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• Error compiling / linking e text editor on Linux

  - by jckdnk111

  The code compiles without too much complaint, but the last step fails with the error below. There is some discussion about it on the e forum, but still no answer. [LD] e ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x0): multiple definition of `_pcre_OP_lengths' .objs.release/cx_pcre_tables.o:(.rodata+0x0): first defined here ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x70): multiple definition of `_pcre_utf8_table1' .objs.release/cx_pcre_tables.o:(.rodata+0x70): first defined here ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x88): multiple definition of `_pcre_utf8_table1_size' .objs.release/cx_pcre_tables.o:(.rodata+0x88): first defined here ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x8c): multiple definition of `_pcre_utf8_table2' .objs.release/cx_pcre_tables.o:(.rodata+0x8c): first defined here ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0xa4): multiple definition of `_pcre_utf8_table3' .objs.release/cx_pcre_tables.o:(.rodata+0xa4): first defined here ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0xc0): multiple definition of `_pcre_utf8_table4' .objs.release/cx_pcre_tables.o:(.rodata+0xc0): first defined here ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x180): multiple definition of `_pcre_utt_names' .objs.release/cx_pcre_tables.o:(.rodata+0x100): first defined here /usr/bin/ld: Warning: size of symbol `_pcre_utt_names' changed from 657 in .objs.release/cx_pcre_tables.o to 740 in ../external/out.release/lib/libpcre.a(pcre_tables.o) ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x480): multiple definition of `_pcre_utt' .objs.release/cx_pcre_tables.o:(.rodata+0x3a0): first defined here /usr/bin/ld: Warning: size of symbol `_pcre_utt' changed from 630 in .objs.release/cx_pcre_tables.o to 696 in ../external/out.release/lib/libpcre.a(pcre_tables.o) ../external/out.release/lib/libpcre.a(pcre_tables.o):(.rodata+0x738): multiple definition of `_pcre_utt_size' .objs.release/cx_pcre_tables.o:(.rodata+0x618): first defined here .objs.release/cx_pcre_exec.o: In function `match(doc_byte_iter, unsigned char const*, doc_byte_iter, int, match_data*, unsigned long, eptrblock*, int, unsigned int)': cx_pcre_exec.cpp:(.text+0x1c2a): undefined reference to `_pcre_ord2utf8(int, unsigned char*)' .objs.release/eauibook.o: In function `eAuiNotebook::LoadPerspective(wxString const&)': eauibook.cpp:(.text+0x9ad): undefined reference to `wxTabFrame::SetTabCtrlHeight(int)' .objs.release/PreviewDlg.o: In function `global constructors keyed to _ZN10PreviewDlg13sm_eventTableE': PreviewDlg.cpp:(.text+0x11b2): undefined reference to `wxEVT_WEB_TITLECHANGE' PreviewDlg.cpp:(.text+0x11ee): undefined reference to `wxEVT_WEB_DOMCONTENTLOADED' .objs.release/PreviewDlg.o: In function `PreviewDlg::RefreshBrowser(PreviewDlg::cxUpdateMode)': PreviewDlg.cpp:(.text+0x2a47): undefined reference to `wxWebControl::OpenURI(wxString const&, unsigned int, wxWebPostData*, bool)' .objs.release/PreviewDlg.o: In function `PreviewDlg::OnWebDocumentComplete(wxWebEvent&)': PreviewDlg.cpp:(.text+0x3259): undefined reference to `wxWebControl::GetCurrentURI() const' .objs.release/PreviewDlg.o: In function `PreviewDlg::PreviewDlg(EditorFrame&)': PreviewDlg.cpp:(.text+0x4984): undefined reference to `wxWebControl::IsInitialized()' PreviewDlg.cpp:(.text+0x49c5): undefined reference to `wxWebControl::wxWebControl(wxWindow*, int, wxPoint const&, wxSize const&)' PreviewDlg.cpp:(.text+0x562f): undefined reference to `wxWebControl::InitEngine(wxString const&)' .objs.release/PreviewDlg.o: In function `PreviewDlg::PreviewDlg(EditorFrame&)': PreviewDlg.cpp:(.text+0x68e4): undefined reference to `wxWebControl::IsInitialized()' PreviewDlg.cpp:(.text+0x6925): undefined reference to `wxWebControl::wxWebControl(wxWindow*, int, wxPoint const&, wxSize const&)' PreviewDlg.cpp:(.text+0x758f): undefined reference to `wxWebControl::InitEngine(wxString const&)' .objs.release/PreviewDlg.o: In function `PreviewDlg::OnButtonForward(wxCommandEvent&)': PreviewDlg.cpp:(.text+0x132): undefined reference to `wxWebControl::GoForward()' .objs.release/PreviewDlg.o: In function `PreviewDlg::OnButtonBack(wxCommandEvent&)': PreviewDlg.cpp:(.text+0x182): undefined reference to `wxWebControl::GoBack()' ../ecore/libecore.so(cxInternal.o): In function `cxInternal::MoveOldSettings(eSettings&)': cxInternal.cpp:(.text+0x4d29): undefined reference to `eSettings::SetPageSettings(unsigned int, wxString const&, doc_id, int, int, wxString const&, std::vector<unsigned int, std::allocator<unsigned int> > const&, std::vector<cxBookmark, std::allocator<cxBookmark> > const&, eSettings::SubPage)' collect2: ld returned 1 exit status make: *** [e] Error 1 EDIT: Forgot the link http://github.com/etexteditor/e

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• DynamicMethod for ConstructorInfo.Invoke, what do I need to consider?

  - by Lasse V. Karlsen

  My question is this: If I'm going to build a DynamicMethod object, corresponding to a ConstructorInfo.Invoke call, what types of IL do I need to implement in order to cope with all (or most) types of arguments, when I can guarantee that the right type and number of arguments is going to be passed in before I make the call? Background I am on my 3rd iteration of my IoC container, and currently doing some profiling to figure out if there are any areas where I can easily shave off large amounts of time being used. One thing I noticed is that when resolving to a concrete type, ultimately I end up with a constructor being called, using ConstructorInfo.Invoke, passing in an array of arguments that I've worked out. What I noticed is that the invoke method has quite a bit of overhead, and I'm wondering if most of this is just different implementations of the same checks I do. For instance, due to the constructor matching code I have, to find a matching constructor for the predefined parameter names, types, and values that I have passed in, there's no way this particular invoke call will not end up with something it should be able to cope with, like the correct number of arguments, in the right order, of the right type, and with appropriate values. When doing a profiling session containing a million calls to my resolve method, and then replacing it with a DynamicMethod implementation that mimics the Invoke call, the profiling timings was like this: ConstructorInfo.Invoke: 1973ms DynamicMethod: 93ms This accounts for around 20% of the total runtime of this profiling application. In other words, by replacing the ConstructorInfo.Invoke call with a DynamicMethod that does the same, I am able to shave off 20% runtime when dealing with basic factory-scoped services (ie. all resolution calls end up with a constructor call). I think this is fairly substantial, and warrants a closer look at how much work it would be to build a stable DynamicMethod generator for constructors in this context. So, the dynamic method would take in an object array, and return the constructed object, and I already know the ConstructorInfo object in question. Therefore, it looks like the dynamic method would be made up of the following IL: l001: ldarg.0 ; the object array containing the arguments l002: ldc.i4.0 ; the index of the first argument l003: ldelem.ref ; get the value of the first argument l004: castclass T ; cast to the right type of argument (only if not "Object") (repeat l001-l004 for all parameters, l004 only for non-Object types, varying l002 constant from 0 and up for each index) l005: newobj ci ; call the constructor l006: ret Is there anything else I need to consider? Note that I'm aware that creating dynamic methods will probably not be available when running the application in "reduced access mode" (sometimes the brain just won't give up those terms), but in that case I can easily detect that and just calling the original constructor as before, with the overhead and all.

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• Java Builder pattern with Generic type bounds

  - by I82Much

  Hi all, I'm attempting to create a class with many parameters, using a Builder pattern rather than telescoping constructors. I'm doing this in the way described by Joshua Bloch's Effective Java, having private constructor on the enclosing class, and a public static Builder class. The Builder class ensures the object is in a consistent state before calling build(), at which point it delegates the construction of the enclosing object to the private constructor. Thus public class Foo { // Many variables private Foo(Builder b) { // Use all of b's variables to initialize self } public static final class Builder { public Builder(/* required variables */) { } public Builder var1(Var var) { // set it return this; } public Foo build() { return new Foo(this); } } } I then want to add type bounds to some of the variables, and thus need to parametrize the class definition. I want the bounds of the Foo class to be the same as that of the Builder class. public class Foo<Q extends Quantity> { private final Unit<Q> units; // Many variables private Foo(Builder<Q> b) { // Use all of b's variables to initialize self } public static final class Builder<Q extends Quantity> { private Unit<Q> units; public Builder(/* required variables */) { } public Builder units(Unit<Q> units) { this.units = units; return this; } public Foo build() { return new Foo<Q>(this); } } } This compiles fine, but the compiler is allowing me to do things I feel should be compiler errors. E.g. public static final Foo.Builder<Acceleration> x_Body_AccelField = new Foo.Builder<Acceleration>() .units(SI.METER) .build(); Here the units argument is not Unit<Acceleration> but Unit<Length>, but it is still accepted by the compiler. What am I doing wrong here? I want to ensure at compile time that the unit types match up correctly.

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• how to organise my abstraction?

  - by DaveM

  I have a problem that I can't decide how to best handle, so I'm asking for advice. Please bear with me if my question isn't clear, it is possiblybecause I'm not sure exacly how to solve! I have a set of function that I have in a class. These function are a set of lowest commonality. To be able to run this I need to generate certain info. But this info can arrive with my class from one of 2 routes. I'll try to summarise my situation.... Lets say that I have a class as follows. public class onHoliday(){ private Object modeOfTravel; private Object location; public onHoliday(Object vehicle, Location GPScoords) { private boolean haveFun(){//function to have fun, needs 4 people }//end haveFun() } } Lets imagine I can get to my holiday either by car or by bike. my haveFun() function is dependant my type of vehicle. But only loosely. I have another function that determines my vehicle type, and extracts the required values. for example if I send a car I may get 4 people in one go, but if I send I bike I need at least 2 to get the required 4 I have currently 2 options: Overload my constructor, so as I can send either 2 bikes or a single car into it, then I can call one of 2 intermediate functions (to get the names of my 4 people for instance) before I haveFun() - this is what I am currently doing. split the 2 constructors into 2 separate classes, and repeat my haveFun() in a third class, that becomes an object of my 2 other classes. my problem with this is that my intermediate functions are all but a few lines of code, and I don't want to have them in a separate file! (I allways put classes in separate files!) Please note, my haveFun() isn't something that I'm going to need outside of these 2 classes, or even being onHoliday (ie. there is no chance of me doing some haveFun() over a weekend or of an evening!). I have though about putting haveFun() into an interface, but it seems a bit worthless having an interface with only a single method! Even then I would have to have the method in both of the classes -one for bike and another for car! I have thought about having my onHoliday class accepting any object type, but then I don't want someone accidentally sending in a boat to my onHoliday class (imagine I can't swim, so its not about to happen). It may be important to note that my onHoliday class is package private, and final. It in fact is only accessed via other 'private methods' in other classes, and has only private methods itself. Thanks in advance. David

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• using Java interfaces

  - by mike_hornbeck

  I need to create interface MultiLingual, that allows to display object's data in different languages (not data itself, but introduction like "Author", "Title" etc.). Printed data looks like this : 3 grudnia 1998 10th of June 1924 Autor: Tolkien Tytul: LoTR Wydawnictwo: Amazon 2010 Author: Mitch Albom Title: Tuesdays with Morrie Publishing House: Time Warner Books 2003 37 360,45 PLN 5,850.70 GBP 3rd of December 1998 10th of June 1924 Author: Tolkien Title: LoTR Publishing House: Amazon 2010 Author: Mitch Albom Title: Tuesdays with Morrie Publishing House: Time Warner Books 2003 37,360.45 GBP 5,850.70 GBP Test code looks like this : public class Main { public static void main(String[] args){ MultiLingual gatecrasher[]={ new Data(3,12,1998), new Data(10,6,1924,MultiLingual.ENG), new Book("LoTR", "Tolkien", "Amazon", 2010), new Book("Tuesdays with Morrie", "Mitch Albom", "Time Warner Books",2003, MultiLingual.ENG), new Money(1232895/33.0,MultiLingual.PL), new Money(134566/23.0,MultiLingual.ENG), }; for(int i=0;i < gatecrasher.length;i++) System.out.println(gatecrasher[i]+"\n"); for(int i=0;i < gatecrasher.length;i++) System.out.println(gatecrasher[i].get(MultiLingual.ENG)+"\n"); } } So i need to introduce constants ENG, PL in MultiLingual interface, as well as method get(int language) : public interface MultiLingual { int ENG = 0; int PL= 1; String get(int lang); } And then I have class Book. Problem starts with the constructors. One of them needs to take MultiLingual.ENG as argument, but how to achieve that ? Is this the proper way? : class Book implements MultiLingual { private String title; private String publisher; private String author; public Book(String t, String a, String p, int y, MultiLingual lang){ } Or should I treat this MultiLingual.ENG as int variable , that will just change automatically constants in interface? Second constructor for book doesn't take MultLingual as argument, but following implementation is somehow wrong : public Book(String t, String a, String p, int y){ Book someBook = new Book(t, a, p, y, MultiLingual m); } I could just send int m in place of MultiLingual m but then I will have no control if language is set to PL or ENG. And finally get() method for Boook but I think at least this should be working fine: public String get(int lang){ String data; if (lang == ENG){ data = "Author: "+this.author+"\n"+ "Title: "+this.title+"\n"+ "Publisher: "+this.publisher+"\n"; } else { data = "Autor: "+this.author+"\n"+ "Tytul: "+this.title+"\n"+ "Wydawca: "+this.publisher+"\n"; } return data; } @Override public String toString(){ return ""; } }

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• redoing object model construction to fit with asynchronous data fetching

  - by Andrew Patterson

  I have a modeled a set of objects that correspond with some real world concepts. TradeDrug, GenericDrug, TradePackage, DrugForm Underlying the simple object model I am trying to provide is a complex medical terminology that uses numeric codes to represent relationships and concepts, all accessible via a REST service - I am trying to hide away some of that complexity with an object wrapper. To give a concrete example I can call TradeDrug d = Searcher.FindTradeDrug("Zoloft") or TradeDrug d = new TradeDrug(34) where 34 might be the code for Zoloft. This will consult a remote server to find out some details about Zoloft. I might then call GenericDrug generic = d.EquivalentGeneric() System.Out.WriteLine(generic.ActiveIngredient().Name) in order to get back the generic drug sertraline as an object (again via a background REST call to the remote server that has all these drug details), and then perhaps find its ingredient. This model works fine and is being used in some applications that involve data processing. Recently however I wanted to do a silverlight application that used and displayed these objects. The silverlight environment only allows asynchronous REST/web service calls. I have no problems with how to make the asychhronous calls - but I am having trouble with what the design should be for my object construction. Currently the constructors for my objects do some REST calls sychronously. public TradeDrug(int code) { form = restclient.FetchForm(code) name = restclient.FetchName(code) etc.. } If I have to use async 'events' or 'actions' in order to use the Silverlight web client (I know silverlight can be forced to be a synchronous client but I am interested in asychronous approaches), does anyone have an guidance or best practice for how to structure my objects. I can pass in an action callback to the constructor public TradeDrug(int code, Action<TradeDrug> constructCompleted) { } but this then allows the user to have a TradeDrug object instance before what I want to construct is actually finished. It also doesn't support an 'event' async pattern because the object doesn't exist to add the event to until it is constructed. Extending that approach might be a factory object that itself has an asynchronous interface to objects factory.GetTradeDrugAsync(code, completedaction) or with a GetTradeDrugCompleted event? Does anyone have any recommendations?

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• IoC/DI in the face of winforms and other generated code

  - by Kaleb Pederson

  When using dependency injection (DI) and inversion of control (IoC) objects will typically have a constructor that accepts the set of dependencies required for the object to function properly. For example, if I have a form that requires a service to populate a combo box you might see something like this: // my files public interface IDataService { IList<MyData> GetData(); } public interface IComboDataService { IList<MyComboData> GetComboData(); } public partial class PopulatedForm : BaseForm { private IDataService service; public PopulatedForm(IDataService service) { //... InitializeComponent(); } } This works fine at the top level, I just use my IoC container to resolve the dependencies: var form = ioc.Resolve<PopulatedForm>(); But in the face of generated code, this gets harder. In winforms a second file composing the rest of the partial class is generated. This file references other components, such as custom controls, and uses no-args constructors to create such controls: // generated file: PopulatedForm.Designer.cs public partial class PopulatedForm { private void InitializeComponent() { this.customComboBox = new UserCreatedComboBox(); // customComboBox has an IComboDataService dependency } } Since this is generated code, I can't pass in the dependencies and there's no easy way to have my IoC container automatically inject all the dependencies. One solution is to pass in the dependencies of each child component to PopulatedForm even though it may not need them directly, such as with the IComboDataService required by the UserCreatedComboBox. I then have the responsibility to make sure that the dependencies are provided through various properties or setter methods. Then, my PopulatedForm constructor might look as follows: public PopulatedForm(IDataService service, IComboDataService comboDataService) { this.service = service; InitializeComponent(); this.customComboBox.ComboDataService = comboDataService; } Another possible solution is to have the no-args constructor to do the necessary resolution: public class UserCreatedComboBox { private IComboDataService comboDataService; public UserCreatedComboBox() { if (!DesignMode && IoC.Instance != null) { comboDataService = Ioc.Instance.Resolve<IComboDataService>(); } } } Neither solution is particularly good. What patterns and alternatives are available to more capably handle dependency-injection in the face of generated code? I'd love to see both general solutions, such as patterns, and ones specific to C#, Winforms, and Autofac.

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• POD global object initialization

  - by paercebal

  I've got bitten today by a bug. The following source can be copy/pasted (and then compiled) into a main.cpp file #include <iostream> // The point of SomeGlobalObject is for its // constructor to be launched before the main // ... struct SomeGlobalObject { SomeGlobalObject() ; } ; // ... // Which explains the global object SomeGlobalObject oSomeGlobalObject ; // A POD... I was hoping it would be constructed at // compile time when using an argument list struct MyPod { short m_short ; const char * const m_string ; } ; // declaration/Initialization of a MyPod array MyPod myArrayOfPod[] = { { 1, "Hello" }, { 2, "World" }, { 3, " !" } } ; // declaration/Initialization of an array of array of void * void * myArrayOfVoid[][2] = { { (void *)1, "Hello" }, { (void *)2, "World" }, { (void *)3, " !" } } ; // constructor of the global object... Launched BEFORE main SomeGlobalObject::SomeGlobalObject() { std::cout << "myArrayOfPod[0].m_short : " << myArrayOfPod[0].m_short << std::endl ; std::cout << "myArrayOfVoid[0][0] : " << myArrayOfVoid[0][0] << std::endl ; } // main... What else ? int main(int argc, char* argv[]) { return 0 ; } MyPod being a POD, I believed there would be no constructors. Only initialization at compile time. Thus, the global object SomeGlobalObject would have no problem to use the global array of PODs upon its construction. The problem is that in real life, nothing is so simple. On Visual C++ 2008 (I did not test on other compilers), upon execution myArrayOfPodis not initialized, even ifmyArrayOfVoid` is initialized. So my questions is: Are C++ compilers not supposed to initialize global PODs (including POD structures) at compilation time ? Note that I know global variable are evil, and I know that one can't be sure of the order of creation of global variables declared in different compilation units. The problem here is really the POD C-like initialization which seems to call a constructor (the default, compiler-generated one?). And to make everyone happy: This is on debug. On release, the global array of PODs is correctly initialized.

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• objective-c default init method for class?

  - by Alex

  Hello, I have two differing methods for initializing my objective-c class. One is the default, and one takes a configuration parameter. Now, I'm pretty green when it comes to objective-c, but I've implemented these methods and I'm wondering if there's a better (more correct/in good style) way to handle initialization than the way I have done it. Meaning, did I write these initialization functions in accordance with standards and good style? It just doesn't feel right to check for the existence of selfPtr and then return based on that. Below are my class header and implementation files. Also, if you spot anything else that is wrong or evil, please let me know. I am a C++/Javascript developer who is learning objective-c as hobby and would appreciate any tips that you could offer. #import <Cocoa/Cocoa.h> // class for raising events and parsing returned directives @interface awesome : NSObject { // silence is golden. Actually properties are golden. Hence this emptiness. } // properties @property (retain) SBJsonParser* parser; @property (retain) NSString* eventDomain; @property (retain) NSString* appid // constructors -(id) init; -(id) initWithAppId:(id) input; // destructor -(void) dealloc; @end #import "awesome.h" #import "JSON.h" @implementation awesome - (id) init { if (self = [super init]) { // if init is called directly, just pass nil to AppId contructor variant id selfPtr = [self initWithAppId:nil]; } if (selfPtr) { return selfPtr; } else { return self; } } - (id) initWithAppId:(id) input { if (self = [super init]) { if (input = nil) { input = [[NSString alloc] initWithString:@"a369x123"]; } [self setAppid:input]; [self setEventDomain:[[NSString alloc] initWithString:@"desktop"]]; } return self; } // property synthesis @synthesize parser; @synthesize appid; @synthesize eventDomain; // destructor - (void) dealloc { self.parser = nil; self.appid = nil; self.eventDomain = nil; [super dealloc]; } @end Thanks!

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• WPF Custom Control - Designer looks fine, but I get a runtime issue...

  - by myermian

  MainWindow.xaml <Window x:Class="MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:my="clr-namespace:MyStuff;assembly=MyStuff" Title="MainWindow" Height="350" Width="525"> <Grid> <TabControl Margin="5"> <TabItem Header="Start Page" /> <my:XTabItem Header="Tab 1" Image="Resources/icon1.png" /> </TabControl> </Grid> </Window> Generic.xaml <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:MyStuff" > <!-- XTabItem --> <Style TargetType="{x:Type local:XTabItem}"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type local:XTabItem}"> <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}"> <StackPanel Orientation="Horizontal"> <Image Source="{Binding Path=Image, RelativeSource={RelativeSource TemplatedParent}}" Stretch="UniformToFill" MaxHeight="24" /> <TextBlock Text="{TemplateBinding Header}" /> <Button Content="X" /> </StackPanel> </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> </ResourceDictionary> XTabItem.cs using System; using System.ComponentModel; using System.Windows; using System.Windows.Controls; using System.Windows.Media; namespace MyStuff { public class XTabItem : TabItem { #region Dependency Properties public static readonly DependencyProperty ImageProperty; #endregion #region Constructors / Initializer static XTabItem() { //Initialize the control as "lookless". DefaultStyleKeyProperty.OverrideMetadata(typeof(XTabItem), new FrameworkPropertyMetadata(typeof(XTabItem))); //Setup the dependency properties. ImageProperty = DependencyProperty.Register("Image", typeof(ImageSource), typeof(XTabItem), new UIPropertyMetadata(null)); } #endregion #region Custom Control Properties (Image) /// <summary> /// The image (icon) displayed by inside the tab header. /// </summary> /// <remarks>The image is specified in XAML as an absolute or relative path.</remarks> [Description("The image displayed by the button"), Category("Optional Properties")] public ImageSource Image { get { return (ImageSource)GetValue(ImageProperty); } set { SetValue(ImageProperty, value); } } #endregion } } Exception at line #9 () : XamlParseException : 'Provide value on 'System.Windows.Baml2006.TypeConverterMarkupExtension' threw an exception.' Line number '9' and line position '27'.

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• May volatile be in user defined types to help writing thread-safe code

  - by David Rodríguez - dribeas

  I know, it has been made quite clear in a couple of questions/answers before, that volatile is related to the visible state of the c++ memory model and not to multithreading. On the other hand, this article by Alexandrescu uses the volatile keyword not as a runtime feature but rather as a compile time check to force the compiler into failing to accept code that could be not thread safe. In the article the keyword is used more like a required_thread_safety tag than the actual intended use of volatile. Is this (ab)use of volatile appropriate? What possible gotchas may be hidden in the approach? The first thing that comes to mind is added confusion: volatile is not related to thread safety, but by lack of a better tool I could accept it. Basic simplification of the article: If you declare a variable volatile, only volatile member methods can be called on it, so the compiler will block calling code to other methods. Declaring an std::vector instance as volatile will block all uses of the class. Adding a wrapper in the shape of a locking pointer that performs a const_cast to release the volatile requirement, any access through the locking pointer will be allowed. Stealing from the article: template <typename T> class LockingPtr { public: // Constructors/destructors LockingPtr(volatile T& obj, Mutex& mtx) : pObj_(const_cast<T*>(&obj)), pMtx_(&mtx) { mtx.Lock(); } ~LockingPtr() { pMtx_->Unlock(); } // Pointer behavior T& operator*() { return *pObj_; } T* operator->() { return pObj_; } private: T* pObj_; Mutex* pMtx_; LockingPtr(const LockingPtr&); LockingPtr& operator=(const LockingPtr&); }; class SyncBuf { public: void Thread1() { LockingPtr<BufT> lpBuf(buffer_, mtx_); BufT::iterator i = lpBuf->begin(); for (; i != lpBuf->end(); ++i) { // ... use *i ... } } void Thread2(); private: typedef vector<char> BufT; volatile BufT buffer_; Mutex mtx_; // controls access to buffer_ };

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• Passing const CName as this argument discards qualifiers

  - by Geno Diaz

  I'm having trouble with passing a constant class through a function. // test the constructors auto CName nameOne("Robert", "Bresson"); const CName nameTwo = nameOne; auto CName nameThree; // display the contents of each newly-constructed object... // should see "Robert Bresson" cout << "nameOne = "; nameOne.WriteFullName(); cout << endl; // should see "Robert Bresson" again cout << "nameTwo = "; nameTwo.WriteFullName(); cout << endl; As soon as the compiler hits nameTwo.WriteFullName() I get the error of abandoning qualifiers. I know that the class is a constant however I can't figure out how to work around it. The function is in a header file written as so: void const WriteFullName(ostream& outstream = cout) { outstream << m_first << ' ' << m_last; } I receive this error when const is put in back of the function header main.cpp:(.text+0x51): undefined reference to CName::CName()' main.cpp:(.text+0x7c): undefined reference toCName::WriteFullName(std::basic_ostream &) const' main.cpp:(.text+0xbb): undefined reference to CName::WriteFullName(std::basic_ostream<char, std::char_traits<char> >&) const' main.cpp:(.text+0xf7): undefined reference toCName::WriteFullName(std::basic_ostream &) const' main.cpp:(.text+0x133): undefined reference to operator>>(std::basic_istream<char, std::char_traits<char> >&, CName&)' main.cpp:(.text+0x157): undefined reference tooperator<<(std::basic_ostream &, CName const&)' main.cpp:(.text+0x1f4): undefined reference to operator<<(std::basic_ostream<char, std::char_traits<char> >&, CName const&)' main.cpp:(.text+0x22b): undefined reference tooperator<<(std::basic_ostream &, CName const&)' main.cpp:(.text+0x25f): undefined reference to operator<<(std::basic_ostream<char, std::char_traits<char> >&, CName const&)' main.cpp:(.text+0x320): undefined reference tooperator<<(std::basic_ostream &, CName const&)' main.cpp:(.text+0x347): undefined reference to `operator(std::basic_istream &, CName&)'

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• DriverManager always returns my custom driver regardless of the connection URL

  - by JGB146

  I am writing a driver to act as a wrapper around two separate MySQL connections (to distributed databases). Basically, the goal is to enable interaction with my driver for all applications instead of requiring the application to sort out which database holds the desired data. Most of the code for this is in place, but I'm having a problem in that when I attempt to create connections via the MySQL Driver, the DriverManager is returning an instance of my driver instead of the MySQL Driver. I'd appreciate any tips on what could be causing this and what could be done to fix it! Below is a few relevant snippets of code. I can provide more, but there's a lot, so I'd need to know what else you want to see. First, from MyDriver.java: public MyDriver() throws SQLException { DriverManager.registerDriver(this); } public Connection connect(String url, Properties info) throws SQLException { try { return new MyConnection(info); } catch (Exception e) { return null; } } public boolean acceptsURL(String url) throws SQLException { if (url.contains("jdbc:jgb://")) { return true; } return false; } It is my understanding that this acceptsURL function will dictate whether or not the DriverManager deems my driver a suitable fit for a given URL. Hence it should only be passing connections from my driver if the URL contains "jdbc:jgb://" right? Here's code from MyConnection.java: Connection c1 = null; Connection c2 = null; /** *Constructors */ public DDBSConnection (Properties info) throws SQLException, Exception { info.list(System.out); //included for testing Class.forName("com.mysql.jdbc.Driver").newInstance(); String url1 = "jdbc:mysql://server1.com/jgb"; String url2 = "jdbc:mysql://server2.com/jgb"; this.c1 = DriverManager.getConnection( url1, info.getProperty("username"), info.getProperty("password")); this.c2 = DriverManager.getConnection( url2, info.getProperty("username"), info.getProperty("password")); } And this tells me two things. First, the info.list() call confirms that the correct user and password are being sent. Second, because we enter an infinite loop, we see that the DriverManager is providing new instances of my connection as matches for the mysql URLs instead of the desired mysql driver/connection. FWIW, I have separately tested implementations that go straight to the mysql driver using this exact syntax (al beit only one at a time), and was able to successfully interact with each database individually from a test application outside of my driver.

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• How to stream XML data using XOM?

  - by Jonik

  Say I want to output a huge set of search results, as XML, into a PrintWriter or an OutputStream, using XOM. The resulting XML would look like this: <?xml version="1.0" encoding="UTF-8"?> <resultset> <result> [child elements and data] </result> ... ... [1000s of result elements more] </resultset> Because the resulting XML document could be big (tens or hundreds of megabytes, perhaps), I want to output it in a streaming fashion (instead of creating the whole Document in memory and then writing that). The granularity of outputting one <result> at a time is fine, so I want to generate one <result> after another, and write it into the stream. Assume there's already a method that helps with iterating the results and generating Element objects: public nu.xom.Element getNextResult(); So I'd simply like to do something like this pseudocode (automatic flushing enabled, so don't worry about that) : open stream/writer write declaration write start tag for <resultset> while more results: write next <result> element write end tag for <resultset> close stream/writer I've been looking at Serializer, but the necessary methods, writeStartTag(Element), writeEndTag(Element), write(DocType) are protected, not public! Is there no other way than to subclass Serializer to be able to use those methods, or to manually write the start and end tags directly into the stream as Strings, bypassing XOM altogether? (The latter wouldn't be too bad in this simple example, but in the general case it would get quite ugly.) Am I missing something or is XOM just not made for this? With dom4j I could do this easily using XMLWriter - it has constructors that take a Writer or OutputStream, and methods writeOpen(Element), writeClose(Element), writeDocType(DocumentType) etc. Compare to XOM's Serializer where the only public write method is the one that takes a whole Document. Please refrain from answering if you're not familiar with XOM! I specifically want to know if and how you can do this kind of streaming with that library. (This is related to my question about the best dom4j replacement where XOM is a strong contender.)

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• Can I create a custom class that inherits from a strongly typed DataRow?

  - by Calvin Fisher

  I'm working on a huge, old project with a lot of brittle code, some of which has been around since the .NET 1.0 era, and it has been and will be worked on by other people... so I'd like to change as little as possible. I have one project in my solution that contains DataSet.xsd. This project compiles to a separate assembly (Data.dll). The database schema includes several tables arranged more or less hierarchically, but the only way the tables are actually linked together is through joins. I can get, e.g. DepartmentRow and EmployeeRow objects from the autogenerated code. EmployeeRow contains information from the employee's corresponding DepartmentRow through a join. I'm making a new report to view multiple departments and all their employees. If I use the existing data access scheme, all I will be able to get is a spreadsheet-like output where each employee is represented on one line, with department information repeated over and over in its appropriate columns. E.g.: Department1...Employee1... Department1...Employee2... Department2...Employee3... But what the customer would like is to have each department render like a heading, with a list of employees beneath each. E.g.: - Department1... Employee1... Employee2... + Department2... I'm trying to do this by inheriting hierarchical objects from the autogenerated Row objects. E.g.: public class Department : DataSet.DepartmentRow { public List<Employee> Employees; } That way I could nest the data in the report by using a collection of Department objects as the DataSource, each of which will put its list of Employees in a subreport. The problem is that this gives me a The type Data.DataSet.DepartmentRow has no constructors defined error. And when I try to make a constructor, e.g. public class Department : DataSet.DepartmentRow { private Department() { } public List<Employee> Employees; } I get a 'Data.DataSet.DepartmentRow(System.Data.DataRowBuilder)' is inaccessible due to its protection level. error in addition to the first one. Is there a way to accomplish what I'm trying to do? Or is there something else I should be trying entirely?

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• How to combine designable components with dependency injection

  - by Wim Coenen

  When creating a designable .NET component, you are required to provide a default constructor. From the IComponent documentation: To be a component, a class must implement the IComponent interface and provide a basic constructor that requires no parameters or a single parameter of type IContainer. This makes it impossible to do dependency injection via constructor arguments. (Extra constructors could be provided, but the designer would ignore them.) Some alternatives we're considering: Service Locator Don't use dependency injection, instead use the service locator pattern to acquire dependencies. This seems to be what IComponent.Site.GetService is for. I guess we could create a reusable ISite implementation (ConfigurableServiceLocator?) which can be configured with the necessary dependencies. But how does this work in a designer context? Dependency Injection via properties Inject dependencies via properties. Provide default instances if they are necessary to show the component in a designer. Document which properties need to be injected. Inject dependencies with an Initialize method This is much like injection via properties but it keeps the list of dependencies that need to be injected in one place. This way the list of required dependencies is documented implicitly, and the compiler will assists you with errors when the list changes. Any idea what the best practice is here? How do you do it? edit: I have removed "(e.g. a WinForms UserControl)" since I intended the question to be about components in general. Components are all about inversion of control (see section 8.3.1 of the UMLv2 specification) so I don't think that "you shouldn't inject any services" is a good answer. edit 2: It took some playing with WPF and the MVVM pattern to finally "get" Mark's answer. I see now that visual controls are indeed a special case. As for using non-visual components on designer surfaces, I think the .NET component model is fundamentally incompatible with dependency injection. It appears to be designed around the service locator pattern instead. Maybe this will start to change with the infrastructure that was added in .NET 4.0 in the System.ComponentModel.Composition namespace.

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• Question about design (inheritance, polymorphism)

  - by Dan

  Hi, I have a question about a problem I'm struggling with. Hope you can bear with me. Imagine I have an Object class representing the base class of a hierarchy of physical objects. Later I inherit from it to create an Object1D, Object2D and Object3D classes. Each of these derived classes will have some specific methods and attributes. For example, the 3d object might have functionality to download a 3d model to be used by a renderer. So I'd have something like this: class Object {}; class Object1D : public Object { Point mPos; }; class Object2D : public Object { ... }; class Object3D : public Object { Model mModel; }; Now I'd have a separate class called Renderer, which simply takes an Object as argument and well, renders it :-) In a similar way, I'd like to support different kinds of renderers. For instance, I could have a default one that every object could rely on, and then provide other specific renderers for some kind of objects: class Renderer {}; // Default one class Renderer3D : public Renderer {}; And here comes my problem. A renderer class needs to get an Object as an argument, for example in the constructor in order to retrieve whatever data it needs to render the object. So far so good. But a Renderer3D would need to get an Object3D argument, in order to get not only the basic attributes but also the specific attributes of a 3d object. Constructors would look like this: CRenderer(Object& object); CRenderer3D(Object3D& object); Now how do I specify this in a generic way? Or better yet, is there a better way to design this? I know I could rely on RTTI or similar but I'd like to avoid this if possible as I feel there is probably a better way to deal with this. Thanks in advance!

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• Using a function with reference as a function with pointers?

  - by epatel

  Today I stumbled over a piece of code that looked horrifying to me. The pieces was chattered in different files, I have tried write the gist of it in a simple test case below. The code base is routinely scanned with FlexeLint on a daily basis, but this construct has been laying in the code since 2004. The thing is that a function implemented with a parameter passing using references is called as a function with a parameter passing using pointers...due to a function cast. The construct has worked since 2004 on Irix and now when porting it actually do work on Linux/gcc too. My question now. Is this a construct one can trust? I can understand if compiler constructors implement the reference passing as it was a pointer, but is it reliable? Are there hidden risks? Should I change the fref(..) to use pointers and risk braking anything in the process? What to you think? #include <iostream> using namespace std; // ---------------------------------------- // This will be passed as a reference in fref(..) struct string_struct { char str[256]; }; // ---------------------------------------- // Using pointer here! void fptr(const char *str) { cout << "fptr: " << str << endl; } // ---------------------------------------- // Using reference here! void fref(string_struct &str) { cout << "fref: " << str.str << endl; } // ---------------------------------------- // Cast to f(const char*) and call with pointer void ftest(void (*fin)()) { void (*fcall)(const char*) = (void(*)(const char*))fin; fcall("Hello!"); } // ---------------------------------------- // Let's go for a test int main() { ftest((void (*)())fptr); // test with fptr that's using pointer ftest((void (*)())fref); // test with fref that's using reference return 0; }

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• Python4Delphi: Returning a python object in a function. (DelphiWrapper)

  - by Gabriel Fonseca

  I am using python4delphi. ow can I return an object from a wrapped Delphi class function? Code Snippet: I have a simple Delphi Class that i wrapped to Python Script, right? TSimple = Class Private function getvar1:string; Public Published property var1:string read getVar1; function getObj:TSimple; end; ... function TSimple.getVar1:string; begin result:='hello'; end; function TSimple.getObj:TSimple; begin result:=self; end; I made the TPySimple like the demo32 to give class access to the python code. My python module name is test. TPyDado = class(TPyDelphiPersistent) // Constructors & Destructors constructor Create( APythonType : TPythonType ); override; constructor CreateWith( PythonType : TPythonType; args : PPyObject ); override; // Basic services function Repr : PPyObject; override; class function DelphiObjectClass : TClass; override; end; ... { TPyDado } constructor TPyDado.Create(APythonType: TPythonType); begin inherited; // we need to set DelphiObject property DelphiObject := TDado.Create; with TDado(DelphiObject) do begin end; Owned := True; // We own the objects we create end; constructor TPyDado.CreateWith(PythonType: TPythonType; args: PPyObject); begin inherited; with GetPythonEngine, DelphiObject as TDado do begin if PyArg_ParseTuple( args, ':CreateDado' ) = 0 then Exit; end; end; class function TPyDado.DelphiObjectClass: TClass; begin Result := TDado; end; function TPyDado.Repr: PPyObject; begin with GetPythonEngine, DelphiObject as TDado do Result := VariantAsPyObject(Format('',[])); // or Result := PyString_FromString( PAnsiChar(Format('(%d, %d)',[x, y])) ); end; And now the python code: import test a = test.Simple() # try access the property var1 and everything is right print a.var1 # work's, but.. b = a.getObj(); # raise a exception that not find any attributes named getObj. # if the function returns a string for example, it's work.

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• Error Serializing a CLR object for use in a WCF service

  - by user208662

  Hello, I have written a custom exception object. The reason for this is I want to track additional information when an error occurs. My CLR object is defined as follows: public class MyException : Exception { public override string StackTrace { get { return base.StackTrace; } } private readonly string stackTrace; public override string Message { get { return base.Message; } } private readonly string message; public string Element { get { return element; } } private readonly string element; public string ErrorType { get { return errorType; } } private readonly string errorType; public string Misc { get { return misc; } } private readonly string misc; #endregion Properties #region Constructors public MyException() {} public MyException(string message) : base(message) { } public MyException(string message, Exception inner) : base(message, inner) { } public MyException(string message, string stackTrace) : base() { this.message = message; this.stackTrace = stackTrace; } public MyException(string message, string stackTrace, string element, string errorType, string misc) : base() { this.message = message; this.stackTrace = stackTrace; this.element = element; this.errorType = errorType; this.misc = misc; } protected MyException(SerializationInfo info, StreamingContext context) : base(info, context) { element = info.GetString("element"); errorType = info.GetString("errorType"); misc = info.GetString("misc"); } public override void GetObjectData(SerializationInfo info, StreamingContext context) { base.GetObjectData(info, context); info.AddValue("element", element); info.AddValue("errorType", errorType); info.AddValue("misc", misc); } } I have created a copy of this custom xception in a WP7 application. The only difference is, I do not have the GetObjectData method defined or the constructor with SerializationInfo defined. If I run the application as is, I receive an error that says: Type 'My.MyException' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. If I add the DataContract / DataMember attributes to the class and its appropriate members on the server-side, I receive an error that says: Type cannot be ISerializable and have DataContractAttribute attribute. How do I serialize MyException so that I can pass an instance of it to my WCF service. Please note, I want to use my service from an Android app. Because of this, I don't want to do anything too Microsoft centric. That was my fear with DataContract / DataMember stuff. Thank you so much for your help!

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• LINQ Query Returning Multiple Copies Of First Result

  - by Mike G

  I'm trying to figure out why a simple query in LINQ is returning odd results. I have a view defined in the database. It basically brings together several other tables and does some data munging. It really isn't anything special except for the fact that it deals with a large data set and can be a bit slow. I want to query this view based on a long. Two sample queries below show different queries to this view. var la = Runtime.OmsEntityContext.Positions.Where(p => p.AccountNumber == 12345678).ToList(); var deDa = Runtime.OmsEntityContext.Positions.Where(p => p.AccountNumber == 12345678).Select(p => new { p.AccountNumber, p.SecurityNumber, p.CUSIP }).ToList(); The first one should hand back a List. The second one will be a list of anonymous objects. When I do these queries in entities framework the first one will hand me back a list of results where they're all exactly the same. The second query will hand me back data where the account number is the one that I queried and the other values differ. This seems to do this on a per account number basis, ie if I were to query for one account number or another all the Position objects for one account would have the same value (the first one in the list of Positions for that account) and the second account would have a set of Position objects that all had the same value (again, the first one in it's list of Position objects). I can write SQL that is in effect the same as either of the two EF queries. They both come back with results (say four) that show the correct data, one account number with different securities numbers. Why does this happen??? Is there something that I could be doing wrong so that if I had four results for the first query above that the first record's data also appears in the 2-4th's objects??? I cannot fathom what would/could be causing this. I've searched Google for all kinds of keywords and haven't seen anyone with this issue. We partial class out the Positions class for added functionality (smart object) and some smart properties. There are even some constructors that provide some view model type support. None of this is invoked in the request (I'm 99% sure of this). However, we do this same pattern all over the app. The only thing I can think of is that the mapping in the EDMX is screwy. Is there a way that this would happen if the "primary keys" in the EDMX were not in fact unique given the way the view is constructed? I'm thinking that the dev who imported this model into the EDMX let the designer auto select what would be unique. Any help would give a haggered dev some hope!

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• Constructor versus setter injection

  - by Chris

  Hi, I'm currently designing an API where I wish to allow configuration via a variety of methods. One method is via an XML configuration schema and another method is through an API that I wish to play nicely with Spring. My XML schema parsing code was previously hidden and therefore the only concern was for it to work but now I wish to build a public API and I'm quite concerned about best-practice. It seems that many favor javabean type PoJo's with default zero parameter constructors and then setter injection. The problem I am trying to tackle is that some setter methods implementations are dependent on other setter methods being called before them in sequence. I could write anal setters that will tolerate themselves being called in many orders but that will not solve the problem of a user forgetting to set the appropriate setter and therefore the bean being in an incomplete state. The only solution I can think of is to forget about the objects being 'beans' and enforce the required parameters via constructor injection. An example of this is in the default setting of the id of a component based on the id of the parent components. My Interface public interface IMyIdentityInterface { public String getId(); /* A null value should create a unique meaningful default */ public void setId(String id); public IMyIdentityInterface getParent(); public void setParent(IMyIdentityInterface parent); } Base Implementation of interface: public abstract class MyIdentityBaseClass implements IMyIdentityInterface { private String _id; private IMyIdentityInterface _parent; public MyIdentityBaseClass () {} @Override public String getId() { return _id; } /** * If the id is null, then use the id of the parent component * appended with a lower-cased simple name of the current impl * class along with a counter suffix to enforce uniqueness */ @Override public void setId(String id) { if (id == null) { IMyIdentityInterface parent = getParent(); if (parent == null) { // this may be the top level component or it may be that // the user called setId() before setParent(..) } else { _id = Helpers.makeIdFromParent(parent,getClass()); } } else { _id = id; } } @Override public IMyIdentityInterface getParent() { return _parent; } @Override public void setParent(IMyIdentityInterface parent) { _parent = parent; } } Every component in the framework will have a parent except for the top level component. Using the setter type of injection, then the setters will have different behavior based on the order of the calling of the setters. In this case, would you agree, that a constructor taking a reference to the parent is better and dropping the parent setter method from the interface entirely? Is it considered bad practice if I wish to be able to configure these components using an IoC container? Chris

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• Create class instance in assembly from string name

  - by Arcadian

  I'm not sure if this is possible, and I'm quite new to using assemblies in C#.NET. What I would like to do is to create an instance of a class when supplied the string name of that class. Something like this: using MyAssembly; namespace MyNameSpace { Class MyClass { int MyValue1; int MyValue2; public MyClass(string myTypeName) { foreach(Type type in MyAssembly) { if((string)type == myTypeName) { //create a new instance of the type } } AssignInitialValues(//the type created above) } //Here I use an abstract type which the type above inherits from private void AssignInitialValues(AbstractType myClass) { this.value1 = myClass.value1; this.value2 = myClass.value2; } } } Obviously you cannot compare strings to types but it illustrates what I'm trying to do: create a type from a supplied string. Any thoughts? EDIT: After attempting: var myObject = (AbstractType) Activator.CreateInstance(null, myTypeName); AssignInitialValues(myObject); I get a number of errors: Inconsistent accessibility: parameter type 'MyAssembly.AbstractType' is less accessible than method 'MyNameSpace.MyClass.AssignInitialValues(MyAssembly.AstractType)' 'MyAssembly.AstractType' is inaccessible due to it's protection level The type or namespace name 'MyAssembly' could not be found (are you missing a using directive or an assembly reference?) The type or namespace name 'AbstractType' could not be found (are you missing a using directive or an assembly reference?) Not exactly sure why it can't find the assembly; I've added a reference to the assembly and I use a Using Directive for the namespace in the assembly. As for the protection level, it's calling classes (or rather the constructors of classes) which can only be public. Any clues on where the problem is? UPDATE: After looking through several articles on SO I came across this: http://stackoverflow.com/a/1632609/360627 Making the AbstractTypeclass public solved the issue of inconsistent accessibility. The new compiler error is this: Cannot convert type 'System.Runtime.Remoting.ObjectHandle' to 'MyAssembly.AbstractType' The line it references is this one: var myObject = (AbstractType) Activator.CreateInstance(null, myTypeName); Using .Unwrap() get's me past this error and I think it's the right way to do it (uncertain). However, when running the program I then get a TypeLoadException when this code is called. TypeLoadException: Could not load type ‘AbstractType’ from assembly ‘MyNameSpace'... Right away I can spot that the type its looking for is correct but the assembly it's looking in is wrong. Looking up the Activator.CreateInstance(String, String) method revealed that the null as the first argument means that the method will look in the executing assembly. This is contrary to the required behavior as in the original post. I've tried using MyAssembly as the first argument but this produces the error: 'MyAssembly' is a 'namespace' but is used like a 'variable' Any thoughts on how to fix this?

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• Struggling with ASP.NET MVC auto-scaffolder template

  - by DanM

  I'm trying to write an auto-scaffolder template for Index views. I'd like to be able to pass in a collection of models or view-models (e.g., IQueryable<MyViewModel>) and get back an HTML table that uses the DisplayName attribute for the headings (th elements) and Html.Display(propertyName) for the cells (td elements). Each row should correspond to one item in the collection. Here's what I have so far: <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %> <% var items = (IQueryable<TestProj.ViewModels.TestViewModel>)Model; // How do I make this generic? var properties = items.First().GetMetadata().Properties .Where(pm => pm.ShowForDisplay && !ViewData.TemplateInfo.Visited(pm)); %> <table> <tr> <% foreach(var property in properties) { %> <th> <%= property.DisplayName %> </th> <% } %> </tr> <% foreach(var item in items) { HtmlHelper itemHtml = ????; // What should I put in place of "????"? %> <tr> <% foreach(var property in properties) { %> <td> <%= itemHtml.Display(property.DisplayName) %> </td> <% } %> </tr> <% } %> </table> Two problems with this: I'd like it to be generic. So, I'd like to replace var items = (IQueryable<TestProj.ViewModels.TestViewModel>)Model; with var items = (IQueryable<T>)Model; or something to that effect. A property Html is automatically created for me when the view is created, but this HtmlHelper applies to the whole collection. I need to somehow create an itemHtml object that applies just to the current item in the foreach loop. I'm not sure how to do this, however, because the constructors for HtmlHelper don't take a Model object. How do I solve these two problems?

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• C++0x Overload on reference, versus sole pass-by-value + std::move?

  - by dean

  It seems the main advice concerning C++0x's rvalues is to add move constructors and move operators to your classes, until compilers default-implement them. But waiting is a losing strategy if you use VC10, because automatic generation probably won't be here until VC10 SP1, or in worst case, VC11. Likely, the wait for this will be measured in years. Here lies my problem. Writing all this duplicate code is not fun. And it's unpleasant to look at. But this is a burden well received, for those classes deemed slow. Not so for the hundreds, if not thousands, of smaller classes. ::sighs:: C++0x was supposed to let me write less code, not more! And then I had a thought. Shared by many, I would guess. Why not just pass everything by value? Won't std::move + copy elision make this nearly optimal? Example 1 - Typical Pre-0x constructor OurClass::OurClass(const SomeClass& obj) : obj(obj) {} SomeClass o; OurClass(o); // single copy OurClass(std::move(o)); // single copy OurClass(SomeClass()); // single copy Cons: A wasted copy for rvalues. Example 2 - Recommended C++0x? OurClass::OurClass(const SomeClass& obj) : obj(obj) {} OurClass::OurClass(SomeClass&& obj) : obj(std::move(obj)) {} SomeClass o; OurClass(o); // single copy OurClass(std::move(o)); // zero copies, one move OurClass(SomeClass()); // zero copies, one move Pros: Presumably the fastest. Cons: Lots of code! Example 3 - Pass-by-value + std::move OurClass::OurClass(SomeClass obj) : obj(std::move(obj)) {} SomeClass o; OurClass(o); // single copy, one move OurClass(std::move(o)); // zero copies, two moves OurClass(SomeClass()); // zero copies, one move Pros: No additional code. Cons: A wasted move in cases 1 & 2. Performance will suffer greatly if SomeClass has no move constructor. What do you think? Is this correct? Is the incurred move a generally acceptable loss when compared to the benefit of code reduction?

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