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  • Is this a valid, lazy, thread-safe Singleton implementation for C#?

    - by Matthew
    I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling around for C# Singleton implementations, it doesn't seem like this is a common way to do things in C#. I found one similar implementation, but the SingletonHolder class wasn't static, and included an explicit (empty) static constructor. Is this a valid, lazy, thread-safe way to implement the Singleton pattern? Or is there something I'm missing?

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  • How to get rid of this error in asp.net-mvc?

    - by Pandiya Chendur
    I am using Linq-to-sql as an ORM. I wrote this innerjoin public IQueryable<Material> FindAllMaterials() { var materials=from m in db.Materials join Mt in db.MeasurementTypes on m.MeasurementTypeId equals Mt.Id select new { m.Mat_id, m.Mat_Name, Mt.Name, m.Mat_Type }; return materials; } But when i compile this i got an error Cannot implicitly convert type 'System.Linq.IQueryable<AnonymousType#1>' to 'System.Linq.IQueryable<CrMVC.Models.Material>'. An explicit conversion exists (are you missing a cast?) Am i missing some thing... Any suggestion....

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  • Restricting deletion with NHibernate

    - by FrontSvin
    I'm using NHibernate (fluent) to access an old third-party database with a bunch of tables, that are not related in any explicit way. That is a child tables does have parentID columns which contains the primary key of the parent table, but there are no foreign key relations ensuring these relations. Ideally I would like to add some foreign keys, but cannot touch the database schema. My application works fine, but I would really like impose a referential integrity rule that would prohibit deletion of parent objects if they have children, e.i. something similar 'ON DELETE RESTRICT' but maintained by NHibernate. Any ideas on how to approach this would be appreciated. Should I look into the OnDelete() method on the IInterceptor interface, or are there other ways to solve this? Of course any solution will come with a performance penalty, but I can live with that.

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  • C++ conversion operator between types in other libraries

    - by Dave
    For convenience, I'd like to be able to cast between two types defined in other libraries. (Specifically, QString from the Qt library and UnicodeString from the ICU library.) Right now, I have created utility functions in a project namespace: namespace MyProject { const icu_44::UnicodeString ToUnicodeString(const QString& value); const QString ToQString(const icu_44::UnicodeString& value); } That's all well and good, but I'm wondering if there's a more elegant way. Ideally, I'd like to be able to convert between them using a cast operator. I do, however, want to retain the explicit nature of the conversion. An implicit conversion should not be possible. Is there a more elegant way to achieve this without modifying the source code of the libraries? Some operator overload syntax, perhaps?

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  • Avoid Circular Reference in Swing GUI

    - by drhorrible
    Maybe it's not worth worrying about in this scenario, but lets say you have two classes, a JFrame with all its components, and a server-like class that handles requests from remote clients. The user is able to start and stop server objects through the GUI, and is shown various events that happen to each server object. Whether or not I use an explicit pattern (like MVC), it seems like the JFrame needs a reference to the server class (to call start and stop) and the server needs a reference to the JFrame (to notify of it of certain events). Is this a problem, or am I looking at this situation in the wrong way?

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  • Setting Global Variables in VBA

    - by dennis96411
    I'm currently making an "OS" in PowerPoint and I need to know how to set global variables for the settings. I made a module called "Settings" containing: Public Sub Settings() Option Explicit Public UserName, UserIcon, Background, BrowserHomePage As String Public SetupComplete As Boolean SetupComplete = False UserName = "Administrator" UserIcon = Nothing Background = Nothing BrowserHomePage = Nothing 'Set the variables UserName.Text = UserName End Sub Now on the "log in" screen, I have a text box named "UserName". I then made a button just to test out the variables. The button does this: Private Sub CommandButton1_Click() UserName.Value = UserName End Sub The text box has no value when I click the button. I'm super new at VBA, and would like to know how to do this. Also, if anyone knows how to automatically execute codes when starting the PowerPoint, that would be fantastic.

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  • Defining multiple VBA objects within one function or sub-routine?

    - by Harokitty
    I have the following VBA code: Option Explicit Private a(2) as Double Private b(2) as Double Public Function Hello(X1 As Double, X2 As Double) As Double a(1) = X1 + X2 a(2) = X1/X2 b(1) = X1 b(2) = X2^2 Hello = a(1)+a(2)+b(1)+b(2) End Function Within the function Hello I have defined a(1),a(2),b(1),b(2). However, I want to make some function or sub-routine that accepts X1 and X2 as arguments and spits out the values for a(1),a(2),b(1),b(2). This is because I use the above definitions for a(1),a(2),b(1),b(2) in about 20 functions in my module and would like to avoid having to do the following in each function that I use thesis in: a(1) = X1 + X2 a(2) = X1/X2 b(1) = X1 b(2) = X2^2

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  • Array::ConvertAll in managed C++

    - by danny.lesnik
    This is a continuation from this post. I'm trying to parse this string in managed C++: String ^ rgba = "[0.09019608,0.5176471,0.9058824,1]"; cli::array<System::Double> ^ RGB = System::Array::ConvertAll<String,cli::array<System::Double> >((rgba->Substring(1,rgba->Length-2)->Split(',')),double::Parse); Compiler throws me the following error: Error 15 error C2770: invalid explicit generic argument(s) for 'cli::array<Type,dimension> ^System::Array::ConvertAll(cli::array<TInput,1> ^,System::Converter<TInput,TOutput> ^)' What am I doing wrong?

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  • Dollar sign and/or Dash breaking Razor's parser

    - by justSteve
    the end-result i'm trying to render: <input type="radio" name="options" id="options_1" />$1 - A Not Very Expensive Chocolate <input type="radio" name="options" id="options_2" />$10 - A Kinda Expensive Chocolate <input type="radio" name="options" id="options_3" />$100 - A Really Expensive Chocolate From this code: @foreach (var o in Model.Options){ <input type="radio" name="options" id=@("options_" + @o.ID) />[email protected] - @o.Label } If i drop both the '$' and the '-' from what should be plain old text - stuff works. Adding either resulted in compiler warnings and runtime errors. I've tried the explicit syntax as described here but haven't found the right combination yet.

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  • PL/SQL embedded insert into table that may not exist

    - by Richard
    Hi, I much prefer using this 'embedded' style inserts in a pl/sql block (opposed to the execute immediate style dynamic sql - where you have to delimit quotes etc). -- a contrived example PROCEDURE CreateReport( customer IN VARCHAR2, reportdate IN DATE ) BEGIN -- drop table, create table with explicit column list CreateReportTableForCustomer; INSERT INTO TEMP_TABLE VALUES ( customer, reportdate ); END; / The problem here is that oracle checks if 'temp_table' exists and that it has the correct number of colunms and throws a compile error if it doesn't exist. So I was wondering if theres any way round that?! Essentially I want to use a placeholder for the table name to trick oracle into not checking if the table exists.

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  • Faking a Single Address Space

    - by dsimcha
    I have a large scientific computing task that parallelizes very well with SMP, but at too fine grained a level to be easily parallelized via explicit message passing. I'd like to parallelize it across address spaces and physical machines. Is it feasible to create a scheduler that would parallelize already multithreaded code across multiple physical computers under the following conditions: The code is already multithreaded and can scale pretty well on SMP configurations. The fact that not all of the threads are running in the same address space or on the same physical machine must be transparent to the program, even if this comes at a significant performance penalty in some use cases. You may assume that all of the physical machines involved are running operating systems and CPU architectures that are binary compatible. Things like locks and atomic operations may be slow (having network latency to deal with and all) but must "just work".

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  • Specializing a template member function of a template class?

    - by uj2
    I have a template class that has a template member function that needs to be specialized, as in: template <typename T> class X { public: template <typename U> void Y() {} template <> void Y<int>() {} }; Altough VC handles this correctly, apperantly this isn't standard and GCC complains: explicit specialization in non-namespace scope 'class X<T>' I tried: template <typename T> class X { public: template <typename U> void Y() {} }; template <typename T> // Also tried `template<>` here void X<T>::Y<int>() {} But this causes both VC and GCC to complain. What's the right way to do this?

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  • Is there a way to set up a Linux pipe to non-buffering or line-buffering?

    - by ern0
    My program is controlling an external application on Linux, passing in input commands via a pipe to the external applications stdin, and reading output result via a pipe from the external applications stdout. The problem is that writes to pipes are buffered by block, and not by line, and therefore delays occur before my app receives data output by the external application. The external application cannot be altered to add explicit fflush() calls. When I set the external application to /bin/cat -n (it echoes back the input, with line numbers added), it works correctly, it seems, cat flushes after each line. The only way to force the external application to flush, is sending exit command to it; as it receives the command, it flushes, and all the answers appears on the stdout, just before exiting. I'm pretty sure, that Unix pipes are appropiate solution for that kind of interprocess communication (pseudo server-client), but maybe I'm wrong. (I've just copied some text from a similar question: Force another program's standard output to be unbuffered using Python)

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  • 2D Engine scrolling on OpenGL via hardware?

    - by drudru
    hi, I'm using OpenGL as the bottom end for a 2D tiling engine. When everything is 2D, it is simple to optimize certain issues. For example, scrolling. If I know a certain section of the screen needs to scroll off the bottom, then I can just blit over that portion. I'm evening moving more than 1 pixel at a time. Without explicit hardware support (think old nintendo hw), this requires a lot of pixel writes. An on chip bitblt would be the next best thing. Essentially, I'm looking at how I can optimize my GL calls to use VRAM texture renders as efficient hardware blits. Is it possible to have GL scroll the framebuffer, or should I just resign myself to double-buffering and re-rendering an entire scene for each frame? Thx

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  • javascript "associative" array access

    - by cp
    Hello I have a simple simulated aarray with two elements: bowl["fruit"]="apple"; bowl["nuts"]="brazilian"; I can access the value with an event like this: onclick="testButton00_('fruit')">with `testButton00_` function testButton00_(key){ var t = bowl[key]; alert("testButton00_: value = "+t); } However whenever I try to access the aarray from within code with a key that is just a non-explicit string I get undefined. Do I have somehow have to pass the parameter with the escaped 'key'. Any ideas? tia.

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  • problems with Haskell's Number Types

    - by mindeavor.
    I have the following haskell code: fac n = product [1..n] taylor3s w0 f f' f'' t h = w1 : taylor3s w1 f f' f'' (t+h) h where hp i = h^i / fac i w1 = w0 + (hp 1) * f t w0 + (hp 2) * f' t w0 + (hp 3) * f'' t w0 taylor_results = take 4 $ taylor3s 1 f f' f'' 1 0.25 where f t x = t^4 - 4*x/t f' t x = 4*t^3 - 4*(f t x)/t + 4*x/t^2 f'' t x = 12*t^2 - 4*(f' t x)/t + 8*(f t x)/t^2 - 8*x/t^3 taylor_results is supposed to be a use case of taylor3s. However, there is something wrong with the number type inferencing. When I try to compile, this is the error I get: practice.hs:93:26: Ambiguous type variable `a' in the constraints: `Integral a' arising from a use of `taylor3s' at practice.hs:93:26-51 `Fractional a' arising from a use of `f' at practice.hs:93:37 Possible cause: the monomorphism restriction applied to the following: taylor_results :: [a] (bound at practice.hs:93:0) Probable fix: give these definition(s) an explicit type signature or use -XNoMonomorphismRestriction Can someone help me with understanding what the problem is?

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  • Copy Data from One SQL Server Table to Other in Same Database Without Specifying Columns

    - by Scott
    In SQL Server there is the ability to INSERT all of the data from one table into another using the following statement: INSERT INTO TABLE1 SELECT * FROM TABLE2 When running this on a table with an identity column, even though we have run the command SET IDENTITY_INSERT TABLE1 ON, we get the error: An explicit value for the identity column in table can only be specified when a column list is used and IDENTITY_INSERT is ON This implies that we would have to list off all of the columns within the INSERT in order for this to work properly. In the situation that we are in, we do not have access to the column names, only the list of the tables we need to copy over. Is there any way to get around this limitation?

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  • How do I synchronize GUI-Elements?

    - by anonymous2500
    Hello, I have a little problem with my java-program. I wanna use Observer, to synchronize two GUIs. But I can't synchronize the JComponent / JButton elements. For example: I have a GUI-Class which implements the Observer-Class: public class GUI extends JFrame implements Observer I have a second "GUI"-Class which extends the JButton-Class and makes changes on a specific Button-Element. public class Karte extends JButton{ ... this.setEnabled(false); ... How do I synchronize this Button via Observable? I have already tried to use "extends Observable" in this class, but the "setEnabled()" method is explicit for the JButton-Class, which is not Observable! Can someone help? Thanks.

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  • C++ enum casting and templates

    - by JP
    I get the following error with VS2008: Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast) When casting a down casting a ClassA to ClassA_1 and ClassA_1 is a templated class that received an enum for parameter such as: ClassA { virtual ~ClassA(){}; } template <class Param1> ClassA_1 : public ClassA { public: //constructor ClassA_1(Param1 p1) { _p1 = p1; } Param1 _p1; } So I have a upcasted ClassA a = new ClassA_1<myenum>(); When I need to do this: ClassA_1<myenum> a1 = (ClassA_1<myenum> a); // This fails ... The only way it works is: ClassA_1<int> a1 = (ClassA_1<int> a); but this break my template as it must always deal with int... How to properly cast a enum that is now a int, back into the enum?

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  • How can I configure a Hudson job to use a specific JDK?

    - by rewbs
    I have a number of projects running on a Hudson slave. I'd like one of them to run Ant under Java6, rather than the default (which is Java5 in my environment). In the project configuration view, I was hoping to find either: An explicit option allowing me to set a custom JDK location to use for this project. A way to set custom environment variables for this project, which would allow me to set JAVA_HOME to the JDK6 location. The would make Ant pick up and run on Java6 as desired. Is there a way to do either of the above? If one of those facilities is available, I can't see how to access it. I'm running on Hudson 1.285. I would rather avoid using an "execute shell" operation instead of the "invoke Ant" operation if possible: my slave is on z/OS and Hudson doesn't seem to create the temporary shell scripts properly on this platform (probably an encoding issue).

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  • C# Struct No Parameterless Constructor? See what I need to accomplish

    - by Changeling
    I am using a struct to pass to an unmanaged DLL as so - [StructLayout(LayoutKind.Sequential)] public struct valTable { public byte type; public byte map; public byte spare1; public byte spare2; public int par; public int min; public byte[] name; public valTable() { name = new byte[24]; } } The code above will not compile because VS 2005 will complain that "Structs cannot contain explicit parameterless constructors". In order to pass this struct to my DLL, I have to pass an array of struct's like so valTable[] val = new valTable[281]; What I would like to do is when I say new, the constructor is called and it creates an array of bytes like I am trying to demonstrate because the DLL is looking for that byte array of size 24 in each dimension. How can I accomplish this?

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  • NoMethodError using Memcached Sinatra-style

    - by sevennineteen
    I've just installed Memcached on my Mac and updated my Sinatra app configuration as described in Heroku's documentation, but I'm getting a NoMethodError when trying to use the hash-based syntax they specify: >> CACHE['color'] = 'blue' >> CACHE['color'] Using explicit get and set methods as below seems to work fine. >> CACHE.set('color', 'blue') >> CACHE.get('color') If necessary I can use the latter syntax, but the former seems more elegant. I haven't tested this on Heroku's environment since I'd like whatever implementation I use to work on my local environment as well. Thanks!

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  • Container<ImplementerOfIInterface> is not Container<IInterface>. Why not?

    - by Chris Simmons
    Why wouldn't DoesntWork() work below? The error is: Cannot implicitly convert type 'List' to 'IEnumerable'. An explicit conversion exists (are you missing a cast?). I know this is something about generic/templates I'm not getting, but List is IEnumerable and Implementer is an IInterface. I don't see why this needs to be casted (or if it really can be). public interface IInterface { // ... } public class Implementer : IInterface { // ... } IEnumerable<IInterface> DoesntWork() { List<Implementer> result = new List<Implementer>(); return result; }

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  • Reflection for Class of generic parameter in Java?

    - by hatboysam
    Imagine the following scenario: class MyClass extends OtherClass<String>{ String myName; //Whatever } class OtherClass<T> { T myfield; } And I am analyzing MyClass using reflection specifically (MyClass.class).getDeclaredFields(), in this case I will get the following fields (and Types, using getType() of the Field): myName --> String myField --> T I want to get the actual Type for T, which is known at runtime due to the explicit "String" in the extends notation, how do I go about getting the non-genetic type of myField?

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  • Bug in variadic function template specialization with MSVC?

    - by Andrei Tita
    Using the Visual Studio Nov 2012 CTP, which supports variadic templates (among other things). The following code: template<int, typename... Args> void myfunc(Args... args) { } template<> void myfunc<1, float>(float) { } produces the following errors: error C2785: 'void myfunc(Args...)' and 'void myfunc(float)' have different return types error C2912: explicit specialization 'void myfunc(float)' is not a specialization of a function template (yeah, the first one is pretty funny) So my questions are: 1) Am I writing legal C++11 here? 2) If yes, is there a way to find out if this is a known bug in MSVC before submitting it?

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