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• JSF Float Conversion

  - by Phill Sacre

  I'm using JSF 1.2 with IceFaces 1.8 in a project here. I have a page which is basically a big edit grid for a whole bunch of floating-point number fields. This is implemented with inputText fields on the page pointing at a value object with primitive float types Now, as a new requirement sees some of the fields be nullable, I wanted to change the value object to use Float objects rather than primitive types. I didn't think I'd need to do anything to the page to accomodate this. However, when I make the change I get the following error: /pages/page.xhtml @79,14 value="#{row.targetValue}": java.lang.IllegalArgumentException: argument type mismatch And /pages/page.xhtml @79,14 value="#{row.targetValue}": java.lang.IllegalArgumentException: java.lang.ClassCastException@1449aa1 The page looks like this: <ice:inputText value="#{row.targetValue}" size="4"> <f:convertNumber pattern="###.#" /> </ice:inputText> I've also tried adding in <f:convert convertId="javax.faces.Float" /> in there as well but that doesn't seem to work either! Neither does changing the value object types to Double. I'm sure I'm probably missing something really simple but I've been staring at this for a while now and no answers are immediately obvious!

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• Doubts about .NET Garbage Collector

  - by Smjert

  I've read some docs about the .NET Garbage Collector but i still have some doubts (examples in C#): 1)Does GC.Collect() call a partial or a full collection? 2)Does a partial collection block the execution of the "victim" application? If yes.. then i suppose this is a very "light" things to do since i'm running a game server that uses 2-3GB of memory and i "never" have execution stops (or i can't see them..). 3)I've read about GC roots but still can't understand how exactly they works. Suppose that this is the code (C#): MyClass1: [...] public List<MyClass2> classList = new List<MyClass2>(); [...] Main: main() { MyClass1 a = new MyClass1(); MyClass2 b = new MyClass2(); a.classList.Add(b); b = null; DoSomeLongWork(); } Will b ever be eligible to be garbage collected(before the DoSomeLongWork finishes)? The reference to b that classList contains, can it be considered a root? Or a root is only the first reference to the instance? (i mean, b is the root reference because the instantiation happens there).

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• Closures and universal quantification

  - by Apocalisp

  I've been trying to work out how to implement Church-encoded data types in Scala. It seems that it requires rank-n types since you would need a first-class const function of type forAll a. a -> (forAll b. b -> b). However, I was able to encode pairs thusly: import scalaz._ trait Compose[F[_],G[_]] { type Apply = F[G[A]] } trait Closure[F[_],G[_]] { def apply[B](f: F[B]): G[B] } def pair[A,B](a: A, b: B) = new Closure[Compose[PartialApply1Of2[Function1,A]#Apply, PartialApply1Of2[Function1,B]#Apply]#Apply, Identity] { def apply[C](f: A => B => C) = f(a)(b) } For lists, I was able to get encode cons: def cons[A](x: A) = { type T[B] = B => (A => B => B) => B new Closure[T,T] { def apply[B](xs: T[B]) = (b: B) => (f: A => B => B) => f(x)(xs(b)(f)) } } However, the empty list is more problematic and I've not been able to get the Scala compiler to unify the types. Can you define nil, so that, given the definition above, the following compiles? cons(1)(cons(2)(cons(3)(nil)))

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• .NET Web Service hydrate custom class

  - by row1

  I am consuming an external C# Web Service method which returns a simple calculation result object like this: [Serializable] public class CalculationResult { public string Name { get; set; } public string Unit { get; set; } public decimal? Value { get; set; } } When I add a Web Reference to this service in my ASP .NET project Visual Studio is kind enough to generate a matching class so I can easily consume and work with it. I am using Castle Windsor and I may want to plug in other method of getting a calculation result object, so I want a common class CalculationResult (or ICalculationResult) in my solution which all my objects can work with, this will always match the object returned from the external Web Service 1:1. Is there anyway I can tell my Web Service client to hydrate a particular class instead of its generated one? I would rather not do it manually: foreach(var fromService in calcuationResultsFromService) { ICalculationResult calculationResult = new CalculationResult() { Name = fromService.Name }; yield return calculationResult; } Edit: I am happy to use a Service Reference type instead of the older Web Reference.

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• How do I tell if an action is a lambda expression?

  - by Keith

  I am using the EventAgregator pattern to subscribe and publish events. If a user subscribes to the event using a lambda expression, they must use a strong reference, not a weak reference, otherwise the expression can be garbage collected before the publish will execute. I wanted to add a simple check in the DelegateReference so that if a programmer passes in a lambda expression and is using a weak reference, that I throw an argument exception. This is to help "police" the code. Example: eventAggregator.GetEvent<RuleScheduler.JobExecutedEvent>().Subscribe ( e => resetEvent.Set(), ThreadOption.PublisherThread, false, // filter event, only interested in the job that this object started e => e.Value1.JobDetail.Name == jobName ); public DelegateReference(Delegate @delegate, bool keepReferenceAlive) { if (@delegate == null) throw new ArgumentNullException("delegate"); if (keepReferenceAlive) { this._delegate = @delegate; } else { //TODO: throw exception if target is a lambda expression _weakReference = new WeakReference(@delegate.Target); _method = @delegate.Method; _delegateType = @delegate.GetType(); } } any ideas? I thought I could check for @delegate.Method.IsStatic but I don't believe that works... (is every lambda expression a static?)

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• How do I use IIS6 style metabase paths in IIS7 AppCmd tool?

  - by Mike Atlas

  I'm currently in the process of upgrading old II6 automation scripts that use the IISVdir tool to create/modify/update apps and virtual directories, and replacing them with AppCmd for IIS7. The IIS6, "IISVDir" commands reference paths in that are from the metabase, eg, "/W3SVC/1/ROOT/MyApp" - where 1 is ID of the "Default Web Site" site. The command doesn't actually require the display name of the site to make changes to it. This works well, since on a different language OS, the "Default Web Site" site name could be named, for example, "??? Web ???" or anything else for that matter. But this flexibility is lost if AppCmd can only reference "Default Web Site" via its name, and not a language-neutral identifier. So, how can I script AppCmd to refer to sites, vdirs and apps using language neutral identifiers to reference the "Default App Site"? Perhaps I need to start creating my own site instead, from the start, and name it something else specific, and stop using "Default Web Site" as the root? (Disclosure: I only have a IIS7-English machine that I am working on currently, but I have both IIS6-English and IIS6-Japanese machines for testing my old scripts - so perhaps it really is just "Default Web Site" still on Win2k8-Japanese?)

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• django: How to make one form from multiple models containing foreignkeys

  - by Tim

  I am trying to make a form on one page that uses multiple models. The models reference each other. I am having trouble getting the form to validate because I cant figure out how to get the id of two of the models used in the form into the form to validate it. I used a hidden key in the template but I cant figure out how to make it work in the views My code is below: views: def the_view(request, a_id,): if request.method == 'POST': b_form= BForm(request.POST) c_form =CForm(request.POST) print "post" if b_form.is_valid() and c_form.is_valid(): print "valid" b_form.save() c_form.save() return HttpResponseRedirect(reverse('myproj.pro.views.this_page')) else: b_form= BForm() c_form = CForm() b_ide = B.objects.get(pk=request.b_id) id_of_a = A.objects.get(pk=a_id) return render_to_response('myproj/a/c.html', {'b_form':b_form, 'c_form':c_form, 'id_of_a':id_of_a, 'b_id':b_ide }) models class A(models.Model): name = models.CharField(max_length=256, null=True, blank=True) classe = models.CharField(max_length=256, null=True, blank=True) def __str__(self): return self.name class B(models.Model): aid = models.ForeignKey(A, null=True, blank=True) number = models.IntegerField(max_length=1000) other_number = models.IntegerField(max_length=1000) class C(models.Model): bid = models.ForeignKey(B, null=False, blank=False) field_name = models.CharField(max_length=15) field_value = models.CharField(max_length=256, null=True, blank=True) forms from mappamundi.mappa.models import A, B, C class BForm(forms.ModelForm): class Meta: model = B exclude = ('aid',) class CForm(forms.ModelForm): class Meta: model = C exclude = ('bid',) B has a foreign key reference to A, C has a foreign key reference to B. Since the models are related, I want to have the forms for them on one page, 1 submit button. Since I need to fill out fields for the forms for B and C & I dont want to select the id of B from a drop down list, I need to somehow get the id of the B form into the form so it will validate. I have a hidden field in the template, I just need to figure how to do it in the views

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• Why are references compacted inside Perl lists?

  - by parkan

  Putting a precompiled regex inside two different hashes referenced in a list: my @list = (); my $regex = qr/ABC/; push @list, { 'one' => $regex }; push @list, { 'two' => $regex }; use Data::Dumper; print Dumper(\@list); I'd expect: $VAR1 = [ { 'one' => qr/(?-xism:ABC)/ }, { 'two' => qr/(?-xism:ABC)/ } ]; But instead we get a circular reference: $VAR1 = [ { 'one' => qr/(?-xism:ABC)/ }, { 'two' => $VAR1->[0]{'one'} } ]; This will happen with indefinitely nested hash references and shallowly copied $regex. I'm assuming the basic reason is that precompiled regexes are actually references, and references inside the same list structure are compacted as an optimization (\$scalar behaves the same way). I don't entirely see the utility of doing this (presumably a reference to a reference has the same memory footprint), but maybe there's a reason based on the internal representation Is this the correct behavior? Can I stop it from happening? Aside from probably making GC more difficult, these circular structures create pretty serious headaches. For example, iterating over a list of queries that may sometimes contain the same regular expression will crash the MongoDB driver with a nasty segfault (see https://rt.cpan.org/Public/Bug/Display.html?id=58500)

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• Compiling Objective-C project on Linux (Ubuntu)

  - by Alex

  How to make an Objective-C project work on Ubuntu? My files are: Fraction.h #import <Foundation/NSObject.h> @interface Fraction: NSObject { int numerator; int denominator; } -(void) print; -(void) setNumerator: (int) n; -(void) setDenominator: (int) d; -(int) numerator; -(int) denominator; @end Fraction.m #import "Fraction.h" #import <stdio.h> @implementation Fraction -(void) print { printf( "%i/%i", numerator, denominator ); } -(void) setNumerator: (int) n { numerator = n; } -(void) setDenominator: (int) d { denominator = d; } -(int) denominator { return denominator; } -(int) numerator { return numerator; } @end main.m #import <stdio.h> #import "Fraction.h" int main( int argc, const char *argv[] ) { // create a new instance Fraction *frac = [[Fraction alloc] init]; // set the values [frac setNumerator: 1]; [frac setDenominator: 3]; // print it printf( "The fraction is: " ); [frac print]; printf( "\n" ); // free memory [frac release]; return 0; } I've tried two approaches to compile it: Pure gcc: $ sudo apt-get install gobjc gnustep gnustep-devel $ gcc `gnustep-config --objc-flags` -o main main.m -lobjc -lgnustep-base /tmp/ccIQKhfH.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction' I created a GNUmakefile Makefile: include ${GNUSTEP_MAKEFILES}/common.make TOOL_NAME = main main_OBJC_FILES = main.m include ${GNUSTEP_MAKEFILES}/tool.make ... and ran: $ source /usr/share/GNUstep/Makefiles/GNUstep.sh $ make Making all for tool main... Linking tool main ... ./obj/main.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction' So in both cases compiler gets stuck at undefined reference to `__objc_class_name_Fraction' Do you have and idea how to resolve this issue?

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• Some web pages (especially Apple documentation) cause heavy CPU usage in Windows IE8

  - by Mark Lutton

  Maybe this belongs in Server Fault instead, but some of you may have noticed this issue (particularly those developing on Mac, using a Windows machine to read the reference material). I posted the same question on a Microsoft forum and got one answer from someone who reproduced the problem, so it's not just my machine. No solution yet. Ever since this month's security updates, I find that many web pages cause the CPU to run at maximum for as long as the web page is visible. This happens in both IE7 and IE8 on at least three different computers (two with Windows XP, one with Vista). Here is one of the pages, running on XP with IE 8: http://learning2code.blogspot.com/2007/11/update-using-subversion-with-xcode-3.html Here is one that does it in Vista with IE8: http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html You can leave the page open for hours and the CPU is still at high usage. This doesn't happen every time. It is not always reproduceable. Sometimes it is OK the second or third time it loads. In IE7 the high usage is in ieframe.dll, version 7.0.6000.16890. In IE8 the high usage is in iertutil.dll, version 8.0.6001.18806.

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• Ninject: Shared DI/IoC container

  - by joblot

  Hi I want to share the container across various layers in my application. I started creating a static class which initialises the container and register types in the container. public class GeneralDIModule : NinjectModule { public override void Load() { Bind().To().InSingletonScope(); } } public abstract class IoC { private static IKernel _container; public static void Initialize() { _container = new StandardKernel(new GeneralDIModule(), new ViewModelDIModule()); } public static T Get<T>() { return _container.Get<T>(); } } I noticed there is a Resolve method as well. What is the difference between Resolve and Get? In my unit tests I don’t always want every registered type in my container. Is there a way of initializing an empty container and then register types I need. I’ll be mocking types as well in unit test so I’ll have to register them as well. There is an Inject method, but it says lifecycle of instance is not managed? Could someone please set me in right way? How can I register, unregister objects and reset the container. Thanks

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• Unit test project doesn't recognize the classes it was generated from

  - by DougLeary

  I have a fairly simple file-system website consisting of one aspx page and several classes in separate .cs files. Everything is on my own HD. The web app itself builds and runs fine. Out of curiosity I decided to try out Visual Studio's nifty, easy-to-use unit test feature. So I opened each class file and clicked Create Unit Tests. VS generated a test project containing a set of test classes and some other files. Easy! But when I try to build or run the test project it throws a series of build errors, one for every class: The type or namespace name 'class-name' could not be found (are you missing a using directive or an assembly reference?). Somebody asked if my test project has a reference to the original project. Well no, because the original project is a file-system website. It has no bin folder and no DLL, so there's nothing to reference as far as I can tell. I would think that since VS generated these unit tests it would generate whatever references it needs, but apparently not. Is generating unit tests for file-system web apps an undocumented no-no, or is there a magic trick to getting it to work?

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• Java: How to workaround the lack of Equatable interface?

  - by java.is.for.desktop

  Hello, everyone! As far as I know, things such as SortedMap or SortedSet, use compareTo (rather than equals) on Comparable<?> types for checking equality (contains, containsKey). But what if certain types are equatable by concept, but not comparable? I have to declare a Comparator<?> and override the method int compareTo(T o1, To2). OK, I can return 0 for instances which are considered equal. But, for unqeual instances, what do I return when an order is not evident? Is the approach of using SortedMap or SortedSet on equatable but (by concept) not comparable types good anyway? Thank you! EDIT: I don't want to store things sorted, but would I use "usual" Map and Set, I couldn't "override" the equality-behavior. EDIT 2: Why I can't just override equals(...): I need to alter the equality-behavior of a foreign class. Can't edit it. EDIT 3: Just think of .NET: They have IEquatable interface which cat alter the equality-behavior without touching the comparable behavior.

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• StrcutureMap Wiring - Sanity Check Please

  - by Steve Ward

  Hi - Im new to IOC and StructureMap and have an n-level application and am looking at how to setup the wirings (ForRequestedType ...) and just want to check with people with more experience that this is the best way of doing it! I dont want my UI application object to reference my persistence layer directly so am not able to wire everything up in this UI project. I now have it working by defining a Registry class in each project which wires up the types in the project as needed. The layer above registers its types and also calls the assembly below and looks for registries so that all types are registered throught the hierrachy. E.g. I have UI, Service, Domain, and Persistence libraries. In my service layer the registry looks like Scan(x => { x.Assembly("MyPersistenceProject"); x.LookForRegistries(); }); ForRequestedType<IService>().TheDefault.Is.OfConcreteType<MyService>(); Is this a recommended way of doing this in a setup such as this? Are there better ways and what are the advantages / disadvantages of these approaches in this case?

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• Problem in Building mplsh-run in lshkit

  - by Yijinsei

  Hi guy, been trying out this for quite some time but I'm still unable to built mplsh-run from lshkit Not sure if this would help to explain my situation during the building process /tmp/cc17kth4.o: In function `lshkit::MultiProbeLshRecallTable::reset(lshkit::MultiProbeLshModel, unsigned int, double, double)': mplsh-run.cpp:(.text._ZN6lshkit24MultiProbeLshRecallTable5resetENS_18MultiProbeLshModelEjdd[lshkit::MultiProbeLshRecallTable::reset(lshkit::MultiProbeLshModel, unsigned int, double, double)]+0x230): undefined reference to `lshkit::MultiProbeLshModel::recall(double) const' /tmp/cc17kth4.o: In function `void lshkit::MultiProbeLshIndex<unsigned int>::query_recall<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, float, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&) const': mplsh-run.cpp:(.text._ZNK6lshkit18MultiProbeLshIndexIjE12query_recallINS_11TopkScannerINS_6MatrixIfE8AccessorENS_6metric5l2sqrIfEEEEEEvPKffRT_[void lshkit::MultiProbeLshIndex<unsigned int>::query_recall<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, float, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&) const]+0x2c4): undefined reference to `lshkit::MultiProbeLsh::genProbeSequence(float const*, std::vector<unsigned int, std::allocator<unsigned int> >&, unsigned int) const' /tmp/cc17kth4.o: In function `void lshkit::MultiProbeLshIndex<unsigned int>::query<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, unsigned int, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&)': mplsh-run.cpp:(.text._ZN6lshkit18MultiProbeLshIndexIjE5queryINS_11TopkScannerINS_6MatrixIfE8AccessorENS_6metric5l2sqrIfEEEEEEvPKfjRT_[void lshkit::MultiProbeLshIndex<unsigned int>::query<lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> > >(float const*, unsigned int, lshkit::TopkScanner<lshkit::Matrix<float>::Accessor, lshkit::metric::l2sqr<float> >&)]+0x4a): undefined reference to `lshkit::MultiProbeLsh::genProbeSequence(float const*, std::vector<unsigned int, std::allocator<unsigned int> >&, unsigned int) const' collect2: ld returned 1 exit status the command that i used to built mplsh-run is g++ -I./lshkit/include -L/usr/lib -lm -lgsl -lgslcblas -lboost_program_options-mt mplsh-run.cpp Do you guys have any clue on how I could solve this?

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• [Database] How to model this one-to-one relation?

  - by pbean

  I have several entities which respresent different types of users who need to be able to log in to a particular system. Additionally, they have different types of information associated with them. For example: a "general user", which has an e-mail address and "admin user", which has a workstation number (note that this a hypothetical case). Both entities also share common properties like first name, surname, address and telephone number. Finally, they naturally need to have a (unique) user name and a password to log in. In the application, the user just has to fill in his user name and password, and the functionality of the application changes slightly according to the type of the user. You can imagine that the username needs to be unique for this work. How should I model this effectively? I can't just create two tables, because then I can't force a unique constaint on the user name. I also can't put them all in just one table, because they have different types of specific information associated to them. I think I might need 3 seperate tables, one for "users" (with user name and password), one for the "general users" and another one for the "admin users", but how would the relations between these work? Or is there another solution? (By the way, the target DBMS is MySQL, so I don't think generalization is supported in the database system itself).

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• dll's loaded through reflection

  - by Seattle Leonard

  Ok, I got a strange one here and I want to know if any of you have ever run accross anything like it. So I've got this web app that loads up a bunch of dll's through reflection. Basically it looks for Types that are derived from certain abstract types and adds them to the list of things it can make. Here's the weird part. While developing there is never a problem. When installing it, there is never a problem to start with. Then, at a seemingly random time, the application breaks while trying to find all the types. I've had 2 sites sitting side by side and one worked while the other did not, and they were configured exactly(and I mean exactly) the same. IISRESET's never helped, but this did: I simply moved all the dll's out of the bin directory then moved them back. That's right I just moved them out of the bin directory then put them right back where they came from and everything worked fine. Any ideas?

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• A feeling that I'm not that good developer

  - by Karim

  Hi, Im having a strange feeling, but let me first introduce myself as a software developer. I started to program when I was still a kid, I had about 10 or 11 years. I really enjoy my work and never get bored from it. It's amazing how somebody could be paid for what he really likes to do and would be doing it anyway even for free. WHen I first started to program, I was feeling proud of what I was doing, each application I built was for me a success and after 2-3 year I had a feeling that I'm a coding guru. It was a nice feeling ;-) But the more I was in the field, the more types of software I started to develop I was starting to have a feeling that I'm completely wrong in that I'm guru. I felt that I'm not even a mediocre developer. Each new field I start to work on is giving me this feeling. Like when I once developed a device driver for a client, I saw how much I need to learn about device drivers. When I developed a video filter for an application, I saw how much do I still need to learn about DirectShow, Color Spaces, and all the theory behind that. The worst thing was when I started to learn algorithms. It was several years ago. I knew then the basic structures and algorithms like the sorting, some types of trees, some hashtables, strings etc.. and when I really wanted to learn a group of structures I learned about 5-6 new types and saw that in fact even this small group has several hundred subtypes of structures. It's depressing how little time people have in their lives to learn all this stuff. I'm now a software developer with about 10 years of experience and I still feel that I'm not a proficient developer when I think about things that others do in the industry. Is this normal what I'm experiencing or is it a sign of a destructive excessive ambition? Thanks in advance for any comments.

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• How do I dispatch to a method based on a parameter's runtime type in C# < 4?

  - by Evan Barkley

  I have an object o which guaranteed at runtime to be one of three types A, B, or C, all of which implement a common interface I. I can control I, but not A, B, or C. (Thus I could use an empty marker interface, or somehow take advantage of the similarities in the types by using the interface, but I can't add new methods or change existing ones in the types.) I also have a series of methods MethodA, MethodB, and MethodC. The runtime type of o is looked up and is then used as a parameter to these methods. public void MethodA(A a) { ... } public void MethodB(B b) { ... } public void MethodC(C c) { ... } Using this strategy, right now a check has to be performed on the type of o to determine which method should be invoked. Instead, I would like to simply have three overloaded methods: public void Method(A a) { ... } // these are all overloads of each other public void Method(B b) { ... } public void Method(C c) { ... } Now I'm letting C# do the dispatch instead of doing it manually myself. Can this be done? The naive straightforward approach doesn't work, of course: Cannot resolve method 'Method(object)'. Candidates are: void Method(A) void Method(B) void Method(C)

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• Extract data from PostgreSQL DB without using pg_dump

  - by John Horton

  There is a PostgreSQL database on which I only have limited access (e.g, I can't use pg_dump). I am trying to create a local "mirror" by exporting certain tables from the database. I do not have the permissions needed to just dump a table as SQL from within psql. Right now, I just have a Python script that iterates through my table_names, selects all fields and then exports them as a CSV: for table_name, file_name in zip(table_names, file_names): cmd = """echo "\\\copy (select * from %s)" to stdout WITH CSV HEADER | psql -d remote_db | gzip > ./%s/%s.gz"""%(table_name,dir_name,file_name) os.system(cmd) I would like to not use CSV if possible, as I lose the field types and the encoding can get messed up. First best would probably be some way of getting the generating SQL code for the table using \copy. Next best would be XML, ideally with some way of preserving the field types. If that doesn't work, I think the final option might be two queries---one to get the field data types, the other to get the actual data. Any thoughts or advice would be greatly appreciated - thanks!

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• Checking instance of non-class constrained type parameter for null in generic method

  - by casperOne

  I currently have a generic method where I want to do some validation on the parameters before working on them. Specifically, if the instance of the type parameter T is a reference type, I want to check to see if it's null and throw an ArgumentNullException if it's null. Something along the lines of: // This can be a method on a generic class, it does not matter. public void DoSomething<T>(T instance) { if (instance == null) throw new ArgumentNullException("instance"); Note, I do not wish to constrain my type parameter using the class constraint. I thought I could use Marc Gravell's answer on "How do I compare a generic type to its default value?", and use the EqualityComparer<T> class like so: static void DoSomething<T>(T instance) { if (EqualityComparer<T>.Default.Equals(instance, null)) throw new ArgumentNullException("instance"); But it gives a very ambiguous error on the call to Equals: Member 'object.Equals(object, object)' cannot be accessed with an instance reference; qualify it with a type name instead How can I check an instance of T against null when T is not constrained on being a value or reference type?

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• Would making plain int 64-bit break a lot of reasonable code?

  - by R..

  Until recently, I'd considered the decision by most systems implementors/vendors to keep plain int 32-bit even on 64-bit machines a sort of expedient wart. With modern C99 fixed-size types (int32_t and uint32_t, etc.) the need for there to be a standard integer type of each size 8, 16, 32, and 64 mostly disappears, and it seems like int could just as well be made 64-bit. However, the biggest real consequence of the size of plain int in C comes from the fact that C essentially does not have arithmetic on smaller-than-int types. In particular, if int is larger than 32-bit, the result of any arithmetic on uint32_t values has type signed int, which is rather unsettling. Is this a good reason to keep int permanently fixed at 32-bit on real-world implementations? I'm leaning towards saying yes. It seems to me like there could be a huge class of uses of uint32_t which break when int is larger than 32 bits. Even applying the unary minus or bitwise complement operator becomes dangerous unless you cast back to uint32_t. Of course the same issues apply to uint16_t and uint8_t on current implementations, but everyone seems to be aware of and used to treating them as "smaller-than-int" types.

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• Using LINQ to map dynamically (or construct projections)

  - by CodeGrue

  I know I can map two object types with LINQ using a projection as so: var destModel = from m in sourceModel select new DestModelType {A = m.A, C = m.C, E = m.E} where class SourceModelType { string A {get; set;} string B {get; set;} string C {get; set;} string D {get; set;} string E {get; set;} } class DestModelType { string A {get; set;} string C {get; set;} string E {get; set;} } But what if I want to make something like a generic to do this, where I don't know specifically the two types I am dealing with. So it would walk the "Dest" type and match with the matching "Source" types.. is this possible? Also, to achieve deferred execution, I would want it just to return an IQueryable. For example: public IQueryable<TDest> ProjectionMap<TSource, TDest>(IQueryable<TSource> sourceModel) { // dynamically build the LINQ projection based on the properties in TDest // return the IQueryable containing the constructed projection } I know this is challenging, but I hope not impossible, because it will save me a bunch of explicit mapping work between models and viewmodels.

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• How should rules for Aggregate Roots be enforced?

  - by MylesRip

  While searching the web, I came across a list of rules from Eric Evans' book that should be enforced for aggregates: The root Entity has global identity and is ultimately responsible for checking invariants Root Entities have global identity. Entities inside the boundary have local identity, unique only within the Aggregate. Nothing outside the Aggregate boundary can hold a reference to anything inside, except to the root Entity. The root Entity can hand references to the internal Entities to other objects, but they can only use them transiently (within a single method or block). Only Aggregate Roots can be obtained directly with database queries. Everything else must be done through traversal. Objects within the Aggregate can hold references to other Aggregate roots. A delete operation must remove everything within the Aggregate boundary all at once When a change to any object within the Aggregate boundary is committed, all invariants of the whole Aggregate must be satisfied. This all seems fine in theory, but I don't see how these rules would be enforced in the real world. Take rule 3 for example. Once the root entity has given an exteral object a reference to an internal entity, what's to keep that external object from holding on to the reference beyond the single method or block? (If the enforcement of this is platform-specific, I would be interested in knowing how this would be enforced within a C#/.NET/NHibernate environment.)

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• How to enforce users to create objects of class derived from mine with "new" only?

  - by sharptooth

  To implement reference counting we use an IUnknown-like interface and a smart pointer template class. The interface has implementation for all the reference-count methods, including Release(): void IUnknownLike::Release() { if( --refCount == 0 ) { delete this; } } The smart pointer template class has a copy constructor and an assignment operator both accepting raw pointers. So users can do the following: class Class : public IUnknownLike { }; void someFunction( CSmartPointer<Class> object ); //whatever function Class object; someFunction( &object ); and the program runs into undefined behavior - the object is created with reference count zero, the smart pointer is constructed and bumps it to one, then the function returns, smart pointer is destroyed, calls Release() which leads to delete of a stack-allocated variable. Users can as well do the following: struct COuter { //whatever else; Class inner;// IUnknownLike descendant }; COuter object; somefunction( &object.Inner ); and again an object not created with new is deleted. Undefined behavior at its best. Is there any way to change the IUnknownLike interface so that the user is forced to use new for creating all objects derived from IUnknownLike - both directly derived and indirectly derived (with classes in between the most derived and the base)?

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