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• defining a simple implicit Arbitary

  - by FredOverflow

  I have a type Foo with a constructor that takes an Int. How do I define an implicit Arbitrary for Foo to be used with scalacheck? implicit def arbFoo: Arbitrary[Foo] = ??? I came up with the following solution, but it's a bit too "manual" and low-level for my taste: val fooGen = for (i <- Gen.choose(Int.MinValue, Int.MaxValue)) yield new Foo(i) implicit def arbFoo: Arbitrary[Foo] = Arbitrary(fooGen) Ideally, I would want a higher-order function where I just have to plug in an Int => Foo function. I managed to cut it down to: implicit def arbFoo = Arbitrary(Gen.resultOf((i: Int) => new Foo(i))) But I still feel like there has got to be a slightly simpler way.

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• Doubt in abstract classes

  - by mohit

  public abstract class Person { private String name; public Person(String name) { this.name = name; System.out.println("Person"); } public String getName() { return name; } abstract public String getDescription(); } public class Student extends Person { private String major; public Student(String name, String major) { super(name); this.major = major; } public String getMajor() { return major; } @Override public String getDescription() { return "student" + super.getName() + " having" + major; } } public class PersonTest { public static void main(String[] args) { Person person = new Student("XYZ", "ABC"); System.out.println(person.getDescription()); } } Ques: We cannot create objects of abstract classes, then why Person Constructor has been invoked, even its an abstract class?

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• Singletons and other design issues

  - by Ahmed Saleh

  I have worked using different languages like C++/Java and currently AS3. Most applications were computer vision, and small 2D computer games. Most companies that I have worked for, they use Singletons in a language like AS3, to retrieve elements or classes in an easy way. Their problem is basically they needs some variables or to call other functions from other classes. In a language like AS3, there is no private constructor, and they write a hacky code to prevent new instances. In Java and C++ I also faced the situation that I need to use other classe's members or to call their functions in different classes. The question is, is there a better or another design, to let other classes interact with each others without using singletons? I feel that composition is the answer, but I need more detailed solutions or design suggestions.

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• Why does my array initialization code cause a StackOverflowException to be thrown?

  - by MCS

  The following line of code in my class constructor is throwing a StackOverflowException: myList = new string[]{}; // myList is a property of type string[] Why is that happening? And what's the proper way to initialize an empty array? UPDATE: The cause was in the set method, in which I was attempting to trim all values. What's wrong with this code: set { for (int i = 0; i < myList.Length; i++) { if (myList[i] != null) myList[i] = myList[i].Trim(); } }

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• Adding Runtime Intelligence Application Analytics for a library and not an application

  - by brickner

  I want to add usage statistics for a .NET 4.0 library I write on CodePlex. I try to follow the step described here but my problem lies with the fact that what I write is a library and not an application. One of the steps is put the Setup and Teardown attributes. I thought about adding the Setup attribute on a static constructor or a different place that will run once per usage of the library. My problem lies with the Teardown attribute that should be placed on code that ends the usage. I don't know where to put this attribute. Is it possible to get usage statistics on a library? Maybe I can register on an event that will fire when the application unloads the dll?

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• Best way to test if a generic type is a string? (c#)

  - by Rex M

  I have a generic class that should allow any type, primitive or otherwise. The only problem with this is using default(T). When you call default on a value type or a string, it initializes it to a reasonable value (such as empty string). When you call default(T) on an object, it returns null. For various reasons we need to ensure that if it is not a primitive type, then we will have a default instance of the type, not null. Here is attempt 1: T createDefault() { if(typeof(T).IsValueType) { return default(T); } else { return Activator.CreateInstance<T>(); } } Problem - string is not a value type, but it does not have a parameterless constructor. So, the current solution is: T createDefault() { if(typeof(T).IsValueType || typeof(T).FullName == "System.String") { return default(T); } else { return Activator.CreateInstance<T>(); } } But this feels like a kludge. Is there a nicer way to handle the string case?

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• android java.lang.OutOfMemoryError

  - by xiangdream

  hi, all, when i download large data from website, i got this error information: I/global (20094): Default buffer size used in BufferedInputStream constructor. It would be better to be explicit if an 8k buffer is required. D/dalvikvm(20094): GC freed 6153 objects / 3650840 bytes in 335ms I/dalvikvm-heap(20094): Forcing collection of SoftReferences for 3599051-byte al location D/dalvikvm(20094): GC freed 320 objects / 11400 bytes in 144ms E/dalvikvm-heap(20094): Out of memory on a 3599051-byte allocation. I/dalvikvm(20094): "Thread-9" prio=5 tid=17 RUNNABLE I/dalvikvm(20094): | group="main" sCount=0 dsCount=0 s=0 obj=0x439b9480 I/dalvikvm(20094): | sysTid=25762 nice=0 sched=0/0 handle=4065496 anyone can help me?

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• How can I access and modify objects inside frames with AS3 in a permanent way?

  - by curro

  I have a MovieClip symbol created with flash in a fla file library. There is a textfield in frame one of this movieclip's timeline . There is another frame in the movieclip timeline. There is a custon class definition for this symbol. It is a flipping card in a memory game. I access the textfield by going to frame 2 (gotoAndStop(2)) and setting the textfield's text property ( this.field.text = "hello" ). However if I go to frame 1 and then return to frame 2, the text becomes the original one in the library's symbol. I have to modify the text propery again in a showFace method I've written. Besides, I cannot pass parameters in the constructor because it is a symbol in the library and that would give errors. I find this behaviour of flash extremely weird. Is there a way I can set properties inside frames permanently? Thank you

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• How to model dependency injection in UML ?

  - by hjo1620

  I have a Contract class. The contract is valid 1 Jan 2010 - 31 Dec 2010. It can be in state Active or Passive, depending on which date I ask the instance for it's state. ex. if I ask 4 July 2010, it's in state Active, but if I ask 1 Jan 2011, it's in state Passive. Instances are created using constructor dependency injection, i.e. they are either Active or Passive already when created, null is not allowed as a parameter for the internal state member. One initial/created vertex is drawn in UML. I have two arrows, leading out from the initial vertex, one leading to state Active and the other to state Passive. Is this a correct representation of dependency injection in UML ? This is related to http://stackoverflow.com/questions/2779922/how-model-statemachine-when-state-is-dependent-on-a-function which initiated the question on how to model DI in general, in UML.

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• Ruby on Rails: building a model with an attribute not in the database?

  - by randombits

  I have a model that sets one of its attributes based off of a form parameter that a user submits. The model is a child resource to a parent resource Home. A hypothetical example is the following: A class Person has an age attribute. The user submits a birthdate as an HTTP POST parameter and from that, I need to derive the age of the user. So I'd do something like this: @home.people.build(:name => params[:name], :birthdate => params[:birthdate]) Rails would barf on that for obvious reasons, complaining it doesn't know what the attribute birthdate is. What's the proper way of going about this? Is it possible to use the build constructor with the supplied solution so that my foreign key relations are also setup properly? If not, what's a better way to work around this problem?

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• my .jar file won't do anything.

  - by David

  I created a program that more or less holds an array of strings as an object and randomly prints one. so basicaly class Happy { string[] namestrings = new string[#] constructor() { fill with some strings} public static void main (String[]arg) { create instance of class do some junk with it method that prints it } method that prints it {} another method } when i compile and run it on the command line it works fine but when on the comand line i type in jar -cf Happy.jar Fun.class i get a .jar file called Happy and when i click on it i get an error message that reads "the java Jar file happy could not be launched read the consol for possible error messages" I have a mac i'm running lepord if that makes a diference. Whats going on?

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• How to retrieve XML attribute for custom control

  - by David

  I've created a combo box control with a edittext and spinner. I'm trying to let the android:prompt attribute be passed onto the spinner, which means I need to catch it in the constructor which passes my the AttributeSet and set it on the spinner. I can't figure out how to get the value of the prompt. I'm trying, int[] ra = { android.R.attr.prompt }; TypedArray ta = context.getTheme().obtainStyledAttributes(ra); int id = ta.getResourceId(0, 0); I get back 0, which means it didn't find the attribute. I also did a ta.count() which returned 0. So I'm not getting anything back. My XML simply defines an android:prompt value. Thanks

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• Slickgrid, confirm before edit

  - by Evan

  I am making a slick grid and need the ability to add rows with a code column. For this to be possible the code column needs to be editable for the entire table. I am trying to work out a way that I can confirm the edit with a standard javascript confirm popup box. I tried putting one into the onedit event within the slickgrid constructor and that executed after the edit. I am led to believe that the edit function is independent from calling the edit stored procedure of the database. Is there a better way to go about this? RF_tagsTable = new IndustrialSlickGrid( LadlesContainerSG , { URL: Global.DALServiceURL + "CallProcedure" , DatabaseParameters: { Procedure: "dbo.TableRF_tags" , ConnectionStringName: Global.ConnectionStringNames.LadleTracker } , Title: "RF tags" , Attributes: { AllowDelete: true , defaultColumnWidth: 120 , editable: true , enableAddRow: true , enableCellNavigation: true , enableColumnReorder: false , rowHeight: 25 , autoHeight: true , autoEdit: false , forceFitColumns: true } , Events: { onRowEdited : rowEdited /*function(){ //this is my failed attempt var r=confirm("Edit an existing tag?") if (r){ alert(r); } else { alert(r); } }*/ , onRowAdded : rowAdded } });

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• Implementing implicitly shared classes outside of Qt

  - by Timothy Baldridge

  I'm familiar with the way Qt uses D-pointers for managing data. How do I do this in my code? I tried this method: 1) move all data into a struct 2) add a QAtomicInt to the struct 3) implement a = operator and change my constructor/deconstructor to check-up on the reference count. The issue is, when I go to do a shallow copy of the object, I get an error about QObject declaring = as private. How then do I accomplish this? Here's an example of my copy operator: HttpRequest & HttpRequest::operator=(const HttpRequest &other) { other.d->ref.ref(); if (!d->ref.deref()) delete d; d = other.d; return *this; } Am I going about this the wrong way?

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• C# property in a form class only accessable after formload event

  - by Spooky2010

  using vs2008, c# Howdy, Im instantiating and calling Form B from Form A. FormB has some custom properties, to allow me to pass it things like sqlAdaptors and dataset instances. When i instantiate and show Form B from Form A as a dialog form with a Using statement, it all works fine, but i find the properties i pass are not available in Form B until after the form_load event has fired. I was under the impression the properties when passed to a instantiated class should be available from a constructor, but this is not the case. If it try to access the properties before the form load event i get a null reference exception. Is this correct behavior ? It is very annoying. thanks for any help

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• C# how to dynamically cast an object?

  - by JL

  I am building a helper object that has a property called Mailer. In reality Mailer can be either a System.Net.Mail.MailMessage or a Mono.System.Net.Mail.MailMessage. So I would preferably only want 1 declaration of mailer. For example I don't want: private Mono.Mailing.MailMessage MonoMessage = new Mono.Mailing.MailMessage(); private System.Net.Mail.MailMessage MailMessage = new System.Net.Mail.MailMessage(); I would prefer object mailer; Then in constructor switch (software) { case EnunInternalMailingSoftware.dotnet: this.mailer = new System.Net.Mail.MailMessage(); break; case EnunInternalMailingSoftware.mono: this.mailer = new Mono.Mailing.MailMessage(); break; } The problem is that mailer has no properties at design time. So I can't compile my code. How can this be fixed, am I taking the right approach. Thanks in advance

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• Does a static object within a function introduce a potential race condition?

  - by Jeremy Friesner

  I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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• How do I override a Spring bean definition yet still reference the overriden bean?

  - by Kevin

  I'm attempting to implement a delegate Service provider by overriding the bean definition for the original service with my delegate Service. However, as the name would imply, the delegate Service needs a reference to the original service to delegate calls to. I'm having trouble figuring out how to override the bean definition while using the original bean def without running into a circular reference issue. For example: <!-- Original service def in spring-context.xml --> <bean id="service" class="com.mycompany.Service"/> <!-- Overridden definition in spring-plugin-context.xml --> <bean id="service" class="com.mycompany.DelegatedService"/> <constructor-arg ref="service"/> </bean> Is this possible?

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• How to set default values to the properties of dynamically loaded types at runtime for XML serializa

  - by Erkan Y.

  I need to serialize dynamically loaded types' classes using XMLSerializer. When using XML serializer non initialized values are not being serialized. I dont have control over the assemblies I am working with so can not use XML attributes for specifying default values on properties. So I think I need to set all properties and sub properties to their default values recursively and then serialize. ( Please let me know if there is any better way ) Followed this : Activator.CreateInstance(propType); but above line complains about not having a parameterless constructor for some types. Tried this : subObject = FormatterServices.GetUninitializedObject(propType); but this one gives an error "value was invalid" with no inner exception. Please let me know if you need any further information.

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• extension method phone format with country code as parameter

  - by frenchie

  Hi, I'm writing an extension method called ToPhoneFormat that formats a string of digits to phone numbers. Is it possible to add a parameter to the method that would enable me to call it like this: MyPhoneString.ToPhoneFormat(international code) That way, I could write MyPhoneString.ToPhoneFormat(1); to format a US phone number and MyPhoneString.ToPhoneFormat(33) to format a French phone number. I already wrote the method that does the formatting but I'm wondering how to build the constructor so that it works with a parameter when I'm calling it. Thanks.

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• How do I reference members of a single object passed to the View?

  - by Juxtaposed

  I'm new to MVC2 in ASP.NET/C#, so please forgive me if I misunderstand something. I have code similar to this in my Controller: var singleInstance = new Person("John"); ViewData["myInstance"] = singleInstance; return View(); So in my view, Index.aspx, I want to be able to reference members in that object. For example, Person has a member called Name, which is set in the constructor. In the view I want to get Person.Name from what is stored in the ViewData object. Ex.: <%= ViewData["myInstance"].name %> That doesn't work. The only real workaround I've found is to do something like this: <% var thePerson = ViewData["myInstance"]; print (or whatever the method is) thePerson.Name; %> Any help would be much appreciated... This was so much easier in PHP/Zend Framework... sigh

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• AutoMapper and Linq expression.

  - by Raffaeu

  I am exposing the Dto generated from AutoMapper to my WCF services. I would like to offer something like that from WCF: IList GetPersonByQuery(Expression predicate); Unfortunately I need back an expression tree of Person as my DAL doesn't know the DTO. I am trying this wihtout success: var func = new Func<Person, bool>(x => x.FirstName.Contains("John")); var funcDto = Mapper.Map<Func<Person, bool>, Func<PersonDto, bool>>(func); Console.WriteLine(func.ToString()); Console.WriteLine(funcDto.ToString()); THe error that I get is: ----> System.ArgumentException : Type 'System.Func`2[TestAutoMapper.PersonDto,System.Boolean]' does not have a default constructor Do you have any suggestions?

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• Android and Google Maps API - Icons

  - by oriharel

  I want to place markers on the map. I want to use the standard Google Maps icons for markers. how do I use them? I don't want to create my own icons. I'm developing for Android. in the documentation they tell me to create a class that overrides ItemizedOverlay but in the constructor I'm asked to provide a drawable object. how do I point to the standard Google Maps ones? thanks.

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• How do I create a MessageBox in C# ?

  - by Nick Stinemates

  I have just installed C# for the first time, and at first glance it appears to be very similar to VB6. I decided to start off by trying to make a 'Hello, World!' UI Edition. I started in the Form Designer and made a button named "Click Me!" proceeded to double-click it and typed in MessageBox("Hello, World!"); I received the following error: MessageBox is a 'type' but used as a 'variable' Fair enough, it seems in C# MessageBox is an Object. I tried the following MessageBox a = new MessageBox("Hello, World!"); I received the following error: MessageBox does not contain a constructor that takes '1' arguments Now I am stumped. Please help.

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• how to read httpWebRequest's request stream in c#, i got error" the stream is not readable" ?

  - by sam

  hi i want to read request stream from a custom httpWebRequest class that inherits from httpWebRequest and i have tried to read the request stream in different stages but sitll not sure how to archieve that in the class,thanks very much for any help. This custom httpWebRequest is used to serilize soap message and i want to know what request has been sent in string format. I also implemented custom HttpRequestCreator,HttpWebResponse but till cant find a place/stage i can read the request stream. If i output everything in a memory stream then copy the content to request stream, anyone knows which stage i can do it in the constructor, BeginGetRequestStream,EndGetRequestStream or GetRequestStream?

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