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  • How to extract terms of specific data constructor from a list in Haskell

    - by finnsson
    A common problem I got in Haskell is to extract all terms in a list belonging to a specific data constructor and I'm wondering if there are any better ways than the way I'm doing it at the moment. Let's say you got data Foo = Bar | Goo , the list foos = [Bar, Goo, Bar, Bar, Goo] and wish to extract all Goos from foos. At the moment I usually do something like goos = [Goo | Goo <- foos] and all is well. The problem is when Goo got a bunch of fields and I'm forced to write something like goos = [Goo a b c d e f | Goo a b c d e f <- foos] which is far from ideal. How you do usually handle this problem?

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  • python: calling constructor from dictionary?

    - by Jason S
    I'm not quite sure of the terminology here so please bear with me.... Let's say I have a constructor call like this: machineSpecificEnvironment = Environment( TI_C28_ROOT = 'C:/appl/ti/ccs/4.1.1/ccsv4/tools/compiler/c2000', JSDB = 'c:/bin/jsdb/jsdb.exe', PYTHON_PATH = 'c:/appl/python/2.6.4', ) except I would like to replace that by an operation on a dictionary provided to me: keys = {'TI_C28_ROOT': 'C:/appl/ti/ccs/4.1.1/ccsv4/tools/compiler/c2000', 'JSDB': 'c:/bin/jsdb/jsdb.exe', 'PYTHON_PATH': 'c:/appl/python/2.6.4'} machineSpecificEnvironment = Environment( ... what do I put here? it needs to be a function of "keys" ... ) How can I do this?

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  • Result of expression 'xxxx' is not a constructor in JS

    - by Pselus
    Trying to create an object in Javascript (for Appcelerator/Titanium). The "object" is defined like this: function server () { this.cacheimages = 0; this.login = ""; this.name = ""; this.root = ""; this.signup = ""; this.useimages = 0; this.userexists = ""; this.isdefault = 0; return this; } In the same file, in another function when I run this line: var server = new server(); I get the error Result of expression 'server' is not a constructor. I have tried it with and without the "return" line, neither work. What am I doing wrong?

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  • How to deal with constructor argument names?

    - by Bane
    Say I have a class that has some properties, like x, y, width and height. In its constructor, I couldn't do this: class A { public: A(int, int, int, int); int x; int y; int width; int height; }; //Wrong and makes little sense name-wise: A::A(int x, int y, int width, int height) { x = x; y = y; width = width; height = height; } First of all, this doesn't really make sense. Second, x, y, width and height become some weird values (-1405737648) when compiled using g++. It does work, however, if I append "a" to the argument names. What is the optimal way of solving these naming conflicts?

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  • Replacing a website on a Tomcat Server with a static HTML website

    - by Ashin Mandal
    I made a small static website for my client and now they want me to replace their present dynamic website with the static one. They have Ubuntu with SSH installed on the remote location. Their existing website is running on a Tomcat6 server and the site root is in "/var/lib/tomcat6/webapps/ROOT/". My website consists of just static HTML pages. How can I reconfigure/ replace the present website with the one I made? Should I just stop the server and replace the files in the site root with my files?

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  • Running a method after the constructor of any derived class

    - by Alexey Romanov
    Let's say I have a Java class abstract class Base { abstract void init(); ... } and I know every derived class will have to call init() after it's constructed. I could, of course, simply call it in the derived classes' constructors: class Derived1 extends Base { Derived1() { ... init(); } } class Derived2 extends Base { Derived2() { ... init(); } } but this breaks "don't repeat yourself" principle rather badly (and there are going to be many subclasses of Base). Of course, the init() call can't go into the Base() constructor, since it would be executed too early. Any ideas how to bypass this problem? I would be quite happy to see a Scala solution, too.

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  • Bad Design? Constructor of composition uses `this`

    - by tanascius
    Example: class MyClass { Composition m_Composition; void MyClass() { m_Composition = new Composition( this ); } } I am interested in using depenency-injection here. So I will have to refactor the constructor to something like: void MyClass( Composition composition ) { m_Composition = composition; } However I get a problem now, since the Composition-object relies on the object of type MyClass which is just created. Can a dependency container resolve this? Is it supposed to do so? Or is it just bad design from the beginning on?

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  • No Parameterless Constructor defined for - ViewModel with UOW

    - by TheVillageIdiot
    I have a view model class which uses UnitOfWork to some database operations like fetching of items to create select lists and IPrincipal for some auditing (like modified by etc.). It cannot work without this UOW. I have configured my web site to use Ninject to inject UOW into Controllers. From controller I pass this UOW when creating view model. But when performing POST operation I am getting No parameterless constructor defined for this object. I have few SelectList type of properties which I have excluded with Bind attribute. How can I overcome this problem? Can I configure Ninject to create the objects of this type and make ModelBinder use it?

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  • C++: Avoid .cpp files with only an empty (de)constructor

    - by Martijn Courteaux
    Hi, When I have a header file like this: #ifndef GAMEVIEW_H_ #define GAMEVIEW_H_ #include <SDL/SDL.h> class GameView { public: GameView(); virtual ~GameView(); virtual void Update() = 0; virtual void Render(SDL_Surface* buffer) = 0; }; #endif /* GAMEVIEW_H_ */ I need to create a .cpp file like this: #include "GameView.h" GameView::~GameView() { } GameView::GameView() { } This is a bit stupid. Just a .cpp file for an empty constructor and deconstructor. I want to implement that method simply in the header file. That is much cleaner. How to do this?

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  • C++ static classes & shared_ptr memory leaks

    - by HardCoder1986
    Hello! I can't understand why does the following code produce memory leaks (I am using boost::shared_ptr with static class instance). Could someone help me? #include <crtdbg.h> #include <boost/shared_ptr.hpp> using boost::shared_ptr; #define _CRTDBG_MAP_ALLOC #define NEW new(_NORMAL_BLOCK, __FILE__, __LINE__) static struct myclass { static shared_ptr<int> ptr; myclass() { ptr = shared_ptr<int>(NEW int); } } myclass_instance; shared_ptr<int> myclass::ptr; int main() { _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF | _CRTDBG_CHECK_ALWAYS_DF | _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG)); return 0; }

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  • C# Generic List constructor gives me a MethodAccessException

    - by evilfred
    Hi, I make a list in my code like so: List<IConnection> connections = new List<IConnection>(); where IConnection is my own interface. This is in a .NET 2.0 executable. If I run the code on my machine (with lots of .Net versions installed) it works fine. If I run it on my test machine (which only has .NET 3.5 SP1 installed) then I get a MethodAccessException in the System.Collections.Generic.List constructor. Any ideas what could be going wrong?

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  • Call a C++ constructor from an Objective C class

    - by syvex
    How can I call a C++ constructor from inside an Objective C class? class CppClass { public: CppClass(int arg1, const std::string& arg2): _arg1(arg1), _arg2(arg2) { } // ... private: int _arg1; std::string _arg2; }; @interface ObjC: NSObject { CppClass _cppClass; } @end @implementation ObjC - (id)init { self = [super init]; if ( self ) { // what is the syntax to call CppClass::CppClass(5, "hello") on _cppClass? } return self; } @end

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  • Add static const data to a struct already defined

    - by Kyle
    Since static const data inside a class is really just namespace sugar for constants I would think that struct A { float a; struct B { static const int b = a; }; }; would be equivalent to struct A { float a; }; struct A::B { static const int b = a; }; or something similar. Is something like this possible in C++? It would be useful for me to be able to tag class definitions that I'm pulling in from third party libraries with information like this.

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  • C++ Add this pointer to a container by calling it in base class constructor

    - by vivekeviv
    class Base { public: Base (int a, int b); private: int a,b; }; class Derived1 { public: Derived1():base(1,2){} }; similarly Derived2, Derived 3 which doesnt contain any data members on its own Now i need to contain these derived objects in a singleton, so i was thinking to call this in base constructor like Base::Base(int a, int b) { CBaseMgr::GetInstance()->AddtoVector(this); } so now if i construct Derived d1, d2, d3 etc. will the Singleton's container contain all derived objects? My doubt is can i do this adding of objects to container in base ctor or should i do in derived ctor.?

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  • Static dictionary in .Net Thread safety

    - by Emmanuel
    Reading msdn documentation for dictionaries it says : "Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe." Those this mean that with a dictionary such as this : static object syncObject = new object(); static Dictionary<string,MyObject> mydictionary= new Dictionary<string, MyObject>(); Is doing something like the code below unnecessary? lock (syncObject) { context = new TDataContext(); mydictionary.Add("key", myObject); }

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  • static effect on python

    - by fatai
    how we can construct static effect on python instead of using class and global ? not like that one : global a a = [] #simple ex ; fonk ( a , b , d) x = 1 a.append ( x) EDIT: I want to create temporary memory , if I exit the function namely fonk , I want to save change as list on temporary memory . We can do that demand only put static keyword in front of data type but in python , we dont have static, so I want that effect in python . Therefore , how can I do ? As above code say "a" represents temporary memory

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  • Force to reimplement a static function in inherit classes

    - by pacopepe
    Hi, I have a program in C++ with plugins (dynamic libs). In the main program, I want to execute a static function to check if i can create a object of this type. An example without dynamic libs (aren't neccesary to understand the problem): #include "libs/parent.h" #include "libs/one.h" #include "libs/two.h" int main(int argc, char * argv[]) { Parent obj; if (One.match(argv[1])) { obj = new One(); else if (Two.match(argv[1])) { obj = new Two(); } Now, i have a interface class named Parent. All plugins inherit from this class. Ideally, I have a virtual static function in Parent named match, and all the plugins need to reimplement this function. The problem with this code is that i can't do a static virtual function in C++, so i don't know how to solve the problem. Sorry for mi english, i did my best

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  • C++ Declaring an uninitialized variable without a null constructor

    - by xbonez
    Consider the DUPoint class, whose declaration appears below. Assume this code appears in a file named DUPoint.h: #include <string> class DUPoint { public: DUPoint (int x, int y); int getX () const; int getY () const; void setX (int x); void setY (int y); void print(); private: int x_; int y_; }; Is it true that you cannot declare an uninitialized DUPoint variable with a statement such as DUPoint P; using this class as currently configured because it has no null constructor?

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  • Access a static variable by $var::$reference

    - by chuckg
    I am trying to access a static variable within a class by using a variable class name. I'm aware that in order to access a function within the class, you use call_user_func(): class foo { function bar() { echo 'hi'; } } $class = "foo"; all_user_func(array($class, 'bar')); // prints hi However, this does not work when trying to access a static variable within the class: class foo { public static $bar = 'hi'; } $class = "foo"; call_user_func(array($class, 'bar')); // nothing echo $foo::$bar; // invalid How do I get at this variable? Is it even possible? I have a bad feeling this is only available in PHP 5.3 going forward and I'm running PHP 5.2.6. Thanks.

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  • objective-c - calling one constructor from another

    - by synic
    Say you had the following two constructors: - (id)initWithTitle:(NSString *)title; - (id)initWithTitle:(NSString *)title page:(NSString *)page; The second constructor is no different from the first, except that it sets up the member variable "page". Since it basically has to do the same thing, is there a way to call the first one from the second one to reduce code duplication, or do you have to set up a third method to do the common tasks? I'm talking about something similar to this, though I doubt this will work: - (id)initWithTitle:(NSString *)_title { if(self = [super init]) { self.title = _title; } return self; } - (id)initWithTitle:(NSString *)_title page:(NSString *)_page { if(self = [self initWithTitle:_title]) { self.page = _page; } return self; }

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  • C# Generic new() constructor problem

    - by LB
    I'm trying to create a new object of type T via its constructor when adding to the list. I'm getting a compile error: The correct error message is: 'T': cannot provide arguments when creating an instance of a variable But it does! Any ideas? public static string GetAllItems<T>(...) where T : new() { ... List<T> tabListItems = new List<T>(); foreach (ListItem listItem in listCollection) { tabListItems.Add(new T(listItem)); // error here. } ... }

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  • How to initialize static const char array for ASCII codes [C++]

    - by Janney
    I want to initialize a static const char array with ASCII codes in a constructor, here's my code: class Card { public: Suit(void) { static const char *Suit[4] = {0x03, 0x04, 0x05, 0x06}; // here's the problem static const string *Rank[ 13 ] = {'A', '2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K'}; // and here. } However i got a whole lot of errors stating that 'initializing' : cannot convert from 'char' to 'const std::string *' 'initializing' : cannot convert from 'int' to 'const std::string *' please help me! Thank you so much.

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  • Call subclass constructor from abstract class in Java

    - by Joel
    public abstract class Parent { private Parent peer; public Parent() { peer = new ??????("to call overloaded constructor"); } public Parent(String someString) { } } public class Child1 extends parent { } public class Child2 extends parent { } When I construct an instance of Child1, I want a "peer" to automatically be constructed which is also of type Child1, and be stored in the peer property. Likewise for Child2, with a peer of type Child2. The problem is, on the assignment of the peer property in the parent class. I can't construct a new Child class by calling new Child1() because then it wouldn't work for Child2. How can I do this? Is there a keyword that I can use that would refer to the child class? Something like new self()?

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  • Static routing on a TP-Link TL-WR1043ND

    - by igor
    My home network setup looks like this: Both routers are TP-Link TL-WR1043ND routers. The basement router handles all devices in the house that are connected via cable, handing out addresses for the 10.89.49.0/24 network via DHCP. Wireless doesn’t really work from the basement, as the signal is too weak, so I have disabled it. To do WiFi, I have added a second (identical) router downstairs. On the WAN side it is assigned the 10.89.49.101 IP address from the basement router, and on its LAN it provides the 10.89.7.0/24 network. Basic internet access works flawlessly from any device this way. I am now facing the problem that I am not able to communicate (e.g. SSH) between all devices, wired or wireless. I am able to connect from a wireless device to a wired device, for example SSH-ing from 10.89.7.X to 10.89.49.Y, but it doesn’t work the other way round—despite the fact that I have added a static route to the basement router: Does anybody have any idea on how to solve it? Both routers have already been upgraded to use the most recent firmware from TP-Link.com (Build 110429), to no avail. Errata: I would like to stick with the official firmware, switching to something like DD-WRT or OpenWrt only as a last resort.

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  • nginx+passenger +static websites= problems

    - by Eugene K
    I've got a Rails app that nginx serves through passenger. I'd also like to serve some static content for a different domain name. But when I add another server block to my config, both websites become unavailable returning HTTP 204. What have I done wrong? What can I do to fix it? Here's the http block of my nginx.conf: https://gist.github.com/4243256 Here's what I added : server { listen 80; server_name website2; root /var/www/website2; location / { index index.html; } } It's going to be a Rails app as well at some point in the future (though I'm not really sure about that, maybe I'm going to use a different back-end solution.) Either way, I don't want anything dynamic to eat away the resources just yet. As of now, this website consists of nothing but index.html and stylesheet.css files in the root directory. What should I do? Thank you in advance. Sincerely yours, Eugene.

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