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• Determine an object's class returned by a factory method (Error: function does not take 1 arguments

  - by tzippy

  I have a factorymethod that either returns an object of baseclass or one that is of derivedclass (a derived class of baseclass). The derived class has a method virtual void foo(int x) that takes one argument. baseclass however has virtual void foo() without an argument. In my code, a factory method returns a pointer of type bar that definetly points to an object of class derivedclass. However since this is only known at runtime I get a compiler error saying that foo() does not take an argument. Can I cast this pointer to a pointer of type derivedclass? std::auto_ptr<baseclass> bar = classfactory::CreateBar(); //returns object of class derivedclass bar->foo(5); class baseclass { public: virtual void foo(); } class derivedclass : public baseclass { public: virtual void foo(int x); }

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• How to minimize the amount of place used by GPL copyright notice?

  - by Lukasz Lew

  Gnu GPL page advocates a following header in each file of GPL project: This file is part of Foobar. Foobar is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Foobar is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Foobar. If not, see http://www.gnu.org/licenses/. I find this an over kill. Can't it be shorter and somehow refer to COPYING or LICENCE file?

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• Returning two or more values from a function

  - by cf_PhillipSenn

  I need to return multiple values from a ColdFusion function in an ajax callback function. Here's what I've got: $('input[name="StateName"]').live('change', function() { var StateID = $(this).parents('tr').attr('id'); var StateName = $(this).val(); $.ajax({ url: 'Remote/State.cfc' ,type: "POST" ,data: { 'method': 'UpdateStateName' ,'StateID': StateID ,'StateName': StateName } ,success: function(result){ if (isNaN(result)) { $('#msg').text(result).addClass('err'); } else { $('#' + result + ' input[name="StateName"]').addClass('changed'); }; } ,error: function(msg){ $('#msg').text('Connection error').addClass('err'); } }); }); If I trap a database error, then the success callback is fired, and the result is Not a Number (It is in fact, the text of the error message). I need the function to also pass back other values. One might be the primary key of the row that caused the error. Another might be the old StateName, so that I can refresh the old value on the screen so that the client will know absolutely for sure that their change did not take effect. I guess I'm breaking the rule of atomicity here and need to fix that, because I'm using result as both the primary key of the row that was updated, or it's the error message if the update fails. I need to return both the primary key and the error message.

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• Java Null Pointer Exception :-(

  - by John-Michael Reed

  I've got a Null Pointer Exception in my main that just won't go away and I'm totally out of ideas. The error is on the line "Board[x][y].color = 2;" in which Board is a public, static array of piece objects that contain instance variables like the one "color" that is being set to 2 in the above statement. Pieces is not static - that is there are many different copies of pieces, each with its own data, but only one board. The array has been initialized and defined as both public Piece[][] Board = new Piece[8][8] and public static Piece[][] Board = new Piece[8][8], but no matter how I mess around with it (getting rid of static, putting the variable in another object, etc.), I can't seem to get the error to go away. Help?

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• Help me understand the code snippet in c#

  - by Benny

  I am reading this blog: Pipes and filters pattern I am confused by this code snippet: public class Pipeline<T> { private readonly List<IOperation<T>> operations = new List<IOperation<T>>(); public Pipeline<T> Register(IOperation<T> operation) { operations.Add(operation); return this; } public void Execute() { IEnumerable<T> current = new List<T>(); foreach (IOperation<T> operation in operations) { current = operation.Execute(current); } IEnumerator<T> enumerator = current.GetEnumerator(); while (enumerator.MoveNext()); } } what is the purpose of this statement: while (enumerator.MoveNext());? seems this code is a noop.

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• get value of a property o => o.Property1 , defined in lambda

  - by Omu

  I need to get the value of a property defined in a lambda public static MvcHtmlString MyHelper<T, TProperty>( this HtmlHelper<T> html, Expression<Func<T, TProperty>> prop) { var value = \\ get the value of Prop1 (not the name "Prop1") ... } the intended usage is something like: public class FooViewModel { public string Prop1 { get;set; } } <%@ Page ViewPage<FooViewModel> %> <%=Html.MyHelper(o => o.Prop1) %>

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• SELECT product from subclass: How many queries do I need?

  - by Stefano

  I am building a database similar to the one described here where I have products of different type, each type with its own attributes. I report a short version for convenience product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id ... (common attributes to all product) magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id ... (magazine-specific attributes) web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id ... (web-site specific attributes) This way I do not need to make a huge table with a column for each attribute of different product types (most of which will then be NULL) How do I SELECT a product by product.product_id and see all its attributes? Do I have to make a query first to know what type of product I am dealing with and then, through some logic, make another query to JOIN the right tables? Or is there a way to join everything together? (if, when I retrieve the information about a product_id there are a lot of NULL, it would be fine at this point). Thank you

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• Is there a better way to minimize this C# event repetition?

  - by Damien Wildfire

  I have a lot of code like this: public class Microwave { private EventHandler<EventArgs> _doorClosed; public event EventHandler<EventArgs> DoorClosed { add { lock (this) _doorClosed += value; } remove { lock (this) _doorClosed -= value; } } private EventHandler<EventArgs> _lightbulbOn; public event EventHandler<EventArgs> LightbulbOn { add { lock (this) _lightbulbOn += value; } remove { lock (this) _lightbulbOn -= value; } } // ... } You can see that much of this is boilerplate. In Ruby I'd be able to do something like this: class Microwave has_events :door_closed, :lightbulb_on, ... end Is there a similar shorter way of removing this boilerplate in C#?

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• VB.NET: I Cant find the index of an array

  - by steve

  This is the code for my array (which is working) Public numUsers As Integer Public fNameUsers As String = ("..\..\..\users.txt") Public UserRecords As Usersclass() 'note... this line is in a module ' reader = New System.IO.StreamReader(fNameUsers) numUsers = 0 'Split the array up at each delimiter of "," and add new objects ' Do While reader.Peek <> -1 ReDim Preserve UserRecords(numUsers) oneline = reader.ReadLine fields = oneline.Split(",") UserRecords(numUsers) = New Usersclass UserRecords(numUsers).AccountNumber = fields(0) UserRecords(numUsers).CourseName = fields(1) UserRecords(numUsers).FirstName = fields(2) UserRecords(numUsers).LastName = fields(3) UserRecords(numUsers).DOB = fields(4) UserRecords(numUsers).Email = fields(5) UserRecords(numUsers).CourseProgress = (6) UserRecords(numUsers).AdminCheck = fields(7) numUsers = numUsers + 1 Loop reader.Close() My problem is that I don't know how to lookup the index of an array where the .accountNumber = a variable. For example the acccountNumber is 253, what is the code to find the index this relates to???? Thanks in advance

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• How would I associate a "Note" class to 4+ classes without creating lookup table for each associatio

  - by Gthompson83

  Im creating a project tasklist application. I have project, section, task, issue classes, and would like to use one class to be able to add simple notes to any object instance of those classes. The task, issue tables both use a standard identity field as a primary key. The section table has a two field primary key. The project table has a single int primary key defined by the user. Is there a way to associate the note class with each of these without using a seperate lookup table for each class? I'm not so sure my original idea is a decent way to implement this. I considered the following (each variable mapping to a field n the notes table. Private _NoteId As Integer Private _ProjectId As Integer Private _SectionId As Integer Private _SectionId2 As Integer Private _TaskId As Integer Private _IssueId As Integer Private _Note As String Private _UserId As Guid Then I would be able to write seperate methods (getProjectNotes, getTaskNotes) to get notes attached to each class. I started writing this a few weeks ago but got pulled away before i could finish. When revisiting this code today my first thought "this is retarded". Thoughts on drawbacks to this design?

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• Open generic interface types of open implementation don't equal interface type?

  - by George Mauer

  Here's a test that should, in my opinion be passing but is not. [TestMethod] public void can_get_open_generic_interface_off_of_implementor() { typeof(OpenGenericWithOpenService<>).GetInterfaces().First() .ShouldEqual(typeof(IGenericService<>)); } public interface IGenericService<T> { } public class OpenGenericWithOpenService<T> : IGenericService<T> { } Why does this not pass? Given Type t = typeof(OpenGenericWithOpenService<>) how do I get typeof(IGenericService<)? I'm generally curious, but if you're wondering what I'm doing, I'm writing a Structuremap convention that forwards all interfaces implemented by a class to the implementation (as a singleton).

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• difference in using virtual and not using virtual

  - by numerical25

  In C++, whether you choose to use virtual or not, you can still override the base class function. The following compiles just fine... class Enemy { public: void SelectAnimation(); void RunAI(); void Interact() { cout<<"Hi I am a regular Enemy"; } private: int m_iHitPoints; }; class Boss : public Enemy { public: void Interact() { cout<<"Hi I am a evil Boss"; } }; So my question is what is the difference in using or not using the virtual function. And what is the disadvantage.

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• How compiling circular dependencies works?

  - by Fabio F.

  I've made the example in Java but I think (not tested) that it works in other (all?) languages. You have 2 files M.java that says public class MType{ XType x; MType(){ x = null;} } and another file XType.java (in the same directory) public class XType{ MType m; public XType(MType m){ this.m=m;} } Ok it's BAD programming , but.. if you run javac XType it compiles: compiles even MTypes because XType needs it. But.. MType needs XType.. how it works? How does the compiler know what is happening? Probably is a stupid question, but I would like to know how the compiler (javac or other compilers if you know.) manages that situation, not how to avoid it. I'm asking because i'm writing a precompiler and I would like to manage that situation.. Thank you

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• Can C# make my class look like another class?

  - by Vaccano

  I have a class that look like this: public class BasePadWI { public WorkItem WorkItemReference { get; set; } .... Other stuff ...... } I then have a dictionary that is defined like this: public Dictionary<BasePadWI, Canvas> Pad { get; set; } I would then like to make a call like this: List<WorkItem> workItems = Pad.Keys.ToList(); (Note: WorkItem is a sealed class, so I cannot inherit.) Is there some trickery that I could do in the class to make it look like a WorkItem? I have done this in the mean time: List<WorkItem> workItems = Pad.Keys.ToList().ConvertAll(x=>x.WorkItem);

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• Make sure base method gets called in C#

  - by Fnatte

  Can I somehow force a derived class to always call the overridden methods base? public class BaseClass { public virtual void Update() { if(condition) { throw new Exception("..."); // Prevent derived method to be called } } } And then in a derived class : public override void Update() { base.Update(); // Forced call // Do any work } I've searched and found a suggestion to use a non-virtual Update() but also a protected virtual UpdateEx(). It just doesn't feel very neat, isn't there any better way? I hope you get the question and I am sorry for any bad English.

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• Unit Testing: hard dependency MessageBox.Show()

  - by Sean B

  What ways can the SampleConfirmationDialog be unit tested? The SampleConfirmationDialog would be exercised via acceptance tests, however how could we unit test it, seeing as MessageBox is not abstract and no matching interface? public interface IConfirmationDialog { /// <summary> /// Confirms the dialog with the user /// </summary> /// <returns>True if confirmed, false if not, null if cancelled</returns> bool? Confirm(); } /// <summary> /// Implementation of a confirmation dialog /// </summary> public class SampleConfirmationDialog : IConfirmationDialog { /// <summary> /// Confirms the dialog with the user /// </summary> /// <returns>True if confirmed, false if not, null if cancelled</returns> public bool? Confirm() { return MessageBox.Show("do operation x?", "title", MessageBoxButton.YesNo, MessageBoxImage.Question) == MessageBoxResult.Yes; } }

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• ASP webservice serialization of properties

  - by badra

  I got a class like this which gets returned from an ASP webservice: class Data { public int A { get; set; } public int B { get; set; } public int Sum { get { return A + B; } } } When I try to consume the webservice on the client side using Silverlight I only get the properties A and B but I also need Sum. I know I can't return any logic from a webservice, so the expected behavior was it will return the the Sum as a fixed/precalculated property in the client which is what I need. Any ideas except for redesigning my class? Thanks ...

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• Is it a good practice to create a reference to application context and use it anywhere?

  - by kknight

  I have to use context in many places of my code such as database operations, preference operations, etc. I don't want to pass in context for every method. Is it a good practice to create a reference to application context at the main Activity and use it anywhere such as database operations? So, I don't need some many context in method parameters, and the code can avoid position memory leak due to use of Activity Context. public class MainActivity extends Activity { public static Context s_appContext; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); s_appContext = this.getApplicationContext();

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• C# Property inheritance question

  - by mcxiand

  Hi all, How do i inherit a property in c# from an interface and give that property other name on the class? For example: public interface IFoo { int Num {get;set;} } public class IFooCls : IFoo { int Ifoo.Num{get;set} } In this case, what the property name in the interface is also the same in the class. What i want is to give other property name on the class but still pointing to "Num" in the interface in this case. In VB, we can do it like this: Public ReadOnly Property UserId() As String Implements System.Security.Principal.IIdentity.Name Get Return _userId End Get End Property

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• c++ polymorphism and other function question

  - by aharont

  i have got this code: class father{ public: virtual void f() { cout<<1;} }; class son:public father{ public: void f() {cout<<2;} }; void test (father x){x.f();} int main(){ son s; test(s); } the question says: the output is '1', what is the rule about polymorphism that the programmer forgot and how can i fix it so the output would be '2'? there is another rule that the programmer forgot when he wrote the father class, and he need to add an empty function to avoid problems from other sons of the father class. what is the rule and what is the missing function? another question write the g function so the next code would run with no crashes int x=11; g(x)=22;

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• Which is the better way to avoid magic string keys? Using string const keys in a class or using enumeration?

  - by user596314

  My idea is to avoid magic string keys in my Asp.Net MVC application. To do so, I want to create string constant keys to be shared in the application. For example, I can write TempData[MyClass.Message] or TempData[MyEnum.Message.ToString()] instead of TempData["Message"]. public class MyClass { public const string Message = "Message"; } and public enum MyEnum { Message, Others } My questions are: Which is the better way to avoid magic string keys? Using string const keys in a class or using enumeration together with ToString()?

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• Cannot implicitly convert type ...

  - by Newbie

  I have the following function public Dictionary<DateTime, object> GetAttributeList( EnumFactorType attributeType ,Thomson.Financial.Vestek.Util.DateRange dateRange) { DateTime startDate = dateRange.StartDate; DateTime endDate = dateRange.EndDate; return (( //Step 1: Iterate over the attribute list and filter the records by // the supplied attribute type from assetAttribute in AttributeCollection where assetAttribute.AttributeType.Equals(attributeType) //Step2:Assign the TimeSeriesData collection into a temporary variable let timeSeriesList = assetAttribute.TimeSeriesData //Step 3: Iterate over the TimeSeriesData list and filter the records by // the supplied date from timeSeries in timeSeriesList.ToList() where timeSeries.Key >= startDate && timeSeries.Key <= endDate //Finally build the needed collection select new AssetAttribute() { TimeSeriesData = PopulateTimeSeriesData(timeSeries.Key, timeSeries.Value) }).ToList<AssetAttribute>().Select(i => i.TimeSeriesData)); } private Dictionary<DateTime, object> PopulateTimeSeriesData(DateTime dateTime, object value) { Dictionary<DateTime, object> timeSeriesData = new Dictionary<DateTime, object>(); timeSeriesData.Add(dateTime, value); return timeSeriesData; } Error:Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.Dictionary'. An explicit conversion exists (are you missing a cast?) Using C#3.0 Please help

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• Field annotated multiple times by the same attribute

  - by Jaroslaw Waliszko

  For my ASP.NET MVC application I've created custom validation attribute, and indicated that more than one instance of it can be specified for a single field or property: [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = true)] public sealed class SomeAttribute: ValidationAttribute I've created validator for such an attribute: public class SomeValidator : DataAnnotationsModelValidator<SomeAttribute> and wire up this in the Application_Start of Global.asax DataAnnotationsModelValidatorProvider.RegisterAdapter( typeof (SomeAttribute), typeof (SomeValidator)); Finally, if I use my attribute in the desired way: [SomeAttribute(...)] //first [SomeAttribute(...)] //second public string SomeField { get; set; } when validation is executed by the framework, only first attribute instance is invoked. Second one seems to be dead. I've noticed that during each request only single validator instance is created (for the first annotation). How to solve this problem and fire all attributes?

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• MVVM Binding To Property == Null

  - by LnDCobra

  I want to show some elements when a property is not null. What is the best way of achieving this? The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Company Company { get { return _company; } set { SetField(ref _company, value, () => Company); } } private Company _company; ...... } This is part of my View.xaml <GroupBox Visibility="{Binding Path=Trade.Company, Converter={StaticResource boolToVisConverter}}" /> I would like this groupbox to show only if Trade.Company is not null (so when a user selects a company). Would I need to create a custom converter to check for null and return the correct visibility or is there one in .NET?

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• What prevents an attack on Postfix through its named pipes?

  - by Met?Ed

  What prevents an attack on Postfix through its named pipes by writing bogus data to them? I see on my system that they permit write access to other. I wonder if that opens Postfix to DoS or some other form of attack. prw--w--w- 1 postfix postdrop 0 Nov 28 21:13 /var/spool/postfix/public/pickup prw--w--w- 1 postfix postdrop 0 Nov 28 21:13 /var/spool/postfix/public/qmgr I reviewed the pickup(8) man page, and searched here and elsewhere, but failed to turn up any answers.

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