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• How to use Private Inheritence aka C++ in C# and Why not it is present in C#

  - by Vijay

  I know that private inheritance is supported in C++ and only public inheritance is supported in C#. I also came across an article which says that private inheritance usually defines a HAS-A relationship and kind of an aggregation relationship between the classes. EDIT: C++ code for private inheritance: The "Car has-a Engine" relationship can also be expressed using private inheritance: class Car : private Engine { // Car has-a Engine public: Car() : Engine(8) { } // Initializes this Car with 8 cylinders using Engine::start; // Start this Car by starting its Engine }; Now, Is there a way to create a HAS-A relationship between C# classes which is one of the thing that I would like to know - HOW? Another curious question is why doesn't C# support the private (and also protected) inheritance ? - Is not supporting multiple implementation inheritance a valid reason or any other? Is private (and protected) inheritance planned for future versions of C#? Will supporting the private (and protected) inheritance in C# make it a better and widely used language?

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• Outside classes accessing package-private methods

  - by Jake

  Suppose I have a class in my package org.jake and it has a method with default access (no modifier). Then the method is visible inside the package only. However, when someone receives the jar of my framework, what is to stop them from writing a new class, declaring its package as org.jake, and using my supposedly invisible method? In other words, is there anything I can do to prevent them from doing that?

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• iPhone- Linking private framework graphicsservices.framework

  - by Adam

  Anyone know how To link graphicsservices.framework into an app? Do I need to jailbreak my iPhone? Using 3.1.3

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• C# Reflection - Casting private Object field

  - by alhazen

  I have the following classes: public class MyEventArgs : EventArgs { public object State; public MyEventArgs (object state) { this.State = state; } } public class MyClass { // ... public List<string> ErrorMessages { get { return errorMessages; } } } When I raise my event, I set 'State' of the MyEventArgs object to an object of type MyClass. I'm trying to retrieve ErrorMessages by reflection in my event handler: public static void OnEventEnded(object sender, EventArgs args) { Type type = args.GetType(); FieldInfo stateInfo = type.GetField("State"); PropertyInfo errorMessagesInfo = stateInfo.FieldType.GetProperty("ErrorMessages"); object errorMessages = errorMessagesInfo.GetValue(null, null); } But this returns errorMessagesInfo as null (even though stateInfo is not null). Is it possible to retrieve ErrorMessages ? Thank you

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• C# private (hidden) base class

  - by Loadmaster

  It is possible to make a C# base class accessible only within the library assembly it's compiled into, while making other subclasses that inherit from it public? For example: using System.IO; class BaseOutput: Stream // Hidden base class { protected BaseOutput(Stream o) { ... } ...lots of common methods... } public class MyOutput: BaseOutput // Public subclass { public BaseOutput(Stream o): base(o) { ... } public override int Write(int b) { ... } } Here I'd like the BaseOutput class to be inaccessible to clients of my library, but allow the subclass MyOutput to be completely public. I know that C# does not allow base classes to have more restrictive access than subclasses, but is there some other legal way of achieving the same effect?

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• Why does Amazon release private keys instead of public keys?

  - by S37H

  My brain is wrapped around the axle on public and private keys. When you create a cloud server (instance) on Amazon's EC2 service and then want to connect to it via SSH, Amazon requires you to download private a key to make the connection. Doesn't the idea behind public/private key suggest that Amazon should be require you to download a public one? Further, if I set up an SFTP server for a customer to use, should I be installing their key on the server or giving them a key from the server? In either case, should it be a public or private key?

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• Template neglects const (why?)

  - by Gabriel

  Does somebody know, why this compiles?? template< typename TBufferTypeFront, typename TBufferTypeBack = TBufferTypeFront> class FrontBackBuffer{ public: FrontBackBuffer( const TBufferTypeFront front, const TBufferTypeBack back): ////const reference assigned to reference??? m_Front(front), m_Back(back) { }; ~FrontBackBuffer() {}; TBufferTypeFront m_Front; ///< The front buffer TBufferTypeBack m_Back; ///< The back buffer }; int main(){ int b; int a; FrontBackBuffer<int&,int&> buffer(a,b); // buffer.m_Back = 33; buffer.m_Front = 55; } I compile with GCC 4.4. Why does it even let me compile this? Shouldn't there be an error that I cannot assign a const reference to a non-const reference?

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• C++ unrestricted union workaround

  - by Chris

  #include <stdio.h> struct B { int x,y; }; struct A : public B { // This whines about "copy assignment operator not allowed in union" //A& operator =(const A& a) { printf("A=A should do the exact same thing as A=B\n"); } A& operator =(const B& b) { printf("A = B\n"); } }; union U { A a; B b; }; int main(int argc, const char* argv[]) { U u1, u2; u1.a = u2.b; // You can do this and it calls the operator = u1.a = (B)u2.a; // This works too u1.a = u2.a; // This calls the default assignment operator >:@ } Is there any workaround to be able to do that last line u1.a = u2.a with the exact same syntax, but have it call the operator = (don't care if it's =(B&) or =(A&)) instead of just copying data? Or are unrestricted unions (not supported even in Visual Studio 2010) the only option?

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• Pattern for database-wrapper in java

  - by Space_C0wb0y

  I am currently writing a java-class that wraps an SQLite database. This class has two ways to be instantiated: Open an existing database. Create a new database. This is what I cam up with: public class SQLiteDatabaseWrapper { public static SQLiteDatabaseWrapper openExisting(File PathToDB) { return new SQLiteDatabaseWrapper(PathToDB); } public static SQLiteDatabaseWrapper createNew(File PathToDB) { CreateAndInitializeNewDatabase(PathToDB); return new SQLiteDatabaseWrapper(PathToDB); } private SQLiteDatabaseWrapper(File PathToDB) { // Open connection and setup wrapper } } Is this the way to go in Java, or is there any other best practice for this situation?

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• When are Private Clouds a Good Idea?

  This article is taken from the book "The Cloud at Your Service." The authors define the term private cloud and discuss issues to consider before opting for private clouds and concerns about deploying a private cloud.

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• When are Private Clouds a Good Idea?

  This article is taken from the book "The Cloud at Your Service." The authors define the term private cloud and discuss issues to consider before opting for private clouds and concerns about deploying a private cloud.

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• Everything you wanted to know about private database clouds, but were afraid to ask

  - by B R Clouse

  Private Database Clouds have come into their own, and will be a prominent topic at Oracle OpenWorld this year.  In fact while most exhibits will be open from Monday through Wednesday, Private Database Clouds will be available starting Sunday afternoon all the way through Thursday evening.  In addition to the demonstration choices, numerous speaking sessions address Private Database Clouds, including a general session on Monday.  The demos and discussions will help  you chart your path to cloud computing.

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• C++ keeping a list of objects and calling a contructor through another function

  - by Nona Urbiz

  why isnt my object being created? When I do it like so, I am told error C2065: 'AllReferrals' : undeclared identifier as well as error C2228: left of '.push_back' must have class/struct/union. If I put the list initialization before the class I get error C2065: 'AllReferrals' : undeclared identifier. Thanks! #include <iostream> #include <fstream> #include <regex> #include <string> #include <list> #include <map> using namespace std; using namespace tr1; class Referral { public: string url; map<string, int> keywords; static bool submit(string url, string keyword, int occurrences) { //if(lots of things i'll later add){ Referral(url, keyword, occurrences); return true; //} //else // return false; } private: list<string> urls; Referral(string url, string keyword, int occurrences) { url = url; keywords[keyword] = occurrences; AllReferrals.push_back(this); } }; static list<Referral> AllReferrals; int main() { Referral::submit("url", "keyword", 1); cout << AllReferrals.size(); cout << "\n why does that ^^ say 0 (help me make it say one)?"; cout << "\n and how can i AllReferrals.push_back(this) from my constructor?"; cout << " When I do it like so, I am told error C2065: 'AllReferrals' : undeclared identifier"; cout << " as well as error C2228: left of '.push_back' must have class/struct/union."; cout << " If I put the list initialization before the class I get error C2065: 'AllReferrals' : undeclared identifier."; cout << "\n\n\t Thanks!"; getchar(); }

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• In a WPF Application, What happens after my code in the main window constructor is executed?

  - by KyleGobel

  I'm wondering what happens after the constructor is done executing my code, because the constructor is taking like 10 seconds to run on a cold start up, but according to the profiler, my code is done executing in like 2 seconds. Also stepping through the code in the debugger, after the last line of my constructor, I sit there and wait for 7-8 seconds before the window appears. Why is this? If the window is loading content or something, why isn't it displayed on the screen, done loading or not after the constructor finishes it's job? What's the hold up? (or how do i figure that out)

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• How to use reflection to get a default constructor?

  - by Qwertie

  I am writing a library that generates derived classes of abstract classes dynamically at runtime. The constructor of the derived class needs a MethodInfo of the base class constructor so that it can invoke it. However, for some reason Type.GetConstructor() returns null. For example: abstract class Test { public abstract void F(); } public static void Main(string[] args) { ConstructorInfo constructor = typeof(Test).GetConstructor( BindingFlags.NonPublic | BindingFlags.Public, null, System.Type.EmptyTypes, null); // returns null! } Note that GetConstructor returns null even if I explicitly declare a constructor in Test, and even if Test is not abstract.

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• Is there any way to manipulate variables passed in to a child class constructor before passing it of

  - by Matt

  Hi, Is there any way to delay calling a superclass constructor so you can manipulate the variables first? Eg. public class ParentClass { private int someVar; public ParentClass(int someVar) { this.someVar = someVar; } } public class ChildClass : ParentClass { public ChildClass(int someVar) : base(someVar) { someVar = someVar + 1 } } I want to be able to send the new value for someVar (someVar + 1) to the base class constructor rather than the one passed in to the ChildClass constructor. Is there any way to do this? Thanks, Matt

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• Is it possible to defer member initialization to the constructor body?

  - by Kjir

  I have a class with an object as a member which doesn't have a default constructor. I'd like to initialize this member in the constructor, but it seems that in C++ I can't do that. Here is the class: #include <boost/asio.hpp> #include <boost/array.hpp> using boost::asio::ip::udp; template<class T> class udp_sock { public: udp_sock(std::string host, unsigned short port); private: boost::asio::io_service _io_service; udp::socket _sock; boost::array<T,256> _buf; }; template<class T> udp_sock<T>::udp_sock(std::string host = "localhost", unsigned short port = 50000) { udp::resolver res(_io_service); udp::resolver::query query(udp::v4(), host, "spec"); udp::endpoint ep = *res.resolve(query); ep.port(port); _sock(_io_service, ep); } The compiler tells me basically that it can't find a default constructor for udp::socket and by my research I understood that C++ implicitly initializes every member before calling the constructor. Is there any way to do it the way I wanted to do it, or is it too "Java-oriented" and not feasible in C++? I worked around the problem by defining my constructor like this: template<class T> udp_sock<T>::udp_sock(std::string host = "localhost", unsigned short port = 50000) : _sock(_io_service) { udp::resolver res(_io_service); udp::resolver::query query(udp::v4(), host, "spec"); udp::endpoint ep = *res.resolve(query); ep.port(port); _sock.bind(ep); } So my question is more out of curiosity and to better understand OOP in C++

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• Is it OK to write a constructor which does nothing?

  - by Roman

  To use methods of a class I need to instantiate a class. At the moment the class has not constructor (so I want to write it). But than I have realized that the constructor should do nothing (I do need to specify values of fields). In this context I have a question if it is OK to write constructor which does nothing. For example: public Point() { }

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• Why can't I create an abstract constructor on an abstract C# class?

  - by Anthony D

  I am creating an abstract class. I want each of my derived classes to be forced to implement a specific signature of constructor. As such, I did what I would have done has I wanted to force them to implement a method, I made an abstract one. public abstract class A { abstract A(int a, int b); } However I get a message saying the abstract modifier is invalid on this item. My goal was to force some code like this. public class B : A { public B(int a, int b) : base(a, b) { //Some other awesome code. } } This is all C# .NET code. Can anyone help me out? Update 1 I wanted to add some things. What I ended up with was this. private A() { } protected A(int a, int b) { //Code } That does what some folks are saying, default is private, and the class needs to implement a constructor. However that doesn't FORCE a constructor with the signature A(int a, int b). public abstract class A { protected abstract A(int a, int b) { } } Update 2 I should be clear, to work around this I made my default constructor private, and my other constructor protected. I am not really looking for a way to make my code work. I took care of that. I am looking to understand why C# does not let you do this.

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• Implicit constructor available for all types derived from Base excepted the current type?

  - by Vincent

  The following code sum up my problem : template<class Parameter> class Base {}; template<class Parameter1, class Parameter2, class Parameter> class Derived1 : public Base<Parameter> { }; template<class Parameter1, class Parameter2, class Parameter> class Derived2 : public Base<Parameter> { public : // Copy constructor Derived2(const Derived2& x); // An EXPLICIT constructor that does a special conversion for a Derived2 // with other template parameters template<class OtherParameter1, class OtherParameter2, class OtherParameter> explicit Derived2( const Derived2<OtherParameter1, OtherParameter2, OtherParameter>& x ); // Now the problem : I want an IMPLICIT constructor that will work for every // type derived from Base EXCEPT // Derived2<OtherParameter1, OtherParameter2, OtherParameter> template<class Type, class = typename std::enable_if</* SOMETHING */>::type> Derived2(const Type& x); }; How to restrict an implicit constructor to all classes derived from the parent class excepted the current class whatever its template parameters, considering that I already have an explicit constructor as in the example code ? EDIT : For the implicit constructor from Base, I can obviously write : template<class OtherParameter> Derived2(const Base<OtherParameter>& x); But in that case, do I have the guaranty that the compiler will not use this constructor as an implicit constructor for Derived2<OtherParameter1, OtherParameter2, OtherParameter> ? EDIT2: Here I have a test : (LWS here : http://liveworkspace.org/code/cd423fb44fb4c97bc3b843732d837abc) #include <iostream> template<typename Type> class Base {}; template<typename Type> class Other : public Base<Type> {}; template<typename Type> class Derived : public Base<Type> { public: Derived() {std::cout<<"empty"<<std::endl;} Derived(const Derived<Type>& x) {std::cout<<"copy"<<std::endl;} template<typename OtherType> explicit Derived(const Derived<OtherType>& x) {std::cout<<"explicit"<<std::endl;} template<typename OtherType> Derived(const Base<OtherType>& x) {std::cout<<"implicit"<<std::endl;} }; int main() { Other<int> other0; Other<double> other1; std::cout<<"1 = "; Derived<int> dint1; // <- empty std::cout<<"2 = "; Derived<int> dint2; // <- empty std::cout<<"3 = "; Derived<double> ddouble; // <- empty std::cout<<"4 = "; Derived<double> ddouble1(ddouble); // <- copy std::cout<<"5 = "; Derived<double> ddouble2(dint1); // <- explicit std::cout<<"6 = "; ddouble = other0; // <- implicit std::cout<<"7 = "; ddouble = other1; // <- implicit std::cout<<"8 = "; ddouble = ddouble2; // <- nothing (normal : default assignment) std::cout<<"\n9 = "; ddouble = Derived<double>(dint1); // <- explicit std::cout<<"10 = "; ddouble = dint2; // <- implicit : WHY ?!?! return 0; } The last line worry me. Is it ok with the C++ standard ? Is it a bug of g++ ?

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• In Java, can a final field be initialized from a constructor helper?

  - by csj

  I have a final non-static member: private final HashMap<String,String> myMap; I would like to initialize it using a method called by the constructor. Since myMap is final, my "helper" method is unable to initialize it directly. Of course I have options: I could implement the myMap initialization code directly in the constructor. MyConstructor (String someThingNecessary) { myMap = new HashMap<String,String>(); myMap.put("blah","blahblah"); // etc... // other initialization stuff unrelated to myMap } I could have my helper method build the HashMap, return it to the constructor, and have the constructor then assign the object to myMap. MyConstructor (String someThingNecessary) { myMap = InitializeMyMap(someThingNecessary); // other initialization stuff unrelated to myMap } private HashMap<String,String> InitializeMyMap(String someThingNecessary) { HashMap<String,String> initializedMap = new HashMap<String,String>(); initializedMap.put("blah","blahblah"); // etc... return initializedMap; } Method #2 is fine, however, I'm wondering if there's some way I could allow the helper method to directly manipulate myMap. Perhaps a modifier that indicates it can only be called by the constructor? MyConstructor (String someThingNecessary) { InitializeMyMap(someThingNecessary); // other initialization stuff unrelated to myMap } // helper doesn't work since it can't modify a final member private void InitializeMyMap(String someThingNecessary) { myMap = new HashMap<String,String>(); myMap.put("blah","blahblah"); // etc... }

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• Calling a constructor to reinitialize variables doesn't seem to work?

  - by Matt

  I wanted to run 1,000 iterations of a program, so set a counter for 1000 in main. I needed to reinitialize various variables after each iteration, and since the class constructor had all the initializations already written out - I decided to call that after each iteration, with the result of each iteration being stored in a variable in main. However, when I called the constructor, it had no effect...it took me a while to figure out - but it didn't reinitialize anything! I created a function exactly like the constructor - so the object would have its own version. When I called that, it reinitialized everything as I expected. int main() { Class MyClass() int counter = 0; while ( counter < 1000 ) { stuff happens } Class(); // This is how I tried to call the constructor initially. // After doing some reading here, I tried: // Class::Class(); // - but that didn't work either /* Later I used... MyClass.function_like_my_constructor; // this worked perfectly */ } ...Could someone try to explain why what I did was wrong, or didn't work, or was silly or what have you? I mean - mentally, I just figured - crap, I can call this constructor and have all this stuff reinitialized. Are constructors (ideally) ONLY called when an object is created?

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• Tip #19 Module Private Visibility in OSGi

  - by ByronNevins

  I hate public and protected methods and classes.  It requires so much work to change them in a huge project like GlassFish.  Not to mention that you may well have to support those APIs forever.  They are highly overused in GlassFish.  In fact I'd bet that > 95% of classes are marked as public for no good reason.  It's just (bad) habit is my guess. private and default visibility (I call it package-private) is easier to maintain.  It is much much easier to change such classes and methods around.  If you have ANY public method or public class in GlassFish you'll need to grep through a tremendous amount of source code to find all callers.  But even that won't be theoretically reliable.  What if a caller is using reflection to access public methods?  You may never find such usages. If you have package private methods, it's easy.  Simply grep through all the code in that one package.  As long as that package compiles ok you're all set.  There can' be any compile errors anywhere else.  It's a waste of time to even look around or build the "outside" world.  So you may be thinking: "Aha!  I'll just make my module have one giant package with all the java files.  Then I can use the default visibility and maintenance will be much easier.  But there's a problem.  You are wasting a very nice feature of java -- organizing code into separate packages.  It also makes the code much more encapsulated.  Unfortunately to share code between the packages you have no choice but to declare public visibility. What happens in practice is that a module ends up having tons of public classes and methods that are used exclusively inside the module.  Which finally brings me to the point of this blog:  If Only There Was A Module-Private Visibility Available Well, surprise!  There is such a mechanism.  If your project is running under OSGi that is.  Like GlassFish does!  With this mechanism you can easily add another level of visibility by telling OSGi exactly which public you want to be exposed outside of the module.  You get the best of both worlds: Better encapsulation of your code so that maintenance is easier and productivity is increased. Usage of public visibility inside the module so that you can encapsulate intra-module better with packages. How I do this in GlassFish: Carefully plan out at least one package that will contain "true" publics.  This is the package that will be exported by OSGi.  I recommend just one package. Here is how to tell OSGi to use it in GlassFish -- edit osgi.bundle like so:-exportcontents:     org.glassfish.mymodule.truepublics;  version=${project.osgi.version} Now all publics declared in any other packages will be visible module-wide but not outside the module. There is one caveat: Accessing "module-private" items outside of the module is controlled at run-time, not compile-time.  The compiler has no clue that a public in a dependent module isn't really public.  it will happily compile it.  At runtime you will definitely see fireworks.  The good news is that you don't have to wait for the code path that tries to use the "module-private" items to fire.  OSGi will complain loudly when that module gets loaded.  OSGi will refuse to load it.  You will see an error like this: remote failure: Error while loading FOO: Exception while adding the new configuration : Error occurred during deployment: Exception while loading the app : org.osgi.framework.BundleException: Unresolved constraint in bundle com.oracle.glassfish.miscreant.code [115]: Unable to resolve 115.0: missing requirement [115.0] osgi.wiring.package; (osgi.wiring.package=org.glassfish.mymodule.unexported). Please see server.log for more details. That is if you accidentally change code in module B to use a public that is really a "module-private" in module A, then you will see the error immediately when you try to test whatever you were changing in module B.

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• Dependency injection: what belongs in the constructor?

  - by Adam Backstrom

  I'm evaluating my current PHP practices in an effort to write more testable code. Generally speaking, I'm fishing for opinions on what types of actions belong in the constructor. Should I limit things to dependency injection? If I do have some data to populate, should that happen via a factory rather than as constructor arguments? (Here, I'm thinking about my User class that takes a user ID and populates user data from the database during construction, which obviously needs to change in some way.) I've heard it said that "initialization" methods are bad, but I'm sure that depends on what exactly is being done during initialization. At the risk of getting too specific, I'll also piggyback a more detailed example onto my question. For a previous project, I built a FormField class (which handled field value setting, validation, and output as HTML) and a Model class to contain these fields and do a bit of magic to ease working with fields. FormField had some prebuilt subclasses, e.g. FormText (<input type="text">) and FormSelect (<select>). Model would be subclassed so that a specific implementation (say, a Widget) had its own fields, such as a name and date of manufacture: class Widget extends Model { public function __construct( $data = null ) { $this->name = new FormField('length=20&label=Name:'); $this->manufactured = new FormDate; parent::__construct( $data ); // set above fields using incoming array } } Now, this does violate some rules that I have read, such as "avoid new in the constructor," but to my eyes this does not seem untestable. These are properties of the object, not some black box data generator reading from an external source. Unit tests would progressively build up to any test of Widget-specific functionality, so I could be confident that the underlying FormFields were working correctly during the Widget test. In theory I could provide the Model with a FieldFactory() which could supply custom field objects, but I don't believe I would gain anything from this approach. Is this a poor assumption?

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• Purpose of Explicit Default Constructors

  - by Dennis Zickefoose

  I recently noticed a class in C++0x that calls for an explicit default constructor. However, I'm failing to come up with a scenario in which a default constructor can be called implicitly. It seems like a rather pointless specifier. I thought maybe it would disallow Class c; in favor of Class c = Class(); but that does not appear to be the case. Some relevant quotes from the C++0x FCD, since it is easier for me to navigate [similar text exists in C++03, if not in the same places] 12.3.1.3 [class.conv.ctor] A default constructor may be an explicit constructor; such a constructor will be used to perform default-initialization or value initialization (8.5). It goes on to provide an example of an explicit default constructor, but it simply mimics the example I provided above. 8.5.6 [decl.init] To default-initialize an object of type T means: — if T is a (possibly cv-qualified) class type (Clause 9), the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor); 8.5.7 [decl.init] To value-initialize an object of type T means: — if T is a (possibly cv-qualified) class type (Clause 9) with a user-provided constructor (12.1), then the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor); In both cases, the standard calls for the default constructor to be called. But that is what would happen if the default constructor were non-explicit. For completeness sake: 8.5.11 [decl.init] If no initializer is specified for an object, the object is default-initialized; From what I can tell, this just leaves conversion from no data. Which doesn't make sense. The best I can come up with would be the following: void function(Class c); int main() { function(); //implicitly convert from no parameter to a single parameter } But obviously that isn't the way C++ handles default arguments. What else is there that would make explicit Class(); behave differently from Class();? The specific example that generated this question was std::function [20.8.14.2 func.wrap.func]. It requires several converting constructors, none of which are marked explicit, but the default constructor is.

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