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• Extending the .NET type system so the compiler enforces semantic meaning of primitive values in cert

  - by Drew Noakes

  I'm working with geometry a bit at the moment and am converting a lot between degrees and radians. Unfortunately, both of these are represented by double, so there's compile time warning/error if I try to pass a value in degrees where radians are expected. I believe F# has a compile-time solution for this (called units of measure.) I'd like to do something similar in C#. As another example, imagine a SQL library that accepts various query parameters as strings. It'd be good to have a way of enforcing that only clean strings were allowed to be passed in at runtime, and the only way to get a clean string was to pass through some SQL injection attack preventing logic. The obvious solution is to wrap the double/string/whatever in a new type to give it the type information the compiler needs. I'm curious if anyone has an alternative solution. If you do think wrapping is the only/best way, then please go into some of the downsides of the pattern (and any upsides I haven't mentioned too.) I'm especially concerned about the performance of abstracted primitive numeric types on my calculations at runtime.

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• Best way to make a WYSIWYG in Flex?

  - by hngry4powr

  Hello, I have a client that wants a WYSIWYG form that behaves like MS word. It will have some section labels in it, with users expected to enter notes for each section, and it needs a place holder for a chart. The trick is that the user needs to know where page breaks are going to fall when printed. The customer agrees to fixed size paper with fixed sized margins. How should I approach this challenge? Thank you very much for your suggestions. Here is an example: Section 1: Explain Idea Here { As user types in this section, the space between this section and the next section expands, but I as the user can't delete the lines that say Section 1 or 2, or the place holder for the chart. However if I type a lot of text, I need to display where the page breaks are with a dashed line or something, so the user can make sure the content enters appears on the desired page. If I type a lot here for example, section 2 will get pushed onto the next page} Section 2: State why this is a Good Idea [ PLACE HOLDER FOR CHART . . . ] Section 3: Additional Remarks:

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• QT QSslError being signaled with the error code set to NoError

  - by Nantucket

  My Problem I compiled OpenSSL into QT to enable OpenSSL support. Everything appeared to go correctly in the compile. However, when I try to use the official HTTP example application that can be found here, everytime I try to download an https page, it will signal two QSslError, each with contents NoError. The types of QSslErrors, including NoError, are documented here, poorly. There is no explanation on why they even included an error type called NoError, or what it means. Bizarrely, the NoError error code seems to be true, as it downloads the remote https document perfectly even while signaling the error. Does anyone have any idea what this means and what could possibly be causing it? Optional Background Reading Here is the relevant part of the code from the example app (this is connected to the network connection's sslErrors signal by the constructor): void HttpWindow::sslErrors(QNetworkReply*,const QList<QSslError> &errors) { QString errorString; foreach (const QSslError &error, errors) { if (!errorString.isEmpty()) errorString += ", "; errorString += error.errorString(); } if (QMessageBox::warning(this, tr("HTTP"), tr("One or more SSL errors has occurred: %1").arg(errorString), QMessageBox::Ignore | QMessageBox::Abort) == QMessageBox::Ignore) { reply->ignoreSslErrors(); } } I have tried the old version of this example, and it produced the same result. I have tried OpenSSL 1.0.0a and 0.9.8o. I have tried tried compiling OpenSSL myself, I have tried using pre-compiled versions of OpenSSL from the net. All produce the same result. If this were my first time using QT with SSL, I would almost think this is the intended result (even though their example application is popping up error warning message windows), if not for the fact that last time I played with QT, using what would now be an old version of QT with an old version of SSL, I distinctly remember everything working fine with no error windows. My system is running Windows 7 x64.

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• Is context:annotation-config an alternative to @AutoWired?

  - by Antacid

  Is it correct that I can put context:annotation-config in my XML config and it will automatically inject the bean class without needing any annotations? So instead of using these annotation types: public class Mailman { private String name; @Autowired private Parcel Parcel; public Mailman(String name) { this.name = name; } @Autowired public void setParcel(Parcel Parcel) { this.Parcel = Parcel; } @Autowired public void directionsToParcel(Parcel Parcel) { this.Parcel = Parcel; } } I would just need to write this: <beans ... > <bean id="mailMan" class="MailMan"> <constructor-arg value="John Doe"/> </bean> <bean id="parcel" class="Parcel" /> <context:annotation-config /> </beans> and then my MailMan class would look a lot simpler without the need for annotations: public class Mailman { private String name; private Parcel Parcel; public Mailman(String name) { this.name = name; } }

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• Are there solutions for streamlining the update of legacy code in multiple places?

  - by ccomet

  I'm working in some old code which was originally designed for handling two different kinds of files. I was recently tasked with adding a new kind of file to this code. Most of my problems were solved by filling out an extensive XML file with a new entry that handled everything from what lists were named to how the file is written in plural lower case. But this ended up being insufficient, as there were maybe 50 different places in 24 different code files where I had to update hardcoded switch-statements that only branched for the original two file types. Unfortunately there is no consistency in this; there are methods which operate half from the XML file, and half off of hardcode. Some of the files which look like they would operate off of the XML file don't, and some that I would expect that I'd need to update the hardcode don't need it. So the only way to find the majority of these is to run through testing the whole system when only part of it is operational, finding that one step to fix (when I'm lucky that error logging actually tells me what is going on), and then running the whole thing again. This wastes time testing the parts of the code which are already confirmed to work, time better spent testing the new parts I have to add on top of it all. It's a hassle and a half, and to my luck I can expect that I will have to add yet another new kind of file in the near future. Are there any solutions out there which can aid in this kind of endeavour? Something which I can input some parameters of current features, document what points in a whole code project actually need to be updated, and run something nice the next time I need to add a new feature to the code. It needn't even be fully automated, something that'll help me navigate straight to the specific points in everything and maybe even record what kind of parameters need to be loaded. Doubt it matters specifically, but the code is comprised of ASP.NET pages, some ASP.NET controls, hundreds of C# code files, and a handful of additional XML files. It's all currently in a couple big Visual Studio 2008 projects.

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• problem in showing and hiding dialog boxes in MFC

  - by Rakesh

  Hello all, I am trying to create a wizard like structure using dialog boxes...So I replaced the code in CDialog1App as below CDialog1Dlg* dlg = new CDialog1Dlg; m_pMainWnd = dlg; dlg->Create(IDD_DIALOG1); dlg->ShowWindow(SW_SHOW); the above worked fine...its displying the dialog box.but I have added another dialog box... So in the first dialog box if the user clicks Next it has to hide the first dialog box and display the second dialog.. //CDialog1 class void CDialog1Dlg::OnBnClickedNext() { // TODO: Add your control notification handler code here CDialog2* dialog2 = new CDialog2(); dialog2->Create(IDD_DIALOG2); dialog2->ShowWindow(SW_SHOW); this->ShowWindow(SW_HIDE); } in the above code am creating an object for the Dialog2 class and trying to show that.... Now the problem is,when I click next its hiding both the windows..What can I do..I tried several types but its still its not workin..Please dont suggest me to do with PropertySheet..It will work with that, i know ...but I want this using Dialog Box for some reason

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• Google App Engine, parsedatetime and TimeZones

  - by Ron

  Hey guys, I'm working on a Google App Engine / Django app and I encountered the following problem: In my html I have an input for time. The input is free text - the user types "in 1 hour" or "tomorrow at 11am". The text is then sent to the server in AJAX, which parses it using this python library: http://code.google.com/p/parsedatetime/. Once parsed, the server returns an epoch timestamp of the time. Here is the problem - Google App Engine always runs on UTC. Therefore, lets say that the local time is now 11am and the UTC time is 2am. When I send "now" to the server it will return "2am", which is good because I want the date to be received in UTC time. When I send "in 1 hour" the server will return "3am" which is good, again. However, when I send "at noon" the server will return "12pm" because it thinks that I'm talking about noon UTC - but really I need it to return 3am, which is noon for the request sender.. I can pass on the TZ of the browser that sends the request, but that wont really help me - the parsedatetime library wont take a timezone argument (correct me if I'm wrong). Is there a walk around this? Maybe setting the environments TZ somehow? Thanks!

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• How to define multiple elements in XML Schema with the same name and different attribute value allow

  - by David Skyba

  I would like to create XML Schema for this chunk of xml, I would like to restrict the values of "name" attribute, so that in output document on and only one instance of day is allowed for each week day: <a> <day name="monday" /> <day name="tuesday" /> <day name="wednesday" /> </a> I have tried to use this: <xs:complexType name="a"> <xs:sequence> <xs:element name="day" minOccurs="1" maxOccurs="1"> <xs:complexType> <xs:attribute name="name" use="required"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="monday" /> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:complexType> </xs:element> <xs:element name="day" minOccurs="1" maxOccurs="1"> <xs:complexType> <xs:attribute name="name" use="required"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="tuesday" /> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> but XML Schema validator in eclipse says error "Multiple elements with name 'day', with different types, appear in the model group.". Is there any other way?

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• hadoop implementing a generic list writable

  - by Guruprasad Venkatesh

  I am working on building a map reduce pipeline of jobs(with one MR job's output feeding to another as input). The values being passed around are fairly complex, in that there are lists of different types and hash maps with values as lists. Hadoop api does not seem to have a ListWritable. Am trying to write a generic one, but it seems i can't instantiate a generic type in my readFields implementation, unless i pass in the class type itself: public class ListWritable<T extends Writable> implements Writable { private List<T> list; private Class<T> clazz; public ListWritable(Class<T> clazz) { this.clazz = clazz; list = new ArrayList<T>(); } @Override public void write(DataOutput out) throws IOException { out.writeInt(list.size()); for (T element : list) { element.write(out); } } @Override public void readFields(DataInput in) throws IOException{ int count = in.readInt(); this.list = new ArrayList<T>(); for (int i = 0; i < count; i++) { try { T obj = clazz.newInstance(); obj.readFields(in); list.add(obj); } catch (InstantiationException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } } } } But hadoop requires all writables to have a no argument constructor to read the values back. Has anybody tried to do the same and solved this problem? TIA.

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• What Do You Need To Write Your Own Blog Engine?

  - by deworde

  I've been messing around with basic websites for a few years, using companies like www.Fasthosts.co.uk to do my web hosting. But I'd like to expand my skills from C++ and Java app programming into Web-based programming, and I think the best way to do that is with a project. I've chosen to go with a blog engine because it's a relative comprehensive yet non-complex project. I'm aware that you can just go to Blogger and bam! One blog. I've done that, so that I can at least have some content, and work out what I want to do with this blog. At the moment, I'm thinking I'll use it to chart my progress creating the blogging engine. But I have some questions. Do you need to be running your own server? Or is it more sensible in the short-term to use a hosting company? What types of language are worth considering? What's important to focus on from a design perspective? What unexpected problems might I encounter?

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• WCF service reference namespace differs from original

  - by Thorarin

  I'm having a problem regarding namespaces used by my service references. I have a number of WCF services, say with the namespace MyCompany.Services.MyProduct (the actual namespaces are longer). As part of the product, I'm also providing a sample C# .NET website. This web application uses the namespace MyCompany.MyProduct. During initial development, the service was added as a project reference to the website and uses directly. I used a factory pattern that returns an object instance that implements MyCompany.Services.MyProduct.IMyService. So far, so good. Now I want to change this to use an actual service reference. After adding the reference and typing MyCompany.Services.MyProduct in the namespace textbox, it generates classes in the namespace MyCompany.MyProduct.MyCompany.Services.MyProduct. BAD! I don't want to have to change using directives in several places just because I'm using a proxy class. So I tried prepending the namespace with global::, but that is not accepted. Note that I hadn't even deleted the original assembly references yet, and "reuse types" is enabled, but no reusing was done, apparently. However, I don't want to keep the assembly references around in my sample website for it to work anyway. The only solution I've come up with so far is setting the default namespace for my web application to MyCompany (because it cannot be empty), and adding the service reference as Services.MyProduct. Suppose that a customer wants to use my sample website as a starting point, and they change the default namespace to OtherCompany.Whatever, this will obviously break my workaround. Is there a good solution to this problem? To summarize: I want to generate a service reference proxy in the original namespace, without referencing the assembly. Note: I have seen this question, but there was no solution provided that is acceptable for my use case. Edit: As John Saunders suggested, I've submitted some feedback to Microsoft about this: Feedback item @ Microsoft Connect

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• Auto filling polymorphic table on save or on delete in django

  - by Mo J. Mughrabi

  Hi, Am working on an project in which I made an app "core" it will contain some of the reused models across my projects, most of those are polymorphic models (Generic content types) and will be linked to different models. Example below am trying to create audit model and will be linked to several models which may require auditing. This is the polls/models.py from django.db import models from django.contrib.auth.models import User from core.models import * from django.contrib.contenttypes import generic class Poll(models.Model): ## TODO: Document question = models.CharField(max_length=300) question_slug=models.SlugField(editable=False) start_poll_at = models.DateTimeField(null=True) end_poll_at = models.DateTimeField(null=True) is_active = models.BooleanField(default=True) audit_obj=generic.GenericRelation(Audit) def __unicode__(self): return self.question class Choice(models.Model): ## TODO: Document choice = models.CharField(max_length=200) poll=models.ForeignKey(Poll) audit_obj=generic.GenericRelation(Audit) class Vote(models.Model): ## TODO: Document choice=models.ForeignKey(Choice) Ip_Address=models.IPAddressField(editable=False) vote_at=models.DateTimeField("Vote at", editable=False) here is the core/modes.py from django.db import models from django.contrib.auth.models import User from django.contrib.contenttypes.models import ContentType from django.contrib.contenttypes import generic class Audit(models.Model): ## TODO: Document # Polymorphic model using generic relation through DJANGO content type created_at = models.DateTimeField("Created at", auto_now_add=True) created_by = models.ForeignKey(User, db_column="created_by", related_name="%(app_label)s_%(class)s_y+") updated_at = models.DateTimeField("Updated at", auto_now=True) updated_by = models.ForeignKey(User, db_column="updated_by", null=True, blank=True, related_name="%(app_label)s_%(class)s_y+") content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField(unique=True) content_object = generic.GenericForeignKey('content_type', 'object_id') and here is polls/admin.py from django.core.context_processors import request from polls.models import Poll, Choice from core.models import * from django.contrib import admin class ChoiceInline(admin.StackedInline): model = Choice extra = 3 class PollAdmin(admin.ModelAdmin): inlines = [ChoiceInline] admin.site.register(Poll, PollAdmin) Am quite new to django, what am trying to do here, insert a record in audit when a record is inserted in polls and then update that same record when a record is updated in polls.

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• Strongly Typed DataSet column requires custom type to implement IXmlSerializable?

  - by Phil

  I have a strongly typed Dataset with a single table with three columns. These columns all contain custom types. DataColumn1 is of type Parent DataColumn2 is of type Child1 DataColumn3 is of type Child2 Here is what these classes look like: [Serializable] [XmlInclude(typeof(Child1)), XmlInclude(typeof(Child2))] public abstract class Parent { public int p1; } [Serializable] public class Child1 :Parent { public int c1; } [Serializable] public class Child2 : Parent { public int c1; } now, if I add a row with DataColumn1 being null, and DataColumns 2 and 3 populated and try to serialize it, it works: DataSet1 ds = new DataSet1(); ds.DataTable1.AddDataTable1Row(null, new Child1(), new Child2()); StringBuilder sb = new StringBuilder(); using (StringWriter writer = new StringWriter(sb)) { ds.WriteXml(writer);//Works! } However, if I try to add a value to DataColumn1, it fails: DataSet1 ds = new DataSet1(); ds.DataTable1.AddDataTable1Row(new Child1(), new Child1(), new Child2()); StringBuilder sb = new StringBuilder(); using (StringWriter writer = new StringWriter(sb)) { ds.WriteXml(writer);//Fails! } Here is the Exception: "Type 'WindowsFormsApplication4.Child1, WindowsFormsApplication4, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' does not implement IXmlSerializable interface therefore can not proceed with serialization." I have also tried using the XmlSerializer to serialize the dataset, but I get the same exception. Does anyone know of a way to get around this where I don't have to implement IXmlSerializable on all the Child classes? Alternatively, is there a way to implement IXmlSerializable keeping all default behavior the same (ie not having any class specific code in the ReadXml and WriteXml methods)

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• What should I do if i have a factory method which requires different parameters for different implem

  - by Sam Holder

  I have an interface, IMessage and a class which have several methods for creating different types of message like so: class MessageService { IMessage TypeAMessage(param 1, param 2) IMessage TypeBMessage(param 1, param 2, param 3, param 4) IMessage TypeCMessage(param 1, param 2, param 3) IMessage TypeDMessage(param 1) } I don't want this class to do all the work for creating these messages so it simply delegates to a MessageCreatorFactory which produces an IMessageCreator depending on the type given (an enumeration based on the type of the message TypeA, TypeB, TypeC etc) interface IMessageCreator { IMessage Create(MessageParams params); } So I have 4 implementations of IMessageCreator: TypeAMessageCreator, TypeBMessageCreator, TypeCMessageCreator, TypeDMessageCreator I ok with this except for the fact that because each type requires different parameters I have had to create a MessageParams object which contains 4 properties for the 4 different params, but only some of them are used in each IMessageCreator. Is there an alternative to this? One other thought I had was to have a param array as the parameter in the Create emthod, but this seems even worse as you don't have any idea what the params are. Or to create several overloads of Create in the interface and have some of them throw an exception if they are not suitable for that particular implementation (ie you called a method which needs more params, so you should have called one of the other overloads.) Does this seem ok? Is there a better solution?

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• Strange Behaviour in Swift: constant defined with LET but behaving like a variable defined with VAR

  - by Sam

  Stuck on the below for a day! Any insight would be greatly appreciated. The constant in the first block match0 behaves as expected. The constant defined in the second block does not behave as nicely in the face of a change to its "source": var str = "+y+z*1.0*sum(A1:A3)" if let range0 = str.rangeOfString("^\\+|^\\-|^\\*|^\\/", options: NSStringCompareOptions.RegularExpressionSearch){ let match0 = str[range0] println(match0) //yields "+" - as expexted str.removeRange(range0) println(match0) //yields "+" - as expected str.removeRange(range0) println(match0) //yields "+" - as expected } if let range1 = str.rangeOfString("^\\+|^\\-|^\\*|^\\/", options: NSStringCompareOptions.RegularExpressionSearch){ let match1 = str[range1] println(match1) //yields "+" as expected str.removeRange(range1) println(match1) //!@#$ OMG!!!!!!!!!!! a constant variable has changed! This prints "z" } The following are the options I can see: match1 has somehow obtained a reference to its source instead of being copied by value [Problem: Strings are value types in Swift] match1 has somehow obtained a closure to its source instead of just being a normal constant/variable? [Problem: sounds like science fiction & then why does match0 behave so well?] Could there be a bug in the Swift compiler? [Problem: Experience has taught me that this is very very very rarely the solution to your problem...but it is still in beta]

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• Py_INCREF/DECREF: When

  - by Izz ad-Din Ruhulessin

  Is one correct in stating the following: If a Python object is created in a C function, but the function doesn't return it, no INCREF is needed, but a DECREF is. [false]If the function does return it, you do need to INCREF, in the function that receives the return value.[/false] When assigning C typed variables as attributes, like double, int etc., to the Python object, no INCREF or DECREF is needed. Assigning Python objects as attributes to your other Python objects goes like this: PyObject *foo; foo = bar // A Python object tmp = self->foo; Py_INCREF(foo); self->foo = foo; Py_XDECREF(tmp); //taken from the manual, but it is unclear if this works in every situation EDIT: -- can I safely use this in every situation? (haven't run into one where it caused me problems) dealloc of a Python object needs to DECREF for every other Python object that it has as an attribute, but not for attributes that are C types. Edit With 'C type as an attribute I mean bar and baz: typedef struct { PyObject_HEAD PyObject *foo; int bar; double baz; } FooBarBaz;

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• how to store/model users/faceboook users/linkedin users, etc, with ActiveRecord?

  - by crankharder

  My app has "normal" users: those which come through a typical signup page facebook(FB) users: those which come from Facebook connect "FB-normal" users: a user that can log with both email/password * FB connect Further, there's the a slew of other openID-ish login methods (I don't think openID itself will be acceptable since it doesn't link up the accounts and allow the 3rd party specific features (posting to twitter, adding a FB post, etc etc)) So, how do I model this? Right now we have User class with #facebook_user? defined -- but it gets messy with the "FB-normal" users - plus all the validations become very tricky and hard to interpret. Also, there are methods like #deliver_password_reset! which make no sense in the context for facebook-only users. (this is lame) I've thought out STI (User::Facebook, User::Normal, User::FBNormal, etc.) This makes validations super slick, but it doesn't scale to other connection types, and all the permutations between them... User::FacebookLinkedInNormal(wtf?) Doing this with a bunch of modules I think would suck a lot. Any other ideas?

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• C# How can I return my base class in a webservice

  - by HenriM

  I have a class Car and a derived SportsCar: Car Something like this: public class Car { public int TopSpeed{ get; set; } } public class SportsCar : Car { public string GirlFriend { get; set; } } I have a webservice with methods returning Cars i.e: [WebMethod] public Car GetCar() { return new Car() { TopSpeed = 100 }; } It returns: <Car> <TopSpeed>100</TopSpeed> </Car> I have another method that also returns cars like this: [WebMethod] public Car GetMyCar() { Car mycar = new SportsCar() { GirlFriend = "JLo", TopSpeed = 300 }; return mycar; } It compiles fine and everything, but when invoking it I get: System.InvalidOperationException: There was an error generating the XML document. --- System.InvalidOperationException: The type wsBaseDerived.SportsCar was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically. I find it strange that it can't serialize this as a straight car, as mycar is a car. Adding XmlInclude on the WebMethod of ourse removes the error: [WebMethod] [XmlInclude(typeof(SportsCar))] public Car GetMyCar() { Car mycar = new SportsCar() { GirlFriend = "JLo", TopSpeed = 300 }; return mycar; } and it now returns: <Car xsi:type="SportsCar"> <TopSpeed>300</TopSpeed> <GirlFriend>JLo</GirlFriend> </Car> But I really want the base class returned, without the extra properties etc from the derived class. Is that at all possible without creating mappers etc? Please say yes ;)

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• F# and statically checked union cases

  - by Johan Jonasson

  Soon me and my brother-in-arms Joel will release version 0.9 of Wing Beats. It's an internal DSL written in F#. With it you can generate XHTML. One of the sources of inspiration have been the XHTML.M module of the Ocsigen framework. I'm not used to the OCaml syntax, but I do understand XHTML.M somehow statically check if attributes and children of an element are of valid types. We have not been able to statically check the same thing in F#, and now I wonder if someone have any idea of how to do it? My first naive approach was to represent each element type in XHTML as a union case. But unfortunately you cannot statically restrict which cases are valid as parameter values, as in XHTML.M. Then I tried to use interfaces (each element type implements an interface for each valid parent) and type constraints, but I didn't manage to make it work without the use of explicit casting in a way that made the solution cumbersome to use. And it didn't feel like an elegant solution anyway. Today I've been looking at Code Contracts, but it seems to be incompatible with F# Interactive. When I hit alt + enter it freezes. Just to make my question clearer. Here is a super simple artificial example of the same problem: type Letter = | Vowel of string | Consonant of string let writeVowel = function | Vowel str -> sprintf "%s is a vowel" str I want writeVowel to only accept Vowels statically, and not as above, check it at runtime. How can we accomplish this? Does anyone have any idea? There must be a clever way of doing it. If not with union cases, maybe with interfaces? I've struggled with this, but am trapped in the box and can't think outside of it.

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• Creating an application that can open files of a given format

  - by Brian Postow

  I've got an app, written in Obj-C. The info.plist has a list of file types that the app can open. I'm pretty sure that this is working because when I try to drag a file of an unacceptable type, the app doesn't highlight, but when I drag a file of an acceptable type, it does highlight, and lets me drop. When I drop, the app starts up, correctly, however, then I get a dialog saying: The document "foo.tiff" could not be opened. DocView cannot open files in the "TIFF File" format. I DO have this in my info.plist <key>CFBundleTypeExtensions</key> <array> <string>tif</string> <string>tiff</string> </array> <key>CFBundleTypeIconFile</key> <string>TIFFFile.icns</string> <key>CFBundleTypeName</key> <string>TIFF File</string> <key>CFBundleTypeOSTypes</key> <array> <string>TIFF</string> </array> <key>CFBundleTypeRole</key> <string>Viewer</string> <key>LSHandlerRank</key> <string>Documents/</string> Thanks.

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• Can Bonjour browse a service with a particular name?

  - by Roman

  Bonjour provides "DNSSD.browse(serviceType,callBackObject)" method which browses for services of a particular type. If a service of the given type is found, Bonjour call "callBackObject.serviceFound". If the service is lost, Bonjour calls "callBackObject.serviceLost". I alway considered "DNSSD.browse" as a method for monitoring a particular service. Bonjour monitors a particular service and calls necessary method if the service is found (available) or lost (not available). But than I realized that "DNSSD.browse" receives (as argument) a type of service (for example "http.tcp") and there can be several services of this type. So, its probably calls "serviceFound" and "serviceLost" if any service of the specified type is found or lost, respectively. But in my application I would like to browse just for one particular service. What is the best way to do it? I have two potential solutions: When I register a service, I give it a unique type. For example: "server1.http.tcp". I register services with unique names (not types) and ask Bonjour to browse for services with particular names. But I am not sure that Bonjour provide such possibility. Can it browse for services with specific names?

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• C system calls open / read / write / close problem.

  - by Andrei Ciobanu

  Hello, given the following code (it's supposed to write "hellowolrd" in a "helloworld" file, and then read the text): #include <fcntl.h> #include <sys/types.h> #include <sys/stat.h> #define FNAME "helloworld" int main(){ int filedes, nbytes; char buf[128]; /* Creates a file */ if((filedes=open(FNAME, O_CREAT | O_EXCL | O_WRONLY | O_APPEND, S_IRUSR | S_IWUSR)) == -1){ write(2, "Error1\n", 7); } /* Writes hellow world to file */ if(write(filedes, FNAME, 10) != 10) write(2, "Error2\n", 7); /* Close file */ close(filedes); if((filedes = open(FNAME, O_RDONLY))==-1) write(2, "Error3\n", 7); /* Prints file contents on screen */ if((nbytes=read(filedes, buf, 128)) == -1) write(2, "Error4\n", 7); if(write(1, buf, nbytes) != nbytes) write(2, "Error5\n", 7); /* Close rile afte read */ close(filedes); return (0); } The first time i run the program, the output is: helloworld After that every time I to run the program, the output is: Error1 Error2 helloworld I don't understand why the text isn't appended, as I've specified the O_APPEND file. Is it because I've included O_CREAT ? It the file is already created, shouldn't O_CREAT be ignored ?

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• What's a good Java-based Master-Slave communication mechanism?

  - by plecong

  I'm creating a Java application that requires master-slave communication between JVMs, possibly residing on the same physical machine. There will be a "master" server running inside a JEE application server (i.e. JBoss) that will have "slave" clients connect to it and dynamically register itself for communication (that is the master will not know the IP addresses/ports of the slaves so cannot be configured in advance). The master server acts as a controller that will dole work out to the slaves and the slaves will periodically respond with notifications, so there would be bi-directional communication. I was originally thinking of RPC-based systems where each side would be a server, but it could get complicated, so I'd prefer a mechanism where there's an open socket and they talk back and forth. I'm looking for a communication mechanism that would be low-latency where the messages would be mostly primitive types, so no serious serialization is necessary. Here's what I've looked at: RMI JMS: Built-in to Java, the "slave" clients would connect to the existing ConnectionFactory in the application server. JAX-WS/RS: Both master and slave would be servers exposing an RPC interface for bi-directional communication. JGroups/Hazelcast: Use shared distributed data structures to facilitate communication. Memcached/MongoDB: Use these as "queues" to facilitate communication, though the clients would have to poll so there would be some latency. Thrift: This does seem to keep a persistent connection, but not sure how to integrate/embed a Thrift server into JBoss WebSocket/Raw Socket: This would work, but require a lot more custom code than I'd like. Is there any technology I'm missing? Edit: Also looked at: JMX: Have the client connect to JBoss' JMX server and receive JMX notifications for bidirectional comms.

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• Simplest distributed persistent key/value store that supports primary key range queries

  - by StaxMan

  I am looking for a properly distributed (i.e. not just sharded) and persisted (not bounded by available memory on single node, or cluster of nodes) key/value ("nosql") store that does support range queries by primary key. So far closest such system is Cassandra, which does above. However, it adds support for other features that are not essential for me. So while I like it (and will consider using it of course), I am trying to figure out if there might be other mature projects that implement what I need. Specifically, for me the only aspect of value I need is to access it as a blob. For key, however, I need range queries (as in, access values ordered, limited by start and/or end values). While values can have structures, there is no need to use that structure for anything on server side (can do client-side data binding, flexible value/content types etc). For added bonus, Cassandra style storage (journaled, all sequential writes) seems quite optimal for my use case. To help filter out answers, I have investigated some alternatives within general domain like: Voldemort (key/value, but no ordering) and CouchDB (just sharded, more batch-oriented); and am aware of systems that are not quite distributed while otherwise qualifying (bdb variants, tokyo cabinet itself (not sure if Tyrant might qualify), redis (in-memory store only)).

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• Natural problems to solve using closures

  - by m.u.sheikh

  I have read quite a few articles on closures, and, embarassingly enough, I still don't understand this concept! Articles explain how to create a closure with a few examples, but I don't see any point in paying much attention to them, as they largely look contrived examples. I am not saying all of them are contrived, just that the ones I found looked contrived, and I dint see how even after understanding them, I will be able to use them. So in order to understand closures, I am looking at a few real problems, that can be solved very naturally using closures. For instance, a natural way to explain recursion to a person could be to explain the computation of n!. It is very natural to understand a problem like computing the factorial of a number using recursion. Similarly, it is almost a no-brainer to find an element in an unsorted array by reading each element, and comparing with the number in question. Also, at a different level, doing Object-oriented programming also makes sense. So I am trying to find a number of problems that could be solved with or without closures, but using closures makes thinking about them and solving them easier. Also, there are two types to closures, where each call to a closure can create a copy of the environment variables, or reference the same variables. So what sort of problems can be solved more naturally in which of the closure implementations?

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