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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 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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• 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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• 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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• Clojure: Avoiding stack overflow in Sieve of Erathosthene?

  - by nixx

  Here's my implementation of Sieve of Erathosthene in Clojure (based on SICP lesson on streams): (defn nats-from [n] (iterate inc n)) (defn divide? [p q] (zero? (rem q p))) (defn sieve [stream] (lazy-seq (cons (first stream) (sieve (remove #(divide? (first stream) %) (rest stream)))))) (def primes (sieve (nats-from 2))) Now, it's all OK when i take first 100 primes: (take 100 primes) But, if i try to take first 1000 primes, program breaks because of stack overflow. I'm wondering if is it possible to change somehow function sieve to become tail-recursive and, still, to preserve "streamnes" of algorithm? Any help???

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• create_or_update in ModelForm

  - by ykaganovich

  I want to have a ModelForm that can create_or_update a model instance based on the request parameters. I've been trying to cobble something together, but am realizing that my python fu is not strong enough, and the ModelForm implementation code is a quite hairy. I found this create_or_update snipplet for working with a Model, but I think it would be incredibly useful if it were integrated with a ModelForm. I would expect it to behave similarly to ModelForm.save(): class BetterModelForm(forms.ModelForm): def init(self, *args, **kwargs) def create_or_update(self): #magic return (instance, created, updated) Conversely I'd also be interested in hearing compelling reasons why this is not a good idea.

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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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• 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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• Mapping Hilbert values to 3D points

  - by Alexander Gladysh

  I have a set of Hilbert values (length from the start of the Hilbert curve to the given point). What is the best way to convert these values to 3D points? Original Hilbert curve was not in 3D, so I guess I have to pick by myself the Hilbert curve rank I need. I do have total curve length though (that is, the maximum value in the set). Perhaps there is an existing implementation? Some library that would allow me to work with Hilbert curve / values? Language does not matter much.

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• Will news ticker using overflow:hidden cause Google to see site as spam?

  - by molipix

  In the hope of tempting Googlebot with fresh content, I've implemented a homepage news ticker which displays the 20 most recent headlines on our site. The implementation I have chosen is a <ul> with each headline being a <li> Initially all the <li> elements have no style but Javascript kicks in on page load and gives all but one of them a display="style:none" attribute. Javascript then displays each of the other 19 headlines in a loop. So far so good. However, in order to prevent a visually unplesant page load where the 20 items display and then immediately collapse, I am using overflow:hidden on the <ul> element. Anyone got a view on what Googlebot is likely to make of this? Does the fact that I'm using overflow:hidden make the content look like spam?

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• What is more interesting or powerful: Curry/Mercury/Lambda-Prolog/your suggestion.

  - by Bubba88

  Hi! I would like to ask you about what formal system could be more interesting to implement from scratch/reverse engineer. I've looked through some existing and rather open (open in the sense of free/open-source) projects of logical/declarative programming systems. I've decided to make up something similar in my free time, or at least to catch the general idea of implementation. It would be great if some of these systems would provide most of the expressive power and conciseness of modern academic investigations in logic and it's relation with computational models. What would you recommend to study at least at the conceptual level? For example, Lambda-Prolog is interesting particularly because it allows for higher order relations, but AFAIK (I might really be mistaken :)) is based on intuitionist logic and therefore lack the excluded-middle principle; that's generally a disatvantage for me.. I would also welcome any suggestions about modern logical programming systems which are less popular but more expressive/powerful. I guess, this question will need refactoring, but thank you in advance! :)

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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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• Why is the CoreData stack in XCode's CoreData enabled template treated as private?

  - by rob5408

  In regards to XCode templates with CoreData enabled, I've read http://stackoverflow.com/questions/2729055/unclear-use-of-property-in-window-app-using-core-data which goes over the 'what' in the templates. But I am having an issue with the 'why'. By declaring the category in the implementation file, the CoreData accessors act like private methods. The problem with that is whenever you want to use CoreData elsewhere in your app, you need some extra code. I've figured you need to either supply your own method that exposes the managed object context, such as... - (NSManagedObjectContext *)getManagedObjectContext { return self.managedObjectContext; } ...which will allow other parts of your app to use it. Or you would need to jam pack your app delegate with specific methods to return managed objects, ie getProducts or setUser. Can anyone shed light on the reasoning here?

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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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• Determine if a day of week and time fall in a custom weekend period

  - by Y Low

  I've been trying to come up with a method, that given a day of week and time of day, it will return if it falls under a custom weekend period. The weekend period is saved in 4 variables as follows: The day of week when it starts (0-6) The time of day when it starts (0-23) The day of week when it ends (0-6) The time of day when it ends (0-23) Based on these fields, the weekend period can be anything the user selected (even if it is well beyond a regular weekend) I've been banging this one for awhile but to no avail. I'm trying this in delphi but any language will do, as I'm looking for the algorithm and not the implementation.

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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