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  • What is the purpose of "do!" notation in F#?

    - by Yacoder
    I'm a beginner in F#, so it's a simple question and maybe a duplicate, but I couldn't find the answer anywhere... I'm reading this LOGO DSL implementation and I don't understand, what is the meaning of the "do!" notation in here: this.Loaded.Add (fun _ -> async { do! Async.Sleep 200 for cmd in theDrawing do do! this.Execute(cmd) } |> Async.StartImmediate ) Can you help?

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  • What are the benefits of prototypal inheritance over classical?

    - by Pierreten
    So I finally stopped dragging my feet all these years and decided to learn JavaScript "properly". One of the most head-scratching elements of the languages design is it's implementation of inheritance. Having experience in Ruby, I was really happy to see closures and dynamic typing; but for the life of me can't figure out what benefits are to be had from object instances using other instances for inheritance.

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  • Fetch the most viewed data in databases

    - by Erik Edgren
    I want to get the most viewed photo from the database but I don't know how I shall accomplish this. Here's my SQL at the moment: SELECT * FROM photos AS p, viewers AS v WHERE p.id = v.id_photo GROUP BY v.id_photo The databases: CREATE TABLE IF NOT EXISTS `photos` ( `id` int(10) NOT NULL AUTO_INCREMENT, `photo_filename` varchar(50) NOT NULL, `photo_camera` varchar(150) NOT NULL, `photo_taken` datetime NOT NULL, `photo_resolution` varchar(10) NOT NULL, `photo_exposure` varchar(10) NOT NULL, `photo_iso` varchar(3) NOT NULL, `photo_fnumber` varchar(10) NOT NULL, `photo_focallength` varchar(10) NOT NULL, `post_coordinates` text NOT NULL, `post_description` text NOT NULL, `post_uploaded` datetime NOT NULL, `post_edited` datetime NOT NULL, `checkbox_approxcoor` enum('0','1') NOT NULL DEFAULT '0', PRIMARY KEY (`id`), UNIQUE KEY `id` (`id`) ) CREATE TABLE IF NOT EXISTS `viewers` ( `id` int(10) NOT NULL AUTO_INCREMENT, `id_photo` int(10) DEFAULT '0', `ipaddress` text NOT NULL, `date_viewed` datetime NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `id` (`id`) ) The data in viewers looks like this: (1, 85, '3892a0ab97d6ff325f285b27b847070f', '2012-06-21 22:49:25'), (2, 84, '3892a0ab97d6ff325f285b27b847070f', '2012-06-21 22:49:25'), (3, 85, '3892a0ab97d6ff325f285b27b847070f', '2012-06-21 22:49:25'); One single row from the database for photos to understand how the rows looks like in this database: (85, 'P1170986.JPG', 'Panasonic DMC-LX3', '2012-06-19 18:00:40', '3968x2232', '10/8000', '80', '50/10', '51/10', '', '', '2012-06-19 18:45:17', '0000-00-00 00:00:00', '0') At the moment the SQL only prints the photo with ID 84. In this case it's wrong - it should print out the photo with ID 85. How can I fix this problem? Thanks in advance.

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  • scroll/search JList when user starts typing

    - by alex
    I would like to implement one of the fanciest features I every now and then. I would like to allow a user to click on a JList and if words are typed, do a query and advance the caret to the next match (prefix). Is there and example of such an implementation in Java somewhere? I'm thinking a combination of key listeners, getNextMatch() and setSelectValue().

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  • How can I pass a UIEvent to a UIScrollView

    - by rickharrison
    I am subclassing UIWindow and creating an implementation of sendEvent: as follows: - (void)sendEvent:(UIEvent *)event { [super sendEvent:event]; // Send event to UIScrollView here } How can I send the event to a UIScrollView. I tried calling the touchesBegan:, etc. messages, but that did not do anything.

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  • Explicit localization problem

    - by X-Dev
    when trying to translate the confirmation message to Norwegian i get the following error: Cannot have more than one binding on property 'OnClientClick' on 'System.Web.UI.WebControls.LinkButton'. Ensure that this property is not bound through an implicit expression, for example, using meta:resourcekey. i use Explicit localization in the following manner: <asp:LinkButton ID="lnkMarkInvoiced" runat="server" OnClick="lnkMarkInvoiced_OnClick" OnClientClick="<%# Resources: lnkMarkInvoicedResource.OnClientClick%>" Visible="False" CssClass="stdtext" meta:resourcekey="lnkMarkInvoicedResource" ></asp:LinkButton> here's the local resource file entry: <data name="lnkMarkInvoicedResource.OnClientClick" xml:space="preserve"> <value>return confirm('Er du sikker?');</value> if i remove the meta attribute i get the English text(default). how do i get the Norwegian text appearing without resorting to using the code behind? Update: removing the meta attribute prevents the exception from occurring but the original problem still exists. I can't get the Norwegian text to show. only the default English text shows. Another Update: I know this question is getting old but i still can't get the Norwegian text to display. If anyone has some tips please post a response.

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  • Is there a language with native pass-by-reference/pass-by-name semantics, which could be used in mod

    - by Bubba88
    Hi! This is a reopened question. I look for a language and supporting platform for it, where the language could have pass-by-reference or pass-by-name semantics by default. I know the history a little, that there were Algol, Fortran and there still is C++ which could make it possible; but, basically, what I look for is something more modern and where the mentioned value pass methodology is preferred and by default (implicitly assumed). I ask this question, because, to my mind, some of the advantages of pass-by-ref/name seem kind of obvious. For example when it is used in a standalone agent, where copyiong of values is not necessary (to some extent) and performance wouldn't be downgraded much in that case. So, I could employ it in e.g. rich client app or some game-style or standalone service-kind application. The main advantage to me is the clear separation between identity of a symbol, and its current value. I mean when there is no reduntant copying, you know that you're working with the exact symbol/path you have queried/received. And intristing boxing of values will not interfere with the actual logic of program. I know that there is C# ref keyword, but it's something not so intristic, though acceptable. Equally, I realize that pass-by-reference semantics could be simulated in virtually any language (Java as an instant example) and so on.. not sure about pass by name :) What would you recommend - create a something like DSL for such needs wherever it be appropriate; or use some languages that I already know? Maybe, there is something that I'm missing? Thank you!

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  • How do I configure multiple Ubuntu Python installations to avoid App Engine's SSL error?

    - by Linc
    I have Karmic Koala which has Python 2.6 installed by default. However I can't run any Python App Engine projects because they require Python 2.5 and python ssl. To install ssl I installed python2.5-dev first while following some instructions I found elsewhere. sudo apt-get install libssl-dev sudo apt-get install python-setuptools sudo apt-get install python2.5-dev sudo easy_install-2.5 pyopenssl However, I am afraid this is not good for my Ubuntu installation since Ubuntu expects to see version 2.6 of Python when you type 'python' on the command line. Instead, it says '2.5.5'. I tried to revert to the original default version of Python by doing this: sudo apt-get remove python2.5-dev But that didn't seem to do anything either - when I type 'python' on the command line it still say 2.5.5. And App Engine still doesn't work after all this. I continue to get an SSL-related error whenever I try to run my Python app: AttributeError: 'module' object has no attribute 'HTTPSHandler' UPDATE: Just checked whether SSL actually installed as a result of those commands by typing this: $ python2.5 Python 2.5.5 (r255:77872, Apr 29 2010, 23:59:20) [GCC 4.4.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import ssl Traceback (most recent call last): File "<stdin>", line 1, in <module> ImportError: No module named ssl >>> As you can see, SSL is still not installed, which explains the continuing App Engine error. If anyone knows how I can dig myself out of this hole, I would appreciate it.

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  • How can I properly handle 404s in ASP.NET MVC?

    - by Brian
    I am just getting started on ASP.NET MVC so bear with me. I've searched around this site and various others and have seen a few implementations of this. EDIT: I forgot to mention I am using RC2 Using URL Routing: routes.MapRoute( "Error", "{*url}", new { controller = "Errors", action = "NotFound" } //404s ); The above seems to take care of requests like this (assuming default route tables setup by initial MVC project): "/blah/blah/blah/blah" Overriding HandleUnknownAction() in the controller itself: //404s - handle here (bad action requested protected override void HandleUnknownAction(string actionName) { ViewData["actionName"] = actionName; View("NotFound").ExecuteResult(this.ControllerContext); } However the previous strategies do not handle a request to a Bad/Unknown controller. For example, I do not have a "/IDoNotExist", if I request this I get the generic 404 page from the web server and not my 404 if I use routing + override. So finally, my question is: Is there any way to catch this type of request using a route or something else in the MVC framework itself? OR should I just default to using Web.Config customErrors as my 404 handler and forget all this? I assume if I go with customErrors I'll have to store the generic 404 page outside of /Views due to the Web.Config restrictions on direct access. Anyway any best practices or guidance is appreciated.

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  • Who calls the Destructor of the class when operator delete is used in multiple inheritance.

    - by dicaprio-leonard
    This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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  • Does NHibernate SysCache work in a non-web app?

    - by Khash
    I know SysCache uses ASP caching under the hood, but since I'm not aware of the implementation of the ASP cache (and if it depends on anything IIS), I was wondering if SysCache would work in a non-web application (like a Windows Service)? Activating it and using NHprofiler seems to show it is not.

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  • JNI - GetObjectField returns NULL

    - by Daniel
    I'm currently working on Mangler's Android implementation. I have a java class that looks like so: public class VentriloEventData { public short type; public class _pcm { public int length; public short send_type; public int rate; public byte channels; }; _pcm pcm; } The signature for my pcm object: $ javap -s -p VentriloEventData ... org.mangler.VentriloEventData$_pcm pcm; Signature: Lorg/mangler/VentriloEventData$_pcm; I am implementing a native JNI function called getevent, which will write to the fields in an instance of the VentriloEventData class. For what it's worth, it's defined and called in Java like so: public static native int getevent(VentriloEventData data); VentriloEventData data = new VentriloEventData(); getevent(data); And my JNI implementation of getevent: JNIEXPORT jint JNICALL Java_org_mangler_VentriloInterface_getevent(JNIEnv* env, jobject obj, jobject eventdata) { v3_event *ev = v3_get_event(V3_BLOCK); if(ev != NULL) { jclass event_class = (*env)->GetObjectClass(env, eventdata); // Event type. jfieldID type_field = (*env)->GetFieldID(env, event_class, "type", "S"); (*env)->SetShortField( env, eventdata, type_field, 1234 ); // Get PCM class. jfieldID pcm_field = (*env)->GetFieldID(env, event_class, "pcm", "Lorg/mangler/VentriloEventData$_pcm;"); jobject pcm = (*env)->GetObjectField( env, eventdata, pcm_field ); jclass pcm_class = (*env)->GetObjectClass(env, pcm); // Set PCM fields. jfieldID pcm_length_field = (*env)->GetFieldID(env, pcm_class, "length", "I"); (*env)->SetIntField( env, pcm, pcm_length_field, 1337 ); free(ev); } return 0; } The code above works fine for writing into the type field (that is not wrapped by the _pcm class). Once getevent is called, data.type is verified to be 1234 at the java side :) My problem is that the assertion "pcm != NULL" will fail. Note that pcm_field != NULL, which probably indicates that the signature to that field is correct... so there must be something wrong with my call to GetObjectField. It looks fine though if I compare it to the official JNI docs. Been bashing my head on this problem for the past 2 hours and I'm getting a little desperate.. hoping a different perspective will help me out on this one.

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  • How do I add install my own LocationProvider?

    - by gregm
    I would like to create my own implementation of a LocationProvider, there seems to be a way to add a "mock" provider, but that isn't exactly what I want. http://developer.android.com/reference/android/location/LocationManager.html There also appears to be a permission called: android.permission.INSTALL_LOCATION_PROVIDER But there is no documentation about how to use this permission. How do I register a new location provider?

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  • Should an event-sourced aggregate root have access to the event sourcing repository?

    - by JD Courtoy
    I'm working on an event-sourced CQRS implementation, using DDD in the application / domain layer. I have an object model that looks like this: public class Person : AggregateRootBase { private Guid? _bookingId; public Person(Identification identification) { Apply(new PersonCreatedEvent(identification)); } public Booking CreateBooking() { // Enforce Person invariants var booking = new Booking(); Apply(new PersonBookedEvent(booking.Id)); return booking; } public void Release() { // Enforce Person invariants // Should we load the booking here from the aggregate repository? // We need to ensure that booking is released as well. var booking = BookingRepository.Load(_bookingId); booking.Release(); Apply(new PersonReleasedEvent(_bookingId)); } [EventHandler] public void Handle(PersonBookedEvent @event) { _bookingId = @event.BookingId; } [EventHandler] public void Handle(PersonReleasedEvent @event) { _bookingId = null; } } public class Booking : AggregateRootBase { private DateTime _bookingDate; private DateTime? _releaseDate; public Booking() { //Enforce invariants Apply(new BookingCreatedEvent()); } public void Release() { //Enforce invariants Apply(new BookingReleasedEvent()); } [EventHandler] public void Handle(BookingCreatedEvent @event) { _bookingDate = SystemTime.Now(); } [EventHandler] public void Handle(BookingReleasedEvent @event) { _releaseDate = SystemTime.Now(); } // Some other business activities unrelated to a person } With my understanding of DDD so far, both Person and Booking are seperate aggregate roots for two reasons: There are times when business components will pull Booking objects separately from the database. (ie, a person that has been released has a previous booking modified due to incorrect information). There should not be locking contention between Person and Booking whenever a Booking needs to be updated. One other business requirement is that a Booking can never occur for a Person more than once at a time. Due to this, I'm concerned about querying the query database on the read side as there could potentially be some inconsistency there (due to using CQRS and having an eventually consistent read database). Should the aggregate roots be allowed to query the event-sourced backing store by id for objects (lazy-loading them as needed)? Are there any other avenues of implementation that would make more sense?

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  • how to use MessageParameterAttribute in wcf

    - by Archie
    hello, I wanted to know what is the use the MessageParameterAttribute in wcf. In my function: [OperationContract] public float GetAirfare( [MessageParameter(Name=”fromCity”)] string originCity, [MessageParameter(Name=”toCity”)] string destinationCity); I dont use fromCity or toCity anywhere in the implementation or even while using a service. Then whats the point in giving it a name?

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  • AES Cipher Key Strength in BlackBerry

    - by Basilio
    Hi All, I need to create an application that decrypts data that is encrypted using AES with a 512-bit key. What I need to know is whether we can create an AES key of length 512-bits? The documentation says we can create a key of length up to 256-bits. If that is the case, is there any way that I can add my own implementation for 512-bit AES key, or will I have to reduce the key strength used to encrypt the data originally? Thanks, Basilio

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  • Mocking a Wcf ServiceContract

    - by Michael
    I want to mock a ServiceContract. The problem is that Moq (and Castle Dynamic-Proxy) copies the attributes from the interface to the dynamic proxy which Wcf don't like. Wcf sais: The ServiceContractAttribute should only be define on either the interface or the implementation, not both.

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  • Silverlight Assembly.Load() only works with the full/strong name

    - by chris
    Apparently the implementation of Assembly.Load() in Silverlight needs a full/strong name. E.g. this works: Assembly.Load("MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=..."); while this will fail even if MyAssembly is already loaded: Assembly.Load("MyAssembly"); Is there a workaround so that it's possible to use the simple name?

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  • Recommendations for a C++ polymorphic, seekable, binary I/O interface

    - by Trevor Robinson
    I've been using std::istream and ostream as a polymorphic interface for random-access binary I/O in C++, but it seems suboptimal in numerous ways: 64-bit seeks are non-portable and error-prone due to streampos/streamoff limitations; currently using boost/iostreams/positioning.hpp as a workaround, but it requires vigilance Missing operations such as truncating or extending a file (ala POSIX ftruncate) Inconsistency between concrete implementations; e.g. stringstream has independent get/put positions whereas filestream does not Inconsistency between platform implementations; e.g. behavior of seeking pass the end of a file or usage of failbit/badbit on errors Don't need all the formatting facilities of stream or possibly even the buffering of streambuf streambuf error reporting (i.e. exceptions vs. returning an error indicator) is supposedly implementation-dependent in practice I like the simplified interface provided by the Boost.Iostreams Device concept, but it's provided as function templates rather than a polymorphic class. (There is a device class, but it's not polymorphic and is just an implementation helper class not necessarily used by the supplied device implementations.) I'm primarily using large disk files, but I really want polymorphism so I can easily substitute alternate implementations (e.g. use stringstream instead of fstream for unit tests) without all the complexity and compile-time coupling of deep template instantiation. Does anyone have any recommendations of a standard approach to this? It seems like a common situation, so I don't want to invent my own interfaces unnecessarily. As an example, something like java.nio.FileChannel seems ideal. My best solution so far is to put a thin polymorphic layer on top of Boost.Iostreams devices. For example: class my_istream { public: virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) = 0; virtual std::streamsize read(char* s, std::streamsize n) = 0; virtual void close() = 0; }; template <class T> class boost_istream : public my_istream { public: boost_istream(const T& device) : m_device(device) { } virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) { return boost::iostreams::seek(m_device, off, way); } virtual std::streamsize read(char* s, std::streamsize n) { return boost::iostreams::read(m_device, s, n); } virtual void close() { boost::iostreams::close(m_device); } private: T m_device; };

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  • Text message intent - catch and send

    - by Espen
    Hi! I want to be able to control incoming text messages. My application is still on a "proof of concept" version and I'm trying to learn Android programming as I go. First my application need to catch incomming text messages. And if the message is from a known number then deal with it. If not, then send the message as nothing has happened to the default text message application. I have no doubt it can be done, but I still have some concern and I see some pitfalls at how things are done on Android. So getting the incomming text message could be fairly easy - except when there are other messaging applications installed and maybe the user wants to have normal text messages to pop up on one of them - and it will, after my application has had a look at it first. How to be sure my application get first pick of incomming text messages? And after that I need to send most text messages through to any other text message application the user has chosen so the user can actually read the message my application didn't need. Since Android uses intents that are relative at best, I don't see how I can enforce my application to get a peek at all incomming text messages, and then stop it or send it through to the default text messaging application...

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