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  • Factory Method pattern and public constructor

    - by H4mm3rHead
    Hi, Im making a factory method that returns new instances of my objects. I would like to prevent anyone using my code from using a public constructor on my objects. Is there any way of doing this? How is this typically accomplished: public abstract class CarFactory { public abstract ICar CreateSUV(); } public class MercedesFactory : CarFactory { public override ICar CreateSUV() { return new Mercedes4WD(); } } I then would like to limit/prevent the other developers (including me in a few months) from making an instance of Mercedes4WD. But make them call my factory method. How to?

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  • Constructor invocation returned null: what to do?

    - by strager
    I have code which looks like: private static DirectiveNode CreateInstance(Type nodeType, DirectiveInfo info) { var ctor = nodeType.GetConstructor(new[] { typeof(DirectiveInfo) }); if(ctor == null) { throw new MissingMethodException(nodeType.FullName, "ctor"); } var node = ctor.Invoke(new[] { info }) as DirectiveNode; if(node == null) { // ???; } return node; } I am looking for what to do (e.g. what type of exception to throw) when the Invoke method returns something which isn't a DirectiveNode or when it returns null (indicated by // ??? above). (By the method's contract, nodeType will always describe a subclass of DirectiveNode.) I am not sure when calling a constructor would return null, so I am not sure if I should handle anything at all, but I still want to be on the safe side and throw an exception if something goes wrong.

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  • Singleton constructor question

    - by gillyb
    Hi, I created a Singleton class in c#, with a public property that I want to initialize when the Singleton is first called. This is the code I wrote : public class BL { private ISessionFactory _sessionFactory; public ISessionFactory SessionFactory { get { return _sessionFactory; } set { _sessionFactory = value; } } private BL() { SessionFactory = Dal.SessionFactory.CreateSessionFactory(); } private object thisLock = new object(); private BL _instance = null; public BL Instance { get { lock (thisLock) { if (_instance == null) { _instance = new BL(); } return _instance; } } } } As far as I know, when I address the Instance BL object in the BL class for the first time, it should load the constructor and that should initialize the SessionFactory object. But when I try : BL.Instance.SessionFactory.OpenSession(); I get a Null Reference Exception, and I see that SessionFactory is null... why?

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  • Constructor invokation returned null: what to do?

    - by strager
    I have code which looks like: private static DirectiveNode CreateInstance(Type nodeType, DirectiveInfo info) { var ctor = nodeType.GetConstructor(new[] { typeof(DirectiveInfo) }); if(ctor == null) { throw new MissingMethodException(nodeType.FullName, "ctor"); } var node = ctor.Invoke(new[] { info }) as DirectiveNode; if(node == null) { // ???; } return node; } I am looking for what to do (e.g. what type of exception to throw) when the Invoke method returns something which isn't a DirectiveNode or when it returns null (indicated by // ??? above). (By the method's contract, nodeType will always describe a subclass of DirectiveNode.) I am not sure when calling a constructor would return null, so I am not sure if I should handle anything at all, but I still want to be on the safe side and throw an exception if something goes wrong.

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  • Is this class + constructor definition pattern overly redundant?

    - by Protector one
    I often come across a pattern similar to this: class Person { public string firstName, lastName; public Person(string firstName, string lastName) { this.firstName = firstName; this.lastName = lastName; } } This feels overly redundant (I imagine typing "firstName" once, instead of thrice could be enough…), but I can't think of a proper alternative. Any ideas? Maybe I just don't know about a certain design pattern I should be using here? Edit - I think I need to elaborate a little. I'm not asking how to make the example code "better", but rather, "shorter". In its current state, all member names appear 3 times (declaration, initialization, constructor arguments), and it feels rather redundant. So I'm wondering if there is a pattern (or semantic sugar) to get (roughly) the same behavior, but with less bloat. I apologize for being unclear initially.

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • PDF has garbled text when copy pasting

    - by ngm
    I'm trying to copy and paste text from a PDF file. However, whenever I paste the original text it is a huge mess of garbled characters. The text looks like the following (this is just one small extract): 4$/)5=$13! ,4&1*%-! )5'$! 1$2$)&,$40! 65))! .*5)1! -#$! )/'8*/8$03! (4/+$6&4;0!/'1!-&&)0!*0$1!.9!/,,)5%/-5&'!1$2$)&,$403!5'!+*%#!-#$! 0/+$!6/9! -#/-! &,$4/-5'8! 090-$+! 1$2$)&,$40! .*5)1!1$25%$! 1452$40! /'1! &-#$4! 090-$+! 0&(-6/4$! %&+,&'$'-0! *0$1! .9! /,,)5%/-5&'! 1$2$)&,$40!-&1/97!"#$!+5M!&(!,4&1*%-!)5'$!/'1!,4&1*%-!1$2$)&,$40! 65))! .$!+*%#!+&4$! $2$')9! ./)/'%$13! #&6$2$43! -#/'! -#$!+5M! &(! &,$4/-5'8!090-$+!/'1!/,,)5%/-5&'!1$2$)&,$40!-&1/97! )*+*+, C<88,?>8513AG<5A14, I've tried it in both Adobe and Foxit PDF readers. I did a 'Save as text' in Adobe Reader and the resultant text file is the same garbled text. Any ideas how I can get this text out non-garbled? (Other than manual typing... there's a lot of text to extract.)

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  • PDF has garbled text when copy pasting

    - by ngm
    I'm trying to copy and paste text from a PDF file. However, whenever I paste the original text it is a huge mess of garbled characters. The text looks like the following (this is just one small extract): 4$/)5=$13! ,4&1*%-! )5'$! 1$2$)&,$40! 65))! .*5)1! -#$! )/'8*/8$03! (4/+$6&4;0!/'1!-&&)0!*0$1!.9!/,,)5%/-5&'!1$2$)&,$403!5'!+*%#!-#$! 0/+$!6/9! -#/-! &,$4/-5'8! 090-$+! 1$2$)&,$40! .*5)1!1$25%$! 1452$40! /'1! &-#$4! 090-$+! 0&(-6/4$! %&+,&'$'-0! *0$1! .9! /,,)5%/-5&'! 1$2$)&,$40!-&1/97!"#$!+5M!&(!,4&1*%-!)5'$!/'1!,4&1*%-!1$2$)&,$40! 65))! .$!+*%#!+&4$! $2$')9! ./)/'%$13! #&6$2$43! -#/'! -#$!+5M! &(! &,$4/-5'8!090-$+!/'1!/,,)5%/-5&'!1$2$)&,$40!-&1/97! )*+*+, C<88,?>8513AG<5A14, I've tried it in both Adobe and Foxit PDF readers. I did a 'Save as text' in Adobe Reader and the resultant text file is the same garbled text. Any ideas how I can get this text out non-garbled? (Other than manual typing... there's a lot of text to extract.)

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  • TSM Backup Fails with VSS

    - by user176320
    Since we rebuilt our servers to windows servers 2008 x64 r2 we have perpetual problems with scheduled backup (shadow copy). In the Application event log, the following events are logged on both nodes: The description for Event ID 4112 from source TsmVssPlugin cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer. If the event originated on another computer, the display information had to be saved with the event. The following information was included with the event: VSS processing encountered error 'VSS_E_UNEXPECTED_PROVIDER_ERROR' in the Volume Shadow Copy API 'AddToSnapshotSet'. For more information, see the IBM Tivoli Storage Manager client error log. Re installing TSM didn't change anything and still logging same events. TSM Error log file shows following: ANS1327W The snapshot operation for 'C:' failed with error code: -1. ANS5250E An unexpected error was encountered. TSM function name : BaStartSnapshot TSM function : initializeSnapshotSet() failed, check Microsoft Application event log for VSS errors TSM return code : -1

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  • VSS Post Backup failures for Virtual Server 2005 R2 SP1 virtual machines

    - by califguy4christ
    We've been seeing strange errors with Volume Shadow Copy services on our Virtual Server 2005 R2 SP1 host. It appears to be failing on a strange mountpoint in the C:\WINDOWS\Temp\ folders, which I believe is used by VSS to mount a writeable image file. To summarize: The Microsoft Virtual Server 2005 Writer continually goes into a failed retryable state The Virtual Server log reports errors during the Post Backup phase VSS reports errors backing up a mount point of unknown origins The mount point causes NTFS and ftdisk errors The host is x86 Windows Server 2003 Standard, SP2. The virtual machine is the same. Both use basic disks. Here is the writer state: Writer name: 'Microsoft Virtual Server 2005 Writer' Writer Id: {76afb926-87ad-4a20-a50f-cdc69412ddfc} Writer Instance Id: {78df98e2-bf19-4804-890b-15865efef3bd} State: [11] Failed Last error: Retryable error From the Virtual Server log: Virtual Server - Vss Writer - Event ID: 1035: The VSS writer for Virtual Server failed during the PostBackup phase. The guest shadow copies did not get exposed on the host machine, after mounting all the virtual hard disks of the virtual machine VMACHINE. From the Application log: VSS - None - Event ID: 12290: Volume Shadow Copy Service warning: GetVolumeInformationW( \\?\Volume{fb84bae7-87f5-11dd-9832-001cc4961ca6}\,NULL,0, NULL,NULL,[0x00000000], , 260) == 0x0000045d. hr = 0x00000000. From the System log: Ntfs - Disk - Event ID: 55: The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume C:\WINDOWS\Temp\ {fb84bae7-87f5-11dd-9832-001cc49.... My current theory is that VSS creates a mount point for an image file of the VHD, then the software panics for some reason, leaving everything in an inconsistent state. Removing the mount point doesn't resolve the problem. All of the other disks check out fine with CHKDSK. There's no exclusion option for VHDs or to turn off online backups. Has anyone seen this kind of thing before or point me in the right direction for getting more information about the mount point and it's origins? I haven't been able to trace what application is creating that mount point.

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  • Long 'pause' after copying large files on windows 2008

    - by Ian
    I have a mystery regarding pauses after file copies on windows server 2088 (and other releases) When copying large files, like vhds, to locally attached USB disks I often see a long pause after the copy has completed 100%. As an example: robocopying vhd files. The bytes read/written count matches the vhd file size and robocopy shows 100% but it pauses for several minutes. If I do nothing it will continue, but I will have to wait for quite some time - about the same amount of time as it took to get to 100%. The bytes read/bytes written counters for robocopy do not change. My first thought was that the AV had to scan it, but I'm looking at a machine right now which doesn't have an AV installed and this is occurring, so impossible. No other processes are showing read/write byte counts as going up. The behavior is the same if I use the copy command or xcopy. I've seen this on other systems but have never worked out what the cause is. Anyone got any suggestions as to what might be going on?

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