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  • F# Class with Generics : 'constructor deprecated' error

    - by akaphenom
    I am trying to create a a class that will store a time series of data - organized by groups, but I had some compile errors so I stripped down to the basics (just a simple instantiation) and still can't overcome the compile error. I was hoping some one may have seen this issue before. Clas is defined as: type TimeSeriesQueue<'V, 'K when 'K: comparison> = class val private m_daysInCache: int val private m_cache: Map<'K, 'V list ref > ref; val private m_getKey: ('V -> 'K) ; private new(getKey) = { m_cache = ref Map.empty m_daysInCache = 7 ; m_getKey = getKey ; } end So that looks OK to me (it may not be, but doesnt have any errors or warnings) - the instantiation gets the error: type tempRec = { someKey: string ; someVal1: int ; someVal2: int ; } let keyFunc r:tempRec = r.someKey // error occurs on the following line let q = new TimeSeriesQueue<tempRec, string> keyFunc This construct is deprecated: The use of the type syntax 'int C' and 'C ' is not permitted here. Consider adjusting this type to be written in the form 'C' NOTE This may be simple stupidity - I am just getting back from holiday and my brain is still on time zone lag...

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  • Scala Array constructor?

    - by Lukasz Lew
    scala> val a = Array [Double] (10) a: Array[Double] = Array(10.0) scala> val a = new Array [Double] (10) a: Array[Double] = Array(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0) Why these two expressions have different semantics?

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  • Simple factory to retrieve files using constructor dependency injection

    - by mrblah
    I want to create a class, that is flexible so I can switch implementations. Problem: Store files/documents Options: either store locally on the server filesystem, database or etc. Can someone help with a skeleton structure of the class, and how I would call it? I am not using an IoC, and don't really want to just yet. I just want the flexibility where I would make maybe 1 code change in the factory to call another implementation.

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  • Classes, constructor and pointer class members

    - by pocoa
    I'm a bit confused about the object references. Please check the examples below: class ListHandler { public: ListHandler(vector<int> &list); private: vector<int> list; } ListHandler::ListHandler(vector<int> &list) { this->list = list; } Here I would be wasting memory right? So the right one would be: class ListHandler { public: ListHandler(vector<int>* list); private: vector<int>* list; } ListHandler::ListHandler(vector<int>* list) { this->list = list; } ListHandler::~ListHandler() { delete list; }

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  • troubles with generated constructor in linq2sql

    - by zerkms
    After adding one more table to linq2sql .dbml schema i got Value cannot be null. Parameter name: mapping Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentNullException: Value cannot be null. Parameter name: mapping and it refers to autogenerated file: Line 45: #endregion Line 46: Line 47: public db() : Line 48: base(global::data.Properties.Settings.Default.nanocrmConnectionString, mappingSource) Line 49: { Any ideas why this hapenned and how to solve this?

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  • Constructor is being invoked twice

    - by Knowing me knowing you
    In code: LINT a = "12"; LINT b = 3; a = "3";//WHY THIS LINE INVOKES CTOR? std::string t = "1"; //LINT a = t;//Err NO SUITABLE CONV FROM STRING TO LINT. Shouldn't ctor do it? #pragma once #include "LINT_rep.h" class LINT { private: typedef LINT_rep value_type; const value_type* my_data_; template<class T> void init_(const T&); public: LINT(const char* = 0); LINT(const std::string&); LINT(const LINT&); LINT(const long_long&); LINT& operator=(const LINT&); virtual ~LINT(void); LINT operator+()const; //DONE LINT operator+(const LINT&)const;//DONE LINT operator-()const; //DONE LINT operator-(const LINT&)const;//DONE LINT operator*(const LINT&)const;//DONE LINT operator/(const LINT&)const;///WAITS FOR APPROVAL LINT& operator+=(const LINT&);//DONE LINT& operator-=(const LINT&);//DONE LINT& operator*=(const LINT&);//DONE LINT operator/=(const LINT&);///WAITS FOR APPROVAL }; in line number 3 instead of assignment optor ctor is invoked. Why? I'm willing to uppload entire solution on some server otherwise it's hard to put everything in here. I can also upload video file. Another thing is that when I implement this assignment optor I'm getting an error that this optor is already in obj file? What's going on?

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  • Use Lambda in Attribute constructor to get method's parameters

    - by Anthony Shaw
    I'm not even sure if this is possible, but I've exhausted all of my ideas trying to figure this out, so I figured I'd send this out to the community and see what you thought. And, if it's not possible, maybe you'd have some ideas as well. I'm trying to make an Attribute class that I can add to a method that would allow me to use a lambda expression to get each parameter of the method public ExampleAttribute : Attribute { public object Value { get; set; } public ExampleAttribute(--something here to make the lambda work--, object value) { Value = value; } } I'd like to be able to something like this below: [Example(x=x.Id, 4)] [Example(x=x.filter, "string value")] public ActionResult Index(int Id, string filter) { return View(); } I understand that I might be completely dreaming with this idea. I'm basically trying to write a model to allow for self-documenting REST API Documentation. In a recent project here at work we wrote a dozen or so services with 5 to 15 methods on each, I figure it's easier to write something to do this, than to hand code a documentation page for each. I would plan to eventually release this as an open-source project once I have it in a place that I feel it's releasable.

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  • explicit copy constructor or implicit parameter by value

    - by R Samuel Klatchko
    I recently read (and unfortunately forgot where), that the best way to write operator= is like this: foo &operator=(foo other) { swap(*this, other); return *this; } instead of this: foo &operator=(const foo &other) { foo copy(other); swap(*this, copy); return *this; } The idea is that if operator= is called with an rvalue, the first version can optimize away construction of a copy. So when called with a rvalue, the first version is faster and when called with an lvalue the two are equivalent. I'm curious as to what other people think about this? Would people avoid the first version because of lack of explicitness? Am I correct that the first version can be better and can never be worse?

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  • Can't seem to redirect from a ViewScoped constructor.

    - by Andrew
    I'm having trouble redirecting from a view scoped bean in the case that we don't have the required info for the page in question. The log entry in the @PostContruct is visible in the log right before a NPE relating to the view trying to render itself instead of following my redirect. Why is it ignoring the redirect? Here's my code: @ManagedBean public class WelcomeView { private String sParam; private String aParam; public WelcomeView() { super(); sParam = getURL_Param("surveyName"); aParam = getURL_Param("accountName"); project = fetchProject(sParam, aParam); } @PostConstruct public void redirectWithoutProject() { if (null == project) { try { logger.warn("NO project [" + sParam + "] for account [" + aParam + "]"); FacesContext fc = FacesContext.getCurrentInstance(); fc.getExternalContext().redirect("/errors/noSurvey.jsf"); return; } catch (Exception e) { e.printStackTrace(); } } } .... public boolean getAuthenticated() { if (project.getPasswordProtected()) { return enteredPassword.equals(project.getLoginPassword()); } else return true; } } Here's the stack trace: SEVERE: Error Rendering View[/participant/welcome.xhtml] javax.el.ELException: /templates/participant/welcome.xhtml @80,70 rendered="#{welcomeView.authenticated}": Error reading 'authenticated' on type com.MYCODE.general.controllers.participant.WelcomeView at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:107) at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:190) at javax.faces.component.UIComponentBase.isRendered(UIComponentBase.java:416) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1607) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1616) at javax.faces.render.Renderer.encodeChildren(Renderer.java:168) at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:848) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1613) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1616) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1616) at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:380) at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:126) at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:127) at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139) at javax.faces.webapp.FacesServlet.service(FacesServlet.java:313) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at com.MYCODE.general.filters.StatsFilter.doFilter(StatsFilter.java:28) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:568) at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:421) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447) at java.lang.Thread.run(Thread.java:637) Caused by: java.lang.NullPointerException at com.MYCODE.general.controllers.participant.WelcomeView$$M$863c205f.getAuthenticated(WelcomeView.java:127) at com.MYCODE.general.controllers.participant.WelcomeView$$A$863c205f.getAuthenticated(<generated>) at com.MYCODE.general.controllers.participant.WelcomeView.getAuthenticated(WelcomeView.java:125) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at javax.el.BeanELResolver.getValue(BeanELResolver.java:62) at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:53) at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72) at org.apache.el.parser.AstValue.getValue(AstValue.java:118) at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186) at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:102) ... 33 more

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  • Define data members within constructor

    - by bertsisterwanda
    I have got this little snippet of code, I want to be able to define each array element as a new data member. class Core_User { protected $data_memebers = array( 'id' = '%d', 'email' = '"%s"', 'password' = '"%s"', 'title' = '"%s"', 'first_name' = '"%s"', 'last_name' = '"%s"', 'time_added' = '%d' , 'time_modified' = '%d' , ); function __construct($id = 0, $data = NULL) { foreach($data_memebers as $member){ //protected new data member } }

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  • Need some help with constructor

    - by mousey
    you have a class A, where you set ctor to be private, so a client can't call "A a;" to create obj on stack. But someday another developer add a new ctor: "A(int)" and try to call "A a(1);" inside main(). So this will create a obj on stack. How do you prevent that?

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  • JavaScript: using constructor without operator 'new'

    - by GetFree
    Please help me to understand why the following code works: <script> var re = RegExp('\\ba\\b') ; alert(re.test('a')) ; alert(re.test('ab')) ; </script> In the first line there is no new operator. As far as I know, a contructor in JavaScript is a function that initialize objects created by the operator new and they are not meant to return anything.

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  • static readonly field initializer vs static constructor initialization

    - by stackoverflowuser
    Below are 2 different ways to initialize static readonly fields. Is there a difference between the 2 approaches? If yes, when should one be preferred over the other? class A { private static readonly string connectionString = WebConfigurationManager.ConnectionStrings["SomeConnection"].ConnectionString; } class B { private static readonly string connectionString; static B() { connectionString = WebConfigurationManager.ConnectionStrings["SomeConnection"].ConnectionString; } } Thanks.

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  • constructor function's object literal returns toString() method but no other method

    - by JohnMerlino
    I'm very confused with javascript methods defined in objects and the "this" keyword. In the below example, the toString() method is invoked when Mammal object instantiated: function Mammal(name){ this.name=name; this.toString = function(){ return '[Mammal "'+this.name+'"]'; } } var someAnimal = new Mammal('Mr. Biggles'); alert('someAnimal is '+someAnimal); Despite the fact that the toString() method is not invoked on the object someAnimal like this: alert('someAnimal is '+someAnimal.toString()); It still returns 'someAnimal is [Mammal "Mr. Biggles"]' . That doesn't make sense to me because the toString() function is not being called anywhere. Then to add even more confusion, if I change the toString() method to a method I make up such as random(): function Mammal(name){ this.name=name; this.random = function(){ return Math.floor(Math.random() * 15); } } var someAnimal = new Mammal('Mr. Biggles'); alert(someAnimal); It completely ignores the random method (despite the fact that it is defined the same way was the toString() method was) and returns: [object object] Another issue I'm having trouble understanding with inheritance is the value of "this". For example, in the below example function person(w,h){ width.width = w; width.height = h; } function man(w,h,s) { person.call(this, w, h); this.sex = s; } "this" keyword is being send to the person object clearly. However, does "this" refer to the subclass (man) or the super class (person) when the person object receives it? Thanks for clearing up any of the confusion I have with inheritance and object literals in javascript.

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  • DSACryptoServiceProvider constructor throws CryptographicException

    - by Rick
    This code below thows the following error: System.Security.Cryptography.CryptographicException "The handle is invalid" CspParameters CSPParam = new System.Security.Cryptography.CspParameters(13, null, null); CSPParam.Flags = CspProviderFlags.UseMachineKeyStore; CSPParam.KeyContainerName = "MyKeys"; System.Security.Cryptography.DSACryptoServiceProvider r = new System.Security.Cryptography.DSACryptoServiceProvider(CSPParam); //Error occurs here This code had been working with no issues then it started throwing this error. I can't think of anything that I have changed that relates to this. Has nayone seen this error? Any ideas of what to try?

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  • Trouble with an depreciated constructor visual basic visual studio 2010

    - by VBPRIML
    My goal is to print labels with barcodes and a date stamp from an entry to a zebra TLP 2844 when the user clicks the ok button/hits enter. i found what i think might be the code for this from zebras site and have been integrating it into my program but part of it is depreciated and i cant quite figure out how to update it. below is what i have so far. The printer is attached via USB and the program will also store the entered numbers in a database but i have that part done. any help would be greatly Appreciated.   Public Class ScanForm      Inherits System.Windows.Forms.Form    Public Const GENERIC_WRITE = &H40000000    Public Const OPEN_EXISTING = 3    Public Const FILE_SHARE_WRITE = &H2      Dim LPTPORT As String    Dim hPort As Integer      Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String,                                                                           ByVal dwDesiredAccess As Integer,                                                                           ByVal dwShareMode As Integer, <MarshalAs(UnmanagedType.Struct)> ByRef lpSecurityAttributes As SECURITY_ATTRIBUTES,                                                                           ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer,                                                                           ByVal hTemplateFile As Integer) As Integer          Public Declare Function CloseHandle Lib "kernel32" Alias "CloseHandle" (ByVal hObject As Integer) As Integer      Dim retval As Integer           <StructLayout(LayoutKind.Sequential)> Public Structure SECURITY_ATTRIBUTES          Private nLength As Integer        Private lpSecurityDescriptor As Integer        Private bInheritHandle As Integer      End Structure            Private Sub OKButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OKButton.Click          Dim TrNum        Dim TrDate        Dim SA As SECURITY_ATTRIBUTES        Dim outFile As FileStream, hPortP As IntPtr          LPTPORT = "USB001"        TrNum = Me.ScannedBarcodeText.Text()        TrDate = Now()          hPort = CreateFile(LPTPORT, GENERIC_WRITE, FILE_SHARE_WRITE, SA, OPEN_EXISTING, 0, 0)          hPortP = New IntPtr(hPort) 'convert Integer to IntPtr          outFile = New FileStream(hPortP, FileAccess.Write) 'Create FileStream using Handle        Dim fileWriter As New StreamWriter(outFile)          fileWriter.WriteLine(" ")        fileWriter.WriteLine("N")        fileWriter.Write("A50,50,0,4,1,1,N,")        fileWriter.Write(Chr(34))        fileWriter.Write(TrNum) 'prints the tracking number variable        fileWriter.Write(Chr(34))        fileWriter.Write(Chr(13))        fileWriter.Write(Chr(10))        fileWriter.Write("A50,100,0,4,1,1,N,")        fileWriter.Write(Chr(34))        fileWriter.Write(TrDate) 'prints the date variable        fileWriter.Write(Chr(34))        fileWriter.Write(Chr(13))        fileWriter.Write(Chr(10))        fileWriter.WriteLine("P1")        fileWriter.Flush()        fileWriter.Close()        outFile.Close()        retval = CloseHandle(hPort)          'Add entry to database        Using connection As New SqlClient.SqlConnection("Data Source=MNGD-LABS-APP02;Initial Catalog=ScannedDB;Integrated Security=True;Pooling=False;Encrypt=False"), _        cmd As New SqlClient.SqlCommand("INSERT INTO [ScannedDBTable] (TrackingNumber, Date) VALUES (@TrackingNumber, @Date)", connection)            cmd.Parameters.Add("@TrackingNumber", SqlDbType.VarChar, 50).Value = TrNum            cmd.Parameters.Add("@Date", SqlDbType.DateTime, 8).Value = TrDate            connection.Open()            cmd.ExecuteNonQuery()            connection.Close()        End Using          'Prepare data for next entry        ScannedBarcodeText.Clear()        Me.ScannedBarcodeText.Focus()      End Sub

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  • const object and const constructor

    - by Muhammad alaa
    Is there any way to know if an object is a const object or regular object, for instance consider the following class class String { String(const char* str); }; if user create a const object from String then there is no reason to copy the passed native string and that because he will not make any manipulation on it, the only thing he will do is get string size, string search and other functions that will not change the string.

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  • Why do not C++11's move constructor/assignment operator act as expected

    - by xmllmx
    #include <iostream> using namespace std; struct A { A() { cout << "A()" << endl; } ~A() { cout << "~A()" << endl; } A(A&&) { cout << "A(A&&)" << endl; } A& operator =(A&&) { cout << "A& operator =(A&&)" << endl; return *this; } }; struct B { // According to the C++11, the move ctor/assignment operator // should be implicitly declared and defined. The move ctor // /assignment operator should implicitly call class A's move // ctor/assignment operator to move member a. A a; }; B f() { B b; // The compiler knows b is a temporary object, so implicitly // defined move ctor/assignment operator of class B should be // called here. Which will cause A's move ctor is called. return b; } int main() { f(); return 0; } My expected output should be: A() A(A&&) ~A() ~A() However, the actual output is: (The C++ compiler is: Visual Studio 2012) A() ~A() ~A() Is this a bug of VC++? or just my misunderstanding?

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  • Nested class with hidden constructor impossible in c#?

    - by luckyluke
    I' ve been doing some programming lately and faced an issue which i found weird in c#. (at least for me) public class Foo { //whatever public class FooSpecificCollection : List<Bar> { //implementation details } public FooSpecificCollection GetFoosStuff() { //return the collection } } I want the consumer of Foo to be able to obtain a reference to FooSpecificCollection, even perform some operations on it. Maybe even set it to some other property of Foo or smth like that, but not To be able to CREATE an instance of this class. (the only class that should be able to instatiate this collection should be Foo. Is my request really that far-fetched? I know that people way smarter defined c# but shouldn't there be such an option that a parent class can create a nested class instance but nobody else can't. So far I created a solution to make an abstract class, or interface available through the property and implement a concrete private class that is not available anywhere else. Is this a correct way to handle such a situation.?

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  • Using a constructor for return.

    - by Fecal Brunch
    Hi, Just a quick question. I've written some code that returns a custom class Command, and the code I've written seems to work fine. I was wondering if there are any reasons that I shouldn't be doing it this way. It's something like this: Command Behavior::getCommand () { char input = 'x'; return Command (input, -1, -1); } Anyway, I read that constructors aren't meant to have a return value, but this works in g++. Thanks for any advice, Rhys

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  • How to run Jquery constructor from own function?

    - by Invidian
    I need to create a function which will returning jQuery.Color object and i have no idea how to do it. Here is code example function newcolor () { var obj = new $.Color( 'rgb(0,0,0)' ); return obj;} var foo = newcolor(); foo.red(); Edit: My full code: function my (element,a,b,c){ //class my this.target = $(elem); this.new_color = function (a,b,c) { return new $.Color( 'rgb('+a+','+b+','+c+')'); } this.base_color = new_color (a,b,c); this.colorize = function () ( this.target.css({ background-color: new_color }); } var div = new My($('foo'),0,0,0); div.new_color(255,255,255); div.colorize(); My goal is to create class which can hold jquery element and operate on it. Now I'm stuck on returning $.Color().

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  • C++ Virtual Constructor, without clone()

    - by Julien L.
    I want to perform "deep copies" of an STL container of pointers to polymorphic classes. I know about the Prototype design pattern, implemented by means of the Virtual Ctor Idiom, as explained in the C++ FAQ Lite, Item 20.8. It is simple and straightforward: struct ABC // Abstract Base Class { virtual ~ABC() {} virtual ABC * clone() = 0; }; struct D1 : public ABC { virtual D1 * clone() { return new D1( *this ); } // Covariant Return Type }; A deep copy is then: for( i = 0; i < oldVector.size(); ++i ) newVector.push_back( oldVector[i]->clone() ); Drawbacks As Andrei Alexandrescu states it: The clone() implementation must follow the same pattern in all derived classes; in spite of its repetitive structure, there is no reasonable way to automate defining the clone() member function (beyond macros, that is). Moreover, clients of ABC can possibly do something bad. (I mean, nothing prevents clients to do something bad, so, it will happen.) Better design? My question is: is there another way to make an abstract base class clonable without requiring derived classes to write clone-related code? (Helper class? Templates?) Following is my context. Hopefully, it will help understanding my question. I am designing a class hierarchy to perform operations on a class Image: struct ImgOp { virtual ~ImgOp() {} bool run( Image & ) = 0; }; Image operations are user-defined: clients of the class hierarchy will implement their own classes derived from ImgOp: struct CheckImageSize : public ImgOp { std::size_t w, h; bool run( Image &i ) { return w==i.width() && h==i.height(); } }; struct CheckImageResolution; struct RotateImage; ... Multiple operations can be performed sequentially on an image: bool do_operations( std::vector< ImgOp* > v, Image &i ) { std::for_each( v.begin(), v.end(), /* bind2nd(mem_fun(&ImgOp::run), i ...) don't remember syntax */ ); } int main( ... ) { std::vector< ImgOp* > v; v.push_back( new CheckImageSize ); v.push_back( new CheckImageResolution ); v.push_back( new RotateImage ); Image i; do_operations( v, i ); } If there are multiple images, the set can be split and shared over several threads. To ensure "thread-safety", each thread must have its own copy of all operation objects contained in v -- v becomes a prototype to be deep copied in each thread.

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  • C++ explicit template specialization of templated constructor of templated class

    - by Victor Liu
    I have a class like template <class T> struct A{ template <class U> A(U u); }; I would like to write an explicit specialization of this for a declaration like A<int>::A(float); In the following test code, if I comment out the specialization, it compiles with g++. Otherwise, it says I have the wrong number of template parameters: #include <iostream> template <class T> struct A{ template <class U> A(T t, U *u){ *u += U(t); } }; template <> template <> A<int>::A<int,float>(int t, float *u){ *u += U(2*t); } int main(){ float f = 0; int i = 1; A<int>(i, &f); std::cout << f << std::endl; return 0; }

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  • Copy constructor called even when returning by reference?

    - by Johnyy
    Hi, I am testing the return of local objects by reference. My original test went well but something else happens unexpected. #include <iostream> using namespace std; class MyInt { public: MyInt(int i){ value = new int(i); } ~MyInt(){ delete value; } int getValue(){ return *value; } MyInt(const MyInt &b){ cout<<"Copy"<<endl; } private: int* value; }; MyInt& returnref(){ MyInt a(10); cout<<"Returning from returnref()"<<endl; return a; } int main(){ MyInt a = returnref(); cout<<a.getValue()<<endl; return 0; } My console prints "Returning from ..." then "Copy" then a random value. My understanding of pass by reference is that it does not need to make any copy. Why is it not doing what I expected?

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