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  • Why is there "data" and "newtype" in Haskell?

    - by martingw
    To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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  • Why would a 'public event EventHandler cccc' be null?

    - by Matt
    Why would a 'public event EventHandler cccc' be null? I have a class that's public class Builder { public event EventHandler StartedWorking; public Builder() { // Constructor does some stuff } public void Start() { StartedWorking(this, eventargobject); //StartedWorking is null -- } } This seems straightforward and something I do all the time? Am I missing something obvious or is there something that could cause this? EDIT: Does this mean that if I fire an event that is not subscribed to in a client class I have to check that it is not null? EDIT-2: I guess I'd never had events that were never not subscribed to and hence never ran into this -- You learn something new every day Sorry about the seemingly stupid question....

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  • Is it a bad idea to create tests that rely on each other within a test fixture?

    - by nbolton
    For example: // NUnit-like pseudo code (within a TestFixture) Ctor() { m_globalVar = getFoo(); } [Test] Create() { a(m_globalVar) } [Test] Delete() { // depends on Create being run b(m_globalVar) } … or… // NUnit-like pseudo code (within a TestFixture) [Test] CreateAndDelete() { Foo foo = getFoo(); a(foo); // depends on Create being run b(foo); } … I’m going with the later, and assuming that the answer to my question is: No, at least not with NUnit, because according to the NUnit manual: The constructor should not have any side effects, since NUnit may construct the class multiple times in the course of a session. ... also, can I assume it's bad practice in general? Since tests can usually be run separately. So the result of Create may never be cleaned up by Delete.

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  • Unity 2.0. How to throw ResolutionFailedException

    - by Andrey Khataev
    Hello, I have my app, using functionality that is based on unity application block. Sometimes I need to throw ResolutionFailedException manually. In v1.2 constructor of ResolutionFailedException had three parameters - typerequested, namerequested and exception. In v2.0 fourth parameter was added - buildercontext. I'm not creating it manually, so I have no reference to it and no idea where I can get it. Roughly speaking, I'm only overriding Resolve method in particular way and I'm not interfere in standard mechanism of policies, strategies and so on. Could anyone help?

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  • Javascript - Function call will not enter function body

    - by Mike S
    I have a function acting as a constructor that, when called, gets as far as the function definition in the debugger, but never to the function body. Is there a common reason this may happen that I am overlooking? Example code below: myconstructor.js function MyConstructor(optionalParam) { //this breakpoint gets hit var newobj = {}; //breakpoint never hit //code to check for null parameter //other code }; main.js var myConstructor = new MyConstructor(); There must be something I have overlooked, but I can't see what that is. Neither firefox/firebug nor VS report errors or warnings. Thanks!

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  • C# ToolTip will not re-appear after first use.

    - by Roberto Sebestyen
    I have a Forms C# application where I would like to use a toolTip on one of the text boxes. I Initialize the tool-tip in the constructor of the Form class, and it works the first time. So when I hover over the text box with my mouse it works, but once the toolTip times out and it goes away, it does not re-appear when I move my mouse away and back onto the control. I would expect it to come back and I'm wondering what I'm doing wrong. Here is how I initialize the tooltip: myTip = new ToolTip(); myTip.ToolTipIcon = ToolTipIcon.Info; myTip.IsBalloon = true; myTip.ShowAlways = true; myTip.SetToolTip(txtMyTextBox,"My Tooltip Text");

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  • Problem with Refreshing data in ExpendableListView

    - by -providerivan.longin1
    Hi! My problem is when I want to refresh data in ExpendableListView while being in that current activity. I create adapter and when I want to add new data to list I call again constructor of that adapter(it is my private variable) with all new data....and then I call onContentChanged() method to redraw my list. But what happens is that I cant expand my list any more...like it is blocked or something and logcat isn't saying anything... This is the code that i call after setting new data in arraylists and maps: mAdapter = new MyExpandableListAdapter( this, groupData, R.layout.contact_list_parent, new String[] { NAME ,NUM_PHOTOS},//NUM_PHOTOS new int[] { R.id.rowText1, R.id.rowText2, R.id.photoAlbumImg }, childData, R.layout.contact_list_child, new String[] { NAME,NUM_PHOTOS}, //NUM_PHOTOS new int[] { R.id.rowText1, R.id.rowText2, R.id.photoAlbumImg } ); this.onContentChanged(); If anyone knows answer to this question please help me:) Thanks.

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  • Empty Datagrid problem in VB6

    - by Hybrid SyntaX
    Hello Recently, i encountered a problem; when I bind a recordset to datagrid ,and run the application the datagrid is not populated even though recordset has data I use the following code Option Explicit Dim conn As New ADODB.Connection Dim cmd As New ADODB.Command Dim recordset As New ADODB.recordset Private Sub InitializeConnection() Dim str As String str = _ "Provider=Microsoft.Jet.OLEDB.4.0;" & _ "Data Source=" + App.Path + "\phonebook.mdb;" & _ "Persist Security Info=False" conn.CursorLocation = adUseClient conn.ConnectionString = str conn.Open (conn.ConnectionString) End Sub Private Sub AbandonConnection() If conn.State <> 0 Then conn.Close End If End Sub Private Sub Persons_Read() Dim qry_all As String ' qry_all = "select * from person,web,phone Where web.personid = person.id And phone.personid = person.id" qry_all = "SELECT * FROM person" Call InitializeConnection cmd.CommandText = qry_all cmd.CommandType = adCmdText Set cmd.ActiveConnection = conn If conn.State = 1 Then Set recordset = cmd.Execute() End If Call BindDatagrid Call AbandonConnection End Sub Private Function Person_Add() End Function Private Function Person_Delete() End Function Private Function Person_Update() End Function Private Sub BindDatagrid() Set dg_Persons.DataSource = recordset dg_Persons.Refresh End Sub Private Sub cmd_Add_Click() Person_Add End Sub Private Sub cmd_Delete_Click() Person_Delete End Sub Private Sub cmd_Update_Click() Person_Update End Sub Private Sub Form_Load() Call Persons_Read End Sub Private Sub mnu_About_Click() frm_About.Show End Sub Thanks in advance

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  • Strange type-related error

    - by vsb
    I wrote following program: isPrime x = and [x `mod` i /= 0 | i <- [2 .. truncate (sqrt x)]] primes = filter isPrime [1 .. ] it should construct list of prime numbers. But I got this error: [1 of 1] Compiling Main ( 7/main.hs, interpreted ) 7/main.hs:3:16: Ambiguous type variable `a' in the constraints: `Floating a' arising from a use of `isPrime' at 7/main.hs:3:16-22 `RealFrac a' arising from a use of `isPrime' at 7/main.hs:3:16-22 `Integral a' arising from a use of `isPrime' at 7/main.hs:3:16-22 Possible cause: the monomorphism restriction applied to the following: primes :: [a] (bound at 7/main.hs:3:0) Probable fix: give these definition(s) an explicit type signature or use -XNoMonomorphismRestriction Failed, modules loaded: none. If I specify signature for isPrime function explicitly: isPrime :: Integer -> Bool isPrime x = and [x `mod` i /= 0 | i <- [2 .. truncate (sqrt x)]] I can't even compile isPrime function: [1 of 1] Compiling Main ( 7/main.hs, interpreted ) 7/main.hs:2:45: No instance for (RealFrac Integer) arising from a use of `truncate' at 7/main.hs:2:45-61 Possible fix: add an instance declaration for (RealFrac Integer) In the expression: truncate (sqrt x) In the expression: [2 .. truncate (sqrt x)] In a stmt of a list comprehension: i <- [2 .. truncate (sqrt x)] 7/main.hs:2:55: No instance for (Floating Integer) arising from a use of `sqrt' at 7/main.hs:2:55-60 Possible fix: add an instance declaration for (Floating Integer) In the first argument of `truncate', namely `(sqrt x)' In the expression: truncate (sqrt x) In the expression: [2 .. truncate (sqrt x)] Failed, modules loaded: none. Can you help me understand, why am I getting these errors?

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  • Call an AsyncTask inside a Thread

    - by Arun
    I am working in an android application and I want to call an AsyncTask from my UI main thread. For that I want to call my AsyncTask from a thread. This is the method that I call from my main UI thread. This is working correctly CommonAysnk mobjCommonAysnk = new CommonAysnk(this, 1); mobjCommonAysnk.execute(); CommonAysnk is my AsyncTask class.I want to pass my activity and an integer parameter to the AsyncTask constructor. How can I call this from a thread as shown below method. Thread t = new Thread() { public void run() { try { CommonAysnk mobjCommonAysnk = new CommonAysnk(this, 1); mobjCommonAysnk.execute(); } catch (Exception ex) { }}}; t.start(); When I tried to call it from a Thread and I am not able to pass the activity parameter correctly. How can we sole this. Thanks

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  • WPF data binding issue .

    - by Praveen
    Hi All, I have a wpf app and there i simply have a dock panel and inside dock panel i have a textblock. I want to bind the text property of textblock to my custom objects property but that' not working. I think i am missing something here but don't know what. Here is the code snippet. <TextBlock Text="{Binding Source=myDataSource, Path=ColorName}"/> </DockPanel> My custom class. class MyData { public string ColorName { get; set; } } and main window constructor.. public partial class MainWindow : Window { MyData myDataSource; public MainWindow() { InitializeComponent(); myDataSource = new MyData { ColorName = "Red" }; } }

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  • Sorting and displaying a custom QVariant type.

    - by Kranar
    Hello, I have a custom type I'd like to use with QVariant but I don't know how to get the QVariant to display in a table or have it sort in a QSortFilterProxyModel. I register the type with Q_DECLARE_METATYPE and wrote streaming operators registered via qRegisterMetaTypeStreamOperators but for whatever reason when I use the type with a table model, it doesn't display anything and it doesn't sort. I should specify that this custom type can not be modified. It has a copy and default constructor, but I can not go in and modify the source code to get it to work with QVariant. Is there a way of non-intrusively getting the behaviour I'd like?

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  • Unable to use JAR in Eclipse

    - by Myn
    Hi guys, I have just created my first JAR in Eclipse, just a simple program with a single class Database.class. It is not in a package. public class Database { public Database() { int dbInit = 1; } } I have added it as an external JAR to the build path libraries for another project in Eclipse, but for some reason I cannot get Database db = new Database(), the default constructor, to work - it's as if the contents of the JAR are not being recognised. Could anyone please offer any advice on this? Thanks very much, M

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  • Disallow taking pointer/reference to const to a temporary object in C++ (no C++0X)

    - by KRao
    Hi, I am faced with the following issue. Consider the following class: //Will be similar to bost::reference_wrapper template<class T> class Ref { public: explicit Ref(T& t) : m_ptr(&t) {} private: T* m_ptr; }; and this function returning a double double fun() {return 1.0;} If we now have double x = 1.0; const double xc = 1.0; Ref<double> ref1(x); //OK Ref<const double> refc1(cx); //OK good so far, however: //Ref<double> ref2( fun() ); //Fails as I want it to Ref<const double> refc2( fun() ); //Works but I would like it not to Is there a way to modify Ref (the way you prefer) but not the function fun, so that the last line returns a compile-time error? Please notice you can modify the constructor signature (as long as I am able to initialise the Ref as intended). Thank you in advance for your help!

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  • C++11 initialize array with uniform value in constexpr function

    - by marack
    I have a class template which builds a simple array based on the template parameters as one of its members. I need to be able to initialize every element in the array to a single value in one of the constructors. Unfortunately this constructor must be constexpr. The relevant part boils down to: template <typename T, size_t N> class foo { T data[N]; constexpr foo(T val) { // initialize data with N copies of val } }; Using std::fill or a loop is incompatible with the constexpr requirement. Initializing with : data{val} only sets the first element of the array and zero-initializes the remainder. How can this be achieved? I feel like there should be a solution with variadic templates and tuples etc...

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  • Passing derived objects in a constructure

    - by Clarence Klopfstein
    This is a bit of a convoluted question, hopefully I can make it clear. I am finding that this may not be possible, but am trying to see if anybody has a solution. I have four classes, two are core classes and two are those core classes extended: extUser Extends coreUser extSecurity Extends coreSecurity In the constructor for coreUser you have this: public coreUser(string id, ref coreSecurity cs) When trying to extend coreUser you would have this: public extUser(string id ref extSecurity es) : base(id, ref es) This fails because es is of type, extSecurity and the base class expects a type of coreSecurity. I've not found anyway to cast this to allow for me to override this base class in C#. In VB it works just fine. Ideas?

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  • C# language questions

    - by Water Cooler v2
    1) What is int? Is it any different from the struct System.Int32? I understand that the former is a C# alias (typedef or #define equivalant) for the CLR type System.Int32. Is this understanding correct? 2) When we say: IComparable x = 10; Is that like saying: IComparable x = new System.Int32(); But we can't new a struct, right? or in C like syntax: struct System.In32 *x; x=>someThing = 10; 3) What is String with a capitalized S? I see in Reflector that it is the sealed String class, which, of course, is a reference type, unlike the System.Int32 above, which is a value type. What is string, with an uncapitalized s, though? Is that also the C# alias for this class? Why can I not see the alias definitions in Reflector? 4) Try to follow me down this subtle train of thought, if you please. We know that a storage location of a particular type can only access properties and members on its interface. That means: Person p = new Customer(); p.Name = "Water Cooler v2"; // legal because as Name is defined on Person. but // illegal without an explicit cast even though the backing // store is a Customer, the storage location is of type // Person, which doesn't support the member/method being // accessed/called. p.GetTotalValueOfOrdersMade(); Now, with that inference, consider this scenario: int i = 10; // obvious System.object defines no member to // store an integer value or any other value in. // So, my question really is, when the integer is // boxed, what is the *type* it is actually boxed to. // In other words, what is the type that forms the // backing store on the heap, for this operation? object x = i;

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  • TDD, Unit Test and architectural changes

    - by Leandro
    I'm writing an RPC middleware in C++. I have a class named RPCClientProxy that contains a socket client inside: class RPCClientProxy { ... private: Socket* pSocket; ... } The constructor: RPCClientProxy::RPCClientProxy(host, port) { pSocket = new Socket(host, port); } As you can see, I don't need to tell the user that I have a socket inside. Although, to make unit tests for my proxies it would be necessary to create mocks for sockets and pass them to the proxies, and to do so I must use a setter or pass a factory to the sockets in the proxies's constructors. My question: According to TDD, is it acceptable to do it ONLY because the tests? As you can see, these changes would change the way the library is used by a programmer.

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  • How do I convert c struct from dll to C#

    - by poco
    I am converting a application from c++ to C# and have a question about the proper way to handle importing structs. I am attempting to convert a struct from a c dll into c# The struct in c looks like this typedef struct card_info { ushort r; ushort s; enum_a a; usinged long ul; ushort n; ushort* b; ushort id; } CARD_INFO; when i use [StructLayout(LayoutKind.Sequentaial)] the size of the array is 20 bytes in c#. However, if take a look at my working c++ code it is 24 bytes. I changed my c# to look like this: [StructLayout(LayoutKind.Explicit)] public struct CardInfo { [FieldOffset(0) public ushort r; [FieldOffset(2) public ushort s; [FieldOffset(4) public EnumA a; [FieldOffset(8) public ushort ul; [FieldOffset(12) public ushort n; [FieldOffset(16) public UInt32 b; [FieldOffset(20) public ushort id; } This seems to compile but I'm not convinced this is the correct way to go about doing this. Please let me know if this is correct or if there is a better way. Thanks

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  • Class basic operators

    - by swan
    Hi, Is it necessary to have a copy constructor, destructor and operator= in a class that have only static data member, no pointer class myClass{ int dm; public: myClass(){ dm = 1; } ~myClass(){ } // Is this line usefull ? myClass(const myClass& myObj){ // and that operator? this->dm = myObj.dm; } myClass& operator=(const myClass& myObj){ // and that one? if(this != &myObj){ this->dm = myObj.dm; } return *this; } }; I read that the compiler build one for us, so it is better to not have one (when we add a data member we have to update the operators)

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  • Actionscript / Flex: a question about handleAllEvents() method.

    - by Patrick
    Hi, in Adobe tutorials, they suggest to create a class to handle the events (see below the copy/pasted code, and link to page). I was wondering if I have to handle all events with the function handleAllEvents, using if statements to check if the target is the one I want, and the event is the one I want. i.e. if (event.type=="click") && (event.currentTarget == "myId") Should I have a list of ifs (for each target and each event type ?) thanks // events/MyStaticEventHandler.as package { // Empty package. import flash.events.Event; import mx.controls.Alert; public class MyStaticEventHandler { public function MyStaticEventHandler() { // Empty constructor. } public static function handleAllEvents(event:Event):void { Alert.show("Some event happened."); } } } Link (at the bottom): http://livedocs.adobe.com/flex/3/html/help.html?content=events_05.html

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  • C++ enforce conditions on inherited classes

    - by user231536
    I would like to define an abstract base class X and enforce the following: a) every concrete class Y that inherits from X define a constructor Y(int x) b) it should be possible to test whether two Y objects are equal. For a, one not very good solution is to put a pure virtual fromInt method in X which concrete class will have to define. But I cannot enforce construction. For b), I cannot seem to use a pure virtual method in X bool operator == (const X& other) const =0; because in overridden classes this remains undefined. It is not enough to define bool operator == (const Y& other) const { //stuff} because the types don't match. How do I solve these problems?

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  • Creating Pages with unique PageMaps

    - by Michael Krauklis
    I have a wicket Application that has long lived Pages. I would like each instance of this Page to be created with a unique PageMap for reasons I won't get into here, but when I try to specify a PageMap on the constructor of my Page I end up getting OOM and StackOverflow errors. Here is the code: public <CTOR>() { super(Session.get().newPageMap("" + System.currentTimeMillis())); ... I'm using a custom BookmarkablePageLink (custom in that it does not pass on the current PageMap name to the new Page) to effectively abandon the old Page/PageMap and create a new one with a new PageMap. The errors seem to be coming from page serialization after only two or three pages have been created. Can anyone find issue with this approach?

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  • any way to simplify this with a form of dynamic class instantiation?

    - by gnychis
    I have several child classes that extend a parent class, forced to have a uniform constructor. I have a queue which keeps a list of these classes, which must extend MergeHeuristic. The code that I currently have looks like the following: Class<? extends MergeHeuristic> heuristicRequest = _heuristicQueue.pop(); MergeHeuristic heuristic = null; if(heuristicRequest == AdjacentMACs.class) heuristic = new AdjacentMACs(_parent); if(heuristicRequest == SimilarInterfaceNames.class) heuristic = new SimilarInterfaceNames(_parent); if(heuristicRequest == SameMAC.class) heuristic = new SameMAC(_parent); Is there any way to simplify that to dynamically instantiate the class, something along the lines of: heuristic = new heuristicRequest.somethingSpecial(); That would flatten that block of if statements.

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  • Java swing doesn't show changes to source

    - by out_sider
    I'm using Java Swing graphical editor with netbeans to make my project...but using it brings some limitations like I can't add to a jpanel an image,using java swing options. So i'll need to code it, implementing a new jPanel. My problem is that the code generated by the java swing graphical editor can't be edited so instead of adding the new JPanel code in the initComponents() section I'm doing it after this function is called in the constructor of my main JPanel. But any code I add is not recognized by the "Designer" which means that after making my coded objects I can't use them in the "Designer" and everything must be coded, which is a pain considering how much easier is previewing and moving elements in the "Designer" tool. How can I code what I want but steel appear in the "DEsigner"? Thx in advance

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