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• Throw exception from initializer list

  - by aaa

  hello. what is the best way to throw exception from initializer list? for example: class C { T0 t0; // can be either valid or invalid, but does not throw directly T1 t1; // heavy object, do not construct if t0 is invalid, by throwing before C(int n) : t0(n), // throw exception if t0(n) is not valid t1() {} }; I thought maybe making wrapper, e.g. t0(throw_if_invalid(n)). What is the practice to handle such cases? Thanks

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• Concrete Types or Interfaces for return types?

  - by SDReyes

  Today I came to a fundamental paradox of the object programming style, concrete types or interfaces. Whats the better election for a method's return type: a concrete type or an interface? In most cases, I tend to use concrete types as the return type for methods. because I believe that an concrete type is more flexible for further use and exposes more functionality. The dark side of this: Coupling. The angelic one: A concrete type contains per-se the interface you would going to return initially, and extra functionality. What's your thumb's rule? Is there any programming principle for this? BONUS: This is an example of what I mean http://stackoverflow.com/questions/491375/readonlycollection-or-ienumerable-for-exposing-member-collections

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• Is ACE reactor timer managment thread safe?

  - by idimba

  I have a module that manages timers in my aplication. This class has basibly three functions: Instance of ACE_Reactor is used internally by the module to manage the timers. schedule timer - calls ACE_Reactor::schedule_timer(). One of the arguments is a callback, called upon timer experation. cancel timer - calls ACE_Reactor::cancel_timer() The reactor executed in private timer of execution, so schedule/cancel and timeout callback are executed in different threads. ACE_Reactor::schedule_timer() receives a heap allocatec structure ( arg argument). This structure later deleted when canceling timer or when timeout handler is called. But since cancel and timeout handler are executed in different threads it looks like there's cases that the structure is deleted twice. Isn't it responsibility of reactor to ensure that timer is canceled when timeout handler is called?

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• Combinatorics, probability, dice

  - by TarGz

  A friend of mine asked: if I have two dice and I throw both of them, what is the most frequent sum (of the two dice' numbers)? I wrote a small script: from random import randrange d = dict((i, 0) for i in range(2, 13)) for i in xrange(100000): d[randrange(1, 7) + randrange(1, 7)] += 1 print d Which prints: 2: 2770, 3: 5547, 4: 8379, 5: 10972, 6: 13911, 7: 16610, 8: 14010, 9: 11138, 10: 8372, 11: 5545, 12: 2746 The question I have, why is 11 more frequent than 12? In both cases there is only one way (or two, if you count reverse too) how to get such sum (5 + 6, 6 + 6), so I expected the same probability..?

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• VS2010 / Code Analysis: Turn off a rule for a project without custom ruleset....

  - by TomTom

  ...any change? The scenario is this: For our company we develop a standard how code should look. This will be the MS full rule set as it looks now. For some specific projects we may want to turn off specific rules. Simply because for a specific project this is a "known exception". Example? CA1026 - while perfectly ok in most cases, there are 1-2 specific libraries we dont want to change those. We also want to avoid having a custom rule set. OTOH putting in a suppress attribute on every occurance gets pretty convoluted pretty fast. Any way to turn off a code analysis warning for a complete assembly without a custom rule set? We rather have that in a specific file (GlobalSuppressions.cs) than in a rule set for maintenance reasons, and to be more explicit ;)

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• Cassandra/HBase or just MySQL: Potential problems doing the next thing

  - by alexeypro

  Say I have "user". It's the key. And I need to keep "user count". I am planning to have record with key "user" and value "0" to "9999+ ;-)" (as many as I'll have). What problems I will drive in if I use Cassandra, HBase or MySQL for that? Say, I have thousand of new updates to this "user" key, where I need to increment the value. Am I in trouble? Locked for writes? Any other way of doing that? Why this is done -- there will be a lot of "user"-like keys. Different other cases. But the idea is the same. Why keep it this way -- because I'll have more reads, so I can always get "counted value" very fast.

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• EnvDTE: ArgumentException when accessing the ActiveConfiguration

  - by Smith

  Hello, I'm writing an addin for Visual Studio 2008. At some point in my code, I'm attempting to access the current active configuration for a project: var configName = _Project.ConfigurationManager.ActiveConfiguration.ConfigurationName; Sometimes, in some very obscure cases, the getter for ActiveConfiguration throws an ArgumentException. Nothing in the documentation says anything about this (but given the very poor quality of the documentation, it was to be expected), and the exception's message is not helping at all. Also, ConfigurationManager is an interface, and I don't know what's the real implementation behind it, so I can't simply disassemble it in Reflector to know the cause. Any help would be greatly appreciated.

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• How to remove check digit from a barcode

  - by Teddy

  Hi. I have barcodes generated with Code 39 symbology. Some of the barcodes contain check digit, and some does not. So, how can I prevent barcode scanner to pass the check digit to the pc? Or is there another way I can check if the barcode has a check digit in .Net? For example, the encoded data is 1642, but the the barcode scanner reads 16425 and I might have data a barcode with encoded data 16425. I need to distinguish both cases either in the code, or in the barcode scanner. Thanks.

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• Event Capturing vs Event Bubbling

  - by Rajat

  I just wanted to get the general consensus on which is a better mode of event delegation in JS between bubbling and capturing. Now I understand that depending on a particular use-case, one might want to use capturing phase over bubbling or vice versa but I want to understand what delegation mode is preferred for most general cases and why (to me it seems bubbling mode). Or to put it in other words, is there a reason behind W3C addEventListener implementation to favor the bubbling mode. [capturing is initiated only when you specify the 3rd parameter and its true. However, you can forget that 3rd param and bubbling mode is kicked in] I looked up the JQuery's bind function to get an answer to my question and it seems it doesn't even support events in capture phase (it seems to me because of IE not support capturing mode). So looks like bubbling mode is the default choice but why?

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• WinForms prints to default printer even if it's not available/connected

  - by Valentein

  How can I determine if printer is connected? Typically this application prints to the default printer but in some cases that printer may not be available. If so I don't want the job sent to it's queue but rather printed to another available printer. I understand the PinterSettings.InstalledPrinters property. Does PrintDocument.PrinterSettings.IsValid return false if a printer is not available? Does WPF provide this kind of functionality? My problem is different than Printing problem in C# windows app - Always prints to default printer

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• Are document-oriented databases meant to replace relational databases?

  - by evolve

  Recently I've been working a little with MongoDB and I have to say I really like it. However it is a completely different type of database then I am used. I've noticed that it is most definitely better for certain types of data, however for heavily normalized databases it might not be the best choice. It appears to me however that it can completely take the place of just about any relational database you may have and in most cases perform better, which is mind boggling. This leads me to ask a few questions: Are document-oriented databases have been developed to be the next generation of databases and basically replace relational databases completely? Is it possible that projects would be better off using both a document-oriented database and a relational database side by side for various data which is better suited for one or the other? If document-oriented databases are not meant to replace relational databases, then does anyone have an example of a database structure which would absolutely be better off in a relational database (or vice-versa)?

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• Any working tutorials for Authlogic?

  - by Mark Wilbur

  I've been trying to build my first rails app and have gotten stuck on the issue of user authentication. I've found a number of tutorials for using various plug-ins to do this, but so far every single one of them is out-dated, and as a result, broken! From what I've read, I think Authlogic may be the best fit for me, and I've tried two things: 1) Going through Railscast, episode #160 (which is a tutorial for setting it up) 2) Using Ryan B's nifty_authentication gem with the --authlogic tag In both cases, I get the following error as soon as I try to do anything with a user: undefined local variable or method `acts_as_authentic' for # I believe this is from the User model: class User < ActiveRecord::Base acts_as_authentic end I'm sure I've installed the authlogic gem, and I've added config.gem "authlogic" to my environment.rb Any ideas about what's wrong? Anybody know of a complete and up to date tutorial for adding user authentication?

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• When we should use pushScene and replaceScene in cocos2d ?

  - by srikanth rongali

  Hi, I cocos2d, I am using pushScene and replaceScene to move to next scene. But, I am confused which we should use? When I am using replaceScene in some places app is crashing and giving errors like -[UITextView length]: unrecognized selector sent to instance 0x842a750 Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UITextView length]: unrecognized selector sent to instance 0x842a750' But, in my program I am not passing length to UITextView. My program is in this way In scene1 I have UITextView, and I am replacing this scene with scene2. Then -(id)buttonPressed:(id)sender { [description removeFromSuperview]; // It is the textView(description) CCScene *Scene = [CCScene node]; CCLayer *Layer = [scene2 node]; [Scene addChild:Layer]; [[CCDirector sharedDirector] setAnimationInterval:1.0/60]; [[CCDirector sharedDirector] replaceScene: Scene]; } But, when I am using pushScene in presence of replaceScene it is working good. Please clarify me which one should use in which cases ? Thank You

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• Avoiding symbol capture when using macros to generate functions (or other macros)

  - by Rob Lachlan

  I'm a bit confused as to exactly when symbol capture will occur with clojure macros. Suppose that I have a macro which defines a function from keywords. In this trivial example, (defmacro foo [keywd1 keywd2] `(defn ~(symbol (name keywd1)) [~(symbol (name keywd2))] (* 2 ~(symbol (name keywd2))))) I call (foo :bar :baz), and this gets expanded into (defn bar [baz] (* 2 baz)). So now the question -- can this lead to symbol capture? If so, under what circumstances? I know that it's preferred to use gensym (e.g. bar#) to prevent symbol capture, but in some cases (not many, but still) I'd like to have a pretty macro-expansion, without the auto-generated symbols. Bonus question: does the answer change if we are considering a macro that creates macros?

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• How to geocoding big number of addresses?

  - by user308569

  I need to geocode, i.e. translate street address to latitude,longitude for ~8,000 street addresses. I am using both Yahoo and Google geocoding engines at http://www.gpsvisualizer.com/geocoder/, and found out that for a big number of addresses those engines (one of them or both) either could not perform geocoding (i.e.return latitude=0,longitude=0), or return wrong coordinates (incl. cases when Yahoo and Google give different results). What is the best way to handle this problem? Which engine is (usually) more accurate? I would appreciate any thoughts, suggestions, ideas from people who had previous experience with this kind of task.

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• XML: What to use as a list separator

  - by Heinzi

  There are two ways to specify lists of values in XML. Variant 1: <Database Name="myDatabase"> <Table Name="myTable1" /> <Table Name="myTable2" /> <Table Name="myTable3" /> ... </Database> Variant 2: <Database Name="myDatabase" Tables="myTable1 myTable2 myTable3 ..." /> Clearly, Variant 1 is cleaner and can be extended more easily, but im many cases Variant 2 is more readable and "user-friendly". When using Variant 2, what should be used as the separator? The XML Schema standard seems to prefer whitespace, whereas some real-world examples use commas instead. Is there a particular reason to choose one over the other (assuming that the values contain neither whitspace nor commas)?

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• Why does Silverlight 4 Tools only give partial intellisense?

  - by Edward Tanguay

  I finally got Silverlight 4 Toolkit installed , referenced and working after the difficulty of finding the right namespace described in this question. But intellisense doesn't work fully: after I type "tk:", it doesn't pop up the various controls I have available, but if I type a control name out, e.g. DockPanel, then it works, as shown below. It will even give me intellisense after I type tk:DropPanel, which is odd. How can I get intellisense to work in all cases for the Silverlight 4 Toolkit? I can imagine I need another namespace, but this site says that this reference: is now all you need (and will be automatically used by both Visual Studio and Blend)

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• Efficient algorithm for finding largest eigenpair of small general complex matrix

  - by mklassen

  I am looking for an efficient algorithm to find the largest eigenpair of a small, general (non-square, non-sparse, non-symmetric), complex matrix, A, of size m x n. By small I mean m and n is typically between 4 and 64 and usually around 16, but with m not equal to n. This problem is straight forward to solve with the general LAPACK SVD algorithms, i.e. gesvd or gesdd. However, as I am solving millions of these problems and only require the largest eigenpair, I am looking for a more efficient algorithm. Additionally, in my application the eigenvectors will generally be similar for all cases. This lead me to investigate Arnoldi iteration based methods, but I have neither found a good library nor algorithm that applies to my small general complex matrix. Is there an appropriate algorithm and/or library?

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• When would ShowDialog() return null?

  - by Joe White

  WPF's Window.ShowDialog method returns a nullable boolean. So does CommonDialog.ShowDialog. Now, I understand cases where these would return false (user clicked Cancel or pressed Esc), and when they would return true (code sets Window.DialogResult to true, probably in response to OK being clicked). But null? My first thought is that clicking the title bar's Close button might return null. But the docs state (and I confirmed by testing) that the title-bar Close button is treated as a Cancel. So when would Window.ShowDialog or CommonDialog.ShowDialog ever return null?

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• Dns.GetHostEntry returns multiple IP addresses

  - by spender

  This question probably highlights a lack of understanding of networking principals on my part, rather than a programming issue. I'm doing a lookup on a hostname using Dns.GetHostEntry This returns an IPHostEntry to me, which has an AddressList property which is an array of IPAddress. I always thought there is a 1 to 1 mapping between hostname and IP, but I'm finding that in some cases I get back several IPAddress(es) for the same host. This is a surprise to me. Which part of domain name resolution do I not understand?

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• Comparing (similar) images with Python/PIL

  - by Attila Oláh

  I'm trying to calculate the similarity (read: Levenshtein distance) of two images, using Python 2.6 and PIL. I plan to use the python-levenshtein library for fast comparison. Main question: What is a good strategy for comparing images? My idea is something like: Convert to RGB (transparent - white) (or maybe convert to monochrome?) Scale up the smaller one to the larger one's size Convert each channel (= the only channel, if converted to monochrome) to a sequence (item value = color value of the pixel) Calculate the Levenshtein distance between the two sequences Of course, this will not handle cases like mirrored images, cropped images, etc. But for basic comparison, this should be useful. Is there a better strategy documented somewhere?

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• Problems with matching emails with regex

  - by Gandalf StormCrow

  Hello, I'm trying to match an email address here is what I've come up with so far : String text = "[email protected]"; String regex = "(\\w+)@{1}(\\w+){2,}\\.{1}\\w{2,4}"; This however works with following cases : [email protected] [email protected] [email protected] So it matches any alphanumeric character repeated once or more that comes before one @ followed by any alphanumeric character repeated at least two times(which is minimal characters for any domain name) followed by one .(dot) and followed by any alphanumeric character repeated at least 2 times and at most 4 times(because there are domains such as .us or .mobi). This expression however does not work with emails such as : [email protected] [email protected] [email protected] [email protected] etc as many subdomains or [email protected] [email protected] [email protected] [email protected] I've just started to learn regex and I found interesting to try to solve problems such as these by using regex .. not partially but for each case, any help would be much appriciated. Thank you

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• ASP.NET MVC Model Binding

  - by Noel

  If i have a Controller Action that may recieve both HTTP GET and HTTP POST from a number of different sources with each source sending different data e.g. Source1 performs a form POST with two form items Item1 and Item2 Source2 performs a GET where the data is contained in the query string (?ItemX=2&ItemY=3) Is it possible to have a controller action that will cater for all these cases and perform binding automatically e.g. public ActionResult Test(Dictionary data) { // Do work ... return View(); } Is this possible with a custom binder or some other way? Dont want to work directly with HttpContext.Request if possible

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• A definitive guide to Url Encoding in ASP .NET

  - by cbp

  I am starting to realise that there are about a bazillion different methods for encoding urls in .NET. I keep finding new ones. They all work slightly differently, but they all have essentially the same summary comments. Does anyone have a definitive matrix that shows the exact differences between the following methods: HttpUtility.UrlEncode HttpUtility.UrlPathEncode Server.UrlEncode Uri.EscapeUriString Uri.EscapeDataString ... are they any more? Also it would be good to match these up with use-cases e.g.: Urls in href attributes of a tags Urls to be displayed to the user in HTML Urls as querystring values (i.e. to be sent in GET requests) Urls to be sent in POST requests etc

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• Can django's auth_user.username be varchar(75)?

  - by perrierism

  Django's auth_user.username field is 30 characters. That means you can't have auth_user.username store an email address. If you want to have users authenticate based on their email address it would seem you have to do some wonky stuff like writing your own authentication backend which authenticates based on (email, password) instead of (username, password) and furthermore, figuring out what you're going to put in the username field since it is required and it is a primary key. Do you put a hash in there, do you try to put the id in there... bleh! Why should you have to write all this code and consider edge cases simply because username is too small for your (farily common) purposes? Is there anything wrong with running alter table on auth_user to make username be varchar(75) so it can fit an email? What does that break if anything?

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