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• Java "Pool" of longs or Oracle sequence with reusable values

  - by Anthony Accioly

  Several months ago I implemented a solution to choose unique values from a range between 1 and 65535 (16 bits). This range is used to generate unique Route Targets suffixes, which for this customer massive network (it's a huge ISP) are a very disputed resource, so any free index needs to become immediately available to the end user. To tackle this requirement I used a BitSet. Allocate on the RT index with set and deallocate a suffix with clear. The method nextClearBit() can find the next available index. I handle synchronization / concurrency issues manually. This works pretty well for a small range... The entire index is small (around 10k), it is blazing fast and can be easy serialized into a Blob field. The problem is, some new devices can handle RTs of 32 bits (range 1 / 4294967296). Which can't be managed with a BitSet (it would, by itself, consume around 600Mb, plus be limited to int range). Even with this massive range available, the client still wants to free available Route Targets for the end user, mainly because the lowest ones (up to 65535) - which are compatible with old routers - are being heavily disputed. Before I tell the customer that this is impossible and he will have to conform with my reusable index for lower RTs (up to 65550) and use a database sequence for the other ones (which means that when the user frees a Route Target, it will not become available again). Would anyone shed some light? Maybe some kind soul already implemented a high performance number pool for Java (6 if it matters), or I am missing a killer feature of Oracle database (11R2 if it matters)... Wishful thinking. Thank you very much in advance.

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• Developing a 2D Game for Windows Phone 8

  - by Vaccano

  I would like to develop a 2D game for Windows Phone 8. I am a professional Application Developer by day and this seems like a fun hobby. But I have been disapointed trying to get going. It seems that 2D games (far and away the majority of games) do not have any real support. It seems the Windows Phone makers did not include support for Direct2D. So unless you are planning to make a fully 3D app, you are out of luck. So, if you just wanted to make a nice 2D app, these are your choices: Write your game using Xaml and C# (Performance Issues?) Write your game using Direct3D and but only draw on one plane. Use the DirectX Took Kit found on codeplex. It allows you to use the dying XNA framework's API for development. Number 3 seems the best for my game. But I hate to waste my time learning the XNA api when Microsoft has clearly stated that it is not going to be supported going forward. Number 2 would work, but 3D development is really hard. I would rather not have to do all that to get the 2D effect. (Assuming Direct2D is easier. I have yet to look into that.) Number 1 seems the easiest, but I worry that my app will not run well if it is based off of xaml rendering rather than DirectX. What is the suggested method from Microsoft? And who decided that 2D games were going to get shortchanged?

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• Data structure to build and lookup set of integer ranges

  - by actual

  I have a set of uint32 integers, there may be millions of items in the set. 50-70% of them are consecutive, but in input stream they appear in unpredictable order. I need to: Compress this set into ranges to achieve space efficient representation. Already implemented this using trivial algorithm, since ranges computed only once speed is not important here. After this transformation number of resulting ranges is typically within 5 000-10 000, many of them are single-item, of course. Test membership of some integer, information about specific range in the set is not required. This one must be very fast -- O(1). Was thinking about minimal perfect hash functions, but they do not play well with ranges. Bitsets are very space inefficient. Other structures, like binary trees, has complexity of O(log n), worst thing with them that implementation make many conditional jumps and processor can not predict them well giving poor performance. Is there any data structure or algorithm specialized in integer ranges to solve this task?

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• Is this 2D array initialization a bad idea?

  - by Brendan Long

  I have something I need a 2D array for, but for better cache performance, I'd rather have it actually be a normal array. Here's the idea I had but I don't know if it's a terrible idea: const int XWIDTH = 10, YWIDTH = 10; int main(){ int * tempInts = new int[XWIDTH * YWIDTH]; int ** ints = new int*[XWIDTH]; for(int i=0; i<XWIDTH; i++){ ints[i] = &tempInts[i*YWIDTH]; } // do things with ints delete[] ints[0]; delete[] ints; return 0; } So the idea is that instead of newing a bunch of arrays (and having them placed in different places in memory), I just point to an array I made all at once. The reason for the delete[] (int*) ints; is because I'm actually doing this in a class and it would save [trivial amounts of] memory to not save the original pointer. Just wondering if there's any reasons this is a horrible idea. Or if there's an easier/better way. The goal is to be able to access the array as ints[x][y] rather than ints[x*YWIDTH+y].

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• Creating collaborative whiteboard drawing application

  - by Steven Sproat

  I have my own drawing program in place, with a variety of "drawing tools" such as Pen, Eraser, Rectangle, Circle, Select, Text etc. It's made with Python and wxPython. Each tool mentioned above is a class, which all have polymorphic methods, such as left_down(), mouse_motion(), hit_test() etc. The program manages a list of all drawn shapes -- when a user has drawn a shape, it's added to the list. This is used to manage undo/redo operations too. So, I have a decent codebase that I can hook collaborative drawing into. Each shape could be changed to know its owner -- the user who drew it, and to only allow delete/move/rescale operations to be performed on shapes owned by one person. I'm just wondering the best way to develop this. One person in the "session" will have to act as the server, I have no money to offer free central servers. Somehow users will need a way to connect to servers, meaning some kind of "discover servers" browser...or something. How do I broadcast changes made to the application? Drawing in realtime and broadcasting a message on each mouse motion event would be costly in terms of performance and things get worse the more users there are at a given time. Any ideas are welcome, I'm not too sure where to begin with developing this (or even how to test it)

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• How To perform a SQL Query to DataTable Operation That Can Be Cancelled

  - by David W

  I tried to make the title as specific as possible. Basically what I have running inside a backgroundworker thread now is some code that looks like: SqlConnection conn = new SqlConnection(connstring); SqlCommand cmd = new SqlCommand(query, conn); conn.Open(); SqlDataAdapter sda = new SqlDataAdapter(cmd); sda.Fill(Results); conn.Close(); sda.Dispose(); Where query is a string representing a large, time consuming query, and conn is the connection object. My problem now is I need a stop button. I've come to realize killing the backgroundworker would be worthless because I still want to keep what results are left over after the query is canceled. Plus it wouldn't be able to check the canceled state until after the query. What I've come up with so far: I've been trying to conceptualize how to handle this efficiently without taking too big of a performance hit. My idea was to use a SqlDataReader to read the data from the query piece at a time so that I had a "loop" to check a flag I could set from the GUI via a button. The problem is as far as I know I can't use the Load() method of a datatable and still be able to cancel the sqlcommand. If I'm wrong please let me know because that would make cancelling slightly easier. In light of what I discovered I came to the realization I may only be able to cancel the sqlcommand mid-query if I did something like the below (pseudo-code): while(reader.Read()) { //check flag status //if it is set to 'kill' fire off the kill thread //otherwise populate the datatable with what was read } However, it would seem to me this would be highly ineffective and possibly costly. Is this the only way to kill a sqlcommand in progress that absolutely needs to be in a datatable? Any help would be appreciated!

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• Fastest way to clamp a real (fixed/floating point) value?

  - by Niklas

  Hi, Is there a more efficient way to clamp real numbers than using if statements or ternary operators? I want to do this both for doubles and for a 32-bit fixpoint implementation (16.16). I'm not asking for code that can handle both cases; they will be handled in separate functions. Obviously, I can do something like: double clampedA; double a = calculate(); clampedA = a > MY_MAX ? MY_MAX : a; clampedA = a < MY_MIN ? MY_MIN : a; or double a = calculate(); double clampedA = a; if(clampedA > MY_MAX) clampedA = MY_MAX; else if(clampedA < MY_MIN) clampedA = MY_MIN; The fixpoint version would use functions/macros for comparisons. This is done in a performance-critical part of the code, so I'm looking for an as efficient way to do it as possible (which I suspect would involve bit-manipulation) EDIT: It has to be standard/portable C, platform-specific functionality is not of any interest here. Also, MY_MIN and MY_MAX are the same type as the value I want clamped (doubles in the examples above).

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• Common "truisms" needing correction the most

  - by Charles Bretana

  In addition to "I never met a man I didn't like", Will Rogers had another great little ditty I've always remembered. It went: "It's not what you don't know that'll hurt you, it's what you do know that ain't so." We all know or subscribe to many IT "truisms" that mostly have a strong basis in fact, in something in our professional careers, something we learned from others, lessons learned the hard way by ourselves, or by others who came before us. Unfortuntely, as these truisms spread throughout the community, the details—why they came about and the caveats that affect when they apply—tend to not spread along with them. We all have a tendency to look for, and latch on to, small "rules" or principles that we can use to avoid doing a complete exhaustive analysis for every decision. But even though they are correct much of the time, when we sometimes misapply them, we pay a penalty that could be avoided by understooding the details behind them. For example, when user-defined functions were first introduced in SQL Server it became "common knowledge" within a year or so that they had extremely bad performance (because it required a re-compilation for each use) and should be avoided. This "trusim" still increases many database developers' aversion to using UDFs, even though Microsoft's introduction of InLine UDFs, which do not suffer from this issue at all, mitigates this issue substantially. In recent years I have run into numerous DBAs who still believe you should "never" use UDFs, because of this. What other common not-so-"trusims" do you know, which many developers believe, that are not quite as universally true as is commonly understood, and which the developer community would benefit from being better educated about? Please include why it was "true" to start off with, and under what circumstances it's not true. Limit responses to issues that are technical, where the "common" application of a "rule or principle" is in fact correct most of the time, or was correct back when it was first elucidated, but—in the edge cases, or because of not understanding the principle thoroughly, because technology has changed since it first spread, or applying the rule today without understanding the details behind the rule—can easily backfire or cause the opposite of the intended effect.

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• Approaches for animating a C# property over time?

  - by Mario Fritsch

  I'm currently trying to animate a bunch of public properties on certain objects. Usually they are of type float or vectors of floats (the type is known at compile-time). I want to be able to: assign a static value to them (MyObject.Duration = 10f;) or assign a random value to them by specifying a minimum and maximum value and optionally also a weight (MyObject.Duration = new RandomFloat(5f, 20f, 2f);) or "bind" this property to the property of another object (think of a child object binding some of its properties to its parent object, like its color or size or sth.) or assign sort of a keyframe animation to them, specifying a variable number of keyframes with timecode and the property's value at that specific point in time as well as information about how to interpolate between these frames The keyframes should be able to accept random values for each frame, both for the time and the property's value. What would be a practical approach for this kind of system? Currently I'm thinking about polymorphism: implement a base class or interface with a public Value-property and/or GetValue(float time)-method and then creating different sub classes like StaticValue, RandomValue, BindingValue and AnimatedValue implementing this base class or interface. Doesn't seem very elegant, though, and the initialization of even simple objects becomes a bit tedious. Another idea would be to implement these properties just as regular floats or vectors and create special "Modifier"-types binding to these properties. To retrieve the "real" value of the property, I'd first call any Modifier bound to the property, which would in turn update the actual object's property for me to retrieve later on. That would most likely mean using reflection at some point, which could be quite bad for performance as I'll probably have thousands of properties to update dozens of times per second. Any suggestions on this? Being a novice I'm (hopefully) missing some far more elegant and/or practical solution than I'm already playing around with :( Edit: Probably should have mentioned this earlier, but WPF isn't an option - it's not available on all targetted platforms, so I can't rely on it. I'm aware of its powerful databinding and animation capabilities, but I need to roll my own (or find some other lightweight alternative meeting my needs).

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• Lightweight HTTP application/server for static content

  - by PartlyCloudy

  Hi, I am in need of a scalable and performant HTTP application/server that will be used for static file serving/uploading. So I only need support for GET and PUT operations. However, there are a few extra features that I need: Custom authentication: I need to check credentials against a database for each request. Thus I must be able to integrate propietary database interaction. Support for signed access keys: The access to resources via PUT should be signed using a key like http://uri/?key=foo The key then contains information about the request like md5(user + path + secret) which allows me to block unwanted requests. The application/server should allow me to check for this. Performance: I'd like to avoid piping content as much as possible. Otherwise the whole application could be implemented in Perl/etc. in a few lines as CGI. Perlbal (in webserver mode) looks nice, however the single-threaded model does not fit with my database lookup and it does also not support query strings. Lighttp/Nginx/… have some modules for these tasks, however it is not feasible putting everything together without ending up writing own extensions/modules. So how would you solve this? Are there other leightweight webservers available for this? Should I implement an application inside of a webserver (i.e. CGI). How can I avoid/speed up piping content between the webserver and my application. Thanks in advance!

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• AJAX or a server side framework?

  - by Romansky

  I am working with a friend on building a web site, in general this web site will be a custom web app along with a very custom social network type of thing.. Currently I have a mock-up site that uses simple PHP with AJAX and JSON and JQUERY and I love how it works, I love the way it all fits together. But for a mock-up I did not implement any of the Social Network design patterns such as a login, rating, groups etc.. This brought me to a higher level of decision making requirement, I need to decide if I want to develop all this functionality by hand or use some kind of a framework. I spent this entire day researching, and it would seem that using Drupal and such frameworks will make the Social Network part easy (overlooking the customization requirement for now..) but will make client side Web App development less so. I found some other frameworks that are more developer friendly (customizable) such as Zend and Symfony etc.. but these seem to take allot of the power from the client and implement it in the server side, to me this seems a waste (and an unjustified performance bottleneck) .. Finally I found Aptana Jaxer framework that seems to think the same way I feel. That said it seems a bit under-developed, I didn't find modules for a social network and the community around it seems thin.. (searching Jaxer in StackOverflow returns few results) So other then making server side DB comm a bit simpler it does not help me greatly.. My requirements are a good facility to develop web apps on while containing all the user centric logic usually used for social networks in advance. What would you recommend? EDIT: OK, lats fine tune this question, after considering this abit further, is there a good down loadable source of a social network site in PHP that I can work around in building my web app? (I really like using JQUERY AJAX JSON etc..)

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• Help regarding database and logic layer for my ASP.NET MVC application

  - by Ismail S

  I'm going to start a new project which is going to be small initially but may grow to big over the years. I'm strongly convinced that I'm going to use ASP.NET MVC with jQuery for UI. I want to go for MySQL as database for some reasons but worried on few things. I've a good years of experience working on SQL Server databases and on one project I've had a bad experience creating and managing stored procedures on MySQL database. I'm totally new to Linq but I see that it is easier to use once you are familiar with it. First thing is that accessing data should be easy. So I thought I should use MySQL to Linq but somewhere I read that it is not directly supported but MySQL .NET connector adds support for EntityFramework. I don't know what are the pros and cons of it. I would love if I can implement repository pattern. Will it be possible if I use Entity Framework? I'm not clear on how I should go about all this or I should just forget every thing and directly use SQL to Linq on SQL Server. I'm also concerned about the performance. Someone told me that if we use Entity framework it fetches lot of data and then filter it. Is that right?

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• The question about the basics of LINQ to SQL working

  - by Alex

  I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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• Bash PATH: How long is too long?

  - by ajwood

  Hi, I'm currently designing a software quarantine pattern to use on Ubuntu. I'm not sure how standard "quarantine" is in this context, so here is what I hope to accomplish... Inside a particular quarantine is all of the stuff one needs to run an application (bin, share, lib, etc.). Ideally, the quarantine has no leaks, which means it's not relying on any code outside of itself on the system. A quarantine can be defined as a set of executables (and some environment settings needed to make them run). I think it will be beneficial to separate the built packages enough such that upgrading to a newer version of the quarantine won't require rebuilding the whole thing. I'll be able to update just a few packages, and then the new quarantine can use some of old parts and some of the new parts. One issue I'm wondering about is the environment variables I'll be setting up to use a particular quarantines. Is there a hard limit on how big PATH can be? (either in number of characters, or in the number of directories it contains) Might a path be so long that it affects performance? Thanks very much, Andrew p.s. Any other wisdom that might help my design would be greatly appreciated :)

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• Using array of Action() in a lambda expression

  - by Sean87

  I want to do some performance measurement for a method that does some work with int arrays, so I wrote the following class: public class TimeKeeper { public TimeSpan Measure(Action[] actions) { var watch = new Stopwatch(); watch.Start(); foreach (var action in actions) { action(); } return watch.Elapsed; } } But I can not call the Measure mehotd for the example below: var elpased = new TimeKeeper(); elpased.Measure( () => new Action[] { FillArray(ref a, "a", 10000), FillArray(ref a, "a", 10000), FillArray(ref a, "a", 10000) }); I get the following errors: Cannot convert lambda expression to type 'System.Action[]' because it is not a delegate type Cannot implicitly convert type 'void' to 'System.Action' Cannot implicitly convert type 'void' to 'System.Action' Cannot implicitly convert type 'void' to 'System.Action' Here is the method that works with arrays: private void FillArray(ref int[] array, string name, int count) { array = new int[count]; for (int i = 0; i < array.Length; i++) { array[i] = i; } Console.WriteLine("Array {0} is now filled up with {1} values", name, count); } What I am doing wrong?

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• Multithreaded linked list traversal

  - by Rob Bryce

  Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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• Implement a threading to prevent UI block on a bug in an async function

  - by Marcx

  I think I ran up againt a bug in an async function... Precisely the getDirectoryListingAsync() of the File class... This method is supposted to return an object containing the lists of files in a specified folder. I found that calling this method on a direcory with a lot of files (in my tests more than 20k files), after few seconds there is a block on the UI until the process is completed... I think that this method is separated in two main block: 1) get the list of files 2) create the array with the details of the files The point 1 seems to be async (for a few second the ui is responsive), then when the process pass from point 1 to point 2 the block of the UI occurs until the complete event is dispathed... Here's some (simple) code: private function checkFiles(dir:File):void { if (dir.exists) { dir.addEventListener( FileListEvent.DIRECTORY_LISTING, listaImmaginiLocale); dir.getDirectoryListingAsync(); // after this point, for the firsts seconds the UI respond well (point 1), // few seconds later (point 2) the UI is frozen } } private function listaImmaginiLocale( event:FileListEvent ):void { // from this point on the UI is responsive again... } Actually in my projects there are some function that perform an heavy cpu usage and to prevent the UI block I implemented a simple function that after some iteration will wait giving time to UI to be refreshed. private var maxIteration:int = 150000; private function sampleFunct(offset:int = 0) :void { if (offset < maxIteration) { // do something // call the recursive function using a timeout.. // if the offset in multiple by 1000 the function will wait 15 millisec, // otherwise it will be called immediately // 1000 is a random number for the pourpose of this example, but I usually change the // value based on how much heavy is the function itself... setTimeout(function():void{aaa(++offset);}, (offset%1000?15:0)); } } Using this method I got a good responsive UI without afflicting performance... I'd like to implement it into the getDirectoryListingAsync method but I don't know if it's possibile how can I do it where is the file to edit or extend.. Any suggestion???

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• PHP modifying and combining array

  - by Industrial

  Hi everyone, I have a bit of an array headache going on. The function does what I want, but since I am not yet to well acquainted with PHP:s array/looping functions, so thereby my question is if there's any part of this function that could be improved from a performance-wise perspective? I tried to be as complete as possible in my descriptions in each stage of the functions which shortly described prefixes all keys in an array, fill up eventual empty/non-valid keys with '' and removes the prefixes before returning the array: $var = myFunction ( array('key1', 'key2', 'key3', '111') ); function myFunction ($keys) { $prefix = 'prefix_'; $keyCount = count($keys); // Prefix each key and remove old keys for($i=0;$i<$keyCount; $i++){ $keys[] = $prefix.$keys[$i]; unset($keys[$i]); } // output: array('prefix_key1', 'prefix_key2', 'prefix_key3', '111) // Get all keys from memcached. Only returns valid keys $items = $this->memcache->get($keys); // output: array('prefix_key1' => 'value1', 'prefix_key2' => 'value2', 'prefix_key3'=>'value3) // note: key 111 was not found in memcache. // Fill upp eventual keys that are not valid/empty from memcache $return = $items + array_fill_keys($keys, ''); // output: array('prefix_key1' => 'value1', 'prefix_key2' => 'value2', 'prefix_key3'=>'value3, 'prefix_111' => '') // Remove the prefixes for each result before returning array to application foreach ($return as $k => $v) { $expl = explode($prefix, $k); $return[$expl[1]] = $v; unset($return[$k]); } // output: array('key1' => 'value1', 'key2' => 'value2', 'key3'=>'value3, '111' => '') return $return; } Thanks a lot!

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• Nhibernate + Gridview + TargetInvocationException

  - by Scott

  For our grid views, we're setting the data sources as a list of results from an Nhibernate query. We're using lazy loading, so the objects are actually proxied... most of the time. In some instances the list will consist of types of Student and Composition_Aop_Proxy_jklasjdkl31231, which implements the same members as the Student class. We've still got the session open, so the lazy loading would resolve fine, if GridView didn't throw an error about the different types in the gridview. Our current workaround is to clone the object, which results in fetching all of the data that can be lazily loaded, even though most of it won't be accessed.. ever. This, however, converts the proxy into an actual object and the grid view is happy. The performance implications kind of scare me as we're getting closer to rolling the code out as is. I've tried evicting the object after a save, which should ensure that everything is a proxy, but this doesn't seem like a good idea either. Does anyone have any suggestions/workarounds?

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• How to use db4o IObjectContainer in a web application ? (Container lifetime ?)

  - by driis

  I am evaluating db4o for persistence for a ASP .NET MVC project. I am wondering how I should use the IObjectContainer in a web context with regards to object lifetime. As I see it, I can do one of the following: Create the IObjectContainer at application startup and keep the same instance for the entire application lifetime. Create one IObjectContainer per request. Start a server, and get a client IObjectContainer for each database interaction. What are the implications of these options, in terms of performance and concurrency ? Since the database is locked when an IObjectContainer is opened, I am pretty sure that option 2) would get me some problems with concurrency - would this also be the case for option 1 ? As I understand it, if I retrieve an object from an IObjectContainer, it must be saved by the same IObjectContainer instance - in order for db4o to identify it as being the same object. Therefore, If I choose option 3), I would have to retrieve the original object, make the necessary changes (copy data from a modified object), and then store it using the same IObjectContainer. Is this true ?

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• Best Functional Approach

  - by dbyrne

  I have some mutable scala code that I am trying to rewrite in a more functional style. It is a fairly intricate piece of code, so I am trying to refactor it in pieces. My first thought was this: def iterate(count:Int,d:MyComplexType) = { //Generate next value n //Process n causing some side effects return iterate(count - 1, n) } This didn't seem functional at all to me, since I still have side effects mixed throughout my code. My second thought was this: def generateStream(d:MyComplexType):Stream[MyComplexType] = { //Generate next value n return Stream.cons(n, generateStream(n)) } for (n <- generateStream(initialValue).take(2000000)) { //process n causing some side effects } This seemed like a better solution to me, because at least I've isolated my functional value-generation code from the mutable value-processing code. However, this is much less memory efficient because I am generating a large list that I don't really need to store. This leaves me with 3 choices: Write a tail-recursive function, bite the bullet and refactor the value-processing code Use a lazy list. This is not a memory sensitive app (although it is performance sensitive) Come up with a new approach. I guess what I really want is a lazily evaluated sequence where I can discard the values after I've processed them. Any suggestions?

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• On the search for my next great .Net Read

  - by user127954

  Just got done with "The art of unit testing". It was a great read and i think everyone should go buy a copy. With that said i think the next book I'm like to read would be a architecture / Design type book that would focus heavily on building your objects / software in such a way that it would be: Low Coupling High Cohesion Easily Maintainable / Extended Easy to test Easy to Navigate / Debug The above characteristcs are the most important ones but also maybe it would also include (but not necessary) designing for: Performance - Don't want to design a system at at the end find out its dog slow :) Scalability - Again don't want to design something at the end find out it won't scale. I'd also prefer (but not necessary again): Something newer - Architectural principles seem to gradually evolve / improve over time and id like something with current thinking. .Net as illustrating language - like i said above its not mandatory but since its what i use every day id prefer it to be in .net. Doesn't really matter if its in vb.net or c# Some of the topics that would be talked about its how to minimize dependencies and using interfaces throughout your solution rather than concrete classes. Maybe it would constract /compare some of the newest design principles like DDD, Repository Pattern, Ect... I already have "Clean Code" (don't know if its this type of book or not) and "Working effectively with legacy code" on my radar but id like to read a book based upon the topic i talked about above first. Is there such a book?

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• Saving tags into a database table in CakePHP

  - by Cameron

  I have the following setup for my CakePHP app: Posts id title content Topics id title Topic_Posts id topic_id post_id So basically I have a table of Topics (tags) that are all unique and have an id. And then they can be attached to post using the Topic_Posts join table. When a user creates a new post they will fill in the topics by typing them in to a textarea separated by a comma which will then save these into the Topics table if they do not already exist and then save the references into the Topic_posts table. I have the models set up like so: Post model: class Post extends AppModel { public $name = 'Post'; public $hasAndBelongsToMany = array( 'Topic' => array('with' => 'TopicPost') ); } Topic model: class Topic extends AppModel { public $hasMany = array( 'TopicPost' ); } TopicPost model: class TopicPost extends AppModel { public $belongsTo = array( 'Topic', 'Post' ); } And for the New post method I have this so far: public function add() { if ($this->request->is('post')) { //$this->Post->create(); if ($this->Post->saveAll($this->request->data)) { // Redirect the user to the newly created post (pass the slug for performance) $this->redirect(array('controller'=>'posts','action'=>'view','id'=>$this->Post->id)); } else { $this->Session->setFlash('Server broke!'); } } } As you can see I have used saveAll but how do I go about dealing with the Topic data?

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• Updating UI objects in windows forms

  - by P a u l

  Pre .net I was using MFC, ON_UPDATE_COMMAND_UI, and the CCmdUI class to update the state of my windows UI. From the older MFC/Win32 reference: Typically, menu items and toolbar buttons have more than one state. For example, a menu item is grayed (dimmed) if it is unavailable in the present context. Menu items can also be checked or unchecked. A toolbar button can also be disabled if unavailable, or it can be checked. Who updates the state of these items as program conditions change? Logically, if a menu item generates a command that is handled by, say, a document, it makes sense to have the document update the menu item. The document probably contains the information on which the update is based. If a command has multiple user-interface objects (perhaps a menu item and a toolbar button), both are routed to the same handler function. This encapsulates your user-interface update code for all of the equivalent user-interface objects in a single place. The framework provides a convenient interface for automatically updating user-interface objects. You can choose to do the updating in some other way, but the interface provided is efficient and easy to use. What is the guidance for .net Windows Forms? I am using an Application.Idle handler in the main form but am not sure this is the best way to do this. About the time I put all my UI updates in the Idle event handler my app started to show some performance problems, and I don't have the metrics to track this down yet. Not sure if it's related.

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• return Queryable<T> or List<T> in a Repository<T>

  - by Danny Chen

  Currently I'm building an windows application using sqlite. In the data base there is a table say User, and in my code there is a Repository<User> and a UserManager. I think it's a very common design. In the repository there is a List method: //Repository<User> class public List<User> List(where, orderby, topN parameters and etc) { //query and return } This brings a problem, if I want to do something complex in UserManager.cs: //UserManager.cs public List<User> ListUsersWithBankAccounts() { var userRep = new UserRepository(); var bankRep = new BankAccountRepository(); var result = //do something complex, say "I want the users live in NY //and have at least two bank accounts in the system } You can see, returning List<User> brings performance issue, becuase the query is executed earlier than expected. Now I need to change it to something like a IQueryable<T>: //Repository<User> class public TableQuery<User> List(where, orderby, topN parameters and etc) { //query and return } TableQuery<T> is part of the sqlite driver, which is almost equals to IQueryable<T> in EF, which provides a query and won't execute it immediately. But now the problem is: in UserManager.cs, it doesn't know what is a TableQuery<T>, I need to add new reference and import namespaces like using SQLite.Query in the business layer project. It really brings bad code feeling. Why should my business layer know the details of the database? why should the business layer know what's SQLite? What's the correct design then?

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