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  • Is the Observer pattern adequate for this kind of scenario?

    - by Omega
    I'm creating a simple game development framework with Ruby. There is a node system. A node is a game entity, and it has position. It can have children nodes (and one parent node). Children are always drawn relatively to their parent. Nodes have a @position field. Anyone can modify it. When such position is modified, the node must update its children accordingly to properly draw them relatively to it. @position contains a Point instance (a class with x and y properties, plus some other useful methods). I need to know when a node's @position's state changes, so I can tell the node to update its children. This is easy if the programmer does something like this: @node.position = Point.new(300,300) Because it is equivalent to calling this: # Code in the Node class def position=(newValue) @position = newValue update_my_children # <--- I know that the position changed end But, I'm lost when this happens: @node.position.x = 300 The only one that knows that the position changed is the Point instance stored in the @position property of the node. But I need the node to be notified! It was at this point that I considered the Observer pattern. Basically, Point is now observable. When a node's position property is given a new Point instance (through the assignment operator), it will stop observing the previous Point it had (if any), and start observing the new one. When a Point instance gets a state change, all observers (the node owning it) will be notified, so now my node can update its children when the position changes. A problem is when this happens: @someNode.position = @anotherNode.position This means that two nodes are observing the same point. If I change one of the node's position, the other would change as well. To fix this, when a position is assigned, I plan to create a new Point instance, copy the passed argument's x and y, and store my newly created point instead of storing the passed one. Another problem I fear is this: somePoint = @node.position somePoint.x = 500 This would, technically, modify @node's position. I'm not sure if anyone would be expecting that behavior. I'm under the impression that people see Point as some kind of primitive rather than an actual object. Is this approach even reasonable? Reasons I'm feeling skeptical: I've heard that the Observer pattern should be used with, well, many observers. Technically, in this scenario there is only one observer at a time. When assigning a node's position as another's (@someNode.position = @anotherNode.position), where I create a whole new instance rather than storing the passed point, it feels hackish, or even inefficient.

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  • How to design a streaming API

    - by DotDot
    I want to design a web svc that will push out data as they arrive at the backend server. Something like a twitter streaming API. I want to use the .Net platform The consumers can use json and javascript events to be notified when new stuff is in the pipe. How can I design something like this?

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  • Is this a valid implementation of the repository pattern?

    - by user1578653
    I've been reading up about the repository pattern, with a view to implementing it in my own application. Almost all examples I've found on the internet use some kind of existing framework rather than showing how to implement it 'from scratch'. Here's my first thoughts of how I might implement it - I was wondering if anyone could advise me on whether this is correct? I have two tables, named CONTAINERS and BITS. Each CONTAINER can contain any number of BITs. I represent them as two classes: class Container{ private $bits; private $id; //...and a property for each column in the table... public function __construct(){ $this->bits = array(); } public function addBit($bit){ $this->bits[] = $bit; } //...getters and setters... } class Bit{ //some properties, methods etc... } Each class will have a property for each column in its respective table. I then have a couple of 'repositories' which handle things to do with saving/retrieving these objects from the database: //repository to control saving/retrieving Containers from the database class ContainerRepository{ //inject the bit repository for use later public function __construct($bitRepo){ $this->bitRepo = $bitRepo; } public function getById($id){ //talk directly to Oracle here to all column data into the object //get all the bits in the container $bits = $this->bitRepo->getByContainerId($id); foreach($bits as $bit){ $container->addBit($bit); } //return an instance of Container } public function persist($container){ //talk directly to Oracle here to save it to the database //if its ID is NULL, create a new container in database, otherwise update the existing one //use BitRepository to save each of the Bits inside the Container $bitRepo = $this->bitRepo; foreach($container->bits as $bit){ $bitRepo->persist($bit); } } } //repository to control saving/retrieving Bits from the database class BitRepository{ public function getById($id){} public function getByContainerId($containerId){} public function persist($bit){} } Therefore, the code I would use to get an instance of Container from the database would be: $bitRepo = new BitRepository(); $containerRepo = new ContainerRepository($bitRepo); $container = $containerRepo->getById($id); Or to create a new one and save to the database: $bitRepo = new BitRepository(); $containerRepo = new ContainerRepository($bitRepo); $container = new Container(); $container->setSomeProperty(1); $bit = new Bit(); $container->addBit($bit); $containerRepo->persist($container); Can someone advise me as to whether I have implemented this pattern correctly? Thanks!

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  • What font do you use for your code editor?

    - by Harmen
    For a long time I used Courier New as default font for my code editor, until I got more into typography and found this new fixed-width font called Triskweline: The font is beautiful, but unfortunately it works only at size 10pt. This made me wonder: what (custom) font do you use for your code editor?

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  • JEditorPane Code Completion (Part 2)

    - by Geertjan
    Figured it out! No need to create a fake Java file, unlike what I said in part 1, no need to depend on all the Java Editor modules, if you use DialogBinding.bindComponentToDocument, instead of DialogBinding.bindComponentToFile: public final class CountryEditorTopComponent extends TopComponent {     public CountryEditorTopComponent() {         initComponents();         setName(Bundle.CTL_CountryEditorTopComponent());         setToolTipText(Bundle.HINT_CountryEditorTopComponent());         EditorKit kit = CloneableEditorSupport.getEditorKit("text/plain");         jEditorPane1.setEditorKit(kit);         DialogBinding.bindComponentToDocument(jEditorPane1.getDocument(), 0, 0, jEditorPane1);         jEditorPane1.setText("Egypt");     } The above requires a dependency on Editor Library 2, which is where DialogBinding is found. Aside from that, you need all the dependencies required by the Code Completion API, as described in the Code Completion tutorial on the NetBeans Platform Learning Trail. Once you've done that, go to the Project Properties dialog of the application and then in the "ide" cluster, include "Plain Editor" and "Plain Editor Library". I.e., two additional JARs only. These two are needed because you've set the MIME type to "text/plain", which is needed because DialogBinding expects the JEditorPane to have a MIME type. And now everything works. Press Ctrl-Space in your JEditorPane and, because your CompletionProvider is registered in "text/x-dialog-binding" (via the annotation on CompletionProvider), your completion items are displayed. (The only MIME type for binding a document to a component, by default, is "text/x-dialog-binding", which means the next step is for someone to figure out how to support multiple different of such MIME types, since each JEditorPane in your application is likely to require its own specific code completion support.) I think this is a really workable solution for real scenarios where JEditorPanes in NetBeans Platform applications require code completion.

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  • How to get a ?High Quality? Custom Logo Design

    Custom Logo Design, are logos designed specifically, uniquely and creatively for a business. The competition between the different logo design service providers is fierce. There is a flood of service... [Author: Claudia Winifred - Web Design and Development - March 20, 2010]

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  • Table Design for (Currently Viewing Videos)?

    - by Surya sasidhar
    hi, I am doing a project on video portal, in that i am trying to place for currently viewing videos. People who r currently viewing that video. For this i have design the table like this table:(columns) Sno,videoid,sessionid,userid,createddate these are the columns but it is not sufficient i think if possible can u help me how can i design the table. how can we perfectly represent the currently viewing videos. Please help me thank you

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  • How to propagate http response code from back-end to client

    - by Manoj Neelapu
    Oracle service bus can be used as for pass through casses. Some use cases require propagating the http-response code back to the caller. http://forums.oracle.com/forums/thread.jspa?messageID=4326052&#4326052 is one such example we will try to accomplish in this tutorial.We will try to demonstrate this feature using Oracle Service Bus (11.1.1.3.0. We will also use commons-logging-1.1.1, httpcomponents-client-4.0.1, httpcomponents-core-4.0.1 for writing the client to demonstrate.First we create a simple JSP which will always set response code to 304.The JSP snippet will look like <%@ page language="java"     contentType="text/xml;     charset=UTF-8"        pageEncoding="UTF-8" %><%      System.out.println("Servlet setting Responsecode=304");    response.setStatus(304);    response.flushBuffer();%>We will now deploy this JSP on weblogic server with URI=http://localhost:7021/reponsecode/For this JSP we will create a simple Any XML BS We will also create proxy service as shown below Once the proxy is created we configure pipeline for the proxy to use route node, which invokes the BS(JSPCaller) created in the first place. So now we will create a error handler for route node and will add a stage. When a HTTP BS sends a request, the JSP sends the response back. If the response code is not 200, then the http BS will consider that as error and the above configured error handler is invoked. We will print $outbound to show the response code sent by the JSP. The next actions. To test this I had create a simple clientimport org.apache.http.Header;import org.apache.http.HttpEntity;import org.apache.http.HttpHost;import org.apache.http.HttpResponse;import org.apache.http.HttpVersion;import org.apache.http.client.methods.HttpGet;import org.apache.http.conn.ClientConnectionManager;import org.apache.http.conn.scheme.PlainSocketFactory;import org.apache.http.conn.scheme.Scheme;import org.apache.http.conn.scheme.SchemeRegistry;import org.apache.http.impl.client.DefaultHttpClient;import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;import org.apache.http.params.BasicHttpParams;import org.apache.http.params.HttpParams;import org.apache.http.params.HttpProtocolParams;import org.apache.http.util.EntityUtils;/** * @author MNEELAPU * */public class TestProxy304{    public static void main(String arg[]) throws Exception{     HttpHost target = new HttpHost("localhost", 7021, "http");     // general setup     SchemeRegistry supportedSchemes = new SchemeRegistry();     // Register the "http" protocol scheme, it is required     // by the default operator to look up socket factories.     supportedSchemes.register(new Scheme("http",              PlainSocketFactory.getSocketFactory(), 7021));     // prepare parameters     HttpParams params = new BasicHttpParams();     HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);     HttpProtocolParams.setContentCharset(params, "UTF-8");     HttpProtocolParams.setUseExpectContinue(params, true);     ClientConnectionManager connMgr = new ThreadSafeClientConnManager(params,              supportedSchemes);     DefaultHttpClient httpclient = new DefaultHttpClient(connMgr, params);     HttpGet req = new HttpGet("/HttpResponseCode/ProxyExposed");     System.out.println("executing request to " + target);     HttpResponse rsp = httpclient.execute(target, req);     HttpEntity entity = rsp.getEntity();     System.out.println("----------------------------------------");     System.out.println(rsp.getStatusLine());     Header[] headers = rsp.getAllHeaders();     for (int i = 0; i < headers.length; i++) {         System.out.println(headers[i]);     }     System.out.println("----------------------------------------");     if (entity != null) {         System.out.println(EntityUtils.toString(entity));     }     // When HttpClient instance is no longer needed,      // shut down the connection manager to ensure     // immediate deallocation of all system resources     httpclient.getConnectionManager().shutdown();     }}On compiling and executing this we see the below output in STDOUT which clearly indicates the response code was propagated from Business Service to Proxy serviceexecuting request to http://localhost:7021----------------------------------------HTTP/1.1 304 Not ModifiedDate: Tue, 08 Jun 2010 16:13:42 GMTContent-Type: text/xml; charset=UTF-8X-Powered-By: Servlet/2.5 JSP/2.1----------------------------------------  

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  • Is it bad practice to make an iterator that is aware of its own end

    - by aaronman
    For some background of why I am asking this question here is an example. In python the method chain chains an arbitrary number of ranges together and makes them into one without making copies. Here is a link in case you don't understand it. I decided I would implement chain in c++ using variadic templates. As far as I can tell the only way to make an iterator for chain that will successfully go to the next container is for each iterator to to know about the end of the container (I thought of a sort of hack in where when != is called against the end it will know to go to the next container, but the first way seemed easier and safer and more versatile). My question is if there is anything inherently wrong with an iterator knowing about its own end, my code is in c++ but this can be language agnostic since many languages have iterators. #ifndef CHAIN_HPP #define CHAIN_HPP #include "iterator_range.hpp" namespace iter { template <typename ... Containers> struct chain_iter; template <typename Container> struct chain_iter<Container> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end;//never really used but kept it for consistency public: chain_iter(Container & container, bool is_end=false) : begin(container.begin()),end(container.end()) { if(is_end) begin = container.end(); } chain_iter & operator++() { ++begin; return *this; } auto operator*()->decltype(*begin) { return *begin; } bool operator!=(const chain_iter & rhs) const{ return this->begin != rhs.begin; } }; template <typename Container, typename ... Containers> struct chain_iter<Container,Containers...> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end; bool end_reached = false; chain_iter<Containers...> next_iter; public: chain_iter(Container & container, Containers& ... rest, bool is_end=false) : begin(container.begin()), end(container.end()), next_iter(rest...,is_end) { if(is_end) begin = container.end(); } chain_iter & operator++() { if (begin == end) { ++next_iter; } else { ++begin; } return *this; } auto operator*()->decltype(*begin) { if (begin == end) { return *next_iter; } else { return *begin; } } bool operator !=(const chain_iter & rhs) const { if (begin == end) { return this->next_iter != rhs.next_iter; } else return this->begin != rhs.begin; } }; template <typename ... Containers> iterator_range<chain_iter<Containers...>> chain(Containers& ... containers) { auto begin = chain_iter<Containers...>(containers...); auto end = chain_iter<Containers...>(containers...,true); return iterator_range<chain_iter<Containers...>>(begin,end); } } #endif //CHAIN_HPP

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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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  • django/python: is one view that handles two sibling models a good idea?

    - by clime
    I am using django multi-table inheritance: Video and Image are models derived from Media. I have implemented two views: video_list and image_list, which are just proxies to media_list. media_list returns images or videos (based on input parameter model) for a certain object, which can be of type Event, Member, or Crag. The view alters its behaviour based on input parameter action (better name would be mode), which can be of value "edit" or "view". The problem is that I need to ask whether the input parameter model contains Video or Image in media_list so that I can do the right thing. Similar condition is also in helper method media_edit_list that is called from the view. I don't particularly like it but the only alternative I can think of is to have separate (but almost the same) logic for video_list and image_list and then probably also separate helper methods for videos and images: video_edit_list, image_edit_list, video_view_list, image_view_list. So four functions instead of just two. That I like even less because the video functions would be very similar to the respective image functions. What do you recommend? Here is extract of relevant parts: http://pastebin.com/07t4bdza. I'll also paste the code here: #urls url(r'^media/images/(?P<rel_model_tag>(event|member|crag))/(?P<rel_object_id>\d+)/(?P<action>(view|edit))/$', views.image_list, name='image-list') url(r'^media/videos/(?P<rel_model_tag>(event|member|crag))/(?P<rel_object_id>\d+)/(?P<action>(view|edit))/$', views.video_list, name='video-list') #views def image_list(request, rel_model_tag, rel_object_id, mode): return media_list(request, Image, rel_model_tag, rel_object_id, mode) def video_list(request, rel_model_tag, rel_object_id, mode): return media_list(request, Video, rel_model_tag, rel_object_id, mode) def media_list(request, model, rel_model_tag, rel_object_id, mode): rel_model = tag_to_model(rel_model_tag) rel_object = get_object_or_404(rel_model, pk=rel_object_id) if model == Image: star_media = rel_object.star_image else: star_media = rel_object.star_video filter_params = {} if rel_model == Event: filter_params['event'] = rel_object_id elif rel_model == Member: filter_params['members'] = rel_object_id elif rel_model == Crag: filter_params['crag'] = rel_object_id media_list = model.objects.filter(~Q(id=star_media.id)).filter(**filter_params).order_by('date_added').all() context = { 'media_list': media_list, 'star_media': star_media, } if mode == 'edit': return media_edit_list(request, model, rel_model_tag, rel_object_id, context) return media_view_list(request, model, rel_model_tag, rel_object_id, context) def media_view_list(request, model, rel_model_tag, rel_object_id, context): if request.is_ajax(): context['base_template'] = 'boxes/base-lite.html' return render(request, 'media/list-items.html', context) def media_edit_list(request, model, rel_model_tag, rel_object_id, context): if model == Image: get_media_edit_record = get_image_edit_record else: get_media_edit_record = get_video_edit_record media_list = [get_media_edit_record(media, rel_model_tag, rel_object_id) for media in context['media_list']] if context['star_media']: star_media = get_media_edit_record(context['star_media'], rel_model_tag, rel_object_id) else: star_media = None json = simplejson.dumps({ 'star_media': star_media, 'media_list': media_list, }) return HttpResponse(json, content_type=json_response_mimetype(request)) def get_image_edit_record(image, rel_model_tag, rel_object_id): record = { 'url': image.image.url, 'name': image.title or image.filename, 'type': mimetypes.guess_type(image.image.path)[0] or 'image/png', 'thumbnailUrl': image.thumbnail_2.url, 'size': image.image.size, 'id': image.id, 'media_id': image.media_ptr.id, 'starUrl':reverse('image-star', kwargs={'image_id': image.id, 'rel_model_tag': rel_model_tag, 'rel_object_id': rel_object_id}), } return record def get_video_edit_record(video, rel_model_tag, rel_object_id): record = { 'url': video.embed_url, 'name': video.title or video.url, 'type': None, 'thumbnailUrl': video.thumbnail_2.url, 'size': None, 'id': video.id, 'media_id': video.media_ptr.id, 'starUrl': reverse('video-star', kwargs={'video_id': video.id, 'rel_model_tag': rel_model_tag, 'rel_object_id': rel_object_id}), } return record # models class Media(models.Model, WebModel): title = models.CharField('title', max_length=128, default='', db_index=True, blank=True) event = models.ForeignKey(Event, null=True, default=None, blank=True) crag = models.ForeignKey(Crag, null=True, default=None, blank=True) members = models.ManyToManyField(Member, blank=True) added_by = models.ForeignKey(Member, related_name='added_images') date_added = models.DateTimeField('date added', auto_now_add=True, null=True, default=None, editable=False) class Image(Media): image = ProcessedImageField(upload_to='uploads', processors=[ResizeToFit(width=1024, height=1024, upscale=False)], format='JPEG', options={'quality': 75}) thumbnail_1 = ImageSpecField(source='image', processors=[SmartResize(width=178, height=134)], format='JPEG', options={'quality': 75}) thumbnail_2 = ImageSpecField(source='image', #processors=[SmartResize(width=256, height=192)], processors=[ResizeToFit(height=164)], format='JPEG', options={'quality': 75}) class Video(Media): url = models.URLField('url', max_length=256, default='') embed_url = models.URLField('embed url', max_length=256, default='', blank=True) author = models.CharField('author', max_length=64, default='', blank=True) thumbnail = ProcessedImageField(upload_to='uploads', processors=[ResizeToFit(width=1024, height=1024, upscale=False)], format='JPEG', options={'quality': 75}, null=True, default=None, blank=True) thumbnail_1 = ImageSpecField(source='thumbnail', processors=[SmartResize(width=178, height=134)], format='JPEG', options={'quality': 75}) thumbnail_2 = ImageSpecField(source='thumbnail', #processors=[SmartResize(width=256, height=192)], processors=[ResizeToFit(height=164)], format='JPEG', options={'quality': 75}) class Crag(models.Model, WebModel): name = models.CharField('name', max_length=64, default='', db_index=True) normalized_name = models.CharField('normalized name', max_length=64, default='', editable=False) type = models.IntegerField('crag type', null=True, default=None, choices=crag_types) description = models.TextField('description', default='', blank=True) country = models.ForeignKey('country', null=True, default=None) #TODO: make this not null when db enables it latitude = models.FloatField('latitude', null=True, default=None) longitude = models.FloatField('longitude', null=True, default=None) location_index = FixedCharField('location index', length=24, default='', editable=False, db_index=True) # handled by db, used for marker clustering added_by = models.ForeignKey('member', null=True, default=None) #route_count = models.IntegerField('route count', null=True, default=None, editable=False) date_created = models.DateTimeField('date created', auto_now_add=True, null=True, default=None, editable=False) last_modified = models.DateTimeField('last modified', auto_now=True, null=True, default=None, editable=False) star_image = models.ForeignKey('Image', null=True, default=None, related_name='star_crags', on_delete=models.SET_NULL) star_video = models.ForeignKey('Video', null=True, default=None, related_name='star_crags', on_delete=models.SET_NULL)

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  • Why is x=x++ undefined?

    - by ugoren
    It's undefined because the it modifies x twice between sequence points. The standard says it's undefined, therefore it's undefined. That much I know. But why? My understanding is that forbidding this allows compilers to optimize better. This could have made sense when C was invented, but now seems like a weak argument. If we were to reinvent C today, would we do it this way, or can it be done better? Or maybe there's a deeper problem, that makes it hard to define consistent rules for such expressions, so it's best to forbid them? So suppose we were to reinvent C today. I'd like to suggest simple rules for expressions such as x=x++, which seem to me to work better than the existing rules. I'd like to get your opinion on the suggested rules compared to the existing ones, or other suggestions. Suggested Rules: Between sequence points, order of evaluation is unspecified. Side effects take place immediately. There's no undefined behavior involved. Expressions evaluate to this value or that, but surely won't format your hard disk (strangely, I've never seen an implementation where x=x++ formats the hard disk). Example Expressions x=x++ - Well defined, doesn't change x. First, x is incremented (immediately when x++ is evaluated), then it's old value is stored in x. x++ + ++x - Increments x twice, evaluates to 2*x+2. Though either side may be evaluated first, the result is either x + (x+2) (left side first) or (x+1) + (x+1) (right side first). x = x + (x=3) - Unspecified, x set to either x+3 or 6. If the right side is evaluated first, it's x+3. It's also possible that x=3 is evaluated first, so it's 3+3. In either case, the x=3 assignment happens immediately when x=3 is evaluated, so the value stored is overwritten by the other assignment. x+=(x=3) - Well defined, sets x to 6. You could argue that this is just shorthand for the expression above. But I'd say that += must be executed after x=3, and not in two parts (read x, evaluate x=3, add and store new value). What's the Advantage? Some comments raised this good point. It's not that I'm after the pleasure of using x=x++ in my code. It's a strange and misleading expression. What I want is to be able to understand complicated expressions. Normally, a complicated expression is no more than the sum of its parts. If you understand the parts and the operators combining them, you can understand the whole. C's current behavior seems to deviate from this principle. One assignment plus another assignment suddenly doesn't make two assignments. Today, when I look at x=x++, I can't say what it does. With my suggested rules, I can, by simply examining its components and their relations.

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  • django/python: is one view that handles two separate models a good idea?

    - by clime
    I am using django multi-table inheritance: Video and Image are models derived from Media. I have implemented two views: video_list and image_list, which are just proxies to media_list. media_list returns images or videos (based on input parameter model) for a certain object, which can be of type Event, Member, or Crag. It alters its behaviour based on input parameter action, which can be either "edit" or "view". The problem is that I need to ask whether the input parameter model contains Video or Image in media_list so that I can do the right thing. Similar condition is also in helper method media_edit_list that is called from the view. I don't particularly like it but the only alternative I can think of is to have separate logic for video_list and image_list and then probably also separate helper methods for videos and images: video_edit_list, image_edit_list, video_view_list, image_view_list. So four functions instead of just two. That I like even less because the video functions would be very similar to the respective image functions. What do you recommend? Here is extract of relevant parts: http://pastebin.com/07t4bdza. I'll also paste the code here: #urls url(r'^media/images/(?P<rel_model_tag>(event|member|crag))/(?P<rel_object_id>\d+)/(?P<action>(view|edit))/$', views.video_list, name='image-list') url(r'^media/videos/(?P<rel_model_tag>(event|member|crag))/(?P<rel_object_id>\d+)/(?P<action>(view|edit))/$', views.image_list, name='video-list') #views def image_list(request, rel_model_tag, rel_object_id, action): return media_list(request, Image, rel_model_tag, rel_object_id, action) def video_list(request, rel_model_tag, rel_object_id, action): return media_list(request, Video, rel_model_tag, rel_object_id, action) def media_list(request, model, rel_model_tag, rel_object_id, action): rel_model = tag_to_model(rel_model_tag) rel_object = get_object_or_404(rel_model, pk=rel_object_id) if model == Image: star_media = rel_object.star_image else: star_media = rel_object.star_video filter_params = {} if rel_model == Event: filter_params['media__event'] = rel_object_id elif rel_model == Member: filter_params['media__members'] = rel_object_id elif rel_model == Crag: filter_params['media__crag'] = rel_object_id media_list = model.objects.filter(~Q(id=star_media.id)).filter(**filter_params).order_by('media__date_added').all() context = { 'media_list': media_list, 'star_media': star_media, } if action == 'edit': return media_edit_list(request, model, rel_model_tag, rel_model_id, context) return media_view_list(request, model, rel_model_tag, rel_model_id, context) def media_view_list(request, model, rel_model_tag, rel_object_id, context): if request.is_ajax(): context['base_template'] = 'boxes/base-lite.html' return render(request, 'media/list-items.html', context) def media_edit_list(request, model, rel_model_tag, rel_object_id, context): if model == Image: get_media_record = get_image_record else: get_media_record = get_video_record media_list = [get_media_record(media, rel_model_tag, rel_object_id) for media in context['media_list']] if context['star_media']: star_media = get_media_record(star_media, rel_model_tag, rel_object_id) star_media['starred'] = True else: star_media = None json = simplejson.dumps({ 'star_media': star_media, 'media_list': media_list, }) return HttpResponse(json, content_type=json_response_mimetype(request)) # models class Media(models.Model, WebModel): title = models.CharField('title', max_length=128, default='', db_index=True, blank=True) event = models.ForeignKey(Event, null=True, default=None, blank=True) crag = models.ForeignKey(Crag, null=True, default=None, blank=True) members = models.ManyToManyField(Member, blank=True) added_by = models.ForeignKey(Member, related_name='added_images') date_added = models.DateTimeField('date added', auto_now_add=True, null=True, default=None, editable=False) def __unicode__(self): return self.title def get_absolute_url(self): return self.image.url if self.image else self.video.embed_url class Image(Media): image = ProcessedImageField(upload_to='uploads', processors=[ResizeToFit(width=1024, height=1024, upscale=False)], format='JPEG', options={'quality': 75}) thumbnail_1 = ImageSpecField(source='image', processors=[SmartResize(width=178, height=134)], format='JPEG', options={'quality': 75}) thumbnail_2 = ImageSpecField(source='image', #processors=[SmartResize(width=256, height=192)], processors=[ResizeToFit(height=164)], format='JPEG', options={'quality': 75}) class Video(Media): url = models.URLField('url', max_length=256, default='') embed_url = models.URLField('embed url', max_length=256, default='', blank=True) author = models.CharField('author', max_length=64, default='', blank=True) thumbnail = ProcessedImageField(upload_to='uploads', processors=[ResizeToFit(width=1024, height=1024, upscale=False)], format='JPEG', options={'quality': 75}, null=True, default=None, blank=True) thumbnail_1 = ImageSpecField(source='thumbnail', processors=[SmartResize(width=178, height=134)], format='JPEG', options={'quality': 75}) thumbnail_2 = ImageSpecField(source='thumbnail', #processors=[SmartResize(width=256, height=192)], processors=[ResizeToFit(height=164)], format='JPEG', options={'quality': 75}) class Crag(models.Model, WebModel): name = models.CharField('name', max_length=64, default='', db_index=True) normalized_name = models.CharField('normalized name', max_length=64, default='', editable=False) type = models.IntegerField('crag type', null=True, default=None, choices=crag_types) description = models.TextField('description', default='', blank=True) country = models.ForeignKey('country', null=True, default=None) #TODO: make this not null when db enables it latitude = models.FloatField('latitude', null=True, default=None) longitude = models.FloatField('longitude', null=True, default=None) location_index = FixedCharField('location index', length=24, default='', editable=False, db_index=True) # handled by db, used for marker clustering added_by = models.ForeignKey('member', null=True, default=None) #route_count = models.IntegerField('route count', null=True, default=None, editable=False) date_created = models.DateTimeField('date created', auto_now_add=True, null=True, default=None, editable=False) last_modified = models.DateTimeField('last modified', auto_now=True, null=True, default=None, editable=False) star_image = models.OneToOneField('Image', null=True, default=None, related_name='star_crags', on_delete=models.SET_NULL) star_video = models.OneToOneField('Video', null=True, default=None, related_name='star_crags', on_delete=models.SET_NULL)

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  • How to organize the work when project needs to be re-implemented due to poor code quality?

    - by Dmitriy Nagirnyak
    Hi, I have joined a very small where one main developer has been buiding the web app (.NET 4.0) during ~6 months. The project should be delivered within next 2 months. After first look at the code I can say that I would never allow it to go to production (things like catch { }, not tests at all with WebForms etc). So the code quality is incredibly low. My task is to improve that and still deliver the solution. So I plan to start with unit testing and MVC2 reimplementing most of the functionality (though using some of the existing code). I estimate that I will need about 6 weeks to catch up with the current progress and be on te same functionality level as the application will be in 6 months. The problem is that the main developer who has been working on the project does not seem to be very 'professional' and skillful (he seems to be really starting in IT and many basic things are unknown to him). It will take significant amount of time and effort to educate him how to do the proper testing, development and apply some patterns. I am ready to take responsibility for the reimplemnting the application but at the same time I don't want the main developer to be on idle but as he won't be able to significantly contribute to the better-world project at this stage I am not sure what would the best way to keep productivity high for both of us. Currently I think following solution is good enough: He proceeds doing what he does until I will catch up with him and then start working on a new project together. The problem is that of course this approach is not very productive as one developer will do better-world project while the other will proceed with what he did, effectively doing similar tasks. Can you suggest how we could better organise the work together in order to be most efficient for the overall project? Thanks, Dmitriy.

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  • Is there a way to avoid spaghetti code over the years?

    - by Yoni Roit
    I've had several programming jobs. Each one with 20-50 developers, project going on for 3-5 years. Every time it's the same. Some programmers are bright, some are average. Everyone has their CS degree, everyone read design patterns. Intentions are good, people are trying hard to write good code but still after a couple of years the code turns into spaghetti. Changes in module A suddenly break module B. There are always these parts of code that no one can understand except for the person who wrote it. Changing infrastructure is impossible and backwards compatibility issues prevent good features to get in. Half of the time you just want to rewrite everything from scratch. And people more experienced than me treat this as normal. Is it? Does it have to be? What can I do to avoid this or should I accept it as a fact of life? Edit: Guys, I am impressed with the amount and quality of responses here. This site and its community rock!

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  • Are licenses relevant for small code snippets?

    - by Martin
    When I'm about to write a short algorithm, I first check in the base class library I'm using whether the algorithm is implemented in it. If not, I often do a quick google search to see if someone has done it before (which is the case, 19 times out of 20). Most of the time, I find the exact code I need. Sometimes it's clear what license applies to the source code, sometimes not. It may be GPL, LGPL, BSD or whatever. Sometimes people have posted a code snippet on some random forum which solves my problem. It's clear to me that I can't reuse the code (copy/paste it into my code) without caring about the license if the code is in some way substantial. What is not clear to me is whether I can copy a code snippet containing 5 lines or so without doing a license violation. Can I copy/paste a 5-line code snippet without caring about the license? What about one-liner? What about 10 lines? Where do I draw the line (no pun intended)? My second problem is that if I have found a 10-line code snippet which does exactly what I need, but feel that I cannot copy it because it's GPL-licensed and my software isn't, I have already memorized how to implement it so when I go around implementing the same functionality, my code is almost identical to the GPL licensed code I saw a few minutes ago. (In other words, the code was copied to my brain and my brain after that copied it into my source code).

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  • What are some commonly used source code check-in policies?

    - by rwmnau
    I'm curious what code review policies other development shops apply to their source code when it's checked into the source control repository. I'm setting up a TFS (Team Foundation) server, and I'd like to apply some check-in policies to start to stamp out bad practices. For example, I was thinking of starting with the following couple, so this is the kind of stuff I'm looking for: Prohibit empty "Catch" blocks. This would prevent applications from swallowing any exceptions without at least requiring a comment explaining why it's not necessary to do anything with the exception. Prohibit "Catch ex as Exception" generic exception handling. Instead, require code to catch specific types of exceptions and deal with them appropriately, instead of just building catch-all handling. Require a check-in comment. This one should be self-explanatory, though it seems that TFS (and most other source-control systems) don't require a comment by default. While these are just examples, they're where I'm thinking of starting, and while I'd like some additional examples of what's popular, I'm open to feedback on these. Also, though we're a mostly .NET shop, I imagine the popular policies are universal across languages and IDEs (we have some Java development and a few people who will use the repository develop with Eclipse).

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  • Routes on a sphere surface - Find geodesic?

    - by CaNNaDaRk
    I'm working with some friends on a browser based game where people can move on a 2D map. It's been almost 7 years and still people play this game so we are thinking of a way to give them something new. Since then the game map was a limited plane and people could move from (0, 0) to (MAX_X, MAX_Y) in quantized X and Y increments (just imagine it as a big chessboard). We believe it's time to give it another dimension so, just a couple of weeks ago, we began to wonder how the game could look with other mappings: Unlimited plane with continous movement: this could be a step forward but still i'm not convinced. Toroidal World (continous or quantized movement): sincerely I worked with torus before but this time I want something more... Spherical world with continous movement: this would be great! What we want Users browsers are given a list of coordinates like (latitude, longitude) for each object on the spherical surface map; browsers must then show this in user's screen rendering them inside a web element (canvas maybe? this is not a problem). When people click on the plane we convert the (mouseX, mouseY) to (lat, lng) and send it to the server which has to compute a route between current user's position to the clicked point. What we have We began writing a Java library with many useful maths to work with Rotation Matrices, Quaternions, Euler Angles, Translations, etc. We put it all together and created a program that generates sphere points, renders them and show them to the user inside a JPanel. We managed to catch clicks and translate them to spherical coords and to provide some other useful features like view rotation, scale, translation etc. What we have now is like a little (very little indeed) engine that simulates client and server interaction. Client side shows points on the screen and catches other interactions, server side renders the view and does other calculus like interpolating the route between current position and clicked point. Where is the problem? Obviously we want to have the shortest path to interpolate between the two route points. We use quaternions to interpolate between two points on the surface of the sphere and this seemed to work fine until i noticed that we weren't getting the shortest path on the sphere surface: We though the problem was that the route is calculated as the sum of two rotations about X and Y axis. So we changed the way we calculate the destination quaternion: We get the third angle (the first is latitude, the second is longitude, the third is the rotation about the vector which points toward our current position) which we called orientation. Now that we have the "orientation" angle we rotate Z axis and then use the result vector as the rotation axis for the destination quaternion (you can see the rotation axis in grey): What we got is the correct route (you can see it lays on a great circle), but we get to this ONLY if the starting route point is at latitude, longitude (0, 0) which means the starting vector is (sphereRadius, 0, 0). With the previous version (image 1) we don't get a good result even when startin point is 0, 0, so i think we're moving towards a solution, but the procedure we follow to get this route is a little "strange" maybe? In the following image you get a view of the problem we get when starting point is not (0, 0), as you can see starting point is not the (sphereRadius, 0, 0) vector, and as you can see the destination point (which is correctly drawn!) is not on the route. The magenta point (the one which lays on the route) is the route's ending point rotated about the center of the sphere of (-startLatitude, 0, -startLongitude). This means that if i calculate a rotation matrix and apply it to every point on the route maybe i'll get the real route, but I start to think that there's a better way to do this. Maybe I should try to get the plane through the center of the sphere and the route points, intersect it with the sphere and get the geodesic? But how? Sorry for being way too verbose and maybe for incorrect English but this thing is blowing my mind! EDIT: This code version is related to the first image: public void setRouteStart(double lat, double lng) { EulerAngles tmp = new EulerAngles ( Math.toRadians(lat), 0, -Math.toRadians(lng)); //set route start Quaternion qtStart.setInertialToObject(tmp); //do other stuff like drawing start point... } public void impostaDestinazione(double lat, double lng) { EulerAngles tmp = new AngoliEulero( Math.toRadians(lat), 0, -Math.toRadians(lng)); qtEnd.setInertialToObject(tmp); //do other stuff like drawing dest point... } public V3D interpolate(double totalTime, double t) { double _t = t/totalTime; Quaternion q = Quaternion.Slerp(qtStart, qtEnd, _t); RotationMatrix.inertialQuatToIObject(q); V3D p = matInt.inertialToObject(V3D.Xaxis.scale(sphereRadius)); //other stuff, like drawing point ... return p; } //mostly taken from a book! public static Quaternion Slerp(Quaternion q0, Quaternion q1, double t) { double cosO = q0.dot(q1); double q1w = q1.w; double q1x = q1.x; double q1y = q1.y; double q1z = q1.z; if (cosO < 0.0f) { q1w = -q1w; q1x = -q1x; q1y = -q1y; q1z = -q1z; cosO = -cosO; } double sinO = Math.sqrt(1.0f - cosO*cosO); double O = Math.atan2(sinO, cosO); double oneOverSinO = 1.0f / senoOmega; k0 = Math.sin((1.0f - t) * O) * oneOverSinO; k1 = Math.sin(t * O) * oneOverSinO; // Interpolate return new Quaternion( k0*q0.w + k1*q1w, k0*q0.x + k1*q1x, k0*q0.y + k1*q1y, k0*q0.z + k1*q1z ); } A little dump of what i get (again check image 1): Route info: Sphere radius and center: 200,000, (0.0, 0.0, 0.0) Route start: lat 0,000 °, lng 0,000 ° @v: (200,000, 0,000, 0,000), |v| = 200,000 Route end: lat 30,000 °, lng 30,000 ° @v: (150,000, 86,603, 100,000), |v| = 200,000 Qt dump: (w, x, y, z), rot. angle°, (x, y, z) rot. axis Qt start: (1,000, 0,000, -0,000, 0,000); 0,000 °; (1,000, 0,000, 0,000) Qt end: (0,933, 0,067, -0,250, 0,250); 42,181 °; (0,186, -0,695, 0,695) Route start: lat 30,000 °, lng 10,000 ° @v: (170,574, 30,077, 100,000), |v| = 200,000 Route end: lat 80,000 °, lng -50,000 ° @v: (22,324, -26,604, 196,962), |v| = 200,000 Qt dump: (w, x, y, z), rot. angle°, (x, y, z) rot. axis Qt start: (0,962, 0,023, -0,258, 0,084); 31,586 °; (0,083, -0,947, 0,309) Qt end: (0,694, -0,272, -0,583, -0,324); 92,062 °; (-0,377, -0,809, -0,450)

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  • PDC and Tech-Ed Europe Slides and Code

    - by Stephen Walther
    I spent close to three weeks on the road giving talks at Tech-Ed Europe (Berlin), PDC (Los Angeles), and the Los Angeles Code Camp (Los Angeles). I got to talk about two topics that I am very passionate about: ASP.NET MVC and Ajax. Thanks everyone for coming to all my talks! At PDC, I announced all of the new features of our ASP.NET Ajax Library. In particular, I made five big announcements: ASP.NET Ajax Library Beta Released – You can download the beta from Ajax.CodePlex.com ASP.NET Ajax Library includes the AJAX Control Toolkit – You can use the Ajax Control Toolkit with ASP.NET MVC. ASP.NET Ajax Library being contributed to the CodePlex Foundation – ASP.NET Ajax is the founding project for the CodePlex Foundation (see CodePlex.org) ASP.NET Ajax Library is receiving full product support – Complain to Microsoft Customer Service at midnight on Christmas ASP.NET Ajax Library supports jQuery integration – Use (almost) all of the Ajax Control Toolkit controls in jQuery For more details on the Ajax announcements, see James Senior’s blog entry on the Ajax announcements at: http://jamessenior.com/post/News-on-the-ASPNET-Ajax-Library.aspx In my MVC talks, I discussed the new features being introduced with ASP.NET MVC 2. Here are three of my favorite new features: Client Validation – Client validation done the right way. Do your validation in your model and let the validation bubble up to JavaScript code automatically. Areas – Divide your ASP.NET MVC application into sub-applications. Great for managing both medium and large projects. RenderAction() – Finally, a way to add content to master pages and multiple pages without doing anything strange or twisted. There are demos of all of these features in the MVC downloads below. Here are the power point and code from all of the talks: PDC – Introducing the New ASP.NET Ajax Library PDC – ASP.NET MVC: The New Stuff Tech-Ed Europe - What's New in Microsoft ASP.NET Model-View-Controller Tech-Ed Europe - Microsoft ASP.NET AJAX: Taking AJAX to the Next Level

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  • Winnipeg Code Camp&ndash;Session Announcement

    - by D'Arcy Lussier
    I’ve been updating the Winnipeg Code Camp website over the last few weeks with sessions and speakers as we’ve added them, and I’m happy to announce the full set of sessions!* We have a very interesting mix this year with new speakers and varied technologies! Remember this is a *FREE* event, so head over to our website to find out how to register for what will be a fantastic code camp! *OK, so we still have one session that needs to be have an official title, and one session that’s still TBA…but close enough. ;) What`s New in Entity Framework 4 Aaron Kowall Easy Automation Setup for Everyday Projects Amir Barylko Hackerspaces Everywhere! Winnipeg: Our Time is Now Andrew Orr C# Ninjitsu Chris Eargle Code like a Ninja:Enhance Your Productivity with VS.NET & JustCode Chris Eargle Scala Language Tour Craig Tataryn WP7 - Creating a Data Driven App D`Arcy Lussier TBA (WordPress Related) Dan Bernardic WP7 Development Foundation D'Arcy Lussier HTML5 for .NET Pros Dave Wesst Turbocharge Your Manual Testing Process with VS 2010 Dylan Smith Develop Visual Studio 2010 Extensions - Twitter Studio George Chen Functionality Driven Development with Asp .Net MVC George Chen & Sean Bennett Web Development for Mobile Devices Kelly Cassidy Intro to Nmap Security Scanner Mak Kolybabi My Personal Top 10 SQL Habits Good and Bad Mike Diehl Stupid Mistakes Made By Smart People Ron Bowes Intro to jQuery Stefan Penner Taking Your WP7 Application to the Next Level with Tombstoning Tyler Doerksen Coming Soon! Tyler Doerksen

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  • How can one compile Darwinia under Linux?

    - by Tobias Kienzler
    Introversion is now offering the Darwinia+Multiwinia source for sale, stating Note: You will need Windows and Visual Studio 2008 to build the games. We have tested that the code compiles correctly on the PC, but you will need to put some effort in to compile for Mac / Linux. There is no Xbox code in this release. Has anyone put this effort in already? The best answer would (be yes and) mention modifications that had to be done (also mentioning the distribution used), the second-to-best would explain why it doesn't work right now. Since I haven't bought the source pack I'm relying on up-votes as confirmation, so please comment on answers if something doesn't work or has to be modified e.g. for another Linux distribution. I'm currently using Ubuntu 8.04, but 10.04 or e.g. Gentoo would be a choice, too. EDIT: Clarification: The intention is to make a new game with that engine, but since this question is a prerequisite, it seems suitable here. UPDATE It is a bit off topic, but for those interested, Introversion added the source code of Uplink, Darwinia, Multiwinia and DEFCON to The Humble Introversion Bundle, so don't miss it!

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