repository layer, a service layer that basically defers to the repository, and a delete method on a controller that looks like this: public ActionResult Delete(State model) { try { if( model == null ) { return View( model ); } _stateService.Delete( model ); return RedirectToAction("Index"); } catch { return View( model ); } } I am looking for the proper way to Unit Test this. Currently, I have a fake repository that gets used in the service, and my unit test looks like this: [TestMethod] public void Delete_Post_Passes_With_State_4() { //Arrange var stateService = GetService(); var stateController = new StateController( stateService ); ViewResult result = stateController.Delete( 4 ) as ViewResult; var model = (State)result.ViewData.Model; //Act RedirectToRouteResult redirectResult = stateController.Delete( model ) as RedirectToRouteResult; stateController = new StateController( stateService ); var newresult = stateController.Delete( 4 ) as ViewResult; var newmodel = (State)newresult.ViewData.Model; //Assert Assert.AreEqual( redirectResult.RouteValues["action"], "Index" ); Assert.IsNull( newmodel ); } Is this overkill? Do I need to check to see if the record actually got deleted (as I already have Service and Repository tests that verify this)? Should I even use a fake repository here or would it make more sense just to mock the whole thing? The examples I'm looking at used this model of doing things, and I just copied it, but I'm really open to doing things in a "best practices" way. Thanks.

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• Getting ellipses function parameters without an initial argument

  - by Tox1k

  So I've been making a custom parser for a scripting language, and I wanted to be able to pass only ellipses arguments. I don't need or want an initial variable, however Microsoft and C seem to want something else. FYI, see bottom for info. I've looked at the va_* definitions #define _crt_va_start(ap,v) ( ap = (va_list)_ADDRESSOF(v) + _INTSIZEOF(v) ) #define _crt_va_arg(ap,t) ( *(t *)((ap += _INTSIZEOF(t)) - _INTSIZEOF(t)) ) #define _crt_va_end(ap) ( ap = (va_list)0 ) and the part I don't want is the v in va_start. As a little background I'm competent in goasm and I know how the stack works so I know what's happening here. I was wondering if there is a way to get the function stack base without having to use inline assembly. Ideas I've had: #define im_va_start(ap) (__asm { mov [ap], ebp }) and etc... but really I feel like that's messy and I'm doing it wrong. struct function_table { const char* fname; (void)(*fptr)(...); unsigned char maxArgs; }; function_table mytable[] = { { "MessageBox", &tMessageBoxA, 4 } }; ... some function that sorts through a const char* passed to it to find the matching function in mytable and calls tMessageBoxA with the params. Also, the maxArgs argument is just so I can check that a valid number of parameters is being sent. I have personal reasons for not wanting to send it in the function, but in the meantime we can just say it's because I'm curious. This is just an example; custom libraries are what I would be implementing so it wouldn't just be calling WinAPI stuff. void tMessageBoxA(...) { // stuff to load args passed MessageBoxA(arg1, arg2, arg3, arg4); } I'm using the __cdecl calling convention and I've looked up ways to reliably get a pointer to the base of the stack (not the top) but I can't seem to find any. Also, I'm not worried about function security or typechecking.

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• Getting the time interval between typing characters in a TextBox, in C#

  - by sama

  I have a form that has a TextBox and a Label and I want to get the time of the first character entered in the textbox. Then if the user enters more than ten charcaters, the time between the first charcter entered and the tenth charcter entered is displayed in the label. Can any one help me please? I'm using C# Here is the code but I cannot complete it and I have many things that need to be written but I don't know how to continue. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Threading; namespace n { public partial class Form1 : Form { int count=0; public Form1() { InitializeComponent(); } private void textBox1_TextChanged(object sender, EventArgs e) { DateTime t1 = new DateTime();// the time when entering the first charcter DateTime t2 = new DateTime(); t2 = System.DateTime.Now - t1; int index = textBox1.SelectionStart; Point p; p = textBox1.GetPositionFromCharIndex(index); Thread t = new Thread(counttext); t.Start(); label1.Text = "t2"; } private int counttext() { while (textBox1.Text.Length < 10) { count++; if (count == 10) return count; } } } }

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• CUDA - multiple kernels to compute a single value

  - by Roger

  Hey, I'm trying to write a kernel to essentially do the following in C float sum = 0.0; for(int i = 0; i < N; i++){ sum += valueArray[i]*valueArray[i]; } sum += sum / N; At the moment I have this inside my kernel, but it is not giving correct values. int i0 = blockIdx.x * blockDim.x + threadIdx.x; for(int i=i0; i<N; i += blockDim.x*gridDim.x){ *d_sum += d_valueArray[i]*d_valueArray[i]; } *d_sum= __fdividef(*d_sum, N); The code used to call the kernel is kernelName<<<64,128>>>(N, d_valueArray, d_sum); cudaMemcpy(&sum, d_sum, sizeof(float) , cudaMemcpyDeviceToHost); I think that each kernel is calculating a partial sum, but the final divide statement is not taking into account the accumulated value from each of the threads. Every kernel is producing it's own final value for d_sum? Does anyone know how could I go about doing this in an efficient way? Maybe using shared memory between threads? I'm very new to GPU programming. Cheers

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• Should we retire the term "Context"?

  - by MrGumbe

  I'm not sure if there is a more abused term in the world of programming than "Context." A word that has a very clear meaning in the English language has somehow morphed into a hot mess in software development, where the definition where the connotation can be completely different based on what library you happen to be developing in. Tomcat uses the word context to mean the configuration of a web application. Java applets, on the other hand, use an AppletContext to define attributes of the browser and HTML tag that launched it, but the BeanContext is defined as a container. ASP.NET uses the HttpContext object as a grab bag of state - containing information about the current request / response, session, user, server, and application objects. Context Oriented Programming defines the term as "Any information which is computationally accessible may form part of the context upon which behavioral variations depend," which I translate as "anything in the world." The innards of the Windows OS uses the CONTEXT structure to define properties about the hardware environment. The .NET installation classes, however, use the InstallContext property to represent the command line arguments entered to the installation class. The above doesn't even touch how all of us non-framework developers have used the term. I've seen plenty of developers fall into the subconscious trap of "I can't think of anything else to call this class, so I'll name it 'WidgetContext.'" Do you all agree that before naming our class a "Context," we may want to first consider some more descriptive terms? "Environment", "Configuraton", and "ExecutionState" come readily to mind.

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• How can I spec out an authlogic sessions controller using using a stub?

  - by Dave

  I want to test my User Session Controller testing that a user session is first built then saved. My UserSession class looks like this: class UserSession < Authlogic::Session::Base end The create method of my UserSessionsController looks like this: def create @user_session = UserSession.new(params[:user_session]) if @user_session.save flash[:notice] = "Successfully logged in." redirect_back_or_default administer_home_page_url else render :new end end and my controller spec looks like this: describe UserSessionsController do it "should build a new user session" do UserSession.stub!(:new).with(:email, :password) UserSession.should_receive(:new).with(:email => "[email protected]", :password => "foobar") post :create, :user_session => { :email => "[email protected]", :password => "foobar" } end end I stub out the new method but I still get the following error when I run the test: Spec::Mocks::MockExpectationError in 'UserSessionsController should build a new user session' <UserSession (class)> received :new with unexpected arguments expected: ({:password=>"foobar", :email=>"[email protected]"}) got: ({:priority_record=>nil}, nil) It's although the new method is being called on UserSession before my controller code is getting called. Calling activate_authlogic makes no difference.

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• Specifying character

  - by danutenshu

  So below I have a code in C++ that is supposed to invert the arguments in a vector, but not the sequence. I have listed my problems as sidenotes in the code below. The invert function is supposed to invert each argument, and then the main function just outputs the inverted words in same order For instance, program("one two three four")=ruof eerth owt eno #include <iostream> #include <string> using namespace std; int invert(string normal) { string inverted; for (int num=normal.size()-1; num>=0; num--) { inverted.append(normal[num]); //I don't know how to get each character //I need another command for append } return **inverted**; <---- } int main(int argc, char* argv[]) { string text; for (int a=1; a<argc; a++) { text.append(invert(argv[a])); //Can't run the invert function text.append(" "); } cout << text << endl; return 0; }

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• Mulltiple configurations in Qt

  - by user360607

  Hi all! I'm new to Qt Creator and I have several questions regarding multiple build configurations. A side note: I have the QtCreator 1.3.1 installed on my Linux machine. I need to have two configurations in my Qt Creator project. The thing is that these aren't simply debug and release but are based on the target architecture - x86 or x64. I came across http://stackoverflow.com/questions/2259192/building-multiple-targets-in-qt-qmake and from that I went trying something like: Conf_x86 { TARGET = MyApp_x86 } Conf_x64 { TARGET = MyApp_x64 } This way however I don't seems to be able to use the Qt Creator IDE to build each of these separately (Build All, Rebuild All, etc. options from the IDE menu). Is there a way to achieve this - may be even show Conf_x86 and Conf_x64 as new build configurations in Qt Creator? One other thing the Qt I have is 64 bit so by default the target built using Qt Creator IDE will also be 64 bit. I noticed that the effective qmake call in the build step includes the following option '-spec linux-g++-64'. I also noticed that should I add '-spec linux-g++-32' in 'Additional arguments' it would override '-spec linux-g++-64' and the resulting target will be 32 bit. How can I achieve this by simply editing the contents of the .pro file? I saw that all these changes are initially saved in the .pro.user file but does doesn't suit me at all. I need to be able to make these configurations from the .pro file if possible. Any help will be appreciated. 10x in advance!

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• Scala: Correcting type inference of representation type over if statement

  - by drhagen

  This is a follow-up to two questions on representation types, which are type parameters of a trait designed to represent the type underlying a bounded type member (or something like that). I've had success creating instances of classes, e.g ConcreteGarage, that have instances cars of bounded type members CarType. trait Garage { type CarType <: Car[CarType] def cars: Seq[CarType] def copy(cars: Seq[CarType]): Garage def refuel(car: CarType, fuel: CarType#FuelType): Garage = copy( cars.map { case `car` => car.refuel(fuel) case other => other }) } class ConcreteGarage[C <: Car[C]](val cars: Seq[C]) extends Garage { type CarType = C def copy(cars: Seq[C]) = new ConcreteGarage(cars) } trait Car[C <: Car[C]] { type FuelType <: Fuel def fuel: FuelType def copy(fuel: C#FuelType): C def refuel(fuel: C#FuelType): C = copy(fuel) } class Ferrari(val fuel: Benzin) extends Car[Ferrari] { type FuelType = Benzin def copy(fuel: Benzin) = new Ferrari(fuel) } class Mustang(val fuel: Benzin) extends Car[Mustang] { type FuelType = Benzin def copy(fuel: Benzin) = new Mustang(fuel) } trait Fuel case class Benzin() extends Fuel I can easily create instances of Cars like Ferraris and Mustangs and put them into a ConcreteGarage, as long as it's simple: val newFerrari = new Ferrari(Benzin()) val newMustang = new Mustang(Benzin()) val ferrariGarage = new ConcreteGarage(Seq(newFerrari)) val mustangGarage = new ConcreteGarage(Seq(newMustang)) However, if I merely return one or the other, based on a flag, and try to put the result into a garage, it fails: val likesFord = true val new_car = if (likesFord) newFerrari else newMustang val switchedGarage = new ConcreteGarage(Seq(new_car)) // Fails here The switch alone works fine, it is the call to ConcreteGarage constructor that fails with the rather mystical error: error: inferred type arguments [this.Car[_ >: this.Ferrari with this.Mustang <: this.Car[_ >: this.Ferrari with this.Mustang <: ScalaObject]{def fuel: this.Benzin; type FuelType<: this.Benzin}]{def fuel: this.Benzin; type FuelType<: this.Benzin}] do not conform to class ConcreteGarage's type parameter bounds [C <: this.Car[C]] val switchedGarage = new ConcreteGarage(Seq(new_car)) // Fails here ^ I have tried putting those magic [C <: Car[C]] representation type parameters everywhere, but without success in finding the magic spot.

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• Execute a function to affect different template class instances

  - by Samer Afach

  I have a complicated problem, and I need help. I have a base case, class ParamBase { string paramValue; //... } and a bunch of class templates with different template parameters. template <typename T> class Param : public ParamBase { T value; //... } Now, each instance of Param has different template parameter, double, int, string... etc. To make it easier, I have a vector to their base class pointers that contains all the instances that have been created: vector<ParamBase*> allParamsObjects; The question is: How can I run a single function (global or member or anything, your choice), that converts all of those different instances' strings paramValue with different templates arguments and save the conversion result to the appropriate type in Param::value. This has to be run over all objects that are saved in the vector allParamsObjects. So if the template argument of the first Param is double, paramValue has to be converted to double and saved in value; and if the second Param's argument is int, then the paramValue of the second has to be converted to int and saved in value... etc. I feel it's almost impossible... Any help would be highly appreciated :-)

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• Google App Engine: TypeError problem with Models

  - by Rosarch

  I'm running Google App Engine on the dev server. Here is my models file: from google.appengine.ext import db import pickle import re re_dept_code = re.compile(r'[A-Z]{2,}') re_course_number = re.compile(r'[0-9]{4}') class DependencyArcHead(db.Model): sink = db.ReferenceProperty() tails = db.ListProperty() class DependencyArcTail(db.Model): courses = db.ListProperty() It gives this error: Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 3192, in _HandleRequest self._Dispatch(dispatcher, self.rfile, outfile, env_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 3135, in _Dispatch base_env_dict=env_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 516, in Dispatch base_env_dict=base_env_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 2394, in Dispatch self._module_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 2304, in ExecuteCGI reset_modules = exec_script(handler_path, cgi_path, hook) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 2200, in ExecuteOrImportScript exec module_code in script_module.__dict__ File "main.py", line 19, in <module> from src.Models import Course, findCourse, validateCourse, dictForJSON, clearAndBuildDependencyGraph File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1279, in Decorate return func(self, *args, **kwargs) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1929, in load_module return self.FindAndLoadModule(submodule, fullname, search_path) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1279, in Decorate return func(self, *args, **kwargs) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1831, in FindAndLoadModule description) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1279, in Decorate return func(self, *args, **kwargs) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 1782, in LoadModuleRestricted description) File "src\Models.py", line 14, in <module> class DependencyArcHead(db.Model): File "src\Models.py", line 17, in DependencyArcHead tails = db.ListProperty() TypeError: __init__() takes at least 2 arguments (1 given) What am I doing wrong?

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• recvfrom returns invalid argument when *from* is passed

  - by Aditya Sehgal

  I am currently writing a small UDP server program in linux. The UDP server will receive packets from two different peers and will perform different operations based on from which peer it received the packet. I am trying to determine the source from where I receive the packet. However, when select returns and recvfrom is called, it returns with an error of Invalid Argument. If I pass NULL as the second last arguments, recvfrom succeeds. I have tried declaring fromAddr as struct sockaddr_storage, struct sockaddr_in, struct sockaddr without any success. Is their something wrong with this code? Is this the correct way to determine the source of the packet? The code snippet follows. ` /*TODO : update for TCP. use recv */ if((pkInfo->rcvLen=recvfrom(psInfo->sockFd, pkInfo->buffer, MAX_PKTSZ, 0, /* (struct sockaddr*)&fromAddr,*/ NULL, &(addrLen) )) < 0) { perror("RecvFrom failed\n"); } else { /*Apply Filter */ #if 0 struct sockaddr_in* tmpAddr; tmpAddr = (struct sockaddr_in* )&fromAddr; printf("Received Msg From %s\n",inet_ntoa(tmpAddr->sin_addr)); #endif printf("Packet Received of len = %d\n",pkInfo->rcvLen); } `

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• Learn Prolog Now! DCG Practice Example

  - by Timothy

  I have been progressing through Learn Prolog Now! as self-study and am now learning about Definite Clause Grammars. I am having some difficulty with one of the Practical Session's tasks. The task reads: The formal language anb2mc2mdn consists of all strings of the following form: an unbroken block of as followed by an unbroken block of bs followed by an unbroken block of cs followed by an unbroken block of ds, such that the a and d blocks are exactly the same length, and the c and d blocks are also exactly the same length and furthermore consist of an even number of cs and ds respectively. For example, ε, abbccd, and aaabbbbccccddd all belong to anb2mc2mdn. Write a DCG that generates this language. I am able to write rules that generate andn, b2mc2m, and even anb2m and c2mndn... but I can't seem to join all these rules into anb2mc2mdn. The following are my rules that can generate andn and b2mc2m. s1 --> []. s1 --> a,s1,d. a --> [a]. d --> [d]. s2 --> []. s2 --> c,c,s2,d,d. c --> [c]. d --> [d]. Is anb2mc2mdn really a CFG, and is it possible to write a DCG using only what was taught in the lesson (no additional arguments or code, etc)? If so, can anyone offer me some guidance how I can join these so that I can solve the given task?

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• How to determine a text block of a file in one version come from which file in the previous version?

  - by Muhammad Asaduzzaman

  The problem is described below: Suppose I have a list of files in one version(say A,B,C,D). In the next version I have the following files(A,E,F,G). There are some similarities in their contents. The files in the later version comes from the previous version by file name renaming, content addition, deletion or partial modification or without any change( for example A is not changed). I take a block of text from a file(E, 2nd version) and check which files(in the 1st version) contain this text block. I found that B,C and D contain the text fragment. I want to determine from which file(B or c or d) this text block actually comes from.(I assume that E is a file whose name change in the second version). Since the contents may be changed, added or deleted in the later version, so in order to determine similarity I use LCS algorithm. But I cannot map the file with its previous version. I think one possible approach might be to use the location information of the match text blocks. But this heuristics not always work. Is there any research or algorithm exist to find so. Any direction will be helpful. Thanks in advance.

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