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• Determine asymmetric latencies in a network

  - by BeeOnRope

  Imagine you have many clustered servers, across many hosts, in a heterogeneous network environment, such that the connections between servers may have wildly varying latencies and bandwidth. You want to build a map of the connections between servers my transferring data between them. Of course, this map may become stale over time as the network topology changes - but lets ignore those complexities for now and assume the network is relatively static. Given the latencies between nodes in this host graph, calculating the bandwidth is a relative simply timing exercise. I'm having more difficulty with the latencies - however. To get round-trip time, it is a simple matter of timing a return-trip ping from the local host to a remote host - both timing events (start, stop) occur on the local host. What if I want one-way times under the assumption that the latency is not equal in both directions? Assuming that the clocks on the various hosts are not precisely synchronized (at least that their error is of the the same magnitude as the latencies involved) - how can I calculate the one-way latency? In a related question - is this asymmetric latency (where a link is quicker in direction than the other) common in practice? For what reasons/hardware configurations? Certainly I'm aware of asymmetric bandwidth scenarios, especially on last-mile consumer links such as DSL and Cable, but I'm not so sure about latency. Added: After considering the comment below, the second portion of the question is probably better off on serverfault.

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• C++ reference variable again!!!

  - by kumar_m_kiran

  Hi All, I think most would be surprised about the topic again, However I am referring to a book "C++ Common Knowledge: Essential Intermediate Programming" written by "Stephen C. Dewhurst". In the book, he quotes a particular sentence (in section under Item 5. References Are Aliases, Not Pointers), which is as below A reference is an alias for an object that already exists prior to the initialization of the reference. Once a reference is initialized to refer to a particular object, it cannot later be made to refer to a different object; a reference is bound to its initializer for its whole lifetime Can anyone please explain the context of "cannot later be made to refer to a different object" Below code works for me, #include <iostream> using namespace std; int main(int argc, char *argv[]) { int i = 100; int& ref = i; cout<<ref<<endl; int k = 2000; ref = k; cout<<ref<<endl; return 0; } Here I am referring the variable ref to both i and j variable. And the code works perfectly fine. Am I missing something? I have used SUSE10 64bit linux for testing my sample program. Thanks for your input in advance.

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• Can I strictly evaluate a boolean expression stored as a string in Java?

  - by D Lawson

  I would like to be able to evaluate an boolean expression stored as a string, like the following: "hello" == "goodbye" && 100 < 101 I know that there are tons of questions like this on SO already, but I'm asking this one because I've tried the most common answer to this question, BeanShell, and it allows for the evaluation of statements like this one "hello" == 100 with no trouble at all. Does anyone know of a FOSS parser that throws errors for things like operand mismatch? Or is there a setting in BeanShell that will help me out? I've already tried Interpreter.setStrictJava(true). Here's the code that I'm using currently: Interpreter interpreter = new Interpreter(); interpreter.setStrictJava(true); String testableCondition = "100 == \"hello\""; try { interpreter.eval("boolean result = ("+ testableCondition + ")"); System.out.println("result: "+interpreter.get("result")); if(interpreter.get("result") == null){ throw new ValidationFailure("Result was null"); } } catch (EvalError e) { e.printStackTrace(); throw new ValidationFailure("Eval error while parsing the condition"); }

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• UpdateModelFromDatabaseException when trying to add a table to Entity Framework model

  - by Agent_9191

  I'm running into a weird issue with Entity Framework in .NET 3.5 SP1 within Visual Studio 2008. I created a database with a few tables in SQL Server and then created the associated .edmx Entity Framework model and had no issues. I then created a new table in the database that has a foreign key to an existing table and needed to be added to the .edmx. So I opened the .edmx in Visual Studio and in the models right-clicked and chose "Update Model From Database...". I saw the new table in the "add" tab, so I checked it and clicked finish. However I get an error message with the following text: --------------------------- Microsoft Visual Studio --------------------------- An exception of type 'Microsoft.Data.Entity.Design.Model.Commands.UpdateModelFromDatabaseException' occurred while attempting to update from the database. The exception message is: 'Cannot update from the database. Cannot resolve the Name Target for ScalarProperty 'ID <==> CustomerID'.'. --------------------------- OK --------------------------- For reference, here's the tables seem to be the most pertinent to the error. CustomerPreferences already exists in the .edmx. Diets is the table that was added afterwards and trying to add to the .edmx. CREATE TABLE [dbo].[CustomerPreferences]( [ID] [uniqueidentifier] NOT NULL, [LastUpdatedTime] [datetime] NOT NULL, [LastUpdatedBy] [uniqueidentifier] NOT NULL, PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] CREATE TABLE [dbo].[Diets]( [ID] [uniqueidentifier] NOT NULL, [CustomerID] [uniqueidentifier] NOT NULL, [Description] [nvarchar](50) NOT NULL, [LastUpdatedTime] [datetime] NOT NULL, [LastUpdatedBy] [uniqueidentifier] NOT NULL, PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO ALTER TABLE [dbo].[Diets] WITH CHECK ADD CONSTRAINT [FK_Diets_CustomerPreferences] FOREIGN KEY([CustomerID]) REFERENCES [dbo].[CustomerPreferences] ([ID]) GO ALTER TABLE [dbo].[Diets] CHECK CONSTRAINT [FK_Diets_CustomerPreferences] GO This seems like a fairly common use case, so I'm not sure where I'm going wrong.

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• Django Save Incomplete Progress on Form

  - by jimbob

  I have a django webapp with multiple users logging in and fill in a form. Some users may start filling in a form and lack some required data (e.g., a grant #) needed to validate the form (and before we can start working on it). I want them to be able to fill out the form and have an option to save the partial info (so another day they can log back in and complete it) or submit the full info undergoing validation. Currently I'm using ModelForm for all the forms I use, and the Model has constraints to ensure valid data (e.g., the grant # has to be unique). However, I want them to be able to save this intermediary data without undergoing any validation. The solution I've thought of seems rather inelegant and un-django-ey: create a "Save Partial Form" button that saves the POST dictionary converts it to a shelf file and create a "SavedPartialForm" model connecting the user to partial forms saved in the shelf. Does this seem sensible? Is there a better way to save the POST dict directly into the db? Or is an add-on module that does this partial-save of a form (which seems to be a fairly common activity with webforms)? My biggest concern with my method is I want to eventually be able to do this form-autosave automatically (say every 10 minutes) in some ajax/jquery method without actually pressing a button and sending the POST request (e.g., so the user isn't redirected off the page when autosave is triggered). I'm not that familiar with jquery and am wondering if it would be possible to do this.

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• How often should network traffic/collisions cause SNMP Sets to fail?

  - by A. Levy

  My team has a situation where an SNMP SET will fail once every two weeks or so. Since this set happens automatically, we don't necessarily notice it immediately when it fails, and this can result in an inconsistent configuration and associated wailing and gnashing of teeth. The plan is to fix this by having our software automatically retry the SET when it fails. The problem is, we aren't sure why the failure is happening. My (extremely limited) knowledge of SNMP isn't particularly helpful in diagnosing this problem, so I thought I'd ask StackOverflow for some advice. We think that every so often a spike in network traffic will cause the SET to fail. Since SNMP uses UDP for communication, I would think it would be relatively easy for a command to be drowned out if traffic was high for a short period of time. However, I have no idea how common this is. We have a small network with a single cisco router and there are less than a dozen SNMP controlled devices on that network. In addition to the SNMP traffic, there are some status web pages being loaded from the various devices. In case it makes a difference, I believe we are using the AdventNet SNMP API version 4.0.4 for Java. Does it sound reasonable that there will be some SET commands dropped occasionally, or should we be looking for other causes?

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• Create a function to a function that runs a for loop?

  - by user637364

  Hi, I have made some code that creates a red border around an image when the user click on to highlite thats the choesen one. But I want to erase previous or all border with a white border around all images before a new click is made on another image. My question is how do I activate a call to a function when a click is made and how would a function look in jQuery? I just whant to use the .css to change the border in perhaps a loop and change the id of the images? Can I mix common javascript with jQuery, or should it only be pure jQuery code in a script? This is a simplified part of the code, it contains "minibild_1" to "minibild_5" $(document).ready(function(){ $("#minibild_1").click(function(){ $("#minibild_1").css({"border":"2px solid #D00C33"}); $("#storbild").attr("src","../bilder/bilder_stora/{$row1-bild_1}.jpg"); }); $("#minibild_2").click(function(){ $("#minibild_2").css({"border":"2px solid #D00C33"}); $("#storbild").attr("src","../bilder/bilder_stora/{$row1-bild_2}.jpg"); }); });

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• JavaScript for loop index strangeness

  - by pythonBOI

  I'm relatively new to JS so this may be a common problem, but I noticed something strange when dealing with for loops and the onclick function. I was able to replicate the problem with this code: <html> <head> <script type="text/javascript"> window.onload = function () { var buttons = document.getElementsByTagName('a'); for (var i=0; i<2; i++) { buttons[i].onclick = function () { alert(i); return false; } } } </script> </head> <body> <a href="">hi</a> <br /> <a href="">bye</a> </body> </html> When clicking the links I would expect to get '0' and '1', but instead I get '2' for both of them. Why is this? BTW, I managed to solve my particular problem by using the 'this' keyword, but I'm still curious as to what is behind this behavior.

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• Risky Business with LINQ to SQL and OR Designer?

  - by Toadmyster

  I have two tables with a one to many relationship in SQL 2008. The first table (BBD) PK | BBDataID | int       | Floor_Qty | tinyint       | Construct_Year | char(4)       | etc, etc describes the data common to all buildings and the second (BBDCerts) PK | BBDCertsID | int       | BBDataID | int       | Certification_Type | varchar(20)       | etc, etc is a collection of certifications for a particular building. Thus, the primary key in BBD (BBDataID) is mapped to the corresponding field in BBDCerts via an FK relationship, but BBDCertsID is the second table's primary key and BBDataID is not because it will not be unique. My problem is that I want to be able to use the OR generated data context to get at the list of certs when I access a particular record in the BBD table. For instance: Dim vals = (From q in db.BBD Where q.BBDataID = x Select q.Floor_Qty, q.Construct_Year, q.BBDCerts).SingleOrDefault and later be able to access a particular certification like this: vals.BBDCerts.Certification_Type.First Now, the automatic associations created when the SQL tables are dropped on the design surface don't generate the EntityRef associations that are needed to access the other table using the dot notation. So, I have to use the OR designer to make the BBDCerts BBDataID a primary key (this doesn't affect the actual database), and then manually change the association properties to the appropriate OneToMany settings. There might be a better way to approach this solution but my question is, is the way I've done it safe? I've done a barrage of tests and the correct cert is referenced or updated every time. Frankly, the whole thing makes me nervous.

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• License of popular dictionary word lists (e.g. SOWPODS, TWL)? Copyright? Trademarks?

  - by BobbyJim

  (I'm not sure if this off-topic. I found a lot of voted-up questions about software licenses and this is related. Plus, I'm sure many of us have had the situation that we need to use a dictionary in our code) I'm making a (maybe commercial) word game and need to use a good word dictionary for checking words. The most common dictionaries to use are the SOWPODS or TWL lists that are used Scrabble tournaments; see here: http://www.scrabblist.com/ (I have nothing to do with this site by the way). I've seen loads of websites offering these two dictionaries for download and loads of word games advertise that they use them. However, I cannot find any licensing terms attached to these dictionaries wherever I download them. For the players of my game, I'd want to say what dictionary I'm using (e.g. "this game uses SOWPODS"). However, I'm nervous about what I can do legally. Does anyone know about if you can copyright lists of words? Does anyone know the licenses of TWL and SOWPODS? TWL and SOWPODS don't seem to have trademarks on them but I'd like to know for sure. I cannot find any good sources for this information. EDIT: Great, now the top result for "SOWPODS license" is my stackoverflow question. :)

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• How to accommodate for the next iPhones totally different screen resolution?

  - by mystify

  This is a programming question! Read on before you vote to close! According to Gizmodo, the next iPhone will have a new screen resolution: The 3.5-inch screen has a resolution of 960?×?640 pixels This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most -if not all- developers do is: They designed everything in such a way, that a touchable area is -for example- 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen - let's say the center, or somewhere at the bottom. So the big question is: How will the developers compensate their layout and graphics? Are there already solutions which can be used to calculate coordinates and sizes in a normalized manner, which then appear to be exactly the same when viewing them on a screen of any resolution, assuming at least that the aspect ration won't change? This is community wiki. Just add anything that you think is relevant to this huge problem (constant screen res was one of the main reasons why I didn't go for Android!!).

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• How to acheieve this kind of behaviour in asp.net mvc

  - by kumar

  Hello Friends,, I have this two Action result methods. public ActionResult GetStudentInfo(StudentBE s) { return PartialView("editStudent", s); } public ActionResult GenericList() { StudentBE codes = new StudentBE(); codes.lookcodes= GetStudentCodes(new string[] { "A", "B", "C, "D", "E" }); return PartialView(codes); } // Lookcodes display dropdownlist boxes in the GeneridList view.. In genericList view I hvae beginForm.. <% using (Html.BeginForm("Updatestudent", "expense", FormMethod.Post, new { @id = "id" })) { %> <% } %> so My updatestudent method is [HttpPost] public JsonResult Updatestudent(StudentBE e) { var status = common.Update(e.student); } } return Json(status.ToString()); } Here is my problem.. the GetStudentInfo Actionresult is having each student information.. in UpdateStudent method Update Method calls the DB calls for stored procedure to update each user information now to update each user I need to call GetstudentInfo each time to get student information to update..? how to call GetStudentInfo method here to get studentinformation? student informatin may be multiple that is more than one student informaton... can anybody help me out.. thanks

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• Checked and Unchecked operators don't seem to be working when...

  - by flockofcode

  1) Is UNCHECKED operator in effect only when expression inside UNCHECKED context uses an explicit cast ( such as byte b1=unchecked((byte)2000); ) and when conversion to particular type can happen implicitly? I’m assuming this since the following expression throws a compile time error: byte b1=unchecked(2000); //compile time error 2) a) Do CHECKED and UNCHECKED operators work only when resulting value of an expression or conversion is of an integer type? I’m assuming this since in the first example ( where double type is being converted to integer type ) CHECKED operator works as expected: double m = double.MaxValue; b=checked((byte)m); // reports an exception , while in second example ( where double type is being converted to a float type ) CHECKED operator doesn’t seem to be working. since it doesn't throw an exception: double m = double.MaxValue; float f = checked((float)m); // no exception thrown b) Why don’t the two operators also work with expressions where type of a resulting value is of floating-point type? 2) Next quote is from Microsoft’s site: The unchecked keyword is used to control the overflow-checking context for integral-type arithmetic operations and conversions I’m not sure I understand what exactly have expressions and conversions such as unchecked((byte)(100+200)); in common with integrals? Thank you

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• Tracking a fragment of a file in two places with git

  - by mabraham

  Hi, I have code such as void myfunc() { introduction(); while(condition()) { complex(); loop(); interior(); code(); } cleanup(); } which I wish to duplicate into two versions, viz: void myfuncA() { introduction(); minorchangeA(); while(condition()) { complex(); loop(); interior(); code(); } cleanup(); } void myfuncB() { introduction(); minorchangeB(); while(condition()) { complex(); modifiedB(); loop(); interior(); code(); } cleanup(); extracleanupB(); } git claims to track content rather than files, so do I need to tell it that there are chunks here that are common to both myfuncA and myfuncB so that when merging with upstream changes to myfunc that those changes should propagate to both myfuncA and myfuncB? If so, how? The code could be written so that myfuncAB did the correct thing at each point by testing for condition A or B, but that could seriously hinder readability or performance.

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• multi-threading in MFC

  - by kiddo

  Hello all,in my application there is a small part of function,in which it will read files to get some information,the number of filecount would be utleast 50,So I thought of implementing threading.Say if the user is giving 50 files,I wanted to separate it as 5 *10, 5 thread should be created,so that each thread can handle 10 files which can speed up the process.And also from the below code you can see that some variables are common.I read some articles about threading and I am aware that only one thread should access a variable/contorl at a me(CCriticalStiuation can be used for that).For me as a beginner,I am finding hard to imlplement what I have learned about threading.Somebody please give me some idea with code shown below..thanks in advance file read function:// void CMyClass::GetWorkFilesInfo(CStringArray& dataFilesArray,CString* dataFilesB, int* check,DWORD noOfFiles,LPWSTR path) { CString cFilePath; int cIndex =0; int exceptionInd = 0; wchar_t** filesForWork = new wchar_t*[noOfFiles]; int tempCheck; int localIndex =0; for(int index = 0;index < noOfFiles; index++) { tempCheck = *(check + index); if(tempCheck == NOCHECKBOX) { *(filesForWork+cIndex) = new TCHAR[MAX_PATH]; wcscpy(*(filesForWork+cIndex),*(dataFilesB +index)); cIndex++; } else//CHECKED or UNCHECKED { dataFilesArray.Add(*(dataFilesB+index)); *(check + localIndex) = *(check + index); localIndex++; } } WorkFiles(&cFilePath,dataFilesArray,filesForWork, path, cIndex); dataFilesArray.Add(cFilePath); *(check + localIndex) = CHECKED; }

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• Finding patterns of failure in a Unit Test

  - by Pekka

  I'm new to Unit Testing, and I'm only getting into the routine of building test suites. I have what is going to be a rather large project that I want to build tests for from the start. I'm trying to figure out general strategies and patterns for building test suites. When you look at a class, many tests come to you obviously due to the nature of the class. Say for a "user account" class with basic CRUD operations, being related to a database table, we will want to test - well, the CRUD. creating an object and seeing whether it exists query its properties change some properties change some properties to incorrect values and delete it again. As for how to break things, there are "fail" tests common to most CRUD classes like: Invalid input data types A number as the ID key that exceeds the range of the chosen data type Input in an incorrect character encoding Input that is too long And so on and so on. For a unit test concerned with file operations, the list of "breaking things" could be Invalid characters in file name File name too long File name uses incorrect protocol or path I'm pretty sure similar patterns - applicable beyond the unit test one is currently working on - can be found for most units that are being tested. Now my question is: Am I correct in seeing such "breaking patterns"? Or am I getting something completely wrong about Unit testing, and if I did it right, this wouldn't be an issue at all? Is Unit Testing as a process of finding as many ways to break the unit as possible the right way to go? If I am correct: Are there existing definitions, lists, cheat sheets for such patterns? Are there any provisions (mainly in PHPUnit, as that's the framework I'm working in) to automate such patterns? Is there any assistance - in the form of check lists, or software - to aid in writing complete tests?

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• Large free block of english non-pronoun text

  - by Tom

  As part of teaching myself python I've written a script which allows a user to play hangman. At the moment, the hangman word to be guessed is simply entered manually at the start of the script's code. I want instead for the script to choose randomly from a large list of english words. This I know how to do - my problem is finding that list of words to work from in the first place. Does anyone know of a source on the net for, say, 1000 common english words where they can be downloaded as a block of text or something similar that I can work with? (My initial thought was grabbing a chunk of a novel from project gutenburg [this project is only for my own amusement and won't be available anywhere else so copyright etc doesn't matter hugely to me btw], but anything like that is likely to contain too many names or non-standard words that wouldn't be suitable for hangman. I need text that only has words legal for use in scrabble, basically). It's a slightly odd question for here I suppose, but actually I thought the answer might be of use not just to me but anyone else working on a project for a wordgame or similar that needs a large seed list of words to work from. Many thanks for any links or suggestions :)

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• Permission Denied error in IE when closing popups

  - by Kenia

  Hi everyone! I have a simple web testing application which is supposed to open and close several popups by itself (without user interaction). For this purpose i have a javascript function to access the variable where the popup reference is stored and close it if it´s not null, fairly simple. However I get random errors in IE (in FF it works as expected, all popups are closed correctly) like Message: No such interface supported Line: 86 Char: 3 Code: 0 URI: http://10.10.0.61:10000/savmailer/adm/tests/common_tests_code.js and Message: Permission denied Line: 86 Char: 3 Code: 0 URI: http://10.10.0.61:10000/savmailer/adm/tests/common_tests_code.js The line 86 references exactly the point at which I do popup.close(); in the following function function closePopupWindow(popup){ if (popup != null) { popup.close(); popup = null; } } I have googled and it seems this permission denied error is quite common to come through among IE developers, however there´s no clear solution for it, it´s just a matter of changing the code slightly "to please" IE, so to speak. However i have no idea how to change mine since it´s just 3 lines! Tried also to change the security browser settings by adding my domain to the trusted zone, but nothing, doesn't help either. If anyone has any helpful idea or notices something i might be forgetting, please, reply to this! Thanks in advance, Kenia

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• log activity. intrusion detection. user event notification ( interraction ). messaging

  - by Julian Davchev

  Have three questions that I somehow find related so I put them in same place. Currently building relatively large LAMP system - making use of messaging(activeMQ) , memcache and other goodies. I wonder if there are best practices or nice tips and tricks on howto implement those. System is user aware - meaning all actions done can be bind to particular logged user. 1. How to log all actions/activities of users? So that stats/graphics might be extracted later for analysing. At best that will include all url calls, post data etc etc. Meaning tons of inserts. I am thinking sending messages to activeMQ and later cron dumping in DB and cron analysing might be good idea here. Since using Zend Framework I guess I may use some request plugin so I don't have to make the log() call all over the code. 2.How to log stuff so may be used for intrusion detection? I know most things might be done on http level using apache mods for example but there are also specific cases like (5 failed login attempts in a row (leads to captcha) etc etc..) This also would include tons of inserts. Here I guess direct usage of memcache might be best approach as data don't seem vital to be permanantly persisted. Not sure if cannot use data from point 1. 3.System will notify users of some events. Like need approval , something broke..whatever.Some events will need feedback(action) from user, others are just informational. Wonder if there is common solutions for needs like this. Example: Based on occuring event(s) user will be notifed (user inbox for example) what happend. There will be link or something to lead him to details of thingy that happend and take action accordingly. Those seem trivial at first look but problem I see if coding it directly is becoming really fast hard to maintain.

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• Reference remotely located assembly (web uri) from locally installed application?

  - by moonground.de

  Hi Stackoverflowers! :) We have a .NET application for Windows which is installed locally by Microsoft Installer. Now we have the need to use additional assemblies which are located online at our Web Servers. We'd like to refer to a remote uri like https://www.ourserver.com/OurProductName/ExternalLib.dll and reveal additional functionality, which is described roughly by a known common ("AddIn/Plugin") Interface. These are not 3rd Party Plugins, we just want be able to exchange parts of the application frequently, without the need to have frequent software updates. Our first idea was to add some kind of "remote refence" in Visual Studio by setting the path to the remote assembly uri. But Visual Studio downloaded the assembly immediately to a temporary directory, adding a reference to it. Our second attempt then, is simply using a WebRequest (or WebClient) to retrieve a binary stream of the Assembly, loading it "from image" by using Assembly.Load(...). This actually works, but is not very elegant and requires more additional programming for verification etc. We hoped Clickonce would provide useful techniques but apparently it's suitable for standalone applications only. (Correct me?) Is there a way (.net native or by framework/api) to reference remotely located assemblies? Thanks in advance and have a happy easter!

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• [c++] accessing the hidden 'this' pointer

  - by Kyle

  I have a GUI architecture wherein elements fire events like so: guiManager->fireEvent(BUTTON_CLICKED, this); Every single event fired passes 'this' as the caller of the event. There is never a time I dont want to pass 'this', and further, no pointer except for 'this' should ever be passed. This brings me to a problem: How can I assert that fireEvent is never given a pointer other than 'this', and how can I simplify (and homogenize) calls to fireEvent to just: guiManager->fireEvent(BUTTON_CLICKED); At this point, I'm reminded of a fairly common compiler error when you write something like this: class A { public: void foo() {} }; class B { void oops() { const A* a = new A; a->foo(); } }; int main() { return 0; } Compiling this will give you ../src/sandbox.cpp: In member function ‘void B::oops()’: ../src/sandbox.cpp:7: error: passing ‘const A’ as ‘this’ argument of ‘void A::foo()’ discards qualifiers because member functions pass 'this' as a hidden parameter. "Aha!" I say. This (no pun intended) is exactly what I want. If I could somehow access the hidden 'this' pointer, it would solve both issues I mentioned earlier. The problem is, as far as I know you can't (can you?) and if you could, there would be outcries of "but it would break encapsulation!" Except I'm already passing 'this' every time, so what more could it break. So, is there a way to access the hidden 'this', and if not are there any idioms or alternative approaches that are more elegant than passing 'this' every time?

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• Writing a generic function that can take a Writer as well as an OutputStream

  - by ebruchez

  I wrote a couple of functions that look like this: def myWrite(os: OutputStream) = {} def myWrite(w: Writer) = {} Now both are very similar and I thought I would try to write a single parametrized version of the function. I started with a type with the two methods that are common in the Java OutputStream and Writer: type Writable[T] = { def close() : Unit def write(cbuf: Array[T], off: Int, len: Int): Unit } One issue is that OutputStream writes Byte and Writer writes Char, so I parametrized the type with T. Then I write my function: def myWrite[T, A[T] <: Writable[T]](out: A[T]) = {} and try to use it: val w = new java.io.StringWriter() myWrite(w) Result: <console>:9: error: type mismatch; found : java.io.StringWriter required: ?A[ ?T ] Note that implicit conversions are not applicable because they are ambiguous: both method any2ArrowAssoc in object Predef of type [A](x: A)ArrowAssoc[A] and method any2Ensuring in object Predef of type [A](x: A)Ensuring[A] are possible conversion functions from java.io.StringWriter to ?A[ ?T ] myWrite(w) I tried a few other combinations of types and parameters, to no avail so far. My question is whether there is a way of achieving this at all, and if so how. (Note that the implementation of myWrite will need, internally, to know the type T that parametrizes the write() method, because it needs to create a buffer as in new ArrayT.)

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• Monads with Join() instead of Bind()

  - by MathematicalOrchid

  Monads are usually explained in turns of return and bind. However, I gather you can also implement bind in terms of join (and fmap?) In programming languages lacking first-class functions, bind is excruciatingly awkward to use. join, on the other hand, looks quite easy. I'm not completely sure I understand how join works, however. Obviously, it has the [Haskell] type join :: Monad m = m (m x) - m x For the list monad, this is trivially and obviously concat. But for a general monad, what, operationally, does this method actually do? I see what it does to the type signatures, but I'm trying to figure out how I'd write something like this in, say, Java or similar. (Actually, that's easy: I wouldn't. Because generics is broken. ;-) But in principle the question still stands...) Oops. It looks like this has been asked before: Monad join function Could somebody sketch out some implementations of common monads using return, fmap and join? (I.e., not mentioning >>= at all.) I think perhaps that might help it to sink in to my dumb brain...

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• Creating a join based on data from other tables...

  - by Workshop Alex

  I'm dealing with a database structure that can be defined as "illogical". It has about 100 different schema's with all different table structures per schema. Only one common factor is a "Version" table in each schema containing about 4 fields. (Thus, there are about 100 Version tables in the database.) There's also another table (view, actually) containing a list of all the schema's in the database that have a version table. I need a stored procedure that walks through all the schema's and selects all data from the Version table, adding the schema name as a fifth field to the result. Basically, this stored procedure is to return a list of all version records per schema. My idea: first walk through the schema list to create one new SQL statements that will JOIN all the schema.version tables into one SQL statement. Then I return the result of that query. How to do this? Or does anyone have a better suggestion? (No, redesigning the structure is NOT an option.)

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• What is the strangest programming language you have used?

  - by Anders Sandvig

  For me I think it has to be the scripting language of an old proprietary telephony platform I used in the early 2000s. The language itself was not so bad, but the fact that it was meant to be edited with a drag-and-drop GUI, which did not expose all the functionality I needed, was quite frustrating. I also remember having to manually implement many common functions, such as calculating the length of a string. Whenever I wanted to use "custom" or "advanced" functions, I had to edit the script files in a text editor, but as soon as I opened the files in the GUI again they were reformatted and restructured, which usually resulted in broken code. And, of course, this was an interpreted language, so I would not know it was broken until I actually ran it—oh, and did I mention that it did not run the same in the simulator as in the live environment? So, what is the strangest programming language or environment you have used, and why did you use it? Note that I'm interested in languages and environments that you have actually used for "real-world" situations, so Whitespace, Brainf***k and friends are not valid—unless you have used them for something "real", of course.

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