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• Secure Password Storage and Transfer

  - by Andras Zoltan

  I'm developing a new user store for my organisation and am now tackling password storage. The concepts of salting, HMAC etc are all fine with me - and want to store the users' passwords either salted and hashed, HMAC hashed, or HMAC salted and hashed - not sure what the best way will be - but in theory it won't matter as it will be able to change over time if required. I want to have an XML & JSON service that can act as a Security Token Service for client-side apps. I've already developed one for another system, which requires that the client double-encrypts a clear-text password using SHA1 first and then HMACSHA1 using a 128 unique key (or nonce) supplied by the server for that session only. I'd like to repeat this technique for the new system - upgrading the algo to SHA256 (chosen since implementations are readily available for all aforementioned platforms - and it's much stronger than SHA1) - but there is a problem. If I'm storing the password as a salted hash in the user-store, the client will need to be sent that salt in order to construct the correct hash before being HMACd with the unique session key. This would completely go against the point of using a salt in the first place. Equally, if I don't use salt for password storage, but instead use HMAC, it's still the same problem. At the moment, the only solution I can see is to use naked SHA256 hashing for the password in the user store, so that I can then use this as a starting point on both the server and the client for a more secure salted/hmacd password transfer for the web service. This still leaves the user store vulnerable to a dictionary attack were it ever to be accessed; and however unlikely that might be - assuming it will never happen simply doesn't sit well with me. Greatly appreciate any input.

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• JVM/CLR Source-compatible Language Options

  - by Nathan Voxland

  I have an open source Java database migration tool (http://www.liquibase.org) which I am considering porting to .Net. The majority of the tool (at least from a complexity side) is around logic like "if you are adding a primary key and the database is Oracle use this SQL. If database is MySQL use this SQL. If the primary key is named and the database is Postgres use this SQL". I could fork the Java codebase and covert it (manually and/or automatically), but as updates and bug fixes to the above logic come in I do not want to have to apply it to both versions. What I would like to do is move all that logic into a form that can be compiled and used by both Java and .Net versions naively. The code I am looking to convert does not contain any advanced library usage (JDBC, System.out, etc) that would vary significantly from Java to .Net, so I don't think that will be an issue (at worst it can be designed around). So what I am looking for is: A language in which I can code common parts of my app in and compile it into classes usable by the "standard" languages on the target platform Does not add any runtime requirements to the system Nothing so strange that it scares away potential contributors I know Python and Ruby both have implementations on for the JVM and CLR. How well do they fit my requirements? Has anyone been successful (or unsuccesful) using this technique for cross-platform applications? Are there any gotcha's I need to worry about?

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• WPF/SL EventAggregator implementation with durable subscribers behavior?

  - by sha1dy

  Hi. Currently I'm building an application using latest Prism for Silverlight 4. I've a module and in that module I've two views with view models. Also I've a module view with two regions for each view. In module initialization I'm registering my views and view models in Unity container and also register views with corresponding regions. The problem is that views should display something similar to table-detail information - first view shows available entities ans the second view shows detail of selected entity. I need a way how to pass them initial selected entity. Newly created first view doesn't have any selected entity and newly created second view doesn't show any details. Currently I'm doing that this way: In module I create two view models and register them as instances in Unity container and then I register views as types for corresponding regions. Each view subscribes to EntitySelectedEvent from EventAggregator. Module initializer publish this event after initialization and this way two views are selecting the same entity. I know this looks ugly - I tried publishing this event from one of view models but the problems is that EventAggregator in Prism doesn't support durable subscribers - this means that if the second view model didn't subscribe to event before the first view model fired it, it won't receive and event. I know this is a normal behavior of EventAggregator, but I'm looking for a solution when view models can fire events without depending on initialization order of them - that is the first model can fire event before the second model was created and the second model will receive this 'queued' event after subscribing to it. Are there any other messaging implementations for WPF/SL which do support such behavior or using a mediator (in my example it's a module itself) isn't such a bad idea after all? One big problem with mediator is that models must be created right away in initialize and they can't be registered as types in container because this leads again to missing subscribers.

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• "Public" nested classes or not

  - by Frederick

  Suppose I have a class 'Application'. In order to be initialised it takes certain settings in the constructor. Let's also assume that the number of settings is so many that it's compelling to place them in a class of their own. Compare the following two implementations of this scenario. Implementation 1: class Application { Application(ApplicationSettings settings) { //Do initialisation here } } class ApplicationSettings { //Settings related methods and properties here } Implementation 2: class Application { Application(Application.Settings settings) { //Do initialisation here } class Settings { //Settings related methods and properties here } } To me, the second approach is very much preferable. It is more readable because it strongly emphasises the relation between the two classes. When I write code to instantiate Application class anywhere, the second approach is going to look prettier. Now just imagine the Settings class itself in turn had some similarly "related" class and that class in turn did so too. Go only three such levels and the class naming gets out out of hand in the 'non-nested' case. If you nest, however, things still stay elegant. Despite the above, I've read people saying on StackOverflow that nested classes are justified only if they're not visible to the outside world; that is if they are used only for the internal implementation of the containing class. The commonly cited objection is bloating the size of containing class's source file, but partial classes is the perfect solution for that problem. My question is, why are we wary of the "publicly exposed" use of nested classes? Are there any other arguments against such use?

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• how to get cartesian products between database and local sequences in linq?

  - by JD

  I saw this similar question here but can't figure out how to use Contains in Cartesian product desired result situation: http://stackoverflow.com/questions/1712105/linq-to-sql-exception-local-sequence-cannot-be-used-in-linq-to-sql-implementatio Let's say I have following: var a = new [] { 1, 4, 7 }; var b = new [] { 2, 5, 8 }; var test = from i in a from j in b select new { A = i, B = j, AB = string.Format("{0:00}a{1:00}b", i, j), }; foreach (var t in test) Console.Write("{0}, ", t.AB); This works great and I get a dump like so (note, I want the cartesian product): 01a02b, 01a05b, 01a08b, 04a02b, 04a05b, 04a08b, 07a02b, 07a05b, 07a08b, Now what I really want is to take this and cartesian product it again against an ID from a database table I have. But, as soon as I add in one more from clause that instead of referencing objects, references SQL table, I get an error. So, altering above to something like so where db is defined as a new DataContext (i.e., class deriving from System.Data.Linq.DataContext): var a = new [] { 1, 4, 7 }; var b = new [] { 2, 5, 8 }; var test = from symbol in db.Symbols from i in a from j in b select new { A = i, B = j, AB = string.Format("{0}{1:00}a{2:00}b", symbol.ID, i, j), }; foreach (var t in test) Console.Write("{0}, ", t.AB); The error I get is following: Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator Its related to not using Contains apparently but I'm unsure how Contains would be used when I don't really want to constrict the results - I want the Cartesian product for my situation. Any ideas of how to use Contains above and still yield the Cartesian product when joining database and local sequences?

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• Generics with constraints hierarchy

  - by devoured elysium

  I am currently facing a very disturbing problem: interface IStateSpace<Position, Value> where Position : IPosition // <-- Problem starts here where Value : IValue // <-- and here as I don't { // know how to get away this // circular dependency! // Notice how I should be // defining generics parameters // here but I can't! Value GetStateAt(Position position); void SetStateAt(Position position, State state); } As you'll down here, both IPosition, IValue and IState depend on each other. How am I supposed to get away with this? I can't think of any other design that will circumvent this circular dependency and still describes exactly what I want to do! interface IState<StateSpace, Value> where StateSpace : IStateSpace where Value : IValue { StateSpace StateSpace { get; }; Value Value { get; set; } } interface IPosition { } interface IValue<State> where State : IState { State State { get; } } Basically I have a state space IStateSpace that has states IState inside. Their position in the state space is given by an IPosition. Each state then has one (or more) values IValue. I am simplifying the hierarchy, as it's a bit more complex than described. The idea of having this hierarchy defined with generics is to allow for different implementations of the same concepts (an IStateSpace will be implemented both as a matrix as an graph, etc). Would can I get away with this? How do you generally solve this kind of problems? Which kind of designs are used in these cases? Thanks

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• An implementation of Sharir's or Aurenhammer's deterministic algorithm for calculating the intersect

  - by RGrey

  The problem of finding the intersection/union of 'N' discs/circles on a flat plane was first proposed by M. I. Shamos in his 1978 thesis: Shamos, M. I. “Computational Geometry” Ph.D. thesis, Yale Univ., New Haven, CT 1978. Since then, in 1985, Micha Sharir presented an O(n log2n) time and O(n) space deterministic algorithm for the disc intersection/union problem (based on modified Voronoi diagrams): Sharir, M. Intersection and closest-pair problems for a set of planar discs. SIAM .J Comput. 14 (1985), pp. 448-468. In 1988, Franz Aurenhammer presented a more efficient O(n log n) time and O(n) space algorithm for circle intersection/union using power diagrams (generalizations of Voronoi diagrams): Aurenhammer, F. Improved algorithms for discs and balls using power diagrams. Journal of Algorithms 9 (1985), pp. 151-161. Earlier in 1983, Paul G. Spirakis also presented an O(n^2) time deterministic algorithm, and an O(n) probabilistic algorithm: Spirakis, P.G. Very Fast Algorithms for the Area of the Union of Many Circles. Rep. 98, Dept. Comput. Sci., Courant Institute, New York University, 1983. I've been searching for any implementations of the algorithms above, focusing on computational geometry packages, and I haven't found anything yet. As neither appear trivial to put into practice, it would be really neat if someone could point me in the right direction!

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• ClassNotFoundException when connecting to Mysql with JDBC

  - by Jacob Lyles

  I'm getting the following error when I try to run a simple Java JDBC program at the command line: Exception in thread "main" java.lang.NoClassDefFoundError: LoadDriver/java Caused by: java.lang.ClassNotFoundException: LoadDriver.java at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:315) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330) at java.lang.ClassLoader.loadClass(ClassLoader.java:250) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:398) Here's the simple Java program, copied right out of the JDBC docs: import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; // Notice, do not import com.mysql.jdbc.* // or you will have problems! public class LoadDriver { public static void main(String[] args) { try { // The newInstance() call is a work around for some // broken Java implementations Class.forName("com.mysql.jdbc.Driver").newInstance(); } catch (Exception ex) { throw ex; // handle the error } } } Problem is, I'm bloody sure my bash shell $ClASSPATH variable is pointed at the correct .jar file. To be sure, I copied the JDBC .jar to the same directory as my program and ran it as follows: java -classpath ./mysql-connector-java-5.1.12-bin.jar LoadDriver.java I still get the same error. I'm running under Mac OSX, if it matters.

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• Project Euler 7 Scala Problem

  - by Nishu

  I was trying to solve Project Euler problem number 7 using scala 2.8 First solution implemented by me takes ~8 seconds def problem_7:Int = { var num = 17; var primes = new ArrayBuffer[Int](); primes += 2 primes += 3 primes += 5 primes += 7 primes += 11 primes += 13 while (primes.size < 10001){ if (isPrime(num, primes)) primes += num if (isPrime(num+2, primes)) primes += num+2 num += 6 } return primes.last; } def isPrime(num:Int, primes:ArrayBuffer[Int]):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(num) for (i <- primes){ if(i <= r ){ if (num % i == 0) return false; } } return true; } Later I tried the same problem without storing prime numbers in array buffer. This take .118 seconds. def problem_7_alt:Int = { var limit = 10001; var count = 6; var num:Int = 17; while(count < limit){ if (isPrime2(num)) count += 1; if (isPrime2(num+2)) count += 1; num += 6; } return num; } def isPrime2(n:Int):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(n) var f = 5; while (f <= r){ if (n % f == 0) { return false; } else if (n % (f+2) == 0) { return false; } f += 6; } return true; } I tried using various mutable array/list implementations in Scala but was not able to make solution one faster. I do not think that storing Int in a array of size 10001 can make program slow. Is there some better way to use lists/arrays in scala?

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• SQL Server - Multi-Column substring matching

  - by hamlin11

  One of my clients is hooked on multi-column substring matching. I understand that Contains and FreeText search for words (and at least in the case of Contains, word prefixes). However, based upon my understanding of this MSDN book, neither of these nor their variants are capable of searching substrings. I have used LIKE rather extensively (Select * from A where A.B Like '%substr%') Sample table A: ID | Col1 | Col2 | Col3 | ------------------------------------- 1 | oklahoma | colorado | Utah | 2 | arkansas | colorado | oklahoma | 3 | florida | michigan | florida | ------------------------------------- The following code will give us row 1 and row 2: select * from A where Col1 like '%klah%' or Col2 like '%klah%' or Col3 like '%klah%' This is rather ugly, probably slow, and I just don't like it very much. Probably because the implementations that I'm dealing with have 10+ columns that need searched. The following may be a slight improvement as code readability goes, but as far as performance, we're still in the same ball park. select * from A where (Col1 + ' ' + Col2 + ' ' + Col3) like '%klah%' I have thought about simply adding insert, update, and delete triggers that simply add the concatenated version of the above columns into a separate table that shadows this table. Sample Shadow_Table: ID | searchtext | --------------------------------- 1 | oklahoma colorado Utah | 2 | arkansas colorado oklahoma | 3 | florida michigan florida | --------------------------------- This would allow us to perform the following query to search for '%klah%' select * from Shadow_Table where searchtext like '%klah%' I really don't like having to remember that this shadow table exists and that I'm supposed to use it when I am performing multi-column substring matching, but it probably yields pretty quick reads at the expense of write and storage space. My gut feeling tells me there there is an existing solution built into SQL Server 2008. However, I don't seem to be able to find anything other than research papers on the subject. Any help would be appreciated.

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• Best approach to storing image pixels in bottom-up order in Java

  - by finnw

  I have an array of bytes representing an image in Windows BMP format and I would like my library to present it to the Java application as a BufferedImage, without copying the pixel data. The main problem is that all implementations of Raster in the JDK store image pixels in top-down, left-to-right order whereas BMP pixel data is stored bottom-up, left-to-right. If this is not compensated for, the resulting image will be flipped vertically. The most obvious "solution" is to set the SampleModel's scanlineStride property to a negative value and change the band offsets (or the DataBuffer's array offset) to point to the top-left pixel, i.e. the first pixel of the last line in the array. Unfortunately this does not work because all of the SampleModel constructors throw an exception if given a negative scanlineStride argument. I am currently working around it by forcing the scanlineStride field to a negative value using reflection, but I would like to do it in a cleaner and more portable way if possible. e.g. is there another way to fool the Raster or SampleModel into arranging the pixels in bottom-up order but without breaking encapsulation? Or is there a library somewhere that will wrap the Raster and SampleModel, presenting the pixel rows in reverse order? I would prefer to avoid the following approaches: Copying the whole image (for performance reasons. The code must process hundreds of large (= 1Mpixels) images per second and although the whole image must be available to the application, it will normally access only a tiny (but hard-to-predict) portion of the image.) Modifying the DataBuffer to perform coordinate transformation (this actually works but is another "dirty" solution because the buffer should not need to know about the scanline/pixel layout.) Re-implementing the Raster and/or SampleModel interfaces from scratch (but I have a hunch that I will be unable to avoid this.)

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• How to use Java varargs with the GWT Javascript Native Interface? (aka, "GWT has no printf()")

  - by markerikson

  I'm trying to quickly learn GWT as part of a new project. I found out that GWT doesn't implement Java's String.format() function, so there's no printf()-like functionality. I knew that some printf() implementations exist for Javascript, so I figured I could paste one of those in as a GWT Javascript Native Interface function. I ran into problems, and decided I'd better make sure that the varargs values were being passed in correctly. That's where things got ugly. First, some example code: // From Java, call the JSNI function: test("sourceString", "params1", "params2", "params3"); .... public static native void test(Object... params) /*-{ // PROBLEM: this kills GWT! // alert(params.length); // returns "function" alert(typeof(params)); // returns "[Ljava.lang.Object;@b97ff1" alert(params); }-*/; The GWT docs state that "calling a varargs JavaScript method from Java will result in the callee receiving the arguments in an array". I figured that meant I could at least check params.length, but accessing that throws a JavascriptException wrapped in an UmbrellaException, with no real information. When I do "typeof(params)", it returns "function". As if that weren't odd enough, if I check the string value of params, it returns what appears to be a string version of a Java reference. So, I guess I'm asking a few different questions here: 1) How do GWT/JSNI varargs actually work, and do I need to do something special to pass in values? 2) What is actually going on here? 3) Is there any easier way to get printf()-style formatting in a GWT application?

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• Is there a standard mapping between JSON and Protocol Buffers?

  - by Daniel Earwicker

  From a comment on the announcement blog post: Regarding JSON: JSON is structured similarly to Protocol Buffers, but protocol buffer binary format is still smaller and faster to encode. JSON makes a great text encoding for protocol buffers, though -- it's trivial to write an encoder/decoder that converts arbitrary protocol messages to and from JSON, using protobuf reflection. This is a good way to communicate with AJAX apps, since making the user download a full protobuf decoder when they visit your page might be too much. It may be trivial to cook up a mapping, but is there a single "obvious" mapping between the two that any two separate dev teams would naturally settle on? If two products supported PB data and could interoperate because they shared the same .proto spec, I wonder if they would still be able to interoperate if they independently introduced a JSON reflection of the same spec. There might be some arbitrary decisions to be made, e.g. should enum values be represented by a string (to be human-readable a la typical JSON) or by their integer value? So is there an established mapping, and any open source implementations for generating JSON encoder/decoders from .proto specs?

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• Big-O of PHP functions?

  - by Kendall Hopkins

  After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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• .NET XML serialization

  - by ShdNx

  I would like to serialize and deserialize mixed data into XML. After some searches I found out that there were two ways of doing it: System.Runtime.Serialization.Formatters.Soap.SoapFormatter and System.Xml.Serialization.XmlSerializer. However, neither turned out to match my requirements, since: SoapFormatter doesn't support serialization of generic types XmlSerializer refuses to serialize types that implement IDictionary, not to mention that it's far less easy-to-use than "normal" serialization (e.g. see this SO question) I'm wondering if there exists an implementation that doesn't have these limitations? I have found attempts (for example CustomXmlSerializer and YAXLib as suggested in a related SO question), but they don't seem to work either. I was thinking about writing such serializer myself (though it certainly doesn't seem to be a very easy task), but then I find myself limited by the CLR, as I cannot create object instances of types that won't have a paramaterless constructor, even if I'm using reflection. I recall having read somewhere that implementations in System.Runtime.Serialization somehow bypass the normal object creation mechanism when deserializing objects, though I'm not sure. Any hints of how could this be done? Could somebody please point me to the right direction with this?

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• Why is the Clojure Hello World program so slow compared to Java and Python?

  - by viksit

  Hi all, I'm reading "Programming Clojure" and I was comparing some languages I use for some simple code. I noticed that the clojure implementations were the slowest in each case. For instance, Python - hello.py def hello_world(name): print "Hello, %s" % name hello_world("world") and result, $ time python hello.py Hello, world real 0m0.027s user 0m0.013s sys 0m0.014s Java - hello.java import java.io.*; public class hello { public static void hello_world(String name) { System.out.println("Hello, " + name); } public static void main(String[] args) { hello_world("world"); } } and result, $ time java hello Hello, world real 0m0.324s user 0m0.296s sys 0m0.065s and finally, Clojure - hellofun.clj (defn hello-world [username] (println (format "Hello, %s" username))) (hello-world "world") and results, $ time clj hellofun.clj Hello, world real 0m1.418s user 0m1.649s sys 0m0.154s Thats a whole, garangutan 1.4 seconds! Does anyone have pointers on what the cause of this could be? Is Clojure really that slow, or are there JVM tricks et al that need to be used in order to speed up execution? More importantly - isn't this huge difference in performance going to be an issue at some point? (I mean, lets say I was using Clojure for a production system - the gain I get in using lisp seems completely offset by the performance issues I can see here). The machine used here is a 2007 Macbook Pro running Snow Leopard, a 2.16Ghz Intel C2D and 2G DDR2 SDRAM. BTW, the clj script I'm using is from here and looks like, #!/bin/bash JAVA=/System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home/bin/java CLJ_DIR=/opt/jars CLOJURE=$CLJ_DIR/clojure.jar CONTRIB=$CLJ_DIR/clojure-contrib.jar JLINE=$CLJ_DIR/jline-0.9.94.jar CP=$PWD:$CLOJURE:$JLINE:$CONTRIB # Add extra jars as specified by `.clojure` file if [ -f .clojure ] then CP=$CP:`cat .clojure` fi if [ -z "$1" ]; then $JAVA -server -cp $CP \ jline.ConsoleRunner clojure.lang.Repl else scriptname=$1 $JAVA -server -cp $CP clojure.main $scriptname -- $* fi

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• Documentation for java.util.concurrent.locks.ReentrantReadWriteLock

  - by Andrei Taptunov

  Disclaimer: I'm not very good at Java and just comparing read/writer locks between C# and Java to understand this topic better & decisions behind both implementations. There is JavaDoc about ReentrantReadWriteLock. It states the following about upgrade/downgrade for locks: Lock downgrading ... However, upgrading from a read lock to the write lock is not possible. It also has the following example that shows manual upgrade from read lock to write lock: // Here is a code sketch showing how to exploit reentrancy // to perform lock downgrading after updating a cache void processCachedData() { rwl.readLock().lock(); if (!cacheValid) { // upgrade lock manually #1: rwl.readLock().unlock(); // must unlock first to obtain writelock #2: rwl.writeLock().lock(); if (!cacheValid) { // recheck ... } ... } use(data); rwl.readLock().unlock(); Does it mean that actually the sample from above may not behave correctly in some cases - I mean there is no lock between lines #1 & #2 and underlying structure is exposed to changes from other threads. So it can not be considered as the correct way to upgrade the lock or do I miss something here?

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• NMock2.0 - how to stub a non interface call?

  - by dferraro

  Hello, I have a class API which has full code coverage and uses DI to mock out all the logic in the main class function (Job.Run) which does all the work. I found a bug in production where we werent doing some validation on one of the data input fields. So, I added a stub function called ValidateFoo()... Wrote a unit test against this function to Expect a JobFailedException, ran the test - it failed obviously because that function was empty. I added the validation logic, and now the test passes. Great, now we know the validation works. Problem is - how do I write the test to make sure that ValidateFoo() is actually called inside Job.Run()? ValidateFoo() is a private method of the Job class - so it's not an interface... Is there anyway to do this with NMock2.0? I know TypeMock supports fakes of non interface types. But changing mock libs right now is not an option. At this point if NMock can't support it, I will simply just add the ValidateFoo() call to the Run() method and test things manually - which obviously I'd prefer not to do considering my Job.Run() method has 100% coverage right now. Any Advice? Thanks very much it is appreciated. EDIT: the other option I have in mind is to just create an integration test for my Job.Run functionality (injecting to it true implementations of the composite objects instead of mocks). I will give it a bad input value for that field and then validate that the job failed. This works and covers my test - but it's not really a unit test but instead an integration test that tests one unit of functionality.... hmm.. EDIT2: IS there any way to do tihs? Anyone have ideas? Maybe TypeMock - or a better design?

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• Is an "infinite" iterator bad design?

  - by Adamski

  Is it generally considered bad practice to provide Iterator implementations that are "infinite"; i.e. where calls to hasNext() always(*) return true? Typically I'd say "yes" because the calling code could behave erratically, but in the below implementation hasNext() will return true unless the caller removes all elements from the List that the iterator was initialised with; i.e. there is a termination condition. Do you think this is a legitimate use of Iterator? It doesn't seem to violate the contract although I suppose one could argue it's unintuitive. public class CyclicIterator<T> implements Iterator<T> { private final List<T> l; private Iterator it; public CyclicIterator<T>(List<T> l) { this.l = l; this.it = l.iterator(); } public boolean hasNext() { return !l.isEmpty(); } public T next() { T ret; if (!hasNext()) { throw new NoSuchElementException(); } else if (it.hasNext()) { ret = it.next(); } else { it = l.iterator(); ret = it.next(); } return ret; } public void remove() { it.remove(); } }

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• Considerations when architecting an extensible application using MEF

  - by Dan Bryant

  I've begun experimenting with dependency injection (in particular, MEF) for one of my projects, which has a number of different extensibility points. I'm starting to get a feel for what I can do with MEF, but I'd like to hear from others who have more experience with the technology. A few specific cases: My main use case at the moment is exposing various singleton-like services that my extensions make use of. My Framework assembly exposes service interfaces and my Engine assembly contains concrete implementations. This works well, but I may not want to allow all of my extensions to have access to all of my services. Is there a good way within MEF to limit which particular imports I allow a newly instantiated extension to resolve? This particular application has extension objects that I repeatedly instantiate. I can import multiple types of Controllers and Machines, which are instantiated in different combinations for a Project. I couldn't find a good way to do this with MEF, so I'm doing my own type discovery and instantiation. Is there a good way to do this within MEF or other DI frameworks? I welcome input on any other things to watch out for or surprising capabilities you've discovered that have changed the way you architect.

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• Which PHP library I should choose to work with CouchDB?

  - by Guss

  I want to try playing with CouchDB for a new project I'm writing (as a hobby, not part of my job). I'm well versed in PHP, but I haven't programmed with CouchDB at all, and also I have little experience with non-SQL databases. From looking at CouchDB's "Getting Started with PHP" document they recommend using a third-party library or writing your own client using their RESTful HTTP API. I think I'd rather not mess with writing protocol implementations myself at this point, but what is your experience with writing PHP to work with CouchDB? I haven't tested any of the alternatives yet, but I looked at: PHPillow : I'm interested in the way they implement ORM. I wasn't planning to do ORM, but my problem domain probably map well to that method. PHP Object Freezer: seems like a poor man's ORM - I can use it to implement an actual ORM, or just as an easy store/retrieve document API but it seems too primitive. PHP-on-Couch : Also a bit simple, but they have an interesting API for views and from the documentation it looks usable enough. PHP CouchDB Extension : From the listed options this looks like it has the best chance of making it into the PHP mainline itself, and also has the most complete API. Any opinion one wish to share on each library is welcome.

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• should std::auto_ptr<>::operator = reset / deallocate its existing pointee ?

  - by afriza

  I read here about std::auto_ptr<::operator= Notice however that the left-hand side object is not automatically deallocated when it already points to some object. You can explicitly do this by calling member function reset before assigning it a new value. However, when I read the source code for header file C:\Program Files\Microsoft Visual Studio 8\VC\ce\include\memory template<class _Other> auto_ptr<_Ty>& operator=(auto_ptr<_Other>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr<_Ty>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr_ref<_Ty> _Right) _THROW0() { // assign compatible _Right._Ref (assume pointer) _Ty **_Pptr = (_Ty **)_Right._Ref; _Ty *_Ptr = *_Pptr; *_Pptr = 0; // release old reset(_Ptr); // set new return (*this); } What is the correct/standard behavior? How do other STL implementations behave?

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• Design pattern to use instead of multiple inheritance

  - by mizipzor

  Coming from a C++ background, Im used to multiple inheritance. I like the feeling of a shotgun squarely aimed at my foot. Nowadays, I work more in C# and Java, where you can only inherit one baseclass but implement any number of interfaces (did I get the terminology right?). For example, lets consider two classes that implement a common interface but different (yet required) baseclasses: public class TypeA : CustomButtonUserControl, IMagician { public void DoMagic() { // ... } } public class TypeB : CustomTextUserControl, IMagician { public void DoMagic() { // ... } } Both classes are UserControls so I cant substitute the base class. Both needs to implement the DoMagic function. My problem now is that both implementations of the function are identical. And I hate copy-and-paste code. The (possible) solutions: I naturally want TypeA and TypeB to share a common baseclass, where I can write that identical function definition just once. However, due to having the limit of just one baseclass, I cant find a place along the hierarchy where it fits. One could also try to implement a sort of composite pattern. Putting the DoMagic function in a separate helper class, but the function here needs (and modifies) quite a lot of internal variables/fields. Sending them all as (reference) parameters would just look bad. My gut tells me that the adapter pattern could have a place here, some class to convert between the two when necessery. But it also feels hacky. I tagged this with language-agnostic since it applies to all languages that use this one-baseclass-many-interfaces approach. Also, please point out if I seem to have misunderstood any of the patterns I named. In C++ I would just make a class with the private fields, that function implementation and put it in the inheritance list. Whats the proper approach in C#/Java and the like?

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• RemoteRef.invoke implementation

  - by phill

  Just finished a basic implementation of RMI for a class project, and now I am interested in how it is actually done. Sun is kind enough to provide the source for the majority of the Java classes with the JDK, however an implementation of RemoteRef doesn't seem to be there. I have the source for the interface RemoteRef along with the ServerRef interface and one implementation, ProxyRef, which just calls invoke on another RemoteRef, but none of the classes that implement actual code, ActivatableRef or UnicastRef for example, are included. I mention ActivatableRef and UnicastRef because I believe these have proper implementations of invoke thanks to the wonder that is Eclipse and its class file editor showing that it is more then just a method declaration. Although I can tell that it is more then a declaration, I can't get much more out of it, building a string here, throw exception there, but nothing about the process that is taking place to send the remote method call. Would anyone here happen to know where I can get this code, or if its even available? If it is not available, would anyone happen to know what the message being sent to the server looks like? phill

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• Atomic Instructions and Variable Update visibility

  - by dsimcha

  On most common platforms (the most important being x86; I understand that some platforms have extremely difficult memory models that provide almost no guarantees useful for multithreading, but I don't care about rare counter-examples), is the following code safe? Thread 1: someVariable = doStuff(); atomicSet(stuffDoneFlag, 1); Thread 2: while(!atomicRead(stuffDoneFlag)) {} // Wait for stuffDoneFlag to be set. doMoreStuff(someVariable); Assuming standard, reasonable implementations of atomic ops: Is Thread 1's assignment to someVariable guaranteed to complete before atomicSet() is called? Is Thread 2 guaranteed to see the assignment to someVariable before calling doMoreStuff() provided it reads stuffDoneFlag atomically? Edits: The implementation of atomic ops I'm using contains the x86 LOCK instruction in each operation, if that helps. Assume stuffDoneFlag is properly cleared somehow. How isn't important. This is a very simplified example. I created it this way so that you wouldn't have to understand the whole context of the problem to answer it. I know it's not efficient.

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