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• Delphi> Please explain this: type... procedure of object

  - by Richard Woolf

  I've encountered some code that's new to me... I've never really seen a type declaration of a procedure of object, and I just don't see the point. Why couldn't the developer simply keep a field of type Boolean? interface type TFinishedCaptureEvent = procedure(AFinished: Boolean) of object; TFrameCard = class(TFrame) ... private FOnFinishedCapture: TFinishedCaptureEvent; public property OnFinishedCapture: TFinishedCaptureEvent read FOnFinishedCapture write FOnFinishedCapture; end; implementation ... if Assigned(FOnFinishedCapture) then FOnFinishedCapture(False);

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• C# myths about best practices?

  - by TheMachineCharmer

  My colleague keeps telling me of the things listed in comments. I am confused. Can somebody please demystify these things for me? class Bar { private int _a; public int A { get { return _a; } set { _a = value; } } private Foo _objfoo; public Foo OFoo { get { return _objfoo; } set { _objfoo = value; } } public Bar(int a, Foo foo) { // this is a bad idea A = a; OFoo = foo; } // MYTHS private void Method() { this.A //1 - this._a //2 - use this when inside the class e.g. if(this._a == 2) A //3 - use this outside the class e.g. barObj.A _a //4 - // Not using this.xxx creates threading issues. } } class Foo { // implementation }

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• Why AutoResetEvent and ManualResetEvent does not support name in the constructor?

  - by Ikaso

  On .NET Framework 2.0 AutoResetEvent and ManualResetEvent inherit from EventWaitHandle. The EventWaitHandle class has 4 different constructors. 3 of the constructors support giving a name to the event. On the other hand both ManualResetEvent and AutoResetEvent do not support naming and provide a single constructor that receives the initialState. I can simply inherit from EventWaitHandle and write my own implementation of those classes that support all the constructor overloads, but I don't like to re-invent the wheel if I do not have to. My questions are: Is there a special problem in naming events? Do you have any idea why Microsoft did not support it? Do you have a proposal better than inheriting from the EventWaitHandle class and calling the appropriate constructor as in the following example? public class MyAutoResetEvent: EventWaitHandle { public MyAutoResetEvent(bool initialState) : base(initialState, EventResetMode.AutoReset) { } public MyAutoResetEvent(bool initialState, string name) : base(initialState, EventResetMode.AutoReset, name) { } public MyAutoResetEvent(bool initialState, string name, out bool createdNew) : base(initialState, EventResetMode.AutoReset, name, out createdNew) { } public MyAutoResetEvent(bool initialState, string name, out bool createdNew, EventWaitHandleSecurity eventSecurity) : base(initialState, EventResetMode.AutoReset, string.Empty, out createdNew, eventSecurity) { } }

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• How to handle JPA annotations for a pointer to a generic interface

  - by HDave

  I have a generic class that is also a mapped super class that has a private field that holds a pointer to another object of the same type: @MappedSuperclass public abstract class MyClass<T extends MyIfc<T>> implements MyIfc<T> { @OneToOne() @JoinColumn(name = "previous", nullable = true) private T previous; ... } My problem is that Eclipse is showing an error in the file at the OneToOne "Target Entity "T" for previous is not an Entity." All of the implementations of MyIfc are, in fact, Entities. I should also add that each concrete implementation that inherit from MyClass uses a different value for T (because T is itself) so I can't use the "targetEntity" attribute. I guess if there is no answer then I'll have to move this JPA annotation to all the concrete subclasses of MyClass. It just seems like JPA/Hibernate should be smart enough to know it'll all work out at run-time. Makes me wonder if I should just ignore this error somehow.

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• PyPy -- How can it possibly beat CPython?

  - by Vulcan Eager

  From the Google Open Source Blog: PyPy is a reimplementation of Python in Python, using advanced techniques to try to attain better performance than CPython. Many years of hard work have finally paid off. Our speed results often beat CPython, ranging from being slightly slower, to speedups of up to 2x on real application code, to speedups of up to 10x on small benchmarks. How is this possible? Which Python implementation was used to implement PyPy? CPython? And what are the chances of a PyPyPy or PyPyPyPy beating their score? (On a related note... why would anyone try something like this?)

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• Why do Java/C# edge out C++ as the recommended language to learn OOP on S.O?

  - by viksit

  I noticed after reading the answers/discussion to this question (What is the best language to learn OOP on?) - that more and more people are recommending C# or Java over C++ to learn OOP on. A simple term search on that answer page results in 10 hits for C++, 21 for C# and 27 for Java. Now, I understand that these 2 languages fix a lot of quirks and issues with C++, and looked up these resources that relate mostly to performance, JVM vs native implementation, systems focus vs applications, manual memory management vs automated et al. My question is - are there any fundamental differences in the OO capabilities of Java/C# vs C++? Or are the former recommended purely due to their generic ease of use/improvements over the latter? Thanks. PS, I'm aware of Java interface inheritance vs C++ multiple inheritance as a difference. I would consider that an implementational one rather than functional.

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• What web UI framework is most suitable for building dynamic pages / forms?

  - by waxwing

  Hello, We are at a stage where we are considering different Web UI frameworks (most likely component based ones such as GWT, JSF, Wicket, Vaadin, etc). One of the main use cases / constraints is that it must support generating dynamic pages. I.e., the page/form layout and components is stored in a database and is changeable at runtime, and from this pages are generated. We are also going to write static layouts, but that is not the main focus of this question. I thought maybe the user community here can share experiences of different frameworks in this context. Are there differences in ease of implementation and what is suitable?

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• How to implement arrays in an interpreter?

  - by Ray

  I have managed to write several interpreters including Tokenizing Parsing, including more complicated expressions such as ((x+y)*z)/2 Building bytecode from syntax trees Actual bytecode execution What I didn't manage: Implementation of dictionaries/lists/arrays. I always got stuck with getting multiple values into one variable. My value structure (used for all values passed around, including variables) looks like this, for example: class Value { public: ValueType type; int integerValue; string stringValue; } Works fine with integers and strings, but how could I implement arrays? (From now on with array I mean arrays in my experimental language, not in C++) How can I fit the array concept into the Value class above? Is it possible? How should I make arrays able to be passed around just as you could pass around integers and strings in my language, using the class above? Accessing array elements or memory allocation wouldn't be the problem, I just don't know how to store them.

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• WCF Business logic handling

  - by Raj

  I have a WCF service that supports about 10 contracts, we have been supporting a client with all the business rules specific to this client now we have another client who will be using the exact same contracts (so we cannot change that) they will be calling the service exactly the same way the previous client called now the only way we can differentiate between the two clients is by one of the input parameters. Based on this input parameter we have to use a slightly different business logic – the logic for both the Client will be same 50% of the time the remainder will have different logic (across Business / DAL layers) . I don’t want to use if else statement in each of contract implementation to differentiate and reroute the logic also what if another client comes in. Is there a clean way of handling a situation like this. I am using framework 3.5. Like I said I cannot change any of the contracts (service / data contract ) or the current service calling infrastructure for the new client. Thanks

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• Java: Set<E> collection, where items are identified by its class

  - by mschayna

  I need Set collection, where its items will be identified by items class. Something like ReferenceIdentityMap from Appache Collections, but on class scope i.e. two different instances of same class must be identified as same in this collection. You know, it is a violation of equals()/hashCode() identity principle but in occasional use it makes sense. I have done this in simple class backing with Map<Class<? extends E>, E>, but due to simplicity it doesn't implement Set<E>. There may be a more elegant solution, decorator of any Set<E> would be great. Is there any implementation of such collection there (Apache/Google/something/... Collections)?

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• Is it possible to create thread-safe collections without locks?

  - by Andrey

  This is pure just for interest question, any sort of questions are welcome. So is it possible to create thread-safe collections without any locks? By locks I mean any thread synchronization mechanisms, including Mutex, Semaphore, and even Interlocked, all of them. Is it possible at user level, without calling system functions? Ok, may be implementation is not effective, i am interested in theoretical possibility. If not what is the minimum means to do it? EDIT: Why immutable collections don't work. This of class Stack with methods Add that returns another Stack. Now here is program: Stack stack = new ...; ThreadedMethod() { loop { //Do the loop stack = stack.Add(element); } } this expression stack = stack.Add(element) is not atomic, and you can overwrite new stack from other thread. Thanks, Andrey

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• I need help translating this portion of the ECMAScript grammar?

  - by ChaosPandion

  I've been working on my own implementation of ECMAScript for quite some time now. I have basically done everything by hand to help gain a deep understanding of the process. Repeated attempts to analyze and understand this portion of the grammar have failed so I've been working on the run time instead. Now I am at a point were I will be working on object literals so I really need to polish my syntactic analyzer. Can anyone put this in terms a language parser novice could understand? My biggest source of confusion is the following: new MemberExpression Arguments This is supposed to be a member expression, but this seemingly conflicts with the following: NewExpression : MemberExpression new NewExpression Is a new expression a member expression or a left hand side expression? To be honest I am having trouble laying out the proper C# classes for the concrete grammar. MemberExpression : PrimaryExpression FunctionExpression MemberExpression [ Expression ] MemberExpression . IdentifierName new MemberExpression Arguments NewExpression : MemberExpression new NewExpression CallExpression : MemberExpression Arguments CallExpression Arguments CallExpression [ Expression ] CallExpression . IdentifierName LeftHandSideExpression : NewExpression CallExpression

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• How to log messages to a log file in a specific path from a bash script

  - by Erik

  How do you log messages to a log file in a specific path from a bash script? A naive implementation would be commands like: echo My message >>/my/custom/path/to/my_script.log But this probably has many disadvantages (no log rotation for example). I could use the 'logger' command, but it does not support logs in custom paths as far as I know and is not easy to configure if you have lots of bash scripts that could use a custom log file. In a scripting language like Ruby all this is quite easy: https://github.com/rudionrails/yell/wiki/101-the-datefile-adapter I could also make my own logger command based on this ruby library and call it from my bash scripts, but I guess there is already a well known solution that provides similar behavior for shell scripts?

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• How to implement a lazy loaded Silverlight data grid without using paging

  - by Marc Wittke

  Using the Business Application template from the brand new released RIA Services, you can see lots of examples using the data grid on top of a DomainDataSource in combination with a DataPager. The properties PageSize and LoadSize can be used to adjust the amount of data to be displayed in one page and the data that is prefetched in the background. Now I'd like to have a data grid with a scrollbar and no pager. The underlying DomainDataSource should load only the data that is diplayed in the grid. It should trigger another load, when the user scrolls down to items that are not yet in the data context. Is there any sample implementation how to do this?

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• JavaScript inheritance

  - by Tower

  Hi, Douglas Crockford seems to like the following inheritance approach: if (typeof Object.create !== 'function') { Object.create = function (o) { function F() {} F.prototype = o; return new F(); }; } newObject = Object.create(oldObject); It looks OK to me, but how does it differ from John Resig's simple inheritance approach? Basically it goes down to newObject = Object.create(oldObject); versus newObject = Object.extend(); And I am interested in theories. Implementation wise there does not seem to be much difference.

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• Comet with ASP.NET AsyncHttpHandlers

  - by Sumit

  I am implementing a comet using AsyncHttpHandlers in my current asp.net application. According to my implementation client initially sends Notification Hook request to server (with its user id) on AsyncHttpHandler, and on server side I maintain a Global (Application level) dictionary of userid(key) and IAynsResult (value). So when ever a request is received to send notification to a user I just pick the matching IAsyncResult from the Global Dictionary and send response to the client user. My concern is, is maintaing a Dictionary of Userid and IAsyncResult at Application level a good design? I feel it will put a lot of load on the server, at the time of high traffic. Is there any other way I can achieve the comet. or what will be the good design to achieve comet for high traffic scenarios.

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• How can I simply "run" lisp files

  - by Annan

  Python When I learned Python I installed it on windows with a nice gui installer and all .py files would automatically run in python, from the command line or explorer. I found this very intuitive and easy, because I could instantly make plain text files and run them. Lisp I'm starting to learn lisp and have decided (from reviews) that SBCL is not a bad lisp implementation. Is there a way to setup SBCL to run .lisp files as easily as with Python? Are there other lisp implementations that have this?

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• Nested class with hidden constructor impossible in c#?

  - by luckyluke

  I' ve been doing some programming lately and faced an issue which i found weird in c#. (at least for me) public class Foo { //whatever public class FooSpecificCollection : List<Bar> { //implementation details } public FooSpecificCollection GetFoosStuff() { //return the collection } } I want the consumer of Foo to be able to obtain a reference to FooSpecificCollection, even perform some operations on it. Maybe even set it to some other property of Foo or smth like that, but not To be able to CREATE an instance of this class. (the only class that should be able to instatiate this collection should be Foo. Is my request really that far-fetched? I know that people way smarter defined c# but shouldn't there be such an option that a parent class can create a nested class instance but nobody else can't. So far I created a solution to make an abstract class, or interface available through the property and implement a concrete private class that is not available anywhere else. Is this a correct way to handle such a situation.?

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• Mapping java.util.Date to xs:date instead of xs:dateTime in JAX-WS

  - by Larsing

  Hi all, We hav an EJB, jws-anotated as a web service. It has a pretty complex pojo-model that generates an equally complex xsd. The pojos contain numerous java.util.Date. These all map to xs:dateTime. This service is used as "business service" in Oracle(BEA) OSB(AquaLogic). We also have a "proxy service" which we map to the BS with XQuery (the OSB/AquaLogic way). The proxy service's xsd has xs:date for the corresponding fields. For some reason, Oracle's implementation of XQuery does not support casting from xs:date to xs:dateTime(!). I could solve this by casting to xs:string and concat:ing with "T00:00:00", however, i would rather try to get JAX-WS to generate an xsd with xs:date instead. Only, I can't find any info on how to do this (anotations?). Can anyone give me a hint? Kind regards, Lars

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• Does std::multiset guarntee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• Are any of these quad-tree libraries any good?

  - by Noctis Skytower

  It appears that a certain project of mine will require the use of quad-trees, something that I have never worked with before. From what I have read they should allow substantial performance enhancements than a brute-force attempt at the problem would yield. Are any of these python modules any good? Quadtree 0.1.2 <= No: unable to execute in Python 3.1 QuadTree <= Yes: simple while working with rectangles quadtree.py <= No: no support for needed operations EDIT: Does anyone know of a better implementation that the one presented on the pygame wiki article?

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• Mixing table per subclass and per hierarchy in hibernate

  - by Xelluloid

  In my database there are two three tables. The first one, table ABSTRACT, holds three columns id, type, someText This table contains all abstract information for the abstract class abstract. Now the two tables CONCRETEONE and CONCRETETWO contain all information for the concrete classes concreteOne and concreteTwo. Now I know I could use the table per subclass strategy from hibernate to create a mapping with inheritance. But as I have a column that marks the type of the concrete implementation could it be possible to create some mixed behaviour like a table per subclass strategy with an discriminator?

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• Does "Value Restriction" mean that there is no higher order functional programming?

  - by Sadache

  Does "Value Restriction" mean that there is no higher order functional programming? I have a problem that each time I try to do a bit of HOP I get caught by a VR error. Example: let simple (s:string)= fun rq->1 let oops= simple "" type 'a SimpleType= F of (int ->'a-> 'a) let get a = F(fun req -> id) let oops2= get "" and I would like to know whether it is a problem of a prticular implementation of VR or it is a general problem that has no solution in a mutable type-infered language that doesn't include mutation in the type system.

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• Events raised by BackgroundWorker not executed on expected thread

  - by Topdown

  A winforms dialog is using BackgroundWorker to perform some asynchronous operations with significant success. On occasion, the async process being run by the background worker will need to raise events to the winforms app for user response (a message that asks the user if they wish to cancel), the response of which captured in an CancelEventArgs type of the event. Being an implementation of threading, I would have expected the RaiseEvent of the worker to fire, and then the worker would continue, hence requiring me to pause the worker until the response is received. Instead however, the worker is held to wait for the code executed by the raise event to complete. It seems like method I am calling via the event call is actually on the worker thread used by the background worker, and I am surprised, since I expected to see it on the Main Thread which is where the mainform is running. Also surprisingly, there are no cross thread exceptions thrown. Can somebody please explain why this is not as I expect?

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• How to instantly termainate an un-supervised script on demand?

  - by errr

  I have a GUI which resembles an interpreter. It allows the user to write a script in Jython (implementation of Python in Java) and run it whenever he wants. Apart from that, I also wish to allow the user to instantly terminate the run whenever he wants. Thing is, I don't really know how to do it. The script is being run on a different Thread, but I don't know of any secure way to stop/interrupt/terminate a thread in the middle of its run, let alone not knowing what is being run by the thread/script (it could be a simple task or maybe some sort of a heavy SQL query against a DB, and a DB is something which requires careful resource handling). How can I instantly terminate such run on demand?

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