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  • Object as an array

    - by owca
    I need to create class Dog and PurebredDog extending Dog. Problem is that Dog can be at once single object and array of objects (Dogs and PurebreedDogs : Dog pack[]={new Dog(76589,"As","black",18, "Ann","Kowalsky"), new PurebreedDog(45321,"Labrador","Elf","black",25, "Angus","Mati","Barbara","Smith"), new Dog(102467,"Gamma","brown",89, "Josh","Coke"), new PurebreedDog(9678,"York","Theta","brown",8, "Emka","Figaro","Alice","Cat")}; for(int i=0; i < pack.length; i++) System.out.println(pack[i]+"\n\n"); How to write proper constructor for Dog ?

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  • Implicitly invoking parent class initializer

    - by Matt Joiner
    class A(object): def __init__(self, a, b, c): #super(A, self).__init__() super(self.__class__, self).__init__() class B(A): def __init__(self, b, c): print super(B, self) print super(self.__class__, self) #super(B, self).__init__(1, b, c) super(self.__class__, self).__init__(1, b, c) class C(B): def __init__(self, c): #super(C, self).__init__(2, c) super(self.__class__, self).__init__(2, c) C(3) In the above code, the commented out __init__ calls appear to the be the commonly accepted "smart" way to do super class initialization. However in the event that the class hierarchy is likely to change, I have been using the uncommented form, until recently. It appears that in the call to the super constructor for B in the above hierarchy, that B.__init__ is called again, self.__class__ is actually C, not B as I had always assumed. Is there some way in Python-2.x that I can overcome this, and maintain proper MRO when calling super constructors without actually naming the current class?

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  • Overriding Constructors in F#

    - by kim3er
    How would I write the following C# code in F#? namespace Shared { public class SharedRegistry : PageRegistry { public SharedRegistry(bool useCache = true) : base(useCache) { // Repositories ForRequestedType<IAddressRepository>().TheDefaultIsConcreteType<SqlAddressRepository>(); ForRequestedType<ISharedEnquiryRepository>().TheDefaultIsConcreteType<SharedEnquiryRepository>(); // Services ForRequestedType<IAddressService>().TheDefaultIsConcreteType<AddressService>(); ForRequestedType<ISharedEnquiryService>().TheDefaultIsConcreteType<SharedEnquiryService>(); } } } As is as far as I have managed, but I can't work out to inherit from PageRegistry at the same time as declaring my own default constructor. type SharedRegistry(useCache: bool) = inherit PageRegistry(useCache) new() = new SharedRegistry(true) Rich

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  • By-Name-Parameters for Constructors

    - by hotzen
    Hello, coming from my other question is there a way to get by-name-parameters for constructors working? I need a way to provide a code-block which is executed on-demand/lazy/by-name inside an object and this code-block must be able to access the class-methods as if the code-block were part of the class. Following Testcase fails: package test class ByNameCons(code: => Unit) { def exec() = { println("pre-code") code println("post-code") } def meth() = println("method") def exec2(code2: => Unit) = { println("pre-code") code2 println("post-code") } } object ByNameCons { def main(args: Array[String]): Unit = { val tst = new ByNameCons { println("foo") meth() // knows meth() as code is part of ByNameCons } tst.exec() // ByName fails (executed right as constructor) println("--------") tst.exec2 { // ByName works println("foo") //meth() // does not know meth() as code is NOT part of ByNameCons } } } Output: foo method pre-code post-code -------- pre-code foo post-code

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  • Throwing Exception in CTOR and Smart Pointers

    - by David Relihan
    Is it OK to have the following code in my constructor to load an XML document into a member variable - throwing to caller if there are any problems: MSXML2::IXMLDOMDocumentPtr m_docPtr; //member Configuration() { try { HRESULT hr = m_docPtr.CreateInstance(__uuidof(MSXML2::DOMDocument40)); if ( SUCCEEDED(hr)) { m_docPtr->loadXML(CreateXML()); } else { //throw exception to caller } } catch(...) { //throw exception to caller } } Based on Scott Myers RAII implementations in More Effective C++ I believe I am alright in just allowing exceptions to be thrown from CTOR as I am using a smart pointer(IXMLDOMDocumentPtr). Let me know what you think....

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  • Returning in a static initializer

    - by Martijn Courteaux
    Hello, This isn't valid code: public class MyClass { private static boolean yesNo = false; static { if (yesNo) { System.out.println("Yes"); return; // The return statement is the problem } System.exit(0); } } This is a stupid example, but in a static class constructor we can't return;. Why? Are there good reasons for this? Does someone know something more about this? So the reason why I should do return is to end constructing there. Thanks

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  • Synchronizing reading and writing with synchronous NamedPipes

    - by Mike Trader
    A Named Pipe Server is created with hPipe = CreateNamedPipe( zPipePath, PIPE_ACCESS_DUPLEX, PIPE_TYPE_BYTE | PIPE_WAIT | PIPE_READMODE_BYTE, PIPE_UNLIMITED_INSTANCES, 8192, 8192, NMPWAIT_USE_DEFAULT_WAIT, NULL) Then we immediately call: ConnectNamedPipe( hPipe, BYVAL %NULL ) Which blocks until the client connects. Then we proceed directly to ReadFile( hPipe, ... The problem is that it takes the Client takes a finite amount of time to prepare and write all the fcgi request parameters. This has usually not completed before the Pipe Server performs its ReadFile(). The Read file operation thus finds no data in the pipe and the process fails. Is there a mechanism to tell when a Write() has occurred/finished after a client has connected to a NamedPipe? If I had control of the Client process, I could use a common Mutex, but I don't, and I really do not want to get into I/O completion ports just to solve this problem! I can of course use a simple timer to wait 60m/s or so which is usually plenty of time for the wrote to complete, but that is a horrible hack.

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  • Very basic Javascript constructors problem

    - by misha-moroshko
    Hi, In the following JavaScript code main() is called. My question is why the second constructor is called rather than the first one ? What am I missing here ? Thanks !! function AllInputs() { alert("cons 1"); this.radioInputs = []; alert(this); } function AllInputs(radioElement) { alert("cons 2"); this.radioInputs = [radioElement]; alert(this); } AllInputs.prototype.toString = function() { return "[object AllInputs: radioInputs: " + this.radioInputs.length + "]"; } function main() { var result = new AllInputs(); }

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  • named_scope and substings

    - by Philb28
    I have a named_scope in rails that finds episodes by there directors given name named_scope :director_given, lambda { |dr| {:joins => :director, :conditions => ['given = ?', dr]} } It works great but I would like it to also work on substrings one the name. e.g. instead of having to search for 'Lucy' you could just search 'Lu'. P.S. I also have another named scope which does exactly the same thing but on the directors last name. It there a way to combine the two? Thanks,

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  • Deleting orphans with JPA

    - by homaxto
    I have a one-to-one relation where I use CascadeType.PERSIST. This has over time build up a huge amount of child records that has not been deleted, to such an extend that it is reflected in the performance. Now I wish to add some code that cleans up the database removing all the child records that are not referenced by a parent. At the moment we are talking 400K+ records, at I need to run the code on all customer installations just to be sure they do not run into the same problem. I think the best solution would be to run a named query (because we support two databases) that deletes the necessary records, and this is where I get into problems, because how should I write it in JPQL? The result I want can be defined like the following sql statement, which unfortunaltely does not run on MySQL. DELETE FROM child c1 WHERE c1.pk NOT IN (SELECT DISTINCT p.pk FROM child c2 JOIN parent p ON p.child = c2.pk);

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  • Java/C++ communication via pipe on Windows

    - by Warlax
    Hi, I have two separate programs, one in Java and one in C++, both running on Windows. We need to do bidirectional interprocess communication between the two. Up until now, we were using this awkward solution of writing to text files and reading them on the other side, where the producer would generate a .lock file when it's done writing and the consumer would remove that when it's done reading... like I said, awkward. If we were on *nix, we would use a pipe using popen() on the C++ and RadomAccessFile on the Java side. It seems to work well. What can we do on Windows? Can we use named pipes? Thank you.

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  • template class: ctor against function -> new C++ standard

    - by Oops
    Hi in this question: http://stackoverflow.com/questions/2779155/template-point2-double-point3-double Dennis and Michael noticed the unreasonable foolishly implemented constructor. They were right, I didn't consider this at that moment. But I found out that a constructor does not help very much for a template class like this one, instead a function is here much more convenient and safe namespace point { template < unsigned int dims, typename T > struct Point { T X[ dims ]; std::string str() { std::stringstream s; s << "{"; for ( int i = 0; i < dims; ++i ) { s << " X" << i << ": " << X[ i ] << (( i < dims -1 )? " |": " "); } s << "}"; return s.str(); } Point<dims, int> toint() { Point<dims, int> ret; std::copy( X, X+dims, ret.X ); return ret; } }; template < typename T > Point< 2, T > Create( T X0, T X1 ) { Point< 2, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; return ret; } template < typename T > Point< 3, T > Create( T X0, T X1, T X2 ) { Point< 3, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; ret.X[ 2 ] = X2; return ret; } template < typename T > Point< 4, T > Create( T X0, T X1, T X2, T X3 ) { Point< 4, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; ret.X[ 2 ] = X2; ret.X[ 3 ] = X3; return ret; } }; int main( void ) { using namespace point; Point< 2, double > p2d = point::Create( 12.3, 34.5 ); Point< 3, double > p3d = point::Create( 12.3, 34.5, 56.7 ); Point< 4, double > p4d = point::Create( 12.3, 34.5, 56.7, 78.9 ); //Point< 3, double > p1d = point::Create( 12.3, 34.5 ); //no suitable user defined conversion exists //Point< 3, int > p1i = p4d.toint(); //no suitable user defined conversion exists Point< 2, int > p2i = p2d.toint(); Point< 3, int > p3i = p3d.toint(); Point< 4, int > p4i = p4d.toint(); std::cout << p2d.str() << std::endl; std::cout << p3d.str() << std::endl; std::cout << p4d.str() << std::endl; std::cout << p2i.str() << std::endl; std::cout << p3i.str() << std::endl; std::cout << p4i.str() << std::endl; char c; std::cin >> c; } has the new C++ standard any new improvements, language features or simplifications regarding this aspect of ctor of a template class? what do you think about the implementation of the combination of namespace, stuct and Create function? many thanks in advance Oops

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  • NetNamedPipe: varying response time when communication is idling

    - by Sven Künzler
    I have two WCF apps communicating one-way over named pipes. All is nice, except for one thing: Normally, the request/response cycle takes zero (marginal) time. However, if there was a time span of, say, half a minute without any communication, the request/response increases up to ~300-500ms. I looked around the net and I got the idea of using a heart beat/ping mechanism to keep the communication channel busy. Using trial and error I found that when doing a request each 10 seconds, the response times stay low. Starting at around 15s intervals, the "hiccup" response times begin to appear. Now I'm wondering where this phenomenon is originating from. I tried setting alle conceivable timeouts on both sides to 1 minute, but that did not help. Can anybody explain what's going on there?

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  • What's the benefit of calling new on an object instance?

    - by Geo
    I'm reading [Programming Perl][1], and I found this code snippet: sub new { my $invocant = shift; my $class = ref($invocant) || $invocant; my $self = { color => "bay", legs => 4, owner => undef, @_, # Override previous attributes }; return bless $self, $class; } With constructors like this one, what's the benefit of calling new on an object instance? I assume that it's what it's for, right? My guess is that if anyone would want to write such a constructor, he would have to add some more code that copies the attributes of the first object to the one about to be created.

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  • PHP: How to Pass child class __construct() arguments to parent::__construct() ?

    - by none
    I have a class in PHP like so: class ParentClass { function __construct($arg) { // Initialize a/some variable(s) based on $arg } } It has a child class, as such: class ChildClass extends ParentClass { function __construct($arg) { // Let the parent handle construction. parent::__construct($arg); } } What if, for some reason, the ParentClass needs to change to take more than one optional argument, which I would like my Child class to provide "just in case"? Unless I re-code the ChildClass, it will only ever take the one argument to the constructor, and will only ever pass that one argument. Is this so rare or such a bad practice that the usual case is that a ChildClass wouldn't need to be inheriting from a ParentClass that takes different arguments? Essentially, I've seen in Python where you can pass a potentially unknown number of arguments to a function via somefunction(*args) where 'args' is an array/iterable of some kind. Does something like this exist in PHP? Or should I refactor these classes before proceeding?

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  • Can C++ Constructors be templates?

    - by Gokul
    Hi, I have non-template class with a templatized constructor. This code compiles for me. But i remember that somewhere i have referred that constructors cannot be templates. Can someone explain whether this is a valid usage? typedef double Vector; //enum Method {A, B, C, D, E, F}; struct A {}; class Butcher { public: template <class Method> Butcher(Method); private: Vector a, b, c; }; template <> Butcher::Butcher(struct A) : a(2), b(4), c(2) { // a = 0.5, 1; // b = -1, 1, 3, 2; // c = 0, 1; } Thanks, Gokul.

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  • Is there anything wrong with taking immediate actions in constructors?

    - by pestaa
    I have classes like this one: class SomeObject { public function __construct($param1, $param2) { $this->process($param1, $param2); } ... } So I can instantly "call" it as some sort of global function just like new SomeObject($arg1, $arg2); which has the benefits of staying concise, being easy to understand, but might break unwritten rules of semantics by not waiting till a method is called. Should I continue to feel bad because of a bad practice, or there's really nothing to worry about? Clarification: I do want an instance of the class. I do use internal methods of the class only. I initialize the object in the constructor, but call the "important" action-taker methods too. I am selfish in the light of these sentences.

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  • Static initialization of a struct with class members

    - by JS Bangs
    I have a struct that's defined with a large number of vanilla char* pointers, but also an object member. When I try to statically initialize such a struct, I get a compiler error. typedef struct { const char* pszA; // ... snip ... const char* pszZ; SomeObject obj; } example_struct; // I only want to assign the first few members, the rest should be default example_struct ex = { "a", "b" }; SomeObject has a public default constructor with no arguments, so I didn't think this would be a problem. But when I try to compile this (using VS), I get the following error: error C2248: 'SomeObject::SomeObject' : cannot access private member declared in class 'SomeObject' Any idea why?

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  • How to instantiate objects of classes that have dependencies injected?

    - by chester89
    Let's say I have some class with dependency injected: public class SomeBusinessCaller { ILogger logger; public SomeBusinessCaller(ILogger logger) { this.logger = logger; } } My question is, how do I instantiate an object of that class? Let's say I have an implementation for this, called AppLogger. After I say ObjectFactory.For<ILogger>().Use<AppLogger>(); how do I call constructor of SomeBusinessCaller? Am I calling SomeBusinessCaller caller = ObjectFactory.GetInstance<SomeBusinessCaller>(); or there is a different strategy for that?

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  • How to stable_sort without copying?

    - by Mehrdad
    Why does stable_sort need a copy constructor? (swap should suffice, right?) Or rather, how do I stable_sort a range without copying any elements? #include <algorithm> class Person { Person(Person const &); // Disable copying public: Person() : age(0) { } int age; void swap(Person &other) { using std::swap; swap(this->age, other.age); } friend void swap(Person &a, Person &b) { a.swap(b); } bool operator <(Person const &other) const { return this->age < other.age; } }; int main() { static size_t const n = 10; Person people[n]; std::stable_sort(people, people + n); }

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  • c++ constructors

    - by aharont
    i wrote this code: class A { public: A(){d=2.2;cout<<d;} A(double d):d(d){cout<<d;} double getD(){return d;} private: double d; }; class Bing { public: Bing(){a=A(5.3);} void f(){cout<<a.getD();} private: A a; }; int main() { Bing b; b.f(); } i get the output: 2.2 5.3 5.3 instead of 5.3 5.3. it's something in the constructor.... wahy am i getting this? how can i fix it?

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  • can constructors actually return Strings?

    - by elwynn
    Hi all, I have a class called ArionFileExtractor in a .java file of the same name. public class ArionFileExtractor { public String ArionFileExtractor (String fName, String startText, String endText) { String afExtract = ""; // Extract string from fName into afExtract in code I won't show here return afExtract; } However, when I try to invoke ArionFileExtractor in another .java file, as follows: String afe = ArionFileExtractor("gibberish.txt", "foo", "/foo"); NetBeans informs me that there are incompatible types and that java.lang.String is required. But I coded ArionFileExtractor to return the standard string type, which is java.lang.string. I am wondering, can my ArionFileExtractor constructor legally return a String? I very much appreciate any tips or pointers on what I'm doing wrong here.

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  • Best way to convert Stream (of unknown length) to byte array, in .NET?

    - by Frank Hamming
    Hello, I have the following code to read data from a Stream (in this case, from a named pipe) and into a byte array: // NPSS is an instance of NamedPipeServerStream int BytesRead; byte[] StreamBuffer = new byte[BUFFER_SIZE]; // defined elsewhere (less than total possible message size, though) MemoryStream MessageStream = new MemoryStream(); do { BytesRead = NPSS.Read(StreamBuffer, 0, StreamBuffer.Length); MessageStream.Write(StreamBuffer, 0, BytesRead); } while (!NPSS.IsMessageComplete); byte[] Message = MessageStream.ToArray(); // final data Could you please take a look and let me know if it can be done more efficiently or neatly? Seems a bit messy as it is, using a MemoryStream. Thanks!

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  • Use of .apply() with 'new' operator. Is this possible?

    - by Premasagar
    In JavaScript, I want to create an object instance (via the new operator), but pass an arbitrary number of arguments to the constructor. Is this possible? What I want to do is something like this (but the code below does not work): function Something(){ // init stuff } function createSomething(){ return new Something.apply(null, arguments); } var s = createSomething(a,b,c); // 's' is an instance of Something The Answer From the responses here, it became clear that there's no in-built way to call .apply() with the new operator. However, people suggested a number of really interesting solutions to the problem. My preferred solution was this one from Matthew Crumley (I've modified it to pass the arguments property): var createSomething = (function() { function F(args) { return Something.apply(this, args); } F.prototype = Something.prototype; return function() { return new F(arguments); } })();

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