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• Java operator overloading

  - by nimcap

  Not using operators makes my code obscure. (aNumber / aNother) * count is better than aNumber.divideBy(aNother).times(count) After 6 months of not writing a single comment I had to write a comment to the simple operation above. Usually I refactor until I don't need comment. And this made me realize that it is easier to read and perceive math symbols and numbers than their written forms. For example TWENTY_THOUSAND_THIRTEEN.plus(FORTY_TWO.times(TWO_HUNDERED_SIXTY_ONE)) is more obscure than 20013 + 42*261 So do you know a way to get rid of obscurity while not using operator overloading in Java? Update: I did not think my exaggeration on comments would cause such trouble to me. I am admitting that I needed to write comment a couple of times in 6 months. But not more than 10 lines in total. Sorry for that. Update 2: Another example: budget.plus(bonusCoefficient.times(points)) is more obscure than budget + bonusCoefficient * points I have to stop and think on the first one, at first sight it looks like clutter of words, on the other hand, I get the meaning at first look for the second one, it is very clear and neat. I know this cannot be achieved in Java but I wanted to hear some ideas about my alternatives.

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• What is the rationale to non allow overloading of C++ conversions operator with non-member functio

  - by Vicente Botet Escriba

  C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration operator boost::posix_time::ptime( const boost::chrono::time_point& from) { using namespace boost; typedef chrono::time_point time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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• Different behaviour of method overloading in C#

  - by Wondering

  Hi All, I was going through C# Brainteasers(http://www.yoda.arachsys.com/csharp/teasers.html) and came accross one question:what should be the o/p of below code class Base { public virtual void Foo(int x) { Console.WriteLine ("Base.Foo(int)"); } } class Derived : Base { public override void Foo(int x) { Console.WriteLine ("Derived.Foo(int)"); } public void Foo(object o) { Console.WriteLine ("Derived.Foo(object)"); } } class Test { static void Main() { Derived d = new Derived(); int i = 10; d.Foo(i); // it prints ("Derived.Foo(object)" } } but if I change the code to enter code here class Derived { public void Foo(int x) { Console.WriteLine("Derived.Foo(int)"); } public void Foo(object o) { Console.WriteLine("Derived.Foo(object)"); } } class Program { static void Main(string[] args) { Derived d = new Derived(); int i = 10; d.Foo(i); // prints Derived.Foo(int)"); Console.ReadKey(); } } I want to why the o/p is getting changde when we are inheriting vs not inheriting , why method overloading is behaving differently in both the cases

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• c++ overloading delete, retrieve size

  - by user300713

  Hi, I am currently writing a small custom memory Allocator in c++, and want to use it together with operator overloading of new/delete. Anyways, my memory Allocator basicall checks if the requested memory is over a certain threshold, and if so uses malloc to allocate the requested memory chunk. Otherwise the memory will be provided by some fixedPool allocators. that generally works, but for my deallocation function looks like this: void MemoryManager::deallocate(void * _ptr, size_t _size){ if(_size heapThreshold) deallocHeap(_ptr); else deallocFixedPool(_ptr, _size); } so I need to provide the size of the chunk pointed to, to deallocate from the right place. No the problem is that the delete keyword does not provide any hint on the size of the deleted chunk, so I would need something like this: void operator delete(void * _ptr, size_t _size){ MemoryManager::deallocate(_ptr, _size); } But as far as I can see, there is no way to determine the size inside the delete operator.- If I want to keep things the way it is right now, would I have to save the size of the memory chunks myself? Any ideas on how to solve this are welcome! Thanks!

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• operator overloading of stream extraction operator in C++ help

  - by Crystal

  I'm having some trouble overloading my stream extraction operator in C++ for a hw assignment. I'm not really sure why I am getting these compile errors since I thought I was doing it right... Here is my code: Complex.h #ifndef COMPLEX_H #define COMPLEX_H class Complex { //friend ostream &operator<<(ostream &output, const Complex &complexObj) const; public: Complex(double = 0.0, double = 0.0); // constructor Complex operator+(const Complex &) const; // addition Complex operator-(const Complex &) const; // subtraction void print() const; // output private: double real; // real part double imaginary; // imaginary part }; #endif Complex.cpp #include <iostream> #include "Complex.h" using namespace std; // Constructor Complex::Complex(double realPart, double imaginaryPart) : real(realPart), imaginary(imaginaryPart) { } // addition operator Complex Complex::operator+(const Complex &operand2) const { return Complex(real + operand2.real, imaginary + operand2.imaginary); } // subtraction operator Complex Complex::operator-(const Complex &operand2) const { return Complex(real - operand2.real, imaginary - operand2.imaginary); } // Overload << operator ostream &Complex::operator<<(ostream &output, const Complex &complexObj) const { cout << '(' << complexObj.real << ", " << complexObj.imaginary << ')'; return output; // returning output allows chaining } // display a Complex object in the form: (a, b) void Complex::print() const { cout << '(' << real << ", " << imaginary << ')'; } main.cpp #include <iostream> #include "Complex.h" using namespace std; int main() { Complex x; Complex y(4.3, 8.2); Complex z(3.3, 1.1); cout << "x: "; x.print(); cout << "\ny: "; y.print(); cout << "\nz: "; z.print(); x = y + z; cout << "\n\nx = y + z: " << endl; x.print(); cout << " = "; y.print(); cout << " + "; z.print(); x = y - z; cout << "\n\nx = y - z: " << endl; x.print(); cout << " = "; y.print(); cout << " - "; z.print(); cout << endl; } Compile erros: complex.cpp(23) : error C2039: '<<' : is not a member of 'Complex' complex.h(5) : see declaration of 'Complex' complex.cpp(24) : error C2270: '<<' : modifiers not allowed on nonmember functions complex.cpp(25) : error C2248: 'Complex::real' : cannot access private member declared in class 'Complex' complex.h(13) : see declaration of 'Complex::real' complex.h(5) : see declaration of 'Complex' complex.cpp(25) : error C2248: 'Complex::imaginary' : cannot access private member declared in class 'Complex' complex.h(14) : see declaration of 'Complex::imaginary' complex.h(5) : see declaration of 'Complex' Thanks!

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• VS 2008 irritating copy constructor link dependency

  - by Paul Hollingsworth

  Hi guys, I've run into the following annoying and seemingly incorrect behaviour in the Visual Studio 2008 C++ compiler: Suppose I have a class library - Car.lib - that uses a "Car" class, with a header called "Car.h": class Car { public: void Drive() { Accelerate(); } void Accelerate(); }; What I'm actually trying to do is use the Car headers (for some other functions), but without having to link with Car.lib itself (the actual class is not called "Car" but I am sanitising this example). If I #include "Car.h" in the .cpp file used to build a managed C++ .dll, but never refer to Car, everything compiles and links fine. This is because I never instantiate a Car object. However, the following: namespace { class Car { public: Car(const Car& rhs) { Accelerate(); } void Accelerate(); }; } leaves me with the link error: Error 2 error LNK2001: unresolved external symbol "public: void __thiscall `anonymous namespace'::Car::Accelerate(void)" (?Accelerate@Car@?A0xce3bb5ed@@$$FQAEXXZ) CREObjectWrapper.obj CREObjectBuilderWrapper Note I've declared the whole thing inside an anonymous namespace so there's no way that the Car functions could be exported from the .DLL in any case. Declaring the copy constructor out-of-line makes no difference. i.e. the following also fails to link: class Car { public: Car(const Car& rhs); void Accelerate(); }; Car::Car(const Car& rhs) { Accelerate(); } It's something specifically to do with the copy constructor note, because the following, for example, does link: class Car { public: Car() { Accelerate(); } void Accelerate(); }; I am not a C++ standards guru but this doesn't seem correct to me. Surely the compiler still should not have had to even generate any code that calls the Car copy constructor. Can anyone confirm if this behaviour is correct? It's been a while since I used C++ - but I don't think this used to be an issue with Visual Studio 6.0 for example. Can anyone suggest a workaround that allows one to "re-use" the Accelerate method from within the copy constructor and still have the copy constructor declared inline?

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• Spring constructor injection error

  - by Jeune

  I am getting the following error for a bean in my application context: Related cause: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'businessLogicContext' d efined in class path resource [activemq-jms-consumer.xml]: Unsatisfied dependency expressed through constructor argument with index 0 of type [java.lang.String]: Could not convert constructor argument value of type [java.util.ArrayList] to required type [java.lang.String]: Failed to convert value of type [java.util.ArrayList] to required type [java.lang.Stri ng]; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [java.util.ArrayList] to requi red type [java.lang.String]: no matching editors or conversion strategy found at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:53 4) at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:18 6) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAuto wireCapableBeanFactory.java:855) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutow ireCapableBeanFactory.java:765) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCap ableBeanFactory.java:412) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBea nFactory.java:383) at java.security.AccessController.doPrivileged(Native Method) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapab leBeanFactory.java:353) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:245) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegis try.java:169) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:242) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListable BeanFactory.java:400) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplic ationContext.java:736) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:369) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java :123) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java :66) Here is my bean: <bean id="businessLogicContext" class="org.springframework.context.support.ClassPathXmlApplicationContext" depends-on="resolveProperty"> <constructor-arg index="0"> <list> <value>jms-applicationContext.xml</value> <value>jms-managerBeanContext.xml</value> <value>jms-daoContext.xml</value> <value>jms-serviceContext.xml</value> </list> </constructor-arg> </bean> I don't know what's wrong, I have googled how to inject a string array via constructor injection and the way I do it above seems okay.

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• Android Custom View Constructor

  - by Mitch

  I'm learning about using Custom Views from the following: http://developer.android.com/guide/topics/ui/custom-components.html#modifying The description says: Class Initialization As always, the super is called first. Furthermore, this is not a default constructor, but a parameterized one. The EditText is created with these parameters when it is inflated from an XML layout file, thus, our constructor needs to both take them and pass them to the superclass constructor as well. Is there a better description? I've been trying to figure out what the constructor(s) should look like and I've come up with 4 possible choices (see example at end of post). I'm not sure what these 4 choices do (or don't do), why I should implement them, or what the parameters mean. Is there a description of these? Thanks. Mitch public MyCustomView() { super(); } public MyCustomView(Context context) { super(context); } public MyCustomView(Context context, AttributeSet attrs) { super(context, attrs); } public MyCustomView(Context context, AttributeSet attrs, Map params) { super(context, attrs, params); }

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• Boost Python : How to only expose the constructor of a class with virtual (pure & impure) methods

  - by fallino

  Hello, I'm a newbie with Boost::Python but I tried to search on the web to do so I want to expose a 3rd party library to Python. One of the class of the library (.hpp) is composed of a public constructor with arguments a protected constructor and functions various regular functions various pure virtual functions various non pure virtual functions First, I did not succeed in building it without having errors about this protected constructor. I finally commented it. A first question would be : Is there a way to exclude these protected functions since I don't want to expose them ? (I know it's possible and easy with Py++, but I started without using it) Then I tried to expose all of my functions, beginning with the pure virtual ones (commenting them all except one), which wasn't a success too So I finally decided not to expose these virtual functions (which in fact seems logical...), but, here again, I didn't manage building it with a simple constructor with arguments (without no_init). So my second question is : Is there a way to exclude these virtual functions since I don't want to expose them ? Sorry if it seems trivial but I didn't find anything explicit on the web and I need something rather explicit :). Thanks in advance

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• Swig: No Constructor defined

  - by wheaties

  I added %allowexcept to my *.i file when building a Python <-- C++ bridge using Swig. Then I removed that preprocessing directive. Now I can't get the Python produced code to recognize the constructor of a C++ class. Here's the class file: #include <exception> class Swig_Foo{ public: Swig_Foo(){} virtual ~Swig_Foo(){} virtual getInt() =0; virtual throwException() { throw std::exception(); } }; And here's the code Swig produces from it: class Swig_Foo: __swig_setmethods__ = {} __setattr__ = lambda self, name, value: _swig_setattr(self, Swig_Foo, name, value) __swig_getmethods__ = {} __getattr__ = lambda self, name: _swig_getattr(self, Swig_Foo, name) def __init__(self): raise AttributeError, "No constructor defined" __repr__ = _swig_repr __swig_destroy__ = _foo.delete_Swig_Foo __del__ = lambda self : None; def getInt(*args): return apply(_foo.Swig_Foo_getInt, args) def throwOut(*args): return apply(_foo.Swig_Foo_throwOut, args) Swig_Foo_swigregister = _foo.Swig_Foo_swigregister Swig_Foo_swigregister(Swig_Foo) The problem is the def __init__self): raise AttributeError, "No constructor defined" portion. It never did this before I added the %allowexception and now that I've removed it, I can't get it to create a real constructor. All the other classes have actual constructors. Quite baffled. Anyone know how I can get it to stop doing this?

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• Constructor and Destructors in C++ [Not a question] [closed]

  - by Jack

  I am using gcc. Please tell me if I am wrong - Lets say I have two classes A & B class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; 1) The first line in B's constructor should be a call to A's constructor ( I assume compiler automatically inserts it). Also the last line in B's destructor will be a call to A's destructor (compiler does it again). Why was it built this way? 2) When I say A * a = new B(); compiler creates a new B object and checks to see if A is a base class of B and if it is it allows 'a' to point to the newly created object. I guess that is why we don't need any virtual constructors. ( with help from @Tyler McHenry , @Konrad Rudolph) 3) When I write delete a compiler sees that a is an object of type A so it calls A's destructor leading to a problem which is solved by making A's destructor virtual. As user - Little Bobby Tables pointed out to me all destructors have the same name destroy() in memory so we can implement virtual destructors and now the call is made to B's destructor and all is well in C++ land. Please comment.

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• Dependency Properties, change notification and setting values in the constructor

  - by stefan.at.wpf

  Hello, I have a clas with 3 dependency properties A,B,C. The values of these properties are set by the constructor and every time one of the properties A, B or C changes, the method recalculate() is called. Now during execution of the constructor these method is called 3 times, because the 3 properties A, B, C are changed. Hoewever this isn't necessary as the method recalculate() can't do anything really useful without all 3 properties set. So what's the best way for property change notification but circumventing this change notification in the constructor? I thought about adding the property changed notification in the constructor, but then each object of the DPChangeSample class would always add more and more change notifications. Thanks for any hint! class DPChangeSample : DependencyObject { public static DependencyProperty AProperty = DependencyProperty.Register("A", typeof(int), typeof(DPChangeSample), new PropertyMetadata(propertyChanged)); public static DependencyProperty BProperty = DependencyProperty.Register("B", typeof(int), typeof(DPChangeSample), new PropertyMetadata(propertyChanged)); public static DependencyProperty CProperty = DependencyProperty.Register("C", typeof(int), typeof(DPChangeSample), new PropertyMetadata(propertyChanged)); private static void propertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { ((DPChangeSample)d).recalculate(); } private void recalculate() { // Using A, B, C do some cpu intensive caluclations } public DPChangeSample(int a, int b, int c) { SetValue(AProperty, a); SetValue(BProperty, b); SetValue(CProperty, c); } }

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• Attaching methods to prototype from within constructor function

  - by Matthew Taylor

  Here is the textbook standard way of describing a 'class' or constructor function in JavaScript, straight from the Definitive Guide to JavaScript: function Rectangle(w,h) { this.width = w; this.height = h; } Rectangle.prototype.area = function() { return this.width * this.height; }; I don't like the dangling prototype manipulation here, so I was trying to think of a way to encapsulate the function definition for area inside the constructor. I came up with this, which I did not expect to work: function Rectangle(w,h) { this.width = w; this.height = h; this.constructor.prototype.area = function() { return this.width * this.height; }; } I didn't expect this to work because the this reference inside the area function should be pointing to the area function itself, so I wouldn't have access to width and height from this. But it turns out I do! var rect = new Rectangle(2,3); var area = rect.area(); // great scott! it is 6 Some further testing confirmed that the this reference inside the area function actually was a reference to the object under construction, not the area function itself. function Rectangle(w,h) { this.width = w; this.height = h; var me = this; this.constructor.prototype.whatever = function() { if (this === me) { alert ('this is not what you think');} }; } Turns out the alert pops up, and this is exactly the object under construction. So what is going on here? Why is this not the this I expect it to be?

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• Constructor and Destructors in C++ work?

  - by Jack

  I am using gcc. Please tell me if I am wrong - Lets say I have two classes A & B class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; 1) The first line in B's constructor should be a call to A's constructor ( I assume compiler automatically inserts it). Also the last line in B's destructor will be a call to A's destructor (compiler does it again). Why was it built this way? 2) When I say A * a = new B(); compiler creates a new B object and checks to see if A is a base class of B and if it is it allows 'a' to point to the newly created object. I guess that is why we don't need any virtual constructors. ( with help from @Tyler McHenry , @Konrad Rudolph) 3) When I write delete a compiler sees that a is an object of type A so it calls A's destructor leading to a problem which is solved by making A's destructor virtual. As user - Little Bobby Tables pointed out to me all destructors have the same name destroy() in memory so we can implement virtual destructors and now the call is made to B's destructor and all is well in C++ land. Please comment.

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• Purpose of overloading operators in C++?

  - by Geo Drawkcab

  What is the main purpose of overloading operators in C++? In the code below, << and >> are overloaded; what is the advantage to doing so? #include <iostream> #include <string> using namespace std; class book { string name,gvari; double cost; int year; public: book(){}; book(string a, string b, double c, int d) { a=name;b=gvari;c=cost;d=year; } ~book() {} double setprice(double a) { return a=cost; } friend ostream& operator <<(ostream& , book&); void printbook(){ cout<<"wignis saxeli "<<name<<endl; cout<<"wignis avtori "<<gvari<<endl; cout<<"girebuleba "<<cost<<endl; cout<<"weli "<<year<<endl; } }; ostream& operator <<(ostream& out, book& a){ out<<"wignis saxeli "<<a.name<<endl; out<<"wignis avtori "<<a.gvari<<endl; out<<"girebuleba "<<a.cost<<endl; out<<"weli "<<a.year<<endl; return out; } class library_card : public book { string nomeri; int raod; public: library_card(){}; library_card( string a, int b){a=nomeri;b=raod;} ~library_card() {}; void printcard(){ cout<<"katalogis nomeri "<<nomeri<<endl; cout<<"gacemis raodenoba "<<raod<<endl; } friend ostream& operator <<(ostream& , library_card&); }; ostream& operator <<(ostream& out, library_card& b) { out<<"katalogis nomeri "<<b.nomeri<<endl; out<<"gacemis raodenoba "<<b.raod<<endl; return out; } int main() { book A("robizon kruno","giorgi",15,1992); library_card B("910CPP",123); A.printbook(); B.printbook(); A.setprice(15); B.printbook(); system("pause"); return 0; }

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• Calling a constructor from method within the same class

  - by Nathan

  I'm new to java and I'm learning about creating object classes. One of my homework assignment requires that I call the constructor at least once within a method of the same object class. I'm getting an error that says The method DoubleMatrix(double[][]) is undefined for the type DoubleMatrix Here's my constructor: public DoubleMatrix(double[][] tempArray) { // Declaration int flag = 0; int cnt; // Statement // check to see if doubArray isn't null and has more than 0 rows if(tempArray == null || tempArray.length < 0) { flag++; } // check to see if each row has the same length if(flag == 0) { for(cnt = 0; cnt <= tempArray.length - 1 || flag != 1; cnt++) { if(tempArray[cnt + 1].length != tempArray[0].length) { flag++; } } } else if(flag == 1) { makeDoubMatrix(1, 1);// call makeDoubMatrix method } }// end constructor 2 Here's the method where I try and call the constructor: public double[][] addMatrix(double[][] tempDoub) { // Declaration double[][] newMatrix; int rCnt, cCnt; //Statement // checking to see if both are of same dimension if(doubMatrix.length == tempDoub.length && doubMatrix[0].length == tempDoub[0].length) { newMatrix = new double[doubMatrix.length][doubMatrix[0].length]; // for loop to add matrix to a new one for(rCnt = 0; rCnt <= doubMatrix.length; rCnt++) { for(cCnt = 0; cCnt <= doubMatrix.length; cCnt++) { newMatrix[rCnt][cCnt] = doubMatrix[rCnt][cCnt] + tempDoub[rCnt][cCnt]; } } } else { newMatrix = new double[0][0]; DoubleMatrix(newMatrix) } return newMatrix; }// end addMatrix method Can someone point me to the right direction and explain why I'm getting an error?

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• How to proxy calls to the instance of an object

  - by mr.b

  Edit: Changed question title from "Does C# allow method overloading, PHP style (__call)?" - figured out it doesn't have much to do with actual question. Also edited question text. What I want to accomplish is to proxy calls to a an instance of an object methods, so I could log calls to any of its methods. Right now, I have code similar to this: class ProxyClass { static logger; public AnotherClass inner { get; private set; } public ProxyClass() { inner = new AnotherClass(); } } class AnotherClass { public void A() {} public void B() {} public void C() {} // ... } // meanwhile, in happyCodeLandia... ProxyClass pc = new ProxyClass(); pc.inner.A(); // need to write log message like "method A called" pc.inner.B(); // need to write log message like "method B called" // ... So, how can I proxy calls to an object instance in extensible way? Method overloading would be most obvious solution (if it was supported in PHP way). By extensible, meaning that I don't have to modify ProxyClass whenever AnotherClass changes. In my case, AnotherClass can have any number of methods, so it wouldn't be appropriate to overload or wrap all methods to add logging. I am aware that this might not be the best approach for this kind of problem, so if anyone has idea what approach to use, shoot. Thanks!

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• c# copy constructor generator

  - by Shawn Mclean

  I want to copy values from one object to another object. Something similiar to pass by value but with assignment. Eg. PushPin newValPushPin = oldPushPin; //I want to break the reference here. I was told to write a copy constructor for this. But this class has alot of properties, it will probably take an hour to write a copy constructor by hand. Is there a better way to assign an object to another object by value? If not, is there a copy constructor generator?

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• Constructor in a Interface?

  - by Sebi

  I know its not possible to define a constructor in a interface. But im wondering why, because i think i could be very useful. So you could be sure that some fields in a class are defined for every implementaiton of this interface. For example consider the following message class: public class MyMessage { public MyMessage(String receiver) { this.receiver = receiver; } private String receiver; public void send() { //some implementation for sending the mssage to the receiver } } If a define a Interface for this class so that i can have more classes which implement the message interface, i can only define the send method and not the constructor. So how can i assure that every implementation of this class really has an receiver setted? If i use a method like setReceiver(String receiver) i can't be sure that this method is really called. In the constructor i could assure it.

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• FxCop giving a warning on private constructor CA1823 and CA1053

  - by Luis Sánchez

  I have a class that looks like the following: Public Class Utilities Public Shared Function blah(userCode As String) As String 'doing some stuff End Function End Class I'm running FxCop 10 on it and it says: "Because type 'Utilities' contains only 'static' ( 'Shared' in Visual Basic) members, add a default private constructor to prevent the compiler from adding a default public constructor." Ok, you're right Mr. FxCop, I'll add a private constructor: Private Utilities() Now I'm having: "It appears that field 'Utilities.Utilities' is never used or is only ever assigned to. Use this field or remove it." Any ideas of what should I do to get rid of both warnings?

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• C# Constructor & List Question

  - by ShonnaE

  Ohk, I am doing a c-sharp program, and I get everything but this, I just can't understand what it is asking. I know how to create a list.. and how to create a constructor.. but this is where i get confused.. its probably way simple but i am missing it. I created 2 lists .. now i should create a constructor here is one my lists List<Person> organize = new List<Person>(); THIS PART --- *The constructor should also initialize the two event lists to new empty lists. *

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• javascript constructor reset: What is it ?

  - by Sake

  I came across this slide: http://www.slideshare.net/stoyan/javascript-patterns#postComment at page 35: Option 5 + super + constructor reset function inherit(C, P) { var F = function(){}; F.prototype = P.prototype; C.prototype = new F(); C.uber = P.prototype; C.prototype.constructor = C; // WHY ??? } I don't get it. Can anybody please explain what the last line for ? C.prototype.constructor = C; // WHY ??? Thanks

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• How to initialise a STL vector/list with a class without invoking the copy constructor

  - by Warpspace

  I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks when you need a deep copy. I would love to have the constructor of my class new something and not have to implement a copy constructor just to allocate my memory for the second time and waste runtime. I'd also rather not have to immediately find the class instance from the vector/list and then manually allocate the memory (or do something horrible like allocate the memory in the copy constructor itself). Is there any way around this (I'm not using Visual Studio BTW)?

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• overloading new/delete problem

  - by hidayat

  This is my scenario, Im trying to overload new and delete globally. I have written my allocator class in a file called allocator.h. And what I am trying to achieve is that if a file is including this header file, my version of new and delete should be used. So in a header file "allocator.h" i have declared the two functions extern void* operator new(std::size_t size); extern void operator delete(void *p, std::size_t size); I the same header file I have a class that does all the allocator stuff, class SmallObjAllocator { ... }; I want to call this class from the new and delete functions and I would like the class to be static, so I have done this: template<unsigned dummy> struct My_SmallObjectAllocatorImpl { static SmallObjAllocator myAlloc; }; template<unsigned dummy> SmallObjAllocator My_SmallObjectAllocatorImpl<dummy>::myAlloc(DEFAULT_CHUNK_SIZE, MAX_OBJ_SIZE); typedef My_SmallObjectAllocatorImpl<0> My_SmallObjectAllocator; and in the cpp file it looks like this: allocator.cc void* operator new(std::size_t size) { std::cout << "using my new" << std::endl; if(size > MAX_OBJ_SIZE) return malloc(size); else return My_SmallObjectAllocator::myAlloc.allocate(size); } void operator delete(void *p, std::size_t size) { if(size > MAX_OBJ_SIZE) free(p); else My_SmallObjectAllocator::myAlloc.deallocate(p, size); } The problem is when I try to call the constructor for the class SmallObjAllocator which is a static object. For some reason the compiler are calling my overloaded function new when initializing it. So it then tries to use My_SmallObjectAllocator::myAlloc.deallocate(p, size); which is not defined so the program crashes. So why are the compiler calling new when I define a static object? and how can I solve it?

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• Exceptions in constructors

  - by FredOverflow

  In C++, the lifetime of an object begins when the constructor finishes successfully. Inside the constructor, the object does not exist yet. Q: What does emitting an exception from a constructor mean? A: It means that construction has failed, the object never existed, its lifetime never began. [source] My question is: Does the same hold true for Java? What happens, for example, if I hand this to another object, and then my constructor fails? Foo() { Bar.remember(this); throw new IllegalStateException(); } Is this well-defined? Does Bar now have a reference to a non-object?

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