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• Typeclass instances for unnamed types in Scala

  - by ncreep

  How would one encode the following constraint in Scala (pseudocode)? def foo(x: T forSome { type T has a Numeric[T] instance in scope }) = { val n= implicitly[...] // obtain the Numeric instance for x n.negate(x) // and use it with x } In words: I need a type class instance for my input argument, but I don't care about the argument's type, I just need to obtain the instance and use it on my argument. It doesn't have to be an existential type, but I need to avoid type parameters in the def's signature. Thanks.

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• How to enforce lazy loading of entities on certain conditions

  - by Samuel

  We have an JPA @Entity class (say User) which has a @ManyToOne reference (say Address) loaded using the EAGER option which in turn loads it's own @ManyToOne fields (say Country) in a EAGER fashion. We use the EntityQuery interface to count the list of User's based on a search criteria, during such a load all the @ManyToOne fields which have been marked as EAGER get loaded. But in order to perform a EntityQuery.resultCount(), I actually don't need to load the @ManyToOne fields. Is there a way to prevent loading of the EAGER fields in such cases so that we can avoid the unnecessary joins?

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• [C#] How to create a constructor of a class that return a collection of instances of that class?

  - by codemonkie

  My program has the following class definition: public sealed class Subscriber { private subscription; public Subscriber(int id) { using (DataContext dc = new DataContext()) { this.subscription = dc._GetSubscription(id).SingleOrDefault(); } } } ,where _GetSubscription() is a sproc which returns a value of type ISingleResult<_GetSubscriptionResult> Say, I have a list of type List<int> full of 1000 ids and I want to create a collection of subscribers of type List<Subscriber>. How can I do that without calling the constructor in a loop for 1000 times? Since I am trying to avoid switching the DataContext on/off so frequently that may stress the database. TIA.

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• Preprocessor directive to test if this is C or C++

  - by Collin

  I'm trying to find a standard macro which will test whether a header file is being compiled as C or as C++. The purpose of this is that the header may be included by either C or C++ code, and must behave slightly differently depending on which. Specifically: In C, I need this to be the code: extern size_t insert (const char*); In C++, I need this to be the code: extern "C" size_t insert (const char*); Additionally, is there a way to avoid putting #ifdef's around every declaration in the header?

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• Passing message over network

  - by Sylvestre Equy

  Hi, I'm currently trying to develop a message-oriented networking framework and I'm a bit stuck on the internal mechanism. Here are the problematic interfaces : public interface IMessage { } public class Connection { public void Subscribe<TMessage>(Action<TMessage> messageCallback); public void Send<TMessage>(TMessage message); } The Send method does not seem complicated, though the mechanism behind Subscribe seems a bit more painful. Obviously when receiving a message on one end of the connection, I'll have to invoke the appropriate delegate. Do you have any advice on how to read messages and easily detect their types ? By the way, I'd like to avoid to use MSMQ.

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• How to organize Windows Phone code base to target both 7.x and 8 platforms

  - by ljubomir

  I took over a Windows Phone project which was previously targeting WP 7.1 platform, and with the recent announcement of the new platform it should target WP 8 as well. My VS 2010 solution consists on several projects (Data access, Model, Tests and WP7 client app) and i am wandering on how to include support for WP8. I have to note that the code-base is not compatible with WP8, due to usage of Toolkit controls and other 3rd party libraries targeted for WP7.1 specifically. Also there is another problem with the Visual Studio versions - WP7.1 can work with VS 2010, but WP8 requires VS 2012. Should i move the whole code-base to VS 2012? Any good advice on how to organize code-base in a most meaningful way in order to avoid duplication and possible painful maintenance? I am thinking between one solution - multiple projects vs. multiple solutions - reusable projects approach. Code duplication (like two separate folders/solutions) should be the least possible approach (fallback).

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• c++ polymorphism and other function question

  - by aharont

  i have got this code: class father{ public: virtual void f() { cout<<1;} }; class son:public father{ public: void f() {cout<<2;} }; void test (father x){x.f();} int main(){ son s; test(s); } the question says: the output is '1', what is the rule about polymorphism that the programmer forgot and how can i fix it so the output would be '2'? there is another rule that the programmer forgot when he wrote the father class, and he need to add an empty function to avoid problems from other sons of the father class. what is the rule and what is the missing function? another question write the g function so the next code would run with no crashes int x=11; g(x)=22;

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• Fatal error: Cannot use string offset as an array

  - by learner

  Array ( [0] = Array ( [auth_id] = 1 [auth_section] = Client Data Base [auth_parent_id] = 0 [auth_admin] = 1 [sub] = Array ( [0] = Array ( [auth_id] = 2 [auth_section] = Client Contact [auth_parent_id] = 1 [auth_admin] = 1 ) ) ) [1] => Array ( [auth_id] => 6 [auth_section] => All Back Grounds [auth_parent_id] => 0 [auth_admin] => ,4 [sub] => Array ( [0] => Array ( [auth_id] => 7 [auth_section] => Edit Custom [auth_parent_id] => 6 [auth_admin] => 1 ) ) ) [2] => Array ( [auth_id] => 20 [auth_section] => Order Mail [auth_parent_id] => 0 [auth_admin] => 1 [sub] => ) } When I process the sub inner array it shows this error how can I avoid that :)

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• Accessing php $_SESSION from python (wsgi) - is it possible?

  - by Bill Zimmerman

  Hi, I've got a python/WSGI app which needs to check to see if a user has logged on to a PHP web app. The problem is that the PHP app checks if a user has logged on by comparing a value in the $_SESSION variable to a value in the cookie from the user's browser. I would prefer to avoid changing the behavior of the php app if at all possible. My questions: Is there anyway I can access the session variables from within python? Where should I start to look? Are there any obvious security/performance issues I should be aware of when taking this approach?

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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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• Fusion Table Layer Caching issue

  - by user1854791

  I have created a series of fusion table layers and apply filtering to one of the layers in response to checkbox click events. The base layer of the map contains a gradient applied over county boundaries. When the base layer is unchecked, the filtered layer loses it's styling. I have added unique timestamps to all queries to avoid caching, however I get the feeling that these image tiles are still be cached for this situation. Is there any way to force the google fusion tables api to invalidate a cached image? Test site here: http://map.inquestmarketing.com/new.html Unchecking the Other - Consumer Prospects checkbox reproduces the issue. This is a pure client app, all of the source is in the single page.

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• Can a function defined in a bookmarklet be called from a page-level script?

  - by Soviut

  I have a bookmarklet that needs to open a new window/tab. In order to avoid the popup blocker, I need to call the window.open() method directly in the bookmarklet ie: at the browser-level. However, I want to keep the bookmarklet updatable by loading external Javascript files. To do this, the bookmarklet needs to append script nodes to the DOM. If i were to put window.open() code in one of these externally loaded scripts, the popup blocker would block it since its page-level. What I want to know is if I can create a wrapper function around window.open() in my bookmarklet, then call it from the externally loaded script? What is the scope and what are the permissions on a wrap such as this?

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• database row/ record pointers

  - by David

  Hi I don't know the correct words for what I'm trying to find out about and as such having a hard time googling. I want to know whether its possible with databases (technology independent but would be interested to hear whether its possible with Oracle, MySQL and Postgres) to point to specific rows instead of executing my query again. So I might initially execute a query find some rows of interest and then wish to avoid searching for them again by having a list of pointers or some other metadata which indicates the location on a database which I can go to straight away the next time I want those results. I realise there is caching on databases, but I want to keep these "pointers" else where and as such caching doesn't ultimately solve this problem. Is this just an index and I store the index and look up by this? most of my current tables don't have indexes and I don't want the speed decrease that sometimes comes with indexes. So whats the magic term I've been trying to put into google? Cheers

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• Is the "message" of an exception culturally independent?

  - by Ray Hayes

  In an application I'm developing, I have the need to handle a socket-timeout differently from a general socket exception. The problem is that many different issues result in a SocketException and I need to know what the cause was. There is no inner exception reported, so the only information I have to work with is the message: "A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond" This question has a general and specific part: is it acceptable to write conditional logic based upon the textual representation of an exception? Is there a way to avoid needing exception handling? Example code below... try { IPEndPoint endPoint = null; client.Client.ReceiveTimeout = 1000; bytes = client.Receive(ref endPoint); } catch( SocketException se ) { if ( se.Message.Contains("did not properly respond after a period of time") ) { // Handle timeout differently.. } }

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• What's the easiest way to implement background downloading in Wicket?

  - by David Moles

  I've got a simple Wicket form that lets users select some data and then download a ZIP file (generated on the fly) containing what they asked for. Currently the form button's onSubmit() method looks something like this: public void onSubmit() { IResourceStream stream = /* assemble the data they asked for ... */ ; ResourceStreamRequestTarget target = new ResourceStreamRequestTarget(stream); target.setFileName("download.zip"); RequestCycle.get().setRequestTarget(target); } This works, but of course the request stops there and it's impossible to display any other feedback to the user. What I'd like to have is something like the typical "Your requested download [NAME] should begin automatically. If not, click this link." Ideally, still displaying the same page, so the user can immediately select some different data and download that as well. I imagine it's possible to do this using Wicket's Ajax classes, but I've managed to avoid having to use them so far, and it's not immediately obvious to me how. What's my quickest way out, here?

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• Is it a good practice to create a reference to application context and use it anywhere?

  - by kknight

  I have to use context in many places of my code such as database operations, preference operations, etc. I don't want to pass in context for every method. Is it a good practice to create a reference to application context at the main Activity and use it anywhere such as database operations? So, I don't need some many context in method parameters, and the code can avoid position memory leak due to use of Activity Context. public class MainActivity extends Activity { public static Context s_appContext; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); s_appContext = this.getApplicationContext();

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• Multivalue parametres in SSRS- display in the report

  - by pfeffer

  I just started working with SSRS, so this question might seem silly. Anyway, for now I'm trying to avoid multi-valued parameters, because I want my parameters to be able to be NULL. So I'm just passing a comma-separated string of ID values to my stored procedure, and everything works. The problem I encountered is that I want to display the actual values, not IDs, in the report, so that users can see, what filter was used. If that were a multi-valued parameter, I would simply use JOIN function, but now I am out of ideas and would really appreciate some help. Thanks!

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• Enterprise Library Validation Block - Should validation be placed on class or interface?

  - by Robert MacLean

  I am not sure where the best place to put validation (using the Enterprise Library Validation Block) is? Should it be on the class or on the interface? Things that may effect it Validation rules would not be changed in classes which inherit from the interface. Validation rules would not be changed in classes which inherit from the class. Inheritance will occur from the class in most cases - I suspect some fringe cases to inherit from the interface (but I would try and avoid it). The interface main use is for DI which will be done with the Unity block.

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• How to match the word in jquery

  - by Mirage

  I have the image and i am fade in and fade out the image on click. But i want that if the same is present then it should not fadein/fadeout. My jquery code is switch(current_id) { case 'l1': $("#left_img img").fadeOut(500, function() { $(this).attr("src","rrr.gif").load( function() { $(this).fadeIn(500); }); }); break; case 'l3': $("#left_img img").fadeOut(500, function() { $(this).attr("src","cc1.gif").load( function() { $(this).fadeIn(500); }); }); break; If i click on link 1 then image A appears with fade effect. but if i click again link 1 agan , then again i see fade effect . Is there any way i can avoid that if same link is clicked again

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• Status corresponding to Minimum value

  - by Lijo

  Hi Team, I am using SQL Server 2005. I have a table as given below. There can be multiple cancellations for each FundingID. I want to select the FundingCancellationReason corrersponding to minimum date for each funding. I wrote a query as follows. It is an SQL error 1) Could you please help me to avoid the SQL Error? 2) Is there any better logic to achieve the same? CREATE TABLE #FundingCancellation( [FundingCancellationID] INT IDENTITY(1,1) NOT NULL, [FundingID] INT , FundingCancellationDt SMALLDATETIME , FundingCancellationReason VARCHAR(50) ) SELECT FundingID, MIN(FundingCancellationDt), ( SELECT FundingCancellationReason FROM #FundingCancellation FC2 WHERE FC1.FundingID = FC2.FundingID AND FC2.FundingCancellationDt = MIN(FundingCancellationDt) ) [Reason Corresponding Minimum Date] FROM #FundingCancellation FC1 GROUP BY FundingID -- An aggregate may not appear in the WHERE clause unless it is in a subquery contained in a HAVING clause or a select list, and the column being aggregated is an outer reference. I have seen the similar approach working in a somewhat complex query. So I believe tehre will be a way to correct my query Thanks Lijo

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• jqGrid: Is it possible to commit a cell change when tabbing off instead of pressing Enter?

  - by The Matt

  I have a simple in-line edit in my grid, and I want to commit the change when the user tabs off the textbox. The default behavior of jqGrid forces the user to press 'Enter' to commit the change, but this is non-intuitive for our users. onSelectRow: function(id) { $(gridCoreGroups).editRow(id, true, undefined, function(response) { alert("hello world"); } } I've worked my way through the events provided, but they all happen as a result of the user pressing 'Enter', which I want to avoid. Is there something I can wire up that would trigger an action when the user tabs off this cell?

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• Get previous element in IObservable without re-evaluating the sequence

  - by dcstraw

  In an IObservable sequence (in Reactive Extensions for .NET), I'd like to get the value of the previous and current elements so that I can compare them. I found an example online similar to below which accomplishes the task: sequence.Zip(sequence.Skip(1), (prev, cur) => new { Previous = prev, Current = cur }) It works fine except that it evaluates the sequence twice, which I would like to avoid. You can see that it is being evaluated twice with this code: var debugSequence = sequence.Do(item => Debug.WriteLine("Retrieved an element from sequence")); debugSequence.Zip(debugSequence.Skip(1), (prev, cur) => new { Previous = prev, Current = cur }).Subscribe(); The output shows twice as many of the debug lines as there are elements in the sequence. I understand why this happens, but so far I haven't found an alternative that doesn't evaluate the sequence twice. How can I combine the previous and current with only one sequence evaluation?

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• How to synchronize two (or n) replication processes for MS SQL databases?

  - by Yauheni Sivukha

  There are two master databases and two read-only copies updated by standard transactional replication. It is needed to map some entity from both read-only databases, lets say that A databases contains orders and B databases contains lines. The problem is that replication to one database can lag behind replication of second database, and at the moment of mapping R-databases will have inconsistent data. For example. We stored 2 orders with lines at 19:00 and 19:03. Mapping process started at 19:05, but to the moment of mapping A database replication processed all changes up to 19:03, but B database replication processed only changes up to 19:00. After mapping we will have order entity with order as of 19:03 and lines as of 19:00. The troubles are guaranteed:) In my particular case both databases have temporal model, so it is possible to fetch data for every time slice, but the problem is to identify time of latest replication. Question: How to synchronize replication processes for several databases to avoid situation described above?

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• how to call a C++ dll from C# windows application project

  - by chathuradd

  I have created a dll in C++ using a Class Library project in Visual Studio. I need to call a method in the dll from a C# application. I got to know there are 2 approches. One is to add the dll project reference to C# project or use DllExport to export method. However when I tried in both ways it always gives the following error when the dll method is called in runtime. An unhandled exception of type 'System.BadImageFormatException' occurred in TestClient.exe Additional information: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B) Can i know how to avoid this problem ? Thanks in advance!

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