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  • Inner synchronization on the same object as the outer synchronization

    - by Yaneeve
    Recently I attended a lecture concerning some design patterns: The following code had been displayed: public static Singleton getInstance() { if (instance == null) { synchronized(Singleton.class) { //1 Singleton inst = instance; //2 if (inst == null) { synchronized(Singleton.class) { //3 inst = new Singleton(); //4 } instance = inst; //5 } } } return instance; } taken from: Double-checked locking: Take two My question has nothing to do with the above mentioned pattern but with the synchronized block: Is there any benefit whatsoever to the double synchronization done in lines 1 & 3 with regards to the fact that the synchronize operation is done on the same Object?

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  • NSWindowController and isWindowLoaded

    - by Jim
    Hi, I have an NSWindowController and I initialize it like this; + (MyWindowController *) sharedController { static MyWindowController *singleton = nil; if (!singleton) singleton = [[self alloc] initWithWindowNibName: @"myWindow"]; return singleton; } and I show windows like this; [[MyWindowController sharedController] showWindow: nil]; Now the problem is that I need information from some controls on that window. But I do not want to load the window if it's not yet loaded because then I can just go with the defaults. Should I use @property to access the singleton? or what is recommended here? (If @property, then please give me the readonly, nonatomic attributes too.)

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  • Actions and Controllers managing strategy in MVC apps

    - by singleton
    Can anyone name any usefull strategy/architectural pattern for allocating actions between different controllers when using MVC pattern for developing web application? I am now developing web app using asp.net Mvc3 framework and still can't figure out how to manage actions and controllers. One approach is to create single action controller for each url, but it's not the best choice since to much controllers have to be created. Should I list all available urls that are supported by me web app, devide them into groups and create separate controller for each group or act in any different manner? It seems like I will become face to face with some kind of mess with no consistent approach in managing actions and controllers.

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  • Dealing with institutionalized programmers.

    - by Singleton
    Some times programmers who work in a project for long time tend to get institutionalized. It is difficult to convince them with reasoning. Even if we manage to convince them they will be adamant to take suggestion on board. How do we handle the situation without developing friction in team? Institutionalized in terms of practices. I recently joined in a project where build &release process was made so complicated with unnecessary roadblocks. My suggestion was we can get rid of some of the development overheads(like filling few spreadsheets) just by integrating defect management and version controlling tools (both are IBM-Rational tools integration can be very easy and one-off effort). Also by using tools like Maven & Ant (project involves java and some COTS products) build & release can be simplified and reduce manual errors& intervention. I managed to convince and ready to put efforts for developing proof of concept. But the ‘Senior’ developer is not willing to take it on board. One reason could be the current process makes him valuable in team.

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  • Dealing with inflexible programmers.

    - by Singleton
    Sometimes programmers who work on a project for long time get inflexible, and it becomes difficult to reason with them. Even if we do manage to convince them, they can be unlikely to implement our suggestions. For instance, I recently joined a project where the build & release process is too complicated and has unnecessary roadblocks. I suggested that we get rid of some of the development overhead (like filling a few spreadsheets) just by integrating defect management and version control tools (both are IBM-Rational tools so integration can be a very easy one-off effort). Also, if we use tools like Maven & Ant (the project involves Java and some COTS products) build & release can be simplified which should reduce manual errors & intervention. I managed to convince others and I'm ready to put in the effort to develop a proof of concept. But the ‘Senior’ developer is not willing, possibly because the current process makes him more valuable. How do we handle this situation without developing friction in the team?

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  • Prevent Ninject from calling Initialize multiple times when binding to several interfaces

    - by Ahe
    Hi We have a concrete singleton service which implements Ninject.IInitializable and 2 interfaces. Problem is that services Initialize-methdod is called 2 times, when only one is desired. We are using .NET 3.5 and Ninject 2.0.0.0. Is there a pattern in Ninject prevent this from happening. Neither of the interfaces implement Ninject.IInitializable. the service class is: public class ConcreteService : IService1, IService2, Ninject.IInitializable { public void Initialize() { // This is called twice! } } And module looks like this: public class ServiceModule : NinjectModule { public override void Load() { this.Singleton<Iservice1, Iservice2, ConcreteService>(); } } where Singleton is an extension method defined like this: public static void Singleton<K, T>(this NinjectModule module) where T : K { module.Bind<K>().To<T>().InSingletonScope(); } public static void Singleton<K, L, T>(this NinjectModule module) where T : K, L { Singleton<K, T>(module); module.Bind<L>().ToMethod(n => n.Kernel.Get<T>()); } Of course we could add bool initialized-member to ConcreteService and initialize only when it is false, but it seems quite a bit of a hack. And it would require repeating the same logic in every service that implements two or more interfaces. Thanks for all the answers! I learned something from all of them! (I am having a hard time to decide which one mark correct). We ended up creating IActivable interface and extending ninject kernel (it also removed nicely code level dependencies to ninject, allthough attributes still remain).

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  • What is required for a scope in an injection framework?

    - by johncarl
    Working with libraries like Seam, Guice and Spring I have become accustomed to dealing with variables within a scope. These libraries give you a handful of scopes and allow you to define your own. This is a very handy pattern for dealing with variable lifecycles and dependency injection. I have been trying to identify where scoping is the proper solution, or where another solution is more appropriate (context variable, singleton, etc). I have found that if the scope lifecycle is not well defined it is very difficult and often failure prone to manage injections in this way. I have searched on this topic but have found little discussion on the pattern. Is there some good articles discussing where to use scoping and what are required/suggested prerequisites for scoping? I interested in both reference discussion or your view on what is required or suggested for a proper scope implementation. Keep in mind that I am referring to scoping as a general idea, this includes things like globally scoped singletons, request or session scoped web variable, conversation scopes, and others. Edit: Some simple background on custom scopes: Google Guice custom scope Some definitions relevant to above: “scoping” - A set of requirements that define what objects get injected at what time. A simple example of this is Thread scope, based on a ThreadLocal. This scope would inject a variable based on what thread instantiated the class. Here's an example of this: “context variable” - A repository passed from one object to another holding relevant variables. Much like scoping this is a more brute force way of accessing variables based on the calling code. Example: methodOne(Context context){ methodTwo(context); } methodTwo(Context context){ ... //same context as method one, if called from method one } “globally scoped singleton” - Following the singleton pattern, there is one object per application instance. This applies to scopes because there is a basic lifecycle to this object: there is only one of these objects instantiated. Here's an example of a JSR330 Singleton scoped object: @Singleton public void SingletonExample{ ... } usage: public class One { @Inject SingeltonExample example1; } public class Two { @Inject SingeltonExample example2; } After instantiation: one.example1 == two.example2 //true;

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  • How to make the yuicompressor jar file a singleton, or globally accessible?

    - by Erik Vold
    I'd like to put the yuicompressor jar file in a single folder so that I can call java -jar yuicompressor-2.4.2.jar ... from anywhere on my system, with cygwin. For bash files I use I simply put them in a common folder, and added the folder's path to my windows user's PATH environment variable and the bash commands were found in cygwin. when I echo $PATH I see the folder I put the yuicompressor jar into listed in the $PATH.. But when I try java -jar yuicompressor-2.4.2.jar ... I get the following error message: Unable to access jarfile yuicompressor-2.4.2.jar Even when I try providing an absolute path to the jarfile I get the same error message.. How can I do this?

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  • CodeModel help needed for right-hand singleton.getinstance() assignment.

    - by antarti
    I've been able to generate 99% of what I need with the CodeModel API, but I am stumped here... Using the various "directXX" methods does not add import statements to the generated code, and I can work without the "directXXX" type of methods except for one place in a generated class. Suppose I desire a generated method like: /** * Copies data from this Value-Obj instance, to the returned PERSON instance. * * @return PERSON * */ public PERSON mapVOToPERSON() throws MappingException { Mapper mapper = (com.blah.util.MapperSingleton.getMapperInstance()); return mapper.map(this, PERSON.class); } You can see the right hand of the Mapper assignment in parens. Emitting the entire package+class was the only way I could find to just declare "SomeSingleton.someMethod()" on the right hand side and have the generated code compile. Without the MapperSingleton being added to the object model, there is no import generated... Questions: 1) Is there a way to force an import to be generated? 2) How to declare an expression that gives me the right side of the Mapper assignment within the object model (so that an import of MapperSingleton gets generated. Any help appreciated...

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  • Java regex patterns - compile time constants or instance members?

    - by KepaniHaole
    Currently, I have a couple of singleton objects where I'm doing matching on regular expressions, and my Patterns are defined like so: class Foobar { private final Pattern firstPattern = Pattern.compile("some regex"); private final Pattern secondPattern = Pattern.compile("some other regex"); // more Patterns, etc. private Foobar() {} public static Foobar create() { /* singleton stuff */ } } But I was told by someone the other day that this is bad style, and Patterns should always be defined at the class level, and look something like this instead: class Foobar { private static final Pattern FIRST_PATTERN = Pattern.compile("some regex"); private static final Pattern SECOND_PATTERN = Pattern.compile("some other regex"); // more Patterns, etc. private Foobar() {} public static Foobar create() { /* singleton stuff */ } } The lifetime of this particular object isn't that long, and my main reason for using the first approach is because it doesn't make sense to me to hold on to the Patterns once the object gets GC'd. Any suggestions / thoughts?

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  • Update table columns bound to NSArrayController

    - by Loz
    Hi, I'm fairly new to the world of bindings in cocoa, and I'm having some troubles (perhaps/probably due to a misunderstanding). I have a singleton that contains an NSMutableArray called plugins, containing objects of class Plugin. It has a method called loadPlugins which adds objects to the plugins array. This may be called at any point. It's been added as an instance in Interface Builder. Also in IB is an NSObjectController, whose content outlet is connected to the singleton. There is also an NSArrayController, whose contentArray is bound to the NSObjectController (controller key is 'selection', model key path is 'plugins', object class name is 'Plugin'). And finally I have a table view with 2 columns, the values of which are bound to the NSArrayController's arrangedObjects, using keys of properties in the Plugin class. So far so standard (as far as I can tell from tutorials at least). My trouble is that when the loadPlugins method is called in the singleton, and objects are added to the plugins array, the table doesn't update to show the objects (unless loadPlugins is called before the nib is loaded). -reloadData called on the tableView doesn't do anything. Is there a way to tell the NSArrayController that the referenced array has been updated? I understand there is the -add: method for NSArrayController, which could be used in the loadPlugins, but this isn't desirable as I want to keep the singleton totally separate from the display aspect. This seems related to: http://stackoverflow.com/questions/1623396/refresh-cocoa-binding-nsarraycontroller-combobox The line: "editing the array behind the controller's back" seems to perhaps pinpoint the problem, but I would hope that it would be possible to have the singleton not know about the controller. Thanks in advance.

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  • Register all GUI components as Observers or pass current object to next object as a constructor argu

    - by Jack
    First, I'd like to say that I think this is a common issue and there may be a simple or common solution that I am unaware of. Many have probably encountered a similar problem. Thanks for reading. I am creating a GUI where each component needs to communicate (or at least be updated) by multiple other components. Currently, I'm using a Singleton class to accomplish this goal. Each GUI component gets the instance of the singleton and registers itself. When updates need to be made, the singleton can call public methods in the registered class. I think this is similar to an Observer pattern, but the singleton has more control. Currently, the program is set up something like this: class c1 { CommClass cc; c1() { cc = CommClass.getCommClass(); cc.registerC1( this ); C2 c2 = new c2(); } } class c2 { CommClass cc; c2() { cc = CommClass.getCommClass(); cc.registerC2( this ); C3 c3 = new c3(); } } class c3 { CommClass cc; c3() { cc = CommClass.getCommClass(); cc.registerC3( this ); C4 c4 = new c4(); } } etc. Unfortunately, the singleton class keeps growing larger as more communication is required between the components. I was wondering if it's a good idea to instead of using this singleton, pass the higher order GUI components as arguments in the constructors of each GUI component: class c1 { c1() { C2 c2 = new c2( this ); } } class c2 { C1 c1; c2( C1 c1 ) { this.c1 = c1 C3 c3 = new c3( c1, this ); } } class c3 { C1 c1; C2 c2; c3( C1 c1, C2 c2 ) { this.c1 = c1; this.c2 = c2; C4 c4 = new c4( c1, c2, this ); } } etc. The second version relies less on the CommClass, but it's still very messy as the private member variables increase in number and the constructors grow in length. Each class contains GUI components that need to communicate through CommClass, but I can't think of a good way to do it. If this seems strange or horribly inefficient, please describe some method of communication between classes that will continue to work as the project grows. Also, if this doesn't make any sense to anyone, I'll try to give actual code snippets in the future and think of a better way to ask the question. Thanks.

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  • new Statefull session bean instance without calling lookup

    - by kislo_metal
    Hi! Scenario: I have @Singleton UserFactory (@Stateless could be) , it`s method createSession() generating @Statefull UserSession bean by manual lookup. If I am injecting by DI @EJB - i will get same instance during calling fromFactory() method(as it should be) What I want - is to get new instance of UserSession without preforming lookup. Q1: how could I call new instance of @Statefull session bean? Code: @Singleton @Startup @LocalBean public class UserFactory { @EJB private UserSession session; public UserFactory() { } @Schedule(second = "*/1", minute = "*", hour = "*") public void creatingInstances(){ try { InitialContext ctx = new InitialContext(); UserSession session2 = (UserSession) ctx.lookup("java:global/inferno/lic/UserSession"); System.out.println("in singleton UUID " +session2.getSessionUUID()); } catch (NamingException e) { e.printStackTrace(); } } @Schedule(second = "*/1", minute = "*", hour = "*") public void fromFactory(){ System.out.println("in singleton UUID " +session.getSessionUUID()); } public UserSession creatSession(){ UserSession session2 = null; try { InitialContext ctx = new InitialContext(); session2 = (UserSession) ctx.lookup("java:global/inferno/lic/UserSession"); System.out.println("in singleton UUID " +session2.getSessionUUID()); } catch (NamingException e) { e.printStackTrace(); } return session2; } } As I understand, calling of session.getClass().newInstance(); is not a best idea Q2 : is it true? I am using glassfish v3, ejb 3.1.

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  • new Stateful session bean instance without calling lookup

    - by kislo_metal
    Scenario: I have @Singleton UserFactory (@Stateless could be) , its method createSession() generating @Stateful UserSession bean by manual lookup. If I am injecting by DI @EJB - i will get same instance during calling fromFactory() method(as it should be) What I want - is to get new instance of UserSession without preforming lookup. Q1: how could I call new instance of @Stateful session bean? Code: @Singleton @Startup @LocalBean public class UserFactory { @EJB private UserSession session; public UserFactory() { } @Schedule(second = "*/1", minute = "*", hour = "*") public void creatingInstances(){ try { InitialContext ctx = new InitialContext(); UserSession session2 = (UserSession) ctx.lookup("java:global/inferno/lic/UserSession"); System.out.println("in singleton UUID " +session2.getSessionUUID()); } catch (NamingException e) { e.printStackTrace(); } } @Schedule(second = "*/1", minute = "*", hour = "*") public void fromFactory(){ System.out.println("in singleton UUID " +session.getSessionUUID()); } public UserSession creatSession(){ UserSession session2 = null; try { InitialContext ctx = new InitialContext(); session2 = (UserSession) ctx.lookup("java:global/inferno/lic/UserSession"); System.out.println("in singleton UUID " +session2.getSessionUUID()); } catch (NamingException e) { e.printStackTrace(); } return session2; } } As I understand, calling of session.getClass().newInstance(); is not a best idea Q2 : is it true? I am using glassfish v3, ejb 3.1.

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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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  • General Overview of Design Pattern Types

    Typically most software engineering design patterns fall into one of three categories in regards to types. Three types of software design patterns include: Creational Type Patterns Structural Type Patterns Behavioral Type Patterns The Creational Pattern type is geared toward defining the preferred methods for creating new instances of objects. An example of this type is the Singleton Pattern. The Singleton Pattern can be used if an application only needs one instance of a class. In addition, this singular instance also needs to be accessible across an application. The benefit of the Singleton Pattern is that you control both instantiation and access using this pattern. The Structural Pattern type is a way to describe the hierarchy of objects and classes so that they can be consolidated into a larger structure. An example of this type is the Façade Pattern.  The Façade Pattern is used to define a base interface so that all other interfaces inherit from the parent interface. This can be used to simplify a number of similar object interactions into one single standard interface. The Behavioral Pattern Type deals with communication between objects. An example of this type is the State Design Pattern. The State Design Pattern enables objects to alter functionality and processing based on the internal state of the object at a given time.

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  • So Singletons are bad, then what?

    - by Bobby Tables
    There has been a lot of discussion lately about the problems with using (and overusing) Singletons. I've been one of those people earlier in my career too. I can see what the problem is now, and yet, there are still many cases where I can't see a nice alternative - and not many of the anti-Singleton discussions really provide one. Here is a real example from a major recent project I was involved in: The application was a thick client with many separate screens and components which uses huge amounts of data from a server state which isn't updated too often. This data was basically cached in a Singleton "manager" object - the dreaded "global state". The idea was to have this one place in the app which keeps the data stored and synced, and then any new screens that are opened can just query most of what they need from there, without making repetitive requests for various supporting data from the server. Constantly requesting to the server would take too much bandwidth - and I'm talking thousands of dollars extra Internet bills per week, so that was unacceptable. Is there any other approach that could be appropriate here than basically having this kind of global data manager cache object? This object doesn't officially have to be a "Singleton" of course, but it does conceptually make sense to be one. What is a nice clean alternative here?

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  • C#/.NET Little Wonders: Tuples and Tuple Factory Methods

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can really help improve your code by making it easier to write and maintain.  This week, we look at the System.Tuple class and the handy factory methods for creating a Tuple by inferring the types. What is a Tuple? The System.Tuple is a class that tends to inspire a reaction in one of two ways: love or hate.  Simply put, a Tuple is a data structure that holds a specific number of items of a specific type in a specific order.  That is, a Tuple<int, string, int> is a tuple that contains exactly three items: an int, followed by a string, followed by an int.  The sequence is important not only to distinguish between two members of the tuple with the same type, but also for comparisons between tuples.  Some people tend to love tuples because they give you a quick way to combine multiple values into one result.  This can be handy for returning more than one value from a method (without using out or ref parameters), or for creating a compound key to a Dictionary, or any other purpose you can think of.  They can be especially handy when passing a series of items into a call that only takes one object parameter, such as passing an argument to a thread's startup routine.  In these cases, you do not need to define a class, simply create a tuple containing the types you wish to return, and you are ready to go? On the other hand, there are some people who see tuples as a crutch in object-oriented design.  They may view the tuple as a very watered down class with very little inherent semantic meaning.  As an example, what if you saw this in a piece of code: 1: var x = new Tuple<int, int>(2, 5); What are the contents of this tuple?  If the tuple isn't named appropriately, and if the contents of each member are not self evident from the type this can be a confusing question.  The people who tend to be against tuples would rather you explicitly code a class to contain the values, such as: 1: public sealed class RetrySettings 2: { 3: public int TimeoutSeconds { get; set; } 4: public int MaxRetries { get; set; } 5: } Here, the meaning of each int in the class is much more clear, but it's a bit more work to create the class and can clutter a solution with extra classes. So, what's the correct way to go?  That's a tough call.  You will have people who will argue quite well for one or the other.  For me, I consider the Tuple to be a tool to make it easy to collect values together easily.  There are times when I just need to combine items for a key or a result, in which case the tuple is short lived and so the meaning isn't easily lost and I feel this is a good compromise.  If the scope of the collection of items, though, is more application-wide I tend to favor creating a full class. Finally, it should be noted that tuples are immutable.  That means they are assigned a value at construction, and that value cannot be changed.  Now, of course if the tuple contains an item of a reference type, this means that the reference is immutable and not the item referred to. Tuples from 1 to N Tuples come in all sizes, you can have as few as one element in your tuple, or as many as you like.  However, since C# generics can't have an infinite generic type parameter list, any items after 7 have to be collapsed into another tuple, as we'll show shortly. So when you declare your tuple from sizes 1 (a 1-tuple or singleton) to 7 (a 7-tuple or septuple), simply include the appropriate number of type arguments: 1: // a singleton tuple of integer 2: Tuple<int> x; 3:  4: // or more 5: Tuple<int, double> y; 6:  7: // up to seven 8: Tuple<int, double, char, double, int, string, uint> z; Anything eight and above, and we have to nest tuples inside of tuples.  The last element of the 8-tuple is the generic type parameter Rest, this is special in that the Tuple checks to make sure at runtime that the type is a Tuple.  This means that a simple 8-tuple must nest a singleton tuple (one of the good uses for a singleton tuple, by the way) for the Rest property. 1: // an 8-tuple 2: Tuple<int, int, int, int, int, double, char, Tuple<string>> t8; 3:  4: // an 9-tuple 5: Tuple<int, int, int, int, double, int, char, Tuple<string, DateTime>> t9; 6:  7: // a 16-tuple 8: Tuple<int, int, int, int, int, int, int, Tuple<int, int, int, int, int, int, int, Tuple<int,int>>> t14; Notice that on the 14-tuple we had to have a nested tuple in the nested tuple.  Since the tuple can only support up to seven items, and then a rest element, that means that if the nested tuple needs more than seven items you must nest in it as well.  Constructing tuples Constructing tuples is just as straightforward as declaring them.  That said, you have two distinct ways to do it.  The first is to construct the tuple explicitly yourself: 1: var t3 = new Tuple<int, string, double>(1, "Hello", 3.1415927); This creates a triple that has an int, string, and double and assigns the values 1, "Hello", and 3.1415927 respectively.  Make sure the order of the arguments supplied matches the order of the types!  Also notice that we can't half-assign a tuple or create a default tuple.  Tuples are immutable (you can't change the values once constructed), so thus you must provide all values at construction time. Another way to easily create tuples is to do it implicitly using the System.Tuple static class's Create() factory methods.  These methods (much like C++'s std::make_pair method) will infer the types from the method call so you don't have to type them in.  This can dramatically reduce the amount of typing required especially for complex tuples! 1: // this 4-tuple is typed Tuple<int, double, string, char> 2: var t4 = Tuple.Create(42, 3.1415927, "Love", 'X'); Notice how much easier it is to use the factory methods and infer the types?  This can cut down on typing quite a bit when constructing tuples.  The Create() factory method can construct from a 1-tuple (singleton) to an 8-tuple (octuple), which of course will be a octuple where the last item is a singleton as we described before in nested tuples. Accessing tuple members Accessing a tuple's members is simplicity itself… mostly.  The properties for accessing up to the first seven items are Item1, Item2, …, Item7.  If you have an octuple or beyond, the final property is Rest which will give you the nested tuple which you can then access in a similar matter.  Once again, keep in mind that these are read-only properties and cannot be changed. 1: // for septuples and below, use the Item properties 2: var t1 = Tuple.Create(42, 3.14); 3:  4: Console.WriteLine("First item is {0} and second is {1}", 5: t1.Item1, t1.Item2); 6:  7: // for octuples and above, use Rest to retrieve nested tuple 8: var t9 = new Tuple<int, int, int, int, int, int, int, 9: Tuple<int, int>>(1,2,3,4,5,6,7,Tuple.Create(8,9)); 10:  11: Console.WriteLine("The 8th item is {0}", t9.Rest.Item1); Tuples are IStructuralComparable and IStructuralEquatable Most of you know about IComparable and IEquatable, what you may not know is that there are two sister interfaces to these that were added in .NET 4.0 to help support tuples.  These IStructuralComparable and IStructuralEquatable make it easy to compare two tuples for equality and ordering.  This is invaluable for sorting, and makes it easy to use tuples as a compound-key to a dictionary (one of my favorite uses)! Why is this so important?  Remember when we said that some folks think tuples are too generic and you should define a custom class?  This is all well and good, but if you want to design a custom class that can automatically order itself based on its members and build a hash code for itself based on its members, it is no longer a trivial task!  Thankfully the tuple does this all for you through the explicit implementations of these interfaces. For equality, two tuples are equal if all elements are equal between the two tuples, that is if t1.Item1 == t2.Item1 and t1.Item2 == t2.Item2, and so on.  For ordering, it's a little more complex in that it compares the two tuples one at a time starting at Item1, and sees which one has a smaller Item1.  If one has a smaller Item1, it is the smaller tuple.  However if both Item1 are the same, it compares Item2 and so on. For example: 1: var t1 = Tuple.Create(1, 3.14, "Hi"); 2: var t2 = Tuple.Create(1, 3.14, "Hi"); 3: var t3 = Tuple.Create(2, 2.72, "Bye"); 4:  5: // true, t1 == t2 because all items are == 6: Console.WriteLine("t1 == t2 : " + t1.Equals(t2)); 7:  8: // false, t1 != t2 because at least one item different 9: Console.WriteLine("t2 == t2 : " + t2.Equals(t3)); The actual implementation of IComparable, IEquatable, IStructuralComparable, and IStructuralEquatable is explicit, so if you want to invoke the methods defined there you'll have to manually cast to the appropriate interface: 1: // true because t1.Item1 < t3.Item1, if had been same would check Item2 and so on 2: Console.WriteLine("t1 < t3 : " + (((IComparable)t1).CompareTo(t3) < 0)); So, as I mentioned, the fact that tuples are automatically equatable and comparable (provided the types you use define equality and comparability as needed) means that we can use tuples for compound keys in hashing and ordering containers like Dictionary and SortedList: 1: var tupleDict = new Dictionary<Tuple<int, double, string>, string>(); 2:  3: tupleDict.Add(t1, "First tuple"); 4: tupleDict.Add(t2, "Second tuple"); 5: tupleDict.Add(t3, "Third tuple"); Because IEquatable defines GetHashCode(), and Tuple's IStructuralEquatable implementation creates this hash code by combining the hash codes of the members, this makes using the tuple as a complex key quite easy!  For example, let's say you are creating account charts for a financial application, and you want to cache those charts in a Dictionary based on the account number and the number of days of chart data (for example, a 1 day chart, 1 week chart, etc): 1: // the account number (string) and number of days (int) are key to get cached chart 2: var chartCache = new Dictionary<Tuple<string, int>, IChart>(); Summary The System.Tuple, like any tool, is best used where it will achieve a greater benefit.  I wouldn't advise overusing them, on objects with a large scope or it can become difficult to maintain.  However, when used properly in a well defined scope they can make your code cleaner and easier to maintain by removing the need for extraneous POCOs and custom property hashing and ordering. They are especially useful in defining compound keys to IDictionary implementations and for returning multiple values from methods, or passing multiple values to a single object parameter. Tweet Technorati Tags: C#,.NET,Tuple,Little Wonders

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  • Am I missing a pattern?

    - by Ryan Pedersen
    I have a class that is a singleton and off of the singleton are properties that hold the instances of all the performance counters in my application. public interface IPerformanceCounters { IPerformanceCounter AccountServiceCallRate { get; } IPerformanceCounter AccountServiceCallDuration { get; } Above is an incomplete snippet of the interface for the class "PerformanceCounters" that is the singleton. I really don't like the plural part of the name and thought about changing it to "PerformanceCounterCollection" but stopped because it really isn't a collection. I also thought about "PerformanceCounterFactory" but it is really a factory either. After failing with these two names and a couple more that aren't worth mentioning I thought that I might be missing a pattern. Is there a name that make sense or a change that I could make towards a standardized pattern that would help me put some polish on this object and get rid of the plural name? I understand that I might be splitting hairs here but that is why I thought that the "Programmers" exchange was the place for this kind of thing. If it is not... I am sorry and I will not make that mistake again. Thanks!

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  • Firefox innerHTML Bug?

    - by M. Singleton
    I have a simple piece of HTML <p id="skills">Skills</p> in Firefox 3.6.3 when I call (with JQuery): $("#skills")[0].innerHTML = "some new text" Firefox renders it as <p id="skills"><a xmlns="http://www.w3.org/1999/xhtml">some new text</a></p> Where in the world is that link coming from?? (note the same thing happens by calling $("#skills").html("some new text") with JQuery)

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  • Adding objects to an NSMutableArray, order seems odd when parsing from an XML file

    - by diatrevolo
    Hello: I am parsing an XML file for two elements: "title" and "noType". Once these are parsed, I am adding them to an object called aMaster, an instance of my own Master class that contains NSString variables. I am then adding these instances to an NSMutableArray on a singleton, in order to call them elsewhere in the program. The problem is that when I call them, they don't seem to be on the same NSMutableArray index... each index contains either the title OR the noType element, when it should be both... can anyone see what I may be doing wrong? Below is the code for the parser. Thanks so much!! #import "XMLParser.h" #import "Values.h" #import "Listing.h" #import "Master.h" @implementation XMLParser @synthesize sharedSingleton, aMaster; - (XMLParser *) initXMLParser { [super init]; sharedSingleton = [Values sharedValues]; aMaster = [[Master init] alloc]; return self; } - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict { aMaster = [[Master alloc] init]; //Extract the attribute here. if ([elementName isEqualToString:@"intro"]) { aMaster.intro = [attributeDict objectForKey:@"enabled"]; } else if ([elementName isEqualToString:@"item"]) { aMaster.item_type = [attributeDict objectForKey:@"type"]; //NSLog(@"Did find item with type %@", [attributeDict objectForKey:@"type"]); //NSLog(@"Reading id value :%@", aMaster.item_type); } else { //NSLog(@"No known elements"); } //NSLog(@"Processing Element: %@", elementName); //HERE } - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string { if(!currentElementValue) currentElementValue = [[NSMutableString alloc] initWithString:string]; else { [currentElementValue appendString:string];//[tempString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]]; CFStringTrimWhitespace((CFMutableStringRef)currentElementValue); } } - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName { if ([elementName isEqualToString:@"item"]) { [sharedSingleton.master addObject:aMaster]; NSLog(@"Added %@ and %@ to the shared singleton", aMaster.title, aMaster.noType); //Only having one at a time added... don't know why [aMaster release]; aMaster = nil; } else if ([elementName isEqualToString:@"title"]) { [aMaster setValue:currentElementValue forKey:@"title"]; } else if ([elementName isEqualToString:@"noType"]) { [aMaster setValue:currentElementValue forKey:@"noType"]; //NSLog(@"%@ should load into the singleton", aMaster.noType); } NSLog(@"delimiter"); NSLog(@"%@ should load into the singleton", aMaster.title); NSLog(@"%@ should load into the singleton", aMaster.noType); [currentElementValue release]; currentElementValue = nil; } - (void) dealloc { [aMaster release]; [currentElementValue release]; [super dealloc]; } @end

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  • Java: file write on finalize method

    - by sowrov
    In my understanding a singleton object will destroy only when the application is about to terminate. So in C++ I write a Singleton class to log my application and in that Singleton logger's destructor I log the time when my application was terminated. Things worked perfectly in C++. Now I want to have that same logger in Java, as in java there is no destructor so I implemented the finalize method for that singleton logger. But it seem that finalize method actually never get called. So, I add that System.runFinalizersOnExit(true); line, somewhere in my code (though I know it is deprecated) and that finalize method get called every time before termination of the app. But still there is a problem! If I try to write anything on file in that finalize method, It does not work, though System.out work without any problem! :( Can you guys help me on this problem? Here is a sample code of what I am try to do: Singleton Logger Class: public class MyLogger { FileWriter writer; private MyLogger() { try { this.writer = new FileWriter("log.txt"); } catch (IOException ex) { } } public static MyLogger getInstance() { return MyLoggerHolder.INSTANCE; } private static class MyLoggerHolder { private static final MyLogger INSTANCE = new MyLogger(); } @Override protected void finalize () { try { super.finalize(); System.out.println("Here"); //worked correctly. this.writer.write(new Date().toString()+System.getProperty("line.separator")); this.writer.write("End"); this.writer.flush(); //does not work! this.writer.close(); } catch (Throwable ex) { } } public synchronized void log(String str) { try { this.writer.write(new Date().toString()+System.getProperty("line.separator")); this.writer.write(str+"\n"); this.writer.flush(); } catch (IOException ex) { } } } Main: public class Main { public static void main(String[] args) { System.runFinalizersOnExit(true); MyLogger logger = MyLogger.getInstance(); logger.log("test"); } }

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