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• Delegation, is this just opinionated or is there a common pattern?

  - by user1446714

  If I have a java class containing substantial code and I wish to add extra features, am I right in thinking the delegate class would have the additional features added as methods. Then my original class would create the delegate object and just call the extra functionality via the delegate instance? I am being told by somebody else that my original class should become the delegate and that the class containing the new functionality should contain an instance of the original class, to use as a delegate? This seemed a little backward to me, because there would be far more delegate calls because most of the code is now in the delegate.... I was always under the impression the delegate object would contain the additional new behaviour and an instance of it would be in the original class to inboke the new behaviour from?

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• Circular reference problem Singleton

  - by Ismail

  I'm trying to creating a Singleton class like below where MyRepository lies in separate DAL project. It's causing me a circular reference problem because GetMySingleTon() method returns MySingleTon class and needs its access. Same way I need MyRepository access in constructor of MySingleTon class. public class MySingleTon { static MySingleTon() { if (Instance == null) { MyRepository rep = new MyRepository(); Instance = rep.GetMySingleTon(); } } public static MySingleTon Instance { get; private set; } public string prop1 { get; set; } public string prop2 { get; set; } }

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• SQLite not pluralizing Table Names

  - by weenet

  I am using SQLite as my db during development, and I want to postpone actually creating a final database until my domains are fully mapped. So I have this in my Global.asax.cs file: private void InitializeNHibernateSession() { Configuration cfg = NHibernateSession.Init( webSessionStorage, new [] { Server.MapPath("~/bin/MyNamespace.Data.dll") }, new AutoPersistenceModelGenerator().Generate(), Server.MapPath("~/NHibernate.config")); if (ConfigurationManager.AppSettings["DbGen"] == "true") { var export = new SchemaExport(cfg); export.Execute(true, true, false, NHibernateSession.Current.Connection, File.CreateText(@"DDL.sql")); } } The AutoPersistenceModelGenerator hooks up the various conventions, including a TableNameConvention like so: public void Apply(FluentNHibernate.Conventions.Instances.IClassInstance instance) { instance.Table(Inflector.Net.Inflector.Pluralize(instance.EntityType.Name)); } This is working nicely execpt that the sqlite db generated does not have pluralized table names. Any idea what I'm missing? Thanks.

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• 'is instanceof' Interface bad design

  - by peterRit

  Say I have a class A class A { Z source; } Now, the context tells me that 'Z' can be an instance of different classes (say, B and C) which doesn't share any common class in their inheritance tree. I guess the naive approach is to make 'Z' an Interface class, and make classes B and C implement it. But something still doesn't convince me because every time an instance of class A is used, I need to know the type of 'source'. So all finishes in multiple 'ifs' making 'is instanceof' which doesn't sound quite nice. Maybe in the future some other class implements Z, and having hardcoded 'ifs' of this type definitely could break something. The escence of the problem is that I cannot resolve the issue by adding functions to Z, because the work done in each instance type of Z is different. I hope someone can give me and advice, maybe about some useful design pattern. Thanks

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• Java Thread - Synchronization issue

  - by Yatendra Goel

  From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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• very simple delegate musing

  - by Ted

  Sometimes the simplest questions make me love C/C++ and C# more and more. Today sitting on the bus musing aout delegates I remembered reading somwhere you don't need to use the new keyword when instaniating a new delegate. For example: public static void SomeMethod(string message) { ... } ... public delegate void TestDelgate(string message); //Define a delegate ........... //create a new instance ..METHOD 1 TestDelgate t = new TestDelgate(SomeMethod); //OR another way to create a new instance ..METHOD 2 TestDelgate t = SomeMethod; //create a new instance ..METHOD 2 So todays questions are What happens under the hood in method 2. Does the compiler expand method 2 into method 1, hence writing TestDelgate t = SomeMethod; is just a shortcut for TestDelgate t = new TestDelgate(SomeMethod);, or is there another reason for the exsitence of method 2 Do you guys think method 1 or method 2 is better for readability (this is a subjective question, but I'd just like to get a unscientific feel of general opinion of stackoverflow :-))

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• Haskell: Problems with overloading: Interpreter can´t tell which + to use

  - by Ben

  Hi, I want to make functions Double - Double an instance of the Num typeclass. I want to define the sum of two functions as sum of their images. So I wrote instance Num Function where f + g = (\ x - (f x) + (g x)) Here the compiler complains he can´t tell whether I´m using Prelude.+ or Module.+ in the lambda expression. So I imported Prelude qualified as P and wrote instance Num Function where f + g = (\ x - (f x) P.+ (g x)) This compiles just fine, but when I try to add two functions in GHCi the interpreter complains again he can´t tell whether I´m using Prelude.+ or Module.+. Is there any way I can solve this problem?

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• Is this a valid, lazy, thread-safe Singleton implementation for C#?

  - by Matthew

  I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling around for C# Singleton implementations, it doesn't seem like this is a common way to do things in C#. I found one similar implementation, but the SingletonHolder class wasn't static, and included an explicit (empty) static constructor. Is this a valid, lazy, thread-safe way to implement the Singleton pattern? Or is there something I'm missing?

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• Q about AbstractApplicationContext.getBeansOfType() and getBean()

  - by Paul Reiners

  We have the following legacy 2.0.7 Spring code: final Map<String, MyClass> secondaryFactories = (Map<String, MyClass>) context.getBeansOfType(MyClass.class, false, true); return (MyClass) context.getBean("myClass"); where context is an instance of org.springframework.context.support.AbstractApplicationContext Note that we ignore the return value of getBeansOfType(). This works just fine, but the problem is that the call to getBeansOfType() is time-consuming. However, even though we ignore the return value of this call, if we try to eliminate this call, then the instance of MyClass returned by getBean() is not fully initialized. (So, apparently, the call to getBeansOfType() is having some sort of side-effects that we need.) We suspect that the call to getBeansOfType() is overkill and we could do something more lightweight so that the instance of MyClass obtained by the call to getBean() would be fully initialized (but it's not null and no exception is thrown). So, is there a more efficient way of doing this?

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• Threaded application sleeps with other application

  - by DeeD

  I have a weird problem with my threaded software. I start 2 instances of the software. Each instance has 2 threads, one thread creates a socket to use, and the other one is uses the socket for communication. When one of the threads in one instance calls sleep(3), the other threads in the the other instance sleeps too. And the weirdest thing is that when I rebooted the computer, it works the first time, but after trying a second time, it sleeps like described. How is this possible? Is it using some shared resource?

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• Can connect to EC2 as ubuntu user but not as the user i created

  - by Sid

  I created a new ebs backed EC2-instance and the necessary key-pair. Now I am able to connect to the instance as ubuntu user. Once i did that I created another user and added it to the sudoers list but I am unable to connect to the instance as the new user I created. I get the following error. I am using the same key to connect with the new user i created. Can somebody help me. Am I missing something here? Permission denied (publickey)"

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• jquery "this" binding issue on event handler

  - by clyfe

  In jquery an event hadler's binding is the event generating DOM element (this points to the dom element). In prototype to change the binding of an event handler one can use the bindAsEventListener function; How can I access both the instance and the DOM element from a event handler? Similar to http://stackoverflow.com/questions/117361/how-can-i-bind-an-event-handler-to-an-instance-in-jquery function Car(){ this.km = 0; $("#sprint").click(this.drive); //setup event handler } // event handler // in it I need to access both the clicked element // and the binding object (instance of car) Car.prototype.drive = function(){ this.km += 10; // i'd like to access the binding (but jq changes it) this.css({ left: this.km }); // also the element // NOTE that is inside this function I want to access them not elsewhere } var car = new Car();

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• session variable not available in global before(:each, :type => :controller)

  - by Rob

  Hi, I'm refactoring some specs, in controller specs I have a before(:each) which sets up things required in the session my before filter is... config.before(:each, :type => :controller) do ... session[:current_user] = @user session[:instance] = @instance ... end @user and @instance are also set in the before(:each) i've just hidden them for readability here I get the following error when running the controller tests undefined method `session' for nil:NilClass I would expect the global before callbacks to have the same things as the ones in the individual tests but I guess maybe they are loaded before the rails environment has been initialised? Thanks

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• Why does my CLR function keep disappearing

  - by user208080

  Hi there. I am a rookie to SQL and here is my questions. I have some CLR sql functions and procedures. When I deploy the 1st one, everything is fine. But after the 2nd one deployed, the first one will disappear. Anyone can help me out? Thanks a lot Actually, I simply create a new SQL project in VS, adding a new function or stored procedure, click deploy, and I can see the new function in my SQL instance. Then I close that project and open a new one, repeat the above steps, OK, the 2nd function is there i my instance but the 1st one disappeared or be replaced and no longer queryable for use. Thank you for your reply. All these clr functions and procedures are in the same instance of the database.

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• Field annotated multiple times by the same attribute

  - by Jaroslaw Waliszko

  For my ASP.NET MVC application I've created custom validation attribute, and indicated that more than one instance of it can be specified for a single field or property: [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = true)] public sealed class SomeAttribute: ValidationAttribute I've created validator for such an attribute: public class SomeValidator : DataAnnotationsModelValidator<SomeAttribute> and wire up this in the Application_Start of Global.asax DataAnnotationsModelValidatorProvider.RegisterAdapter( typeof (SomeAttribute), typeof (SomeValidator)); Finally, if I use my attribute in the desired way: [SomeAttribute(...)] //first [SomeAttribute(...)] //second public string SomeField { get; set; } when validation is executed by the framework, only first attribute instance is invoked. Second one seems to be dead. I've noticed that during each request only single validator instance is created (for the first annotation). How to solve this problem and fire all attributes?

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• SQL Compact 2008 Connection String Problem

  - by Seth

  I have the following code to connect to a sql server compact edition 2008: private SqlConnection sqlConn; public void createConnection() { String connectionString = @"Data Source=C:\Projects\somefile.sdf;Persist Security Info=False"; sqlConn = new SqlConnection(connectionString); sqlConn.Open(); } However, I keep getting the following error when sqlConn.Open() is executed: "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)" Does anyone have any ideas what the problem might be? I can create a connection to the db in the database explorer but it doesn't seem to work in code.

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• C# Unit Testing: How do I set a Lazy<T>.ValueCreated to false?

  - by michael paul

  Basically, I have a unit test that gets a singleton instance of a class. Some of my tests required me to mock this singleton, so when I do Foo.Instance I get a different type of instance. The problem is that my checks are passing individually, but failing overall because one test is interfering with another. I tried to do a TestCleanup where I set: Foo_Accessor._instance = null; but that didn't work. What I really need is Foo_Accessor._instance.IsValueCreated = false; (_instance is a Lazy). Any way to unset the Lazy object that I didn't think of?

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• correct technical term for this pattern

  - by Oliver A.

  sometimes I use a pattern which is very similar to the singleton pattern: There is one default instance which and a static get method to aces it. But you may create other instances and pass it as optional parameter and if you want to and you can even replace the default instance with a instance from a child class. So it is NO SINGLETON at all but it is used like one singleton in most cases. Anyone got an idea who to call something like this ? Maybe half*** singleton? domiton?

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• JSF managed bean question

  - by Nitesh Panchal

  Hello, I have one page which uses <ui:insert> called master.xhtml which uses one managedbean named MasterBean.java and its of viewScoped. It calls webservice and has all useful data which will be useful in master.xhtml as well as page which is built using master.xhtml (which uses <ui:include>). When i visit data.xhtml (which uses template as master.xhtml) and which uses managed bean as DataBean.java which is also of view scoped, how do i use MasterBean? If i directly use #{Masterbean.property}, won't it create a new instance again? or will it use the bean which is already in view scope? Also how do i use MasterBean in DataBean in such a way that existing MasterBean's instance is used in DataBean. I don't want new instance of MasterBean in DataBean. Thanks in advance. If i am not clear please let me know.

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• Sharing base object with inheritance

  - by max

  I have class Base. I'd like to extend its functionality in a class Derived. I was planning to write: class Derived(Base): def __init__(self, base_arg1, base_arg2, derived_arg1, derived_arg2): super().__init__(base_arg1, base_arg2) # ... def derived_method1(self): # ... Sometimes I already have a Base instance, and I want to create a Derived instance based on it, i.e., a Derived instance that shares the Base object (doesn't re-create it from scratch). I thought I could write a static method to do that: b = Base(arg1, arg2) # very large object, expensive to create or copy d = Derived.from_base(b, derived_arg1, derived_arg2) # reuses existing b object but it seems impossible. Either I'm missing a way to make this work, or (more likely) I'm missing a very big reason why it can't be allowed to work. Can someone explain which one it is? [Of course, if I used composition rather than inheritance, this would all be easy to do. But I was hoping to avoid the delegation of all the Base methods to Derived through __getattr__.]

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• Memcached in a trusted shared environment?

  - by John Kary

  We are a university IT organization that hosts all of the university's websites on several shared servers on our server room floor. We have several VMs, each running its own instance of Apache as a web server for each respective server. If we were going to setup a memcached server, is it feasible to use it as a shared instance? If shared by several servers, or even multiple web apps running on the same server, what's the best way to keep each app's cache stores separate? Prefix the key? Would each VM require its own instance of memcached, or could we setup 1 memcached server and allow our multiple VMs to read/write to it?

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• Substitute all matches with values in Ruby regular expression

  - by Lewisham

  Hi all, I'm having a problem with getting a Ruby string substitution going. I'm writing a preprocessor for a limited language that I'm using, that doesn't natively support arrays, so I'm hacking in my own. I have a line: x[0] = x[1] & x[1] = x[2] I want to replace each instance with a reformatted version: x__0 = x__1 & x__1 = x__2 The line may include square brackets elsewhere. I've got a regex that will match the array use: array_usage = /(\w+)\[(\d+)\]/ but I can't figure out the Ruby construct to replace each instance one by one. I can't use .gsub() because that will match every instance on the line, and replace every array declaration with whatever the first one was. .scan() complains that the string is being modified if you try and use scan with a .sub()! inside a block. Any ideas would be appreciated!

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• Object initialization sequence in Objective-C

  - by Alex

  Hello everyone. The Cocoa framework has a convention to always call self = [super init] in the init method of an inherited class, because [super init] may return a new instance. What will happen if I do this? @interface MyClass : NSObject /* or any other class */ { int ivar_; } @end @implementation MyClass - (id)init { ivar_ = 12345; if ((self = [super init])) { NSLog(@"ivar_'s value is %d", ivar_); } return self; } @end In the case when [super init] returns a new instance, what will I see in the console? ivar_'s value is 0? I can't think of a way to check this myself, because I don't know which class may return a new instance from its init method. Also, can't seem to find explicit clarification for this scenario in the docs. Could anyone help me out? Thanks!

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• Edit form not being instanciated

  - by 47

  I have two models like this: class OptionsAndFeatures(models.Model): options = models.TextField(blank=True, null=True) entertainment = models.TextField(blank=True, null=True) seats_trim = models.TextField(blank=True, null=True) convenience = models.TextField(blank=True, null=True) body_exterior = models.TextField(blank=True, null=True) lighting = models.TextField(blank=True, null=True) safety = models.TextField(blank=True, null=True) powertrain = models.TextField(blank=True, null=True) suspension_handling = models.TextField(blank=True, null=True) specs_dimensions = models.TextField(blank=True, null=True) offroad_capability = models.TextField(blank=True, null=True) class Vehicle(models.Model): ... options_and_features = models.ForeignKey(OptionsAndFeatures, blank=True, null=True) I have a model form for the OptionsAndFeaturesclass that I'm using in both the add and edit views. In the add view it works just fine. But the edit view renders the OptionsAndFeatures as blank. The code for the edit view is as follows: def edit_vehicle(request, stock_number=None): vehicle = get_object_or_404(Vehicle, stock_number=stock_number) if request.method == 'POST': # save info else: vehicle_form = VehicleForm(instance=vehicle) photos = PhotosFormSet(instance=vehicle) options = OptionsForm(instance=vehicle) #render_to_reponse What could be the problem here?

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• Automatic Backup and Restore MySQL db from Web Server to Local Machine

  - by Rhepungus

  I have a web app that is supposed to be run on a single local machine (kiosk display), but I want the option to let a user make changes on the web (from any PC) and update the instance on their local PC (kiosk display). From what i imagine, the MySQL instance on the web will just be replace the MySQL instance on the local (kiosk display) machine. Does anyone know of a way to do this? I am open to a product or coding it myself... I will appreciate any info or brainstorm. Thanks.

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