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• Haskell: Defaulting constraints to type

  - by yairchu

  Consider this example: applyKTimes :: Integral i => i -> (a -> a) -> a -> a applyKTimes 0 _ x = x applyKTimes k f x = applyKTimes (k-1) f (f x) applyThrice :: (a -> a) -> a -> a applyThrice = applyKTimes 3 The 3 in applyThrice is defaulted by GHC to an Integer as shown when compiling with -Wall: Warning: Defaulting the following constraint(s) to type 'Integer' 'Integral t' arising from a use of 'applyKTimes' So I guess that Integer is the default Integral a => a. Is there a way to define "default types" for other constraints too? Is using default types bad practice? (it does complain when using -Wall..)

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• The type{0} does not support direct content - WPF / XAML

  - by Levo

  Hi there: I defined in my code two classes: a "Person" class with public "Age" and "Name" property, and a "People" class that inherits from Generic.List(of T). The code for People class is as followed: Public Class People Inherits Collections.Generic.List(Of Person) ... End Class What I want to achieve is to directly initialize the People class, and add individual Person to it in XAML, i.e.: <local:People x:Key="Familty"> <local:Person Age="11" Name="John" /> <local:Person Age="12" Name="John2" /> ... </local:People> But I keep getting an error in XAML saying: The type 'People' does not support direct content. Any idea as for how to solve this problem? Thank you very much!

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• Errors when using a Ruby On Rails scaffold with a data type of interger

  - by bublebboy

  I am learning Ruby On Rails. I am on a shared hosting with Ruby version 1.8.1 and Rails version 2.3.10. I am working my way through a tutorial at http://railstutorial.org/chapters/a-demo-app?version=2.3#top and at one point in the tutorial it has me run: script/generate scaffold Micropost content:string user_id:interger The tutorial is using the default database, SQLite3. The command works and I use rake db:migrate to create the database. I can view the page listing the microposts (which is empty), but when I try to add a micropost (microposts/new) I get an error undefined method `user_id' for #<Micropost:0x7f710e4988e8> After doing some testing on my own it seems I experience the problem by using the data type of interger. While I understand that using a scaffold is not the best way of building a ruby on rails, I'm just beginning and would still like to know why I am experiencing this problem to help me better understand how rails works.

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• wrong data type in mysql for grails byte[] property

  - by srkiNZ84

  Hi, I have an application which is trying to save a photo to the database. I've created a grails domain class with a byte[] property and this was working well when using HSQLDB (the default in grails). However, when I changed the database to MySQL I ended up getting the following error: Data truncation: Data too long for column 'photo' at row 1 I then had a look at the schema and found that the byte[] was being created as a TINYBLOB field, which was causing the error. How can I specify that this property should correspond to a BLOB/LONGBLOB type in the database?

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• PHPUnit test for error thrown with wrong argument type

  - by Spencer Mark

  I'm just starting with PHPUnit and am ok with all assert* methods, but can't figure out how to test for error thrown when the wrong argument is provided to the method - say hinted with array like so: public function(array $list) { } and then tested with null as argument. Could someone please provide an example of how to test for this sort of errors? I've checked quite a few posts on stackoverflow, but couldn't find the answer to this specific issue. Edit Ok - just to give you an idea of what I'm testing - here's the ArrayHelper::removeIfValueIsEmpty() method: public static function removeIfValueIsEmpty(array $array) { if (empty($array)) { return array(); } return array_filter($array, function($value) { return !Helper::isEmpty($value); }); } and now test: class ArrayHelperTest extends PHPUnit_Framework_TestCase { public function testRemoveIfValueIsEmpty() { $this->assertEmpty( \Cmd\Helper\ArrayHelper::removeIfValueIsEmpty(null), '\Cmd\Helper\ArrayHelper::removeIfValueIsEmpty method failed (checking with null as argument)' ); } } This throws an error: PHPUnit_Framework_Error : Argument 1 passed to Cmd\Helper\ArrayHelper::removeIfValueIsEmpty() must be of the type array, null given

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• Type hinting and optional attributes in PHP

  - by Álvaro G. Vicario

  I have a class method that deals with dates: public function setAvailability(DateTime $start, DateTime $end){ } Since item availability can have lower limit, upper limit, both or none, I'd like to make setAvailability() accept NULL values as well. However, the NULL constant violates the type hinting: $foo->setAvailability(NULL, $end); triggers: Catchable fatal error: Argument 1 passed to Foo::setAvailability() must be an instance of DateTime, null given And, as far as I know, I cannot have a DateTime instance with no value. (Can I?) For a reason I cannot grasp, this seems to work: public function setAvailability(DateTime $start=NULL, DateTime $end=NULL){ } ... $foo->setAvailability(NULL, $end); But it looks like a hack that works by pure chance. How would you deal with unset dates in PHP classes?

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• non-scalar type requested

  - by lego69

  can somebody please help me with an error conversion from `A' to non-scalar type `B' requested I have class A and derived from it B, but I have problems with these rows: A a(1); A *pb = new B(a); B b = *pb; //here I have an error thanks in advance for any help class A { protected: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); virtual ~A(){}; virtual void foo(); void foo() const; operator int(); }; class B: public A { public: B(int initPlayer): A(initPlayer){}; ~B(){}; virtual void foo(); };

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• SimpleInjector - Register a type for all it's interfaces

  - by Karl Cassar

  Is it possible to register a type for all it's implementing interfaces? E.g, I have a: public class Bow : IWeapon { #region IWeapon Members public string Attack() { return "Shooted with a bow"; } #endregion } public class HumanFighter { private readonly IWeapon weapon = null; public HumanFighter(IWeapon weapon) { this.weapon = weapon; } public string Fight() { return this.weapon.Attack(); } } [Test] public void Test2b() { Container container = new Container(); container.RegisterSingle<Bow>(); container.RegisterSingle<HumanFighter>(); // this would match the IWeapon to the Bow, as it // is implemented by Bow var humanFighter1 = container.GetInstance<HumanFighter>(); string s = humanFighter1.Fight(); }

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• Memory management for "id<ProtocolName> variableName" type properties

  - by Malakim

  Hi, I'm having a problem with properties of the following type: id<ProtocolName> variableName; ..... ..... @property (nonatomic, retain) id<ProtocolName> variableName; I can access and use them just fine, but when I try to call [variableName release]; I get compiler warnings: '-release' not found in protocol(s) Do I need to define a release method in the interface, or how do I release the memory reserved for the variable? Thanks!

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• C++ Boost bind value type

  - by aaa

  hello. I look in documentation and source code but cannot figure out how to get return value type of boost bind functor. I am trying to accomplish following: 35 template<typename T,size_t N, class F> 36 boost::array<typename F::value_type, N> make_array(T (&input)[N], F unary) { 37 boost::array<typename F::value_type, N> array; 38 std::transform(input, input + N, array.begin(), unary); 39 return array; 40 } where F can be bind functor. the above does not work because functor does not have value_type. for that matter, is there standard interface for unary/binary functor as far as return value. Thanks

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• Why so many individual System.Web.* DLLs?

  - by toasteroven

  I've been thinking about ways to refactor a fairly expansive class/utility library I have, and one thing I think I want to do is split off any higher-level helper utilities that introduce new dependencies. I read some previous questions here, and one that I particularly noticed was a comment about how Microsoft freely uses namespaces across DLLs. The example given was System.Web - it's in the base framework, but there's also a System.Web.dll that adds more functionality to the namespace if you want it. I also noticed several other System.Web.* DLLs available, and I was wondering if there's a reason why they wouldn't be combined into a single DLL. Could it be that they have their own individual dependencies and Microsoft (like me) wanted to separate assemblies along those lines? Or is it for easier maintenance? Something else entirely?

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• Can you have an extension method on a type instead of on an instance of a type?

  - by SLC

  I can have an extension method like this: DateTime d = new DateTime(); d = d.GetRandomDate(); GetRandomDate is my extension method. However the above doesn't make much sense. What would be better is: DateTime d = DateTime.GetRandomDate(); However, I don't know how to do this. An extension method created as: public static DateTime GetRandomDate(this System.DateTime dt) will only add the GetRandomDate() in the first example above, not the second one. Is there a way to achieve the desired behaviour?

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• Detect all changes to a <input type="text"> (immediately) using JQuery

  - by Dustin Boswell

  There are many ways the value of a <input type="text"> can change, including: keypresses copy/paste modified with JavaScript auto-completed by browser or a toolbar I want my JavaScript function to be called (with the current input value) any time it changes. And I want it to be called right away, not just when the input loses focus. I'm looking for the cleanest and most robust way to do this across all browsers (using jQuery preferably). Example use case: On the Twitter Signup page, the username field's value gets shown in the url "http://twitter/username" below it.

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• super(type,subclass) in simple singleton implementation

  - by Tianchen Wu

  when I was implementing naive singleton in python, I came up with a problem with super key word. As usual the behavior of super is always tricky and buggy, hope someone can shed light on it. Thanks :) The problem is that: class Singleton(object): def __new__(cls,*args,**kw): if not hasattr(cls,'_instance'): #create a instance of type cls, origin=super(Singleton,Singleton).__new__(cls,*args,**kw) cls._instance=origin return cls._instance class B(Singleton): def __init__(self,b): self.b=b It actually works, but I am wondering Will it be better if I change line 5 to the below, like in most of the books? origin=super(Singleton,cls).__new__(cls,*args,**ks) what's the difference to make?

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• How to use a Visual C++ .Net String type as argument in a function

  - by stefangachter

  Probably this is not a difficult question, but I am always a little bit confused on how to treat String type as an argument in Visual C++. I have the following to functions: void function_1(String ^str_1) { str_1 = gcnew String("Test"); } void function_2() { String ^str_2 = nullptr; function_1(str_2); } After calling function_1, str_2 is still equal to null, but what I want to achieve is that str_2 is equal to Test. So, how can I achieve that the content of str_1 is passed to function_2? Thanks for any advice.

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• how to create property of type generic class?

  - by Anish

  public class SelectionList<T> : ObservableCollection<SelectionItem<T>> where T : IComparable<T> { // Code } public class SelectionItem<T> : INotifyPropertyChanged { // Code } I need to create a property which is of the type SelectionList...as follows: public SelectionList<string> Sports { get; set; }. But when I replace string with DataRowView, as public SelectionList<DataRowView> Sports { get; set; }. I am getting error. Please help

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• SQLite: does data type depend on the quotes?

  - by Septagram

  In SQLite, the datatype of a value is associated with the value itself, not with the column type. So suppose we have a table with an integer primary key "id" and an integer column "some_number". If I do a query like this: INSERT INTO mytable (id, some_number) VALUES (NULL, "1234") Will 123 be inserted as an integer or as string? What consequences it will have later for me, say, when I'm comparing it with other value like "234" (as a number 1234 234, as a string "1234" < "234", right?)?

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• step attribute not working with HTML5 <input type="range"> on Safari

  - by Claudiu

  Are there known issues with range inputs not working fully on Safari? I have the following input element: <input type=?"range" min=?"0" max=?"360" step=?"0.0001" value=?"0">? On Chrome, the input goes according to the step variable. On Safari, it only goes by integer values. Even setting the step to 10 still makes it go by increments of 1. I'm confused because I thought Chrome and Safari both used WebKit.

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• Best use of System.Windows.Forms.Application.Run()

  - by carlos

  Hello i Have a programa that has starts in a main sub, it executes some code and after that code it opens a form using System.Windows.Forms.Application.Run(General) General is a form but also a class, so I wonder what it the pros or cons of using : System.Windows.Forms.Application.Run(General) vs Dim gen as general System.Windows.Forms.Application.Run(gen) In the first I am opening a form using the name of the class, and I read that it is best to declare the instance as an object variable. So far I used the first approach without any problem. Thanks for your comments !

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• Casting to specific asp.net page type

  - by DEH

  I have an asp.net page with a code-behind class definition as follows: public partial class examplepage : System.Web.UI.Page I'd like to set a public property within the page that I can reference from other classes. My understanding is that if I cast to examplepage then I should be able to get at the public property that is specific to example page, as in: string test=((examplepage)HttpContext.Current.Handler).propertyX; However, when I try casting as above the compiler does not recognise examplepage. Can anyone tell me how I can cast? I have no specific namespaces defined. Thanks

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• Mistake in display and insert methods (double-ended queue)

  - by MANAL

  1) My problem when i make remove from right or left program will be remove true but when i call diplay method the content wrong like this I insert 12 43 65 23 and when make remove from left program will remove 12 but when call display method show like this 12 43 65 and when make remove from right program will remove 23 but when call display method show like this 12 43 Why ?????? ); and when i try to make insert after remove write this Can not insert right because the queue is full . first remove right and then u can insert right where is the problem ?? Please Help me please 2) My code FIRST CLASS class dqueue { private int fullsize; //number of all cells private int item_num; // number of busy cells only private int front,rear; public int j; private double [] dqarr; //========================================== public dqueue(int s) //constructor { fullsize = s; front = 0; rear = -1; item_num = 0; dqarr = new double[fullsize]; } //========================================== public void insert(double data) { if (rear == fullsize-1) rear = -1; rear++; dqarr[rear] = data; item_num++; } public double removeLeft() // take item from front of queue { double temp = dqarr[front++]; // get value and incr front if(front == fullsize) front = 0; item_num --; // one less item return temp; } public double removeRight() // take item from rear of queue { double temp = dqarr[rear--]; // get value and decr rear if(rear == -1) // rear = item_num -1; item_num --; // one less item return temp; } //========================================= public void display () //display items { for (int j=0;j<item_num;j++) // for every element System.out.print(dqarr[j] +" " ); // display it System.out.println(""); } //========================================= public int size() //number of items in queue { return item_num; } //========================================== public boolean isEmpty() // true if queue is empty { return (item_num ==0); } } SECOND CLASS import java.util.Scanner; class dqueuetest { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.println(" ***** Welcome here***** "); System.out.println(" ***** Mind Of Programming Group***** "); System.out.println(" _____________________________________________ "); System.out.println("enter size of your dqueue"); int size = input.nextInt(); dqueue mydq = new dqueue(size); System.out.println(""); System.out.println("enter your itemes"); //===================================== for(int i = 0;i<=size-1;i++) { System.out.printf("item %d:",i+1); double item = input.nextDouble(); mydq.insert(item); System.out.println(""); } //===================================== int queue =size ; int c = 0 ; while (c != 6) { System.out.println(""); System.out.println("************************************************"); System.out.println(" MAIN MENUE"); System.out.println("1- INSERT RIGHT "); System.out.println("2- REMOVE LEFT"); System.out.println("3- REMOVE RIGHT"); System.out.println("4- DISPLAY"); System.out.println("5- SIZE"); System.out.println("6- EXIT"); System.out.println("************************************************"); System.out.println("choose your operation by number(1-6)"); c = input.nextInt(); switch (c) { case 1: if (queue == size) System.out.print("Can not insert right because the queue is full . first remove right and then u can insert right "); else { System.out.print("enter your item: "); double item = input.nextDouble(); mydq.insert(item);} break; case 2: System.out.println("REMOVE FROM REAR :"); if( !mydq.isEmpty() ) { double item = mydq.removeLeft(); System.out.print(item + "\t"); } // end while System.out.println(""); mydq.display(); break; case 3: System.out.println("REMOVE FROM FRONT :"); if( !mydq.isEmpty() ) { double item = mydq.removeRight(); System.out.print(item + "\t"); } // end while System.out.println(""); mydq.display(); break; case 4: System.out.println("The items in Queue are :"); mydq.display(); break; case 5: System.out.println("The Size of the Queue is :"+mydq.size()); break; case 6: System.out.println("Good Bye"); break; default: System.out.println("wrong chiose enter again"); } //end switch } //end while } // end main }//end class

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• session variable not available in global before(:each, :type => :controller)

  - by Rob

  Hi, I'm refactoring some specs, in controller specs I have a before(:each) which sets up things required in the session my before filter is... config.before(:each, :type => :controller) do ... session[:current_user] = @user session[:instance] = @instance ... end @user and @instance are also set in the before(:each) i've just hidden them for readability here I get the following error when running the controller tests undefined method `session' for nil:NilClass I would expect the global before callbacks to have the same things as the ones in the individual tests but I guess maybe they are loaded before the rails environment has been initialised? Thanks

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• converting tag number to int

  - by Ehtesham Sajed

  i m using Visual C++2008. i've assigned tag value=2 of all buttons from button property(using drag n drop). now i want to make some math calculation with tag value. need to change it in int. what is the default data type tag? i used this code, //code sample if(((int)this-button1-Tag)((int)this-button2-Tag)((int)this-button3-Tag)==50) { ........ //i.e, if tag value of button1*tag value of button2*tag value of button 3==50 then... ........ } generated following run time error on a messegebox An unhandled exception of type 'System.InvalidCastException' occurred in learncpp1.exe Additional information: Specified cast is not valid.

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• Linking/Combining Type Classes in Haskell

  - by thegravian

  Say I have two type classes defined as follows that are identical in function but different in names: class Monad m where (>>=) :: m a -> (a -> m b) -> m b return :: a -> m a class PhantomMonad p where pbind :: p a -> (a -> p b) -> p b preturn :: a -> p b Is there a way to tie these two classes together so something that is an instance of PhantomMonad will automatically be an instance of Monad, or will instances for each class have to be explicitly written? Any insight would be most appreciated, thanks!

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• system() call returns "Permission Denied" on Windows XP

  - by bde

  I am experiencing a problem with a C program running on Windows XP that is getting Permission Denied (EACCES) errors when it tries to call system(). It doesn't seem to matter what I put in the command string, the commands all work manually but get Permission Denied errors when executed via system() The other interesting thing is that the program works correctly on other XP machines, just not this one. That makes it feel like some kind of OS setting, but I am not totally sure what system() does under the hood and would like to understand what is happening here. Thanks.

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