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• clarification on the concept of "web service"

  - by udit

  Im a little confused on the varying definitions and implementations of web services available as implementations. Need some clarification please. Ones I have used till now: If a vendor gives me a specific format of XML that I can send populated with data to request and I make a simple HTTP POST over the internet passing in the XML String as the payload, is this a web service call ? If so, is there a specific name to it, this kind of web service ? Because obviously, it does not use anything like Axis, WSDL or SOAP to establish this connection. A variant of this is If the vendor gives me an XSD, I use JAXB to make a java class out of it and pass in the serialized version of the object, which eventually works out to be the same as option 1. RESTful web service: Vendor gives me a URL like http://restfulservice/products and I can make HTTP Requests to the URL and depending on what HTTP verb I use, the appropropriate action is called and the response sent over the wire. Ones I have only read about\ have a vague idea about SOAP. How does this work?.. Ive read the W3Schools tutorial and I undertsand that there is a very specific form of XML that is standardized according to W3C standards that we use to pass the same kind of messages as we did in option 1. But how does this work in real life? Vendor sends me what? Do I generate classes? Do I serialize some objects and http post them over to an address? Or do the generated objects themselves have connection methods that will do them for me? What about WSDL? When does a vendor send me WSDL and what do I do with it ? I guess I can generate classes from it. If yes, then what do I do with the generated classes ? When do I need that axis jar to generate classes from something that the vendor sends ? As you can see, I have some clear and other mostly vague ideas about the different kinds of web services available. would help if someone ould clarify and\or point to more real-world resources. I've looked a little bit into Java Web Services on the internet and the numerous four letter acronyms that get thrown at me make me dizzy. Thanks

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• Google Code + SVN or GitHub + Git

  - by Nazgulled

  Let me start by telling you that I never used anything besides SVN and I'm also a Windows user. I have a couple of simple projects that are open-source, others are on there way when I'm happy enough to release their source code but either way, I was thinking of using Google Code and SVN to share the source code of my projects instead of providing a link to the source on my website. This as always been a pain cause I had to update the binaries and the code every time I released a new version. This would also help me out to have a backup of my code some where instead of just my local machine (I used to have a local Subversion server running). What I want from a service like this is very simple... I just want a place to store my source code that people can download if they want, allows me to control revisions and provide a simple and easy issue system so people can submit bugs and stuff like that. I guess both of them have this. But I don't want to host any binaries in their websites, I want this to be hosted on my website so I can control download statistics with my own scripts, I also don't have the need for wiki pages as I prefer to have all the documentation in my own website. Does anyone of this services provide a way to "disable" features like wiki and downloads and don't show them at all for my project(s)? Now, I'm sure there are lots of pros and cons about using Google Code with SVN and GitHub with Git (of course) but here's what it's important for me on each one and why I like them: Google Code: As with any Google page, the complexity is almost non-existent Everyone (or almost) as a Google account and this is nice if people want to report problems using the issues system GitHub: May (or may not) be a little more complex (not a problem for me though) than Google's pages but... ...has a much prettier interface than Google's service It needs people to be registered on GitHub to post about issues I like the fact that with Git, you have your own revisions locally (can I use TortoiseGit for this or?) Basically that's it, not much I know... What other, most common, pros and cons can you tell me about each site/software? Keep in mind that my projects are simple, I'm probably the only one who will ever develop these projects on these repositories (or maybe not, for now I will)

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• How to stream semi-live audio over internet

  - by Thomas Tempelmann

  I want to write something like Skype, i.e. I have a constant audio stream on one computer and then recompress it in a format that's suitable for a latent internet connection, receive it on the other end and play it. Let's also assume that the internet connection is fairly modern and fast, i.e. DSL or alike, no slow connections over phone and such. The involved computers will also be rather modern (Dual Core Intel CPUs at 2GHz or more). I know how to handle the audio on the machines. What I don't know is how to transmit the audio in an efficient way. The challenges are: I'd like get good audio quality across the line. The stream should be received without drops. The stream may, however, be received with a little delay (a second delay is acceptable). I imagine that the transport software could first determine the average (and max) latency, then start the stream and tell the receiver to wait for that max latency before starting to play the audio. With that, if the latency doesn't get any higher, the entire stream will be playable on the other side without stutter or drops. If, due to unexpected IP latencies or blockages, the stream does get cut off, I want to be able to notice this so that I can take actions (e.g. abort the stream) and eventually start a new transmission. What are my options if I want do use ready-made software for the compression and tranmission? I have no intention to write my own audio compression engine, really. OTOH, I plan to sell the solution in a vertical market, meaning I can afford a few dollars of license fees per copy, but not $100s. I guess the simplest solution would be to just open a TCP stream, send a few packets back and forth to determine their running time (or even use UDP for that), then use the results as the guide for my max latency value, then simply fire the audio data in its raw form (uncompressed 16 bit stereo), along with a timing code over the TCP connection. The receiver reads the data and plays it with the pre-determined delay. That might just work with the type of fast connection I expect. I just wonder if there are better solutions to reach this goal, with better performance (lower latency) and less data (compressed). BTW, I first try to implement this on OS X, but might want to do it on Windows, too, if it proves successful.

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• Python: How best to parse a simple grammar?

  - by Rosarch

  Ok, so I've asked a bunch of smaller questions about this project, but I still don't have much confidence in the designs I'm coming up with, so I'm going to ask a question on a broader scale. I am parsing pre-requisite descriptions for a course catalog. The descriptions almost always follow a certain form, which makes me think I can parse most of them. From the text, I would like to generate a graph of course pre-requisite relationships. (That part will be easy, after I have parsed the data.) Some sample inputs and outputs: "CS 2110" => ("CS", 2110) # 0 "CS 2110 and INFO 3300" => [("CS", 2110), ("INFO", 3300)] # 1 "CS 2110, INFO 3300" => [("CS", 2110), ("INFO", 3300)] # 1 "CS 2110, 3300, 3140" => [("CS", 2110), ("CS", 3300), ("CS", 3140)] # 1 "CS 2110 or INFO 3300" => [[("CS", 2110)], [("INFO", 3300)]] # 2 "MATH 2210, 2230, 2310, or 2940" => [[("MATH", 2210), ("MATH", 2230), ("MATH", 2310)], [("MATH", 2940)]] # 3 If the entire description is just a course, it is output directly. If the courses are conjoined ("and"), they are all output in the same list If the course are disjoined ("or"), they are in separate lists Here, we have both "and" and "or". One caveat that makes it easier: it appears that the nesting of "and"/"or" phrases is never greater than as shown in example 3. What is the best way to do this? I started with PLY, but I couldn't figure out how to resolve the reduce/reduce conflicts. The advantage of PLY is that it's easy to manipulate what each parse rule generates: def p_course(p): 'course : DEPT_CODE COURSE_NUMBER' p[0] = (p[1], int(p[2])) With PyParse, it's less clear how to modify the output of parseString(). I was considering building upon @Alex Martelli's idea of keeping state in an object and building up the output from that, but I'm not sure exactly how that is best done. def addCourse(self, str, location, tokens): self.result.append((tokens[0][0], tokens[0][1])) def makeCourseList(self, str, location, tokens): dept = tokens[0][0] new_tokens = [(dept, tokens[0][1])] new_tokens.extend((dept, tok) for tok in tokens[1:]) self.result.append(new_tokens) For instance, to handle "or" cases: def __init__(self): self.result = [] # ... self.statement = (course_data + Optional(OR_CONJ + course_data)).setParseAction(self.disjunctionCourses) def disjunctionCourses(self, str, location, tokens): if len(tokens) == 1: return tokens print "disjunction tokens: %s" % tokens How does disjunctionCourses() know which smaller phrases to disjoin? All it gets is tokens, but what's been parsed so far is stored in result, so how can the function tell which data in result corresponds to which elements of token? I guess I could search through the tokens, then find an element of result with the same data, but that feel convoluted... What's a better way to approach this problem?

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• Opinions on collision detection objects with a moving scene

  - by Evan Teran

  So my question is simple, and I guess it boils down to how anal you want to be about collision detection. To keep things simple, lets assume we're talking about 2D sprites defined by a bounding box. In addition, let's assume that my sprite object has a function to detect collisions like this: S.collidesWith(other); Finally the scene is moving and "walls" in the scene can move, an object may not touch a wall. So a simple implementation might look like this (psuedo code): moveWalls(); moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } The problem with this is that if the sprite and wall move towards each other, depending on the circumstances (such as diagonal moment). They may pass though each other (unlikely but could happen). So I may do this instead. moveWalls(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } This takes care of the passing through each other issue, but another rare issue comes up. If they are adjacent to each other (literally the next pixel) and both the wall and the sprite are moving left, then I will get an invalid collision since the wall moves, checks for collision (hit) then the sprite is moved. Which seems unfair. In addition, to that, the redundant collision detection feels very inefficient. I could give the player movement priority alleviating the first issue but it is still checking twice. moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } moveWalls(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } Am I simply over thinking this issue, should this just be chalked up to "it'll happen rare enough that no one will care"? Certainly looking at old sprite based games, I often find situations where the collision detection has subtle flaws, but I figure by now we can do better :-P. What are people's thoughts?

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• Intent filter for browsing XML (specifically rss) in android

  - by Leif Andersen

  I have an activity that I want to run every time the user goes to an xml (specifically rss) page in the browser (at least assuming the user get's it from the list of apps that can support it). I currently already have the current intent filter: <activity android:name=".activities.EpisodesListActivity" android:theme="@android:style/Theme.NoTitleBar"> <intent-filter> <category android:name="android.intent.category.BROWSABLE"></category> <category android:name="android.intent.category.DEFAULT"></category> <action android:name="android.intent.action.VIEW"></action> <data android:scheme="http"></data> </intent-filter> </activity> Now as you can guess, this is an evil intent, as it wants to open whenever a page is requested via http. However, when I ad the line: <data android:mimeType="application/rss+xml"></data> to make it: <activity android:name=".activities.EpisodesListActivity" android:theme="@android:style/Theme.NoTitleBar"> <intent-filter> <category android:name="android.intent.category.BROWSABLE"></category> <category android:name="android.intent.category.DEFAULT"></category> <action android:name="android.intent.action.VIEW"></action> <data android:scheme="http"></data> <data android:mimeType="application/rss+xml"></data> </intent-filter> </activity> The application no longer claims to be able to run rss files. Also, if I change the line to: <data android:mimeType="application/xml"></data> It also won't work (for generic xml file even). So what intent filter do I need to make in order to claim that the activity supports rss. (Also, bonus points if you can tell me how I know what URL it was the user opened. So far, I've always sent that information from one activity to the other using extras). Thank you for your help

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• Arbitrary Form Processing with Drupal

  - by Aaron

  I am writing a module for my organization to cache XML feeds to static files to an arbitrary place on our webserver. I am new at Drupal development, and would like to know if I am approaching this the right way. Basically I: Expose a url via the menu hook, where a user can enter in a an output directory on the webserver and press the "dump" button and then have PHP go to drupal and get the feed xml. I don't need help with that functionality, because I actually have a prototype working in Python (outside of Drupal).. Provide a callback for the form where I can do my logic, using the form parameters. Here's the menu hook: function ncbi_cache_files_menu() { $items = array(); $items['admin/content/ncbi_cache_files'] = array( 'title' => 'NCBI Cache File Module', 'description' => 'Cache Guide static content to files', 'page callback' => 'drupal_get_form', 'page arguments' => array( 'ncbi_cache_files_show_submit'), 'access arguments' => array( 'administer site configuration' ), 'type' => MENU_NORMAL_ITEM, ); return $items; } I generate the form in: function ncbi_cache_files_show_submit() { $DEFAULT_OUT = 'http://myorg/foo'; $form[ 'ncbi_cache_files' ] = array( '#type' => 'textfield', '#title' => t('Output Directory'), '#description' => t('Where you want the static files to be dumped. This should be a directory that www has write access to, and should be accessible from the foo server'), '#default_value' => t( $DEFAULT_OUT ), '#size' => strlen( $DEFAULT_OUT ) + 5, ); $form['dump'] = array( '#type' => 'submit', '#value' => 'Dump', '#submit' => array( 'ncbi_cache_files_dump'), ); return system_settings_form( $form ); } Then the functionality is in the callback: function ncbi_cache_files_dump( $p, $q) { //dpm( get_defined_vars() ); $outdir = $p['ncbi_cache_files']['#post']['ncbi_cache_files']; drupal_set_message('outdir: ' . $outdir ); } The question: Is this a decent way of processing an arbitrary form in Drupal? I not really need to listen for any drupal hooks, because I am basically just doing some URL and file processing. What are those arguments that I'm getting in the callback ($q)? That's the form array I guess, with the post values? Is this the best way to get the form parameters to work on? Thanks for any advice.

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• libXcodeDebuggerSupport.dylib is missing in iOS 4.2.1 development SDK

  - by Kalle

  Note: creating a symbolic link to use the 4.2 lib seems to work fine -- maybe cd /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1\ \(8C148\)/Symbols/ sudo ln -s ../../4.2 (8C134)/Symbols/Developer Request: See end of this question! After upgrading from 4.2.0 (beta, I believe) to 4.2.1, the libXcodeDebuggerSupport.dylib file is missing, which results in: warning: Unable to read symbols for /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1 (8C148)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib (file not found). which I guess isn't good. Looking at the directory in question I note: .../DeviceSupport/4.2 (8C134)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib but .../DeviceSupport/4.2.1 (8C148)/Symbols/System/ .../DeviceSupport/4.2.1 (8C148)/Symbols/usr/ the above two dirs make up all the content in the 4.2.1 folder. No "Developer" folder. Checking the /usr/ dir there, I find no libXcodeDebuggerSupport.dylib file in the lib dir either, so ln -s'ing isn't an option. Worth mentioning: after the upgrade, I plugged the iPad in and had to click "Use for development" in Xcode organizer. Doing so, I got a message about symbols missing for that version, and Xcode proceeded to generate such, then failed. I restored the iPad and did "Use for development" again, and nothing about missing symbols appeared... Update: deletion of /Developer and reinstallation of Xcode from scratch does not fix this issue. Update 2: I just realized that after the reinstall of Xcode, .../DeviceSupport/4.2 (8C134)/Symbols is now a symbolic link, lrwxr-xr-x 1 root admin 36 Dec 3 17:17 Symbols -> ../../Developer/SDKs/iPhoneOS4.2.sdk And the directory in question has the appropriate files. Maybe this is simply a matter of linking the 4.2.1 dir in the same fashion? I'll try that and see if Xcode freaks out. If someone who has this file could provide a md5 sum that would be splendid. This is what it says for me: $ md5 /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2\ \(8C134\)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib MD5 (/Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2 (8C134)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib) = 08f93a0a2e3b03feaae732691f112688 If the MD5 sum is identical to the output of $ md5 /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1\ \(8C148\)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib then we're all set.

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• Looping through array in PHP to post several multipart form-data

  - by Léon Pelletier

  I'm trying in an asp web application to code a function that would loop through a list of files in a multiple upload form and send them one by one. Is this something that can be done in ASP? Because I've read some posts about how to attach several files together, but saw nothing about looping through the files. I can easily imagine it in C# via HttpWebRequest or with socket, but in php, I guess there are already function designed to handle it? // This is false/pseudo-code :) for (int index = 0; index < number_of_files; index++) { postfile(file[index]); } And in each iteration, it should send a multipart form-data POST. postfile(TheFileInfos) should make a POST like it: POST /afs.aspx?fn=upload HTTP/1.1 [Header stuff] Content-Type: multipart/form-data; boundary=----------Ef1Ef1cH2Ij5GI3ae0gL6KM7GI3GI3 [Header stuff] ------------Ef1Ef1cH2Ij5GI3ae0gL6KM7GI3GI3 Content-Disposition: form-data; name="Filename" myimage1.png ------------Ef1Ef1cH2Ij5GI3ae0gL6KM7GI3GI3 Content-Disposition: form-data; name="fileid" 58e21ede4ead43a5201206101806420000007667212251 ------------Ef1Ef1cH2Ij5GI3ae0gL6KM7GI3GI3 Content-Disposition: form-data; name="Filedata"; filename="myimage1.png" Content-Type: application/octet-stream [Octet Stream] [Edit] I'll try it: <html> <head> <title>Untitled Document</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head> <body> <form name="form1" enctype="multipart/form-data" method="post" action="processFiles.php"> <p> <? // start of dynamic form $uploadNeed = $_POST['uploadNeed']; for($x=0;$x<$uploadNeed;$x++){ ?> <input name="uploadFile<? echo $x;?>" type="file" id="uploadFile<? echo $x;?>"> </p> <? // end of for loop } ?> <p><input name="uploadNeed" type="hidden" value="<? echo $uploadNeed;?>"> <input type="submit" name="Submit" value="Submit"> </p> </form> </body> </html>

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• Loading images to UIScrollview crashes

  - by Icky

  Hello All. I have a Navigationcontroller pushing a UIViewController with a scrollview inside. Within the scrollview I download a certain number of images around 20 (sometimes more) each sized around 150 KB. All these images are added to the scrollview so that their origin is x +imageSize and the following is sorted right to the one before. All in all I think its a lot of data (3-4 MB). On an I pod Touch this sometimes crashes, the IPhone can handle it once, if it has to load the data again (some other images) , it crashes too. I guess its a memory issue but within my code, I download the image, save it to a file on the phone as NSData, read it again from file and add it to a UIImageview which I release. So I have freed the memory I allocated, nevertheless it still crashes. Can anyone help me out? Since Im new to this, I dont know the best way to handle the Images in a scrollview. Besides I create the controller at start from nib, which means I dont have to release it, since I dont use alloc - right? Code: In my rootviewcontroller I do: -(void) showImages { [[self naviController] pushViewController:imagesViewController animated:YES]; [imagesViewController viewWillAppear:YES]; } Then in my Controller handling the scroll View, this is the method to load the images: - (void) loadOldImageData { for (int i = 0; i < 40 ; i++) { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *filePath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"img%d.jpg", i]]; NSData *myImg = [NSData dataWithContentsOfFile:filePath]; UIImage *im = [UIImage imageWithData:myImg]; if([im isKindOfClass:[UIImage class]]) { NSLog(@"IM EXISTS"); UIImageView *imgView = [[UIImageView alloc] initWithImage:im]; CGRect frame = CGRectMake(i*320, 0, 320, 416); imgView.frame = frame; [myScrollView addSubview:imgView]; [imgView release]; //NSLog(@"Adding img %d", i); numberImages = i; NSLog(@"setting numberofimages to %d", numberImages); //NSLog(@"scroll subviews %d", [myScrollView.subviews count]); } } myScrollView.contentSize = CGSizeMake(320 * (numberImages + 1), 416); }

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• Which network protocol to use for lightweight notification of remote apps?

  - by Chris Thornton

  I have this situation.... Client-initiated SOAP 1.1 communication between one server and let's say, tens of thousands of clients. Clients are external, coming in through our firewall, authenticated by certificate, https, etc.. They can be anywhere, and usually have their own firewalls, NAT routers, etc... They're truely external, not just remote corporate offices. They could be in a corporate/campus network, DSL/Cable, even Dialup. Client uses Delphi (2005 + SOAP fixes from 2007), and the server is C#, but from an architecture/design standpoint, that shouldn't matter. Currently, clients push new data to the server and pull new data from the server on 15-minute polling loop. The server currently does not push data - the client hits the "messagecount" method, to see if there is new data to pull. If 0, it sleeps for another 15 min and checks again. We're trying to get that down to 7 seconds. If this were an internal app, with one or just a few dozen clients, we'd write a cilent "listener" soap service, and would push data to it. But since they're external, sit behind their own firewalls, and sometimes private networks behind NAT routers, this is not practical. So we're left with polling on a much quicker loop. 10K clients, each checking their messagecount every 10 seconds, is going to be 1000/sec messages that will mostly just waste bandwidth, server, firewall, and authenticator resources. So I'm trying to design something better than what would amount to a self-inflicted DoS attack. I don't think it's practical to have the server send soap messages to the client (push) as this would require too much configuration at the client end. But I think there are alternatives that I don't know about. Such as: 1) Is there a way for the client to make a request for GetMessageCount() via Soap 1.1, and get the response, and then perhaps, "stay on the line" for perhaps 5-10 minutes to get additional responses in case new data arrives? i.e the server says "0", then a minute later in response to some SQL trigger (the server is C# on Sql Server, btw), knows that this client is still "on the line" and sends the updated message count of "5"? 2) Is there some other protocol that we could use to "ping" the client, using information gathered from their last GetMessageCount() request? 3) I don't even know. I guess I'm looking for some magic protocol where the client can send a GetMessageCount() request, which would include info for "oh by the way, in case the answer changes in the next hour, ping me at this address...". Also, I'm assuming that any of these "keep the line open" schemes would seriously impact the server sizing, as it would need to keep many thousands of connections open, simultaneously. That would likely impact the firewalls too, I think. Is there anything out there like that? Or am I pretty much stuck with polling? TIA, Chris

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• What are the pros and cons of using manual list iteration vs recursion through fail

  - by magus

  I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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• TimeOuts with HttpWebRequest when running Selenium concurrently in .NET

  - by domsom

  I have a download worker that uses ThreadPool-threads to download files. After enhancing these to apply some Selenium tests to the downloaded files, I am constantly experiencing TimeOut-exceptions with the file downloaders and delays running the Selenium tests. More precisely: When the program starts, the download threads start downloading and a couple of pages are seamlessly processed via Selenium Shortly after, the first download threads start throwing TimeOut exceptions from HttpWebRequest. At the same time, commands stop flowing to Selenium (as observed in the SeleniumRC log), but the thread running Selenium is not getting any exception This situation holds as long as there are entries in the download list: new download threads are being started and terminate after receiving TimeOuts (without trying to lock Selenium) As soon as no more download threads are being started, Selenium starts receiving commands again and the threads waiting for the lock are processed sequentially as designed Now here's the download code: HttpWebRequest request = null; WebResponse response = null; Stream stream = null; StreamReader sr = null; try { request = (HttpWebRequest) WebRequest.Create(uri); request.ServicePoint.ConnectionLimit = MAX_CONNECTIONS_PER_HOST; response = request.GetResponse(); stream = response.GetResponseStream(); // Read the stream... } finally { if (request != null) request.Abort(); if (response != null) response.Close(); if (stream != null) { stream.Close(); stream.Dispose(); } if (sr != null) { sr.Close(); sr.Dispose(); } } And this is how Selenium is used afterwards in the same thread: lock(SeleniumLock) { selenium.Open(url); // Run some Selenium commands, but no selenium.stop() } Where selenium is a static variable that is initialized in the static constructor of the class (via selenium.start()). I assume I am running into the CLR connection limit, so I added these lines during initalization: ThreadPool.GetMaxThreads (out maxWorkerThreads, out maxCompletionPortThreads); HttpUtility.MAX_CONNECTIONS_PER_HOST = maxWorkerThreads; System.Net.ServicePointManager.DefaultConnectionLimit = maxWorkerThreads + 1; The + 1 is for the connection to the SeleniumRC, due to my guess that the Selenium client code also uses HttpWebRequest. It seems like I'm still running into some kind of deadlock - although the threads waiting for the Selenium lock do not hold any resources. Any ideas on how to get this working?

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• Generic Type constraint in .net

  - by Jose

  Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes. I want to require a generic type passed into my class to have a constructor like this: new(IDictionary<string,object>) so the class would look like this public MyClass<T> where T : new(IDictionary<string,object>) { T CreateObject(IDictionary<string,object> values) { return new T(values); } } But the compiler doesn't support this, it doesn't really know what I'm asking. Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values. I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options: 1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values. 2) require T to support an interface like so: public interface ILoadValues { void LoadValues(IDictionary values); } and then do this public MyClass<T> where T:new(),ILoadValues { T CreateObject(IDictionary<string,object> values) { T obj = new T(); obj.LoadValues(values); return obj; } } The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this namespace DataSource.Data { public class User { protected internal User(IDictionary<string,object> values) { //Initialize } } } As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!) Anyways any input is welcome.

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• C++ using cdb_read returns extra characters on some reads

  - by Moe Be

  Hi All, I am using the following function to loop through a couple of open CDB hash tables. Sometimes the value for a given key is returned along with an additional character (specifically a CTRL-P (a DLE character/0x16/0o020)). I have checked the cdb key/value pairs with a couple of different utilities and none of them show any additional characters appended to the values. I get the character if I use cdb_read() or cdb_getdata() (the commented out code below). If I had to guess I would say I am doing something wrong with the buffer I create to get the result from the cdb functions. Any advice or assistance is greatly appreciated. char* HashReducer::getValueFromDb(const string &id, vector <struct cdb *> &myHashFiles) { unsigned char hex_value[BUFSIZ]; size_t hex_len; //construct a real hex (not ascii-hex) value to use for database lookups atoh(id,hex_value,&hex_len); char *value = NULL; vector <struct cdb *>::iterator my_iter = myHashFiles.begin(); vector <struct cdb *>::iterator my_end = myHashFiles.end(); try { //while there are more databases to search and we have not found a match for(; my_iter != my_end && !value ; my_iter++) { //cerr << "\n looking for this MD5:" << id << " hex(" << hex_value << ") \n"; if (cdb_find(*my_iter, hex_value, hex_len)){ //cerr << "\n\nI found the key " << id << " and it is " << cdb_datalen(*my_iter) << " long\n\n"; value = (char *)malloc(cdb_datalen(*my_iter)); cdb_read(*my_iter,value,cdb_datalen(*my_iter),cdb_datapos(*my_iter)); //value = (char *)cdb_getdata(*my_iter); //cerr << "\n\nThe value is:" << value << " len is:" << strlen(value)<< "\n\n"; }; } } catch (...){} return value; }

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• How would you implement this "WorkerChain" functionality in .NET?

  - by Dan Tao

  Sorry for the vague question title -- not sure how to encapsulate what I'm asking below succinctly. (If someone with editing privileges can think of a more descriptive title, feel free to change it.) The behavior I need is this. I am envisioning a worker class that accepts a single delegate task in its constructor (for simplicity, I would make it immutable -- no more tasks can be added after instantiation). I'll call this task T. The class should have a simple method, something like GetToWork, that will exhibit this behavior: If the worker is not currently running T, then it will start doing so right now. If the worker is currently running T, then once it is finished, it will start T again immediately. GetToWork can be called any number of times while the worker is running T; the simple rule is that, during any execution of T, if GetToWork was called at least once, T will run again upon completion (and then if GetToWork is called while T is running that time, it will repeat itself again, etc.). Now, this is pretty straightforward with a boolean switch. But this class needs to be thread-safe, by which I mean, steps 1 and 2 above need to comprise atomic operations (at least I think they do). There is an added layer of complexity. I have need of a "worker chain" class that will consist of many of these workers linked together. As soon as the first worker completes, it essentially calls GetToWork on the worker after it; meanwhile, if its own GetToWork has been called, it restarts itself as well. Logically calling GetToWork on the chain is essentially the same as calling GetToWork on the first worker in the chain (I would fully intend that the chain's workers not be publicly accessible). One way to imagine how this hypothetical "worker chain" would behave is by comparing it to a team in a relay race. Suppose there are four runners, W1 through W4, and let the chain be called C. If I call C.StartWork(), what should happen is this: If W1 is at his starting point (i.e., doing nothing), he will start running towards W2. If W1 is already running towards W2 (i.e., executing his task), then once he reaches W2, he will signal to W2 to get started, immediately return to his starting point and, since StartWork has been called, start running towards W2 again. When W1 reaches W2's starting point, he'll immediately return to his own starting point. If W2 is just sitting around, he'll start running immediately towards W3. If W2 is already off running towards W3, then W2 will simply go again once he's reached W3 and returned to his starting point. The above is probably a little convoluted and written out poorly. But hopefully you get the basic idea. Obviously, these workers will be running on their own threads. Also, I guess it's possible this functionality already exists somewhere? If that's the case, definitely let me know!

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• Autoconf -- building with static library (newbie)

  - by EB

  I am trying to migrate my application from manual build to autoconf, which is working very nicely so far. But I have one static library that I can't figure out how to integrate. That library will NOT be located in the usual library locations - the location of the binary (.a file) and header (.h file) will be given as a configure argument. (Notably, even if I move the .a file to /usr/lib or anywhere else I can think of, it still won't work.) It is also not named traditionally (it does not start with "lib" or "l"). Manual compilation is working with these (directory is not predictable - this is just an example): gcc ... -I/home/john/mystuff /home/john/mystuff/helper.a (Uh, I actually don't understand why the .a file is referenced directly, not with -L or anything. Yes, I have a half-baked understanding of building C programs.) So, in my configure.ac, I can use the relevant configure argument to successfully find the header (.h file) using AC_CHECK_HEADER. Inside the AC_CHECK_HEADER I then add the location to CPFLAGS and the #include of the header file in the actual C code picks it up nicely. Given a configure argument that has been put into $location and the name of the needed files are helper.h and helper.a (which are both in the same directory), here is what works so far: AC_CHECK_HEADER([$location/helper.h], [AC_DEFINE([HAVE_HELPER_H], [1], [found helper.h]) CFLAGS="$CFLAGS -I$location"]) Where I run into difficulties is getting the binary (.a file) linked in. No matter what I try, I always get an error about undefined references to the function calls for that library. I'm pretty sure it's a linkage issue, because I can fuss with the C code and make an intentional error in the function calls to that library which produces earlier errors that indicate that the function prototypes have been loaded and used to compile. I tried adding the location that contains the .a file to LDFLAGS and then doing a AC_CHECK_LIB but it is not found. Maybe my syntax is wrong, or maybe I'm missing something more fundamental, which would not be surprising since I'm a newbie and don't really know what I'm doing. Here is what I have tried: AC_CHECK_HEADER([$location/helper.h], [AC_DEFINE([HAVE_HELPER_H], [1], [found helper.h]) CFLAGS="$CFLAGS -I$location"; LDFLAGS="$LDFLAGS -L$location"; AC_CHECK_LIB(helper)]) No dice. AC_CHECK_LIB is looking for -lhelper I guess (or libhelper?) so I'm not sure if that's a problem, so I tried this, too (omit AC_CHECK_LIB and include the .a directly in LDFLAGS), without luck: AC_CHECK_HEADER([$location/helper.h], [AC_DEFINE([HAVE_HELPER_H], [1], [found helper.h]) CFLAGS="$CFLAGS -I$location"; LDFLAGS="$LDFLAGS -L$location/helper.a"]) To emulate the manual compilation, I tried removing the -L but that doesn't help: AC_CHECK_HEADER([$location/helper.h], [AC_DEFINE([HAVE_HELPER_H], [1], [found helper.h]) CFLAGS="$CFLAGS -I$location"; LDFLAGS="$LDFLAGS $location/helper.a"]) I tried other combinations and permutations, but I think I might be missing something more fundamental....

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• SOAP WCF Webservice behaves differently when called locally or remotely

  - by Idriss

  I have a WCF SOAP 1.1 Webservice with the configuration specified below. A concurrent call to any method of this endpoint hangs until the other returns when called remotely (from another computer on the network). I cannot replicate this when these methods are called locally (with a client located on the same machine). I tried to increase the maxConcurrentCalls with no luck ... the service behavior seems to be different according to the client local/remote location. Any guess? Thanks, <?xml version="1.0" encoding="utf-8"?> <configuration> <system.serviceModel> <services> <service behaviorConfiguration="MyCustomBehavior" name="CONTOSO.CONTOSOServerApi.IContosoServiceApiImplV1"> <endpoint address="" binding="customBinding" bindingConfiguration="WebBinding" bindingNamespace="http://contoso.com" contract="CONTOSO.CONTOSOServerApiInterfaceV1.IContosoServiceApiV1" /> </service> </services> <behaviors> <serviceBehaviors> <behavior name="MyCustomBehavior"> <serviceMetadata httpGetEnabled="true" httpGetUrl="http://localhost:8080/MyEndPointV1" /> <serviceDebug httpHelpPageEnabled="false" includeExceptionDetailInFaults="true" /> <serviceThrottling maxConcurrentSessions="10000" maxConcurrentCalls="1000"/> <dataContractSerializer maxItemsInObjectGraph="2147483647" /> </behavior> </serviceBehaviors> </behaviors> <bindings> <customBinding> <binding name="WebBinding"> <textMessageEncoding messageVersion="Soap11" maxReadPoolSize="2147483647" maxWritePoolSize="2147483647"> <readerQuotas maxDepth="2147483647" maxStringContentLength="2147483647" maxArrayLength="2147483647" maxBytesPerRead="2147483647" maxNameTableCharCount="2147483647" /> </textMessageEncoding> <httpsTransport /> </binding> </customBinding> </bindings> </system.serviceModel> </configuration>

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• How can I progrommatically change the target framework from 4.0 to 3.5 of a project/solution?

  - by scott

  Edit 3: After more googling it looks like you can't have the TargetFrameworkMoniker property in a .NET 3.5 application. So I guess I should be asking a different question. How do I change the Target framework from 4.0 to 3.5? Unfortunately, I can only find stuff on how to go the other way. or better yet how do i progrommatically set the target framework version of a project to something other than 4.0? Original question: I just switched to vs2010. I have an application that uses .net 3.5. It loads plugins which are generated by a different app. The plugins are using .net 4 and there for cannot be loaded. I'm using EnvDTE.Project to create a project and set the settings. I can't find what setting needs to be set for this. Edit 1: I'm generating code for about 50 solutions. When I made the switch from vs2005 to vs2010 the projects in those solutions are defaulting to .NET Framework 4.0. So I need to set the .NET Framework to 3.5 when I am generating the code for these solutions. Edit 2: After a lot of googling I found this. so then I tried this: loProp = vsGetProperty("TargetFrameworkMoniker"); vsSetValue(loProp, ".NETFramework,Version=v3.5"); the definitions for those two methods are below. as far as I can tell they do the same this as project.Properties.Item("TargetFrameworkMoniker").Value = ".NETFramework,Version=v4.0,Profile=Client"; I start getting an Property Unavailable Exception later in the code. When I remove the new lines everything works except the projects target framework is still 4.0. The code generators target framework is 3.5 so I can't use the FrameworkName class like shown in the second example in that link. here is vsGetProperty protected Property vsGetProperty(string aProperty) { bool lbDone = false; int liCount = 0; Property loProp; while (!lbDone && liCount < pMaxRetries) { try { loProp = pProject.Properties.Item(aProperty); lbDone = true; return loProp; } catch (System.Runtime.InteropServices.COMException loE) { liCount++; if ((uint)loE.ErrorCode == 0x80010001) { // RPC_E_CALL_REJECTED - sleep half sec then try again System.Threading.Thread.Sleep(pDelayBetweenRetry); } } } return null; } and vsSetValue protected void vsSetValue(Property aProperty, string aValue) { bool lbDone = false; int liCount = 0; while (!lbDone && liCount < pMaxRetries) { try { aProperty.Value = aValue; lbDone = true; } catch (System.Runtime.InteropServices.COMException loE) { liCount++; if ((uint)loE.ErrorCode == 0x80010001) { // RPC_E_CALL_REJECTED - sleep half sec then try again System.Threading.Thread.Sleep(pDelayBetweenRetry); } } } }

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• Is a Multi-DAL Approach the way to go here?

  - by Krisc

  Working on the data access / model layer in this little MVC2 project and trying to think things out to future projects. I have a database with some basic tables and I have classes in the model layer that represent them. I obviously need something to connect the two. The easiest is to provide some sort of 'provider' that can run operations on the database and return objects. But this is for a website that would potentially be used "a lot" (I know, very general) so I want to cache results from the data layer and keep the cache updated as new data is generated. This question deals with how best to approach this problem of dual DALS. One that returns cached data when possible and goes to the data layer when there is a cache miss. But more importantly, how to integrate the core provider (thing that goes into database) with the caching layer so that it too can rely on cached objects rather than creating new ones. Right now I have the following interfaces: IDataProvider is used to reach the database. It doesn't concern itself with the meaning of the objects it produces, but simply the way to produce them. interface IDataProvider{ // Select, Update, Create, et cetera access IEnumerable<Entry> GetEntries(); Entry GetEntryById(int id); } IDataManager is a layer that sits on top of the IDataProvider layer and manages the cache interface IDataManager : IDataProvider{ void ClearCache(); } Note that in practice the IDataManager implementation will have useful helper functions to add objects to their related cache stores. (In the future I may define other functions on the interface) I guess what I am looking for is the best way to approach a loop back from the IDataProvider implementations so that they can access the cache. Or a different approach entirely may be in order? I am not very interested in 3rd party products at the moment as I am interested in the design of these things much more than this specific implementation. Edit: I realize the title may be a bit misleading. I apologize for that... not sure what to call this question.

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• grdb not working variables

  - by stupid_idiot

  hi, i know this is kinda retarded but I just can't figure it out. I'm debugging this: xor eax,eax mov ah,[var1] mov al,[var2] call addition stop: jmp stop var1: db 5 var2: db 6 addition: add ah,al ret the numbers that I find on addresses var1 and var2 are 0x0E and 0x07. I know it's not segmented, but that ain't reason for it to do such escapades, because the addition call works just fine. Could you please explain to me where is my mistake? I see the problem, dunno how to fix it yet though. The thing is, for some reason the instruction pointer starts at 0x100 and all the segment registers at 0x1628. To address the instruction the used combination is i guess [cs:ip] (one of the segment registers and the instruction pointer for sure). The offset to var1 is 0x10 (probably because from the begining of the code it's the 0x10th byte in order), i tried to examine the memory and what i got was: 1628:100 8 bytes 1628:108 8 bytes 1628:110 <- wtf? (assume another 8 bytes) 1628:118 ... whatever tricks are there in the memory [cs:var1] points somewhere else than in my code, which is probably where the label .data would usually address ds.... probably.. i don't know what is supposed to be at 1628:10 ok, i found out what caused the assness and wasted me whole fuckin day. the behaviour described above is just correct, the code is fully functional. what i didn't know is that grdb debugger for some reason sets the begining address to 0x100... the sollution is to insert the directive ORG 0x100 on the first line and that's the whole thing. the code was working because instruction pointer has the right address to first instruction and goes one by one, but your assembler doesn't know what effective address will be your program stored at so it pretty much remains relative to first line of the code which means all the variables (if not using label for data section) will remain pointing as if it started at 0x0. which of course wouldn't work with DOS. and grdb apparently emulates some DOS features... sry for the language, thx everyone for effort, hope this will spare someone's time if having the same problem... heheh.. at least now i know the reason why to use .data section :))))

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• MySQL - Calculating fields on the fly vs storing calculated data

  - by Christian Varga

  Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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• g++ linker error--typeinfo, but not vtable

  - by James

  I know the standard answer for a linker error about missing typeinfo usually also involves vtable and some virtual function that I forgot to actually define. I'm fairly certain that's not the situation this time. Here's the error: UI.o: In function boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::Resource::GroupByState>(boost::shared_ptr<Graphics::Resource::GroupByState> const&, boost::detail::dynamic_cast_tag)': UI.cpp:(.text._ZN5boost10shared_ptrIN8Graphics7Widgets9WidgetSetEEC1INS1_8Resource12GroupByStateEEERKNS0_IT_EENS_6detail16dynamic_cast_tagE[boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::Resource::GroupByState>(boost::shared_ptr<Graphics::Resource::GroupByState> const&, boost::detail::dynamic_cast_tag)]+0x30): undefined reference totypeinfo for Graphics::Widgets::WidgetSet' Running c++filt on the obnoxious mangled name shows that it actually is looking at .boost::shared_ptr::shared_ptr(boost::shared_ptr const&, boost::detail::dynamic_cast_tag) The inheritance hierarchy looks something like class AbstractGroup { typedef boost::shared_ptr<AbstractGroup> Ptr; ... }; class WidgetSet : public AbstractGroup { typedef boost::shared_ptr<WidgetSet> Ptr; ... }; class GroupByState : public AbstractGroup { ... }; Then there's this: class UI : public GroupByState { ... void LoadWidgets( GroupByState::Ptr resource ); }; Then the original implementation: void UI::LoadWidgets( GroupByState::Ptr resource ) { WidgetSet::Ptr tmp( boost::dynamic_pointer_cast< WidgetSet >(resource) ); if( tmp ) { ... } } Stupid error on my part (trying to cast to a sibling class with a shared parent), even if the error is kind of cryptic. Changing to this: void UI::LoadWidgets( AbstractGroup::Ptr resource ) { WidgetSet::Ptr tmp( boost::dynamic_pointer_cast< WidgetSet >(resource) ); if( tmp ) { ... } } (which I'm fairly sure is what I actually meant to be doing) left me with a very similar error: UI.o: In function boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::_Drawer::Group>(boost::shared_ptr<Graphics::_Drawer::Group> const&, boost::detail::dynamic_cast_tag)': UI.cpp:(.text._ZN5boost10shared_ptrIN8Graphics7Widgets9WidgetSetEEC1INS1_7_Drawer5GroupEEERKNS0_IT_EENS_6detail16dynamic_cast_tagE[boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::_Drawer::Group>(boost::shared_ptr<Graphics::_Drawer::Group> const&, boost::detail::dynamic_cast_tag)]+0x30): undefined reference totypeinfo for Graphics::Widgets::WidgetSet' collect2: ld returned 1 exit status dynamic_cast_tag is just an empty struct in boost/shared_ptr.hpp. It's just a guess that boost might have anything at all to do with the error. Passing in a WidgetSet::Ptr totally eliminates the need for a cast, and it builds fine (which is why I think there's more going on than the standard answer for this question). Obviously, I'm trimming away a lot of details that might be important. My next step is to cut it down to the smallest example that fails to build, but I figured I'd try the lazy way out and take a stab on here first. TIA!

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• Mercurial local repository backup

  - by Ricket

  I'm a big fan of backing things up. I keep my important school essays and such in a folder of my Dropbox. I make sure that all of my photos are duplicated to an external drive. I have a home server where I keep important files mirrored across two drives inside the server (like a software RAID 1). So for my code, I have always used Subversion to back it up. I keep the trunk folder with a stable copy of my application, but then I create a branch named with my username, and inside there is my working copy. I make very few changes between commits to that branch, with the understanding that the code in there is my backup. Now I'm looking into Mercurial, and I must admit I haven't truly used it yet so I may have this all wrong. But it seems to me that you have a server-side repository, and then you clone it to a working directory in the form of a local repository. Then as you work on something, you make commits to that local repository, and when things are in a state to be shared with others, you hg push to the parent repository on the server. Between pushes of stable, tested, bug-free code, where is the backup? After doing some thinking, I've come to the conclusion that it is not meant for backup purposes and it assumes you've handled that on your own. I guess I need to keep my Mercurial local repositories in my dropbox or some other backed-up location, since my in-progress code is not pushed to the server. Is this pretty much it, or have I missed something? If you use Mercurial, how do you backup your local repositories? If you had turned on your computer this morning and your hard drive went up in flames (or, more likely, the read head went bad, or the OS corrupted itself, ...), what would be lost? If you spent the past week developing a module, writing test cases for it, documenting and commenting it, and then a virus wipes your local repository away, isn't that the only copy? So then on the flip side, do you create a remote repository for every local repository and push to it all the time? How do you find a balance? How do you ensure your code is backed up? Where is the line between using Mercurial as backup, and using a local filesystem backup utility to keep your local repositories safe?

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• C++ game designing & polymorphism question

  - by Kotti

  Hi! I'm trying to implement some sort of 'just-for-me' game engine and the problem's plot goes the following way: Suppose I have some abstract interface for a renderable entity, e.g. IRenderable. And it's declared the following way: interface IRenderable { // (...) // Suppose that Backend is some abstract backend used // for rendering, and it's implementation is not important virtual void Render(Backend& backend) = 0; }; What I'm doing right now is something like declaring different classes like class Ball : public IRenderable { virtual void Render(Backend& backend) { // Rendering implementation, that is specific for // the Ball object // (...) } }; And then everything looks fine. I can easily do something like std::vector<IRenderable*> items, push some items like new Ball() in this vector and then make a call similiar to foreach (IRenderable* in items) { item->Render(backend); } Ok, I guess it is the 'polymorphic' way, but what if I want to have different types of objects in my game and an ability to manipulate their state, where every object can be manipulated via it's own interface? I could do something like struct GameState { Ball ball; Bonus bonus; // (...) }; and then easily change objects state via their own methods, like ball.Move(...) or bonus.Activate(...), where Move(...) is specific for only Ball and Activate(...) - for only Bonus instances. But in this case I lose the opportunity to write foreach IRenderable* simply because I store these balls and bonuses as instances of their derived, not base classes. And in this case the rendering procedure turns into a mess like ball.Render(backend); bonus.Render(backend); // (...) and it is bad because we actually lose our polymorphism this way (no actual need for making Render function virtual, etc. The other approach means invoking downcasting via dynamic_cast or something with typeid to determine the type of object you want to manipulate and this looks even worse to me and this also breaks this 'polymorphic' idea. So, my question is - is there some kind of (probably) alternative approach to what I want to do or can my current pattern be somehow modified so that I would actually store IRenderable* for my game objects (so that I can invoke virtual Render method on each of them) while preserving the ability to easily change the state of these objects? Maybe I'm doing something absolutely wrong from the beginning, if so, please point it out :) Thanks in advance!

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