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Reducing moire when downsampling halftone comic images.

- by drawnonward

How can I reduce moire effects when downsampling halftone comic book images during live zoom on an iPhone or iPad? I am writing a comic book viewer. It would be nice to provide higher resolution images and allow the user to zoom in while reading the comic book. However, my client is averse to moire effects and will not allow this feature if there are noticeable moire artifacts while zooming, which of course there are. Modifying the images to be less susceptible to moire would only work if the modifications were not perceptible. Blur was specifically prohibited, as is anything that removes the beloved halftone dots. The images are black and white halftone and line art. The originals are 600 dpi but what we ship with the application will be half that at best, so probably 2500 pixels or less tall. So what are my options? If I write a custom downsampling algorithm would it be fast enough for real time on these devices? Are there other tricks I can do? Would it work to just avoid the size ratios that have the most visual moire effects? As you zoom in an out, there are definitely peaks where the moire effects are worst. Is there a way to calculate what those points are and just zoom to a nearby scale that is not as bad? Any suggestions are welcome. I have very little experience with image and signal processing, but am enjoying the opportunity to learn. I know nothing of wavelets and acutance and other jargon, so please be verbose.

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Partial Classes - are they bad design?

- by dferraro

Hello, I'm wondering why the 'partial class' concept even exists in .NET. I'm working on an application and we are reading a (actually very good) book relavant to the development platform we are implementing at work. In the book he provides a large code base /wrapper around the platform API and explains how he developed it as he teaches different topics about the platform development. Anyway, long story short - he uses partial classes, all over the place, as a way to fake multiple inheritence in C# (IMO). Why he didnt just split the classes up into multiple ones and use composition is beyond me. He will have 3 'partial class' files to make up his base class, each w/ 3-500 lines of code... And does this several times in his API. Do you find this justifiable? If it were me, I'd have followed the S.R.P. and created multiple classes to handle different required behaviors, then create a base class that has instances of these classes as members (e.g. composition). Why did MS even put partial class into the framework?? They removed the ability to expand/collapse all code at each scope level in C# (this was allowed in C++) because it was obviously just allowing bad habits - partial class is IMO the same thing. I guess my quetion is: Can you explain to me when there would be a legitimate reason to ever use a partial class? I do not mean this to be a rant / war thread. I'm honeslty looking to learn something here. Thanks

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Adding multiple rss feeds to a script in SCALA InfoChannel Designer 5

- by godleuf

Okay, since it is impossible to talk to anyone on the phone or get support through Scala's "forum", I am going to take a shot and see if anyone out there is feeling my pain. I have a client that uses Scala's InfoChannel Designer and Content Manager. I have had to learn this software from scratch and I have to say it hasn't been easy. I think I am at a point where the overall design is set, but I need to implement a couple of things before I can make this happen. RSS feeds are my issue at this point. Multiple RSS feeds to be specific. I need a feed coming in for 3 areas of content: Wiki News (or equivalent), local weather and a stock ticker. I have learned how to setup a "crawl" using a script example available from Scala's file center and copying and pasting into my design. But from what I have learned first hand and through reading through other forums, you can not have a feed from 3 different sources or urls happening simultaneously. Doesn't seem like it would be an issue, but apparently it is. This small step has held up this project for far too long and I need to get it figured out. This doesn't even touch on my issue of feeding in streaming video as a background but I have gone over this in another question but with no luck thus far. If there is ANYONE out there who is in anything similar using this software, your feedback and/or suggestions would be greatly appreciated. Thanks you for allowing me to vent!

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PHP: tips/resources/patterns for learning to implement a basic ORM

- by BoltClock

I've seen various MVC frameworks as well as standalone ORM frameworks for PHP, as well as other ORM questions here; however, most of the questions ask for existing frameworks to get started with, which is not what I'm looking for. (I have also read this SO question but I'm not sure what to make of it, and the answers are vague.) Instead, I figured I'd learn best by getting my hands dirty and actually writing my own ORM, even a simple one. Except I don't really know how to get started, especially since the code I see in other ORMs is so complicated. With my PHP 5.2.x (this is important) MVC framework I have a basic custom database abstraction layer, that has: Very simple methods like connect($host, $user, $pass, $base), query($sql, $binds), etc Subclasses for each DBMS that it supports A class (and respective subclasses) to represent SQL result sets But does not have: Active Record functionality, which I assume is an ORM thing (correct me if I'm wrong) I've read up a little about ORM, and from my understanding they provide a means to further abstract data models from the database itself by representing data as nothing more than PHP-based classes/objects; again, correct me if I am wrong or have missed out in any way. Still, I'd like some simple tips from anyone else who's dabbled more or less with ORM frameworks. Is there anything else I need to take note of, simple example code for me to refer to, or resources I can read? Thanks a lot in advance!

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Handling learning curve for new developers

- by pete the pagan-gerbil

Our company likes to hire new developers, with no experience. We have a core set of skills that we try to get them up to speed with, like ASP.NET and WinForms - to teach basic programming, the .NET languages, and the things they'll need to maintain and write. We also try and mentor them through early projects, so they can learn from someone more experienced. Recently, we've been seeing the benefits of new frameworks like MVC and ideas like Unit Testing and TDD (by extension, dependancy injection and IoC), and we'd like to start using these in the team. However, this increases the time that a junior would have before they can get started on a new project - because doing something like unit tests wrong could cause major headaches months or years later in maintenance, especially if we believe unit tests to be comprehensive. How do you handle the huge amount of things that a junior will need to take on, acknowledging that the business wants them working independantly as soon as possible? Is it acceptable to tell them not to unit test till a while after they are independant (and give them small, simpler projects in the meantime) before taking them to 'level 2' of the core skills?

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New to Android: Dynamically changing views

- by Josiah Kiehl

I'm trying to learn how to build apps for Android. The first simple app, which will become a component of a bigger app I hope to build, is to have a button on the screen where, when tapped, it adds something new to the view. For instance: Imagine a layout that only has a button: [Create!] When that button, the view gets a new row added to it: [Create!] A Something! Upon subsequent presses, more rows are added [Create!] A Something! A Something! And so on. I've made a LinearLayout and placed the button in it, and have attached a click listener to it. That all works great. What I can't figure out is how to get a handle on the LinearLayout in the onClick function with which I'll addView() the new TextView that says "A Something!" Am I on the right track? What basic thing am I missing? Thanks!

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How to change scope data in controller?

- by Derooie

I am a real newbie at angular. I created something now which will let me retrieve and add items via angular and get/put them in mongodb. I use express and mongoose in the app The question is, how can i modify the data before it reaches the DOM in the controller. In this example i have created a way to retrieve data, and i get it exactly as it is stored in mongodb. What i would like is that the field where i store 1 or 0 in the database, to be shown as text. So if mongo has a value 1 i get "the value in mongo is 1" and when the field has a value of 0 get "the value is zero". (just as an example, i like other texts, but it illustrate what i want) I post my controller, html and current output. Any help would be appreciated. Controller function getGuests($scope, $http) { $scope.formData = {}; $http.get('/api/guests') .success(function(data) { $scope.x = data; }) .error(function(data) { console.log('Error: ' + data); }); } HTML <div ng-controller="getGuests"> <div ng-repeat="guest in x"> {{ guest.voornaam }} {{ guest.aanwezig }} </div> </div> The current scope output, what i see in HTML. I like to change only the value of "aanwezig" in case the value of aanwezig is 0 or 1. firstname1 1 firstname2 0 Something else, but would be great to learn, is how i can do a specific mongodb query by the push of a button and get that result.

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How to start AJAX in Zend?

- by Awan

I am working on some projects as a developer(PHP,MySQL) in which AJAX and jQuery is already implemented. But now I want to learn implementation of AJAX and jQuery stuff. Can anyone tell me the exact steps with explanation? I have created a project in Zend. There is only one controller(IndexController) and two actions(a and b) in my project now. Now I want to use ajax in my project. But I don't know how to start. I read some tutorial but unable to completely understand. I have index.phtml like this: <a href='index/a'>Load info A</a> <br/> <a href='index/b'>Load info B</a> <br /> <div id=one>load first here<div> <div id=two>load second here</div> Here index is controller in links. a and b are actions. now I have four files like this: a1.phtml I am a1 a2.phtml I am a2 b1.phtml I am b1 b2.phtml I am b2 I think you have got my point. When user clicks first link (Load info A) then a1.phtml should be loaded into div one and a2.phtml should be loaded into div two When user clicks second link (Load info B) then b1.phtml should be loaded into div one and b2.phtml should be loaded into div two And someone tell me the purpose of JSON in this process and how to use this also? Thanks

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Do I really need bindParam?

- by sandelius

Hi there! I'm trying to do a little PDO CRUD to learn some PDO. I have a question about bindParam. Here's my update method right now: public static function update($conditions = array(), $data = array(), $table = '') { self::instance(); // Late static bindings (PHP 5.3) $table = ($table === '') ? self::table() : $table; // Check which data array we want to use $values = (empty($data)) ? self::$_fields : $data; $sql = "UPDATE $table SET "; foreach ($values as $f => $v) { $sql .= "$f = ?, "; } // let's build the conditions self::build_conditions($conditions); // fix our WHERE, AND, OR, LIKE conditions $extra = self::$condition_string; // querystring $sql = rtrim($sql, ', ') . $extra; // let's merge the arrays into on $v_val = array_values($values); $c_val = array_values($conditions); $array = array_merge($v_val, self::$condition_array); $stmt = self::$db->prepare($sql); return $stmt->execute($array); } in my "self::$condition_array" I get all the right values from the ?. SO the query looks like this: UPDATE table SET this = ?, another = ? WHERE title = ? AND time = ? as you can see I dont use bindParams instead I pass the right values in the right order ($array) directly into the execute($array) method. This works like a charm BUT is it safe not use use bindParam here? If not then how can I do it? Thanks from Sweden Tobias

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Setting up a domain using WAMP and NameCheap's DNS service

- by Mike Jones

So, I've been working on this for far longer than I should be and I'm quite thoroughly perplexed and lost. I apologize if this turns out to be a facile question, but I'm entirely befuddled and very much in need of some guidance. Earlier today I registered a cheap .info domain on NameCheap just to play around with as I learn webdev. I have WAMP installed on my computer and I've been testing my projects through localhost. I thought it would be a good idea to have a domain at my disposal in order to understand how it works and better test my work. NameCheap has a complimentary DNS service (not that I entirely understand what DNS is, although I tried), so I'm using that. I direct both the "@" and "www" host names to my IP address, as shown in the below tutorial: https://www.namecheap.com/support/knowledgebase/article.aspx/319/78/how-can-i-setup-an-a-address-record-for-my-domain However, now when I go to the URL of the domain I bought, it confronts me with a login box that seems to be coming from my wifi network. How do I set this up so that it hosts the information in my WAMP server? Thanks in advance for any help, I really appreciate it. And, as a side-note, what should read (print or online) to better understand the structure of the internet? I've been studying HTML/CSS/Javascript, but I'm not sure where to look for pragmatic and comprehensive information on how the internet works and how to utilize it as a website administrator. Thanks so much.

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Text message intent - catch and send

- by Espen

Hi! I want to be able to control incoming text messages. My application is still on a "proof of concept" version and I'm trying to learn Android programming as I go. First my application need to catch incomming text messages. And if the message is from a known number then deal with it. If not, then send the message as nothing has happened to the default text message application. I have no doubt it can be done, but I still have some concern and I see some pitfalls at how things are done on Android. So getting the incomming text message could be fairly easy - except when there are other messaging applications installed and maybe the user wants to have normal text messages to pop up on one of them - and it will, after my application has had a look at it first. How to be sure my application get first pick of incomming text messages? And after that I need to send most text messages through to any other text message application the user has chosen so the user can actually read the message my application didn't need. Since Android uses intents that are relative at best, I don't see how I can enforce my application to get a peek at all incomming text messages, and then stop it or send it through to the default text messaging application...

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Assistance with Lua functions

- by Josh

As noted before, I'm relatively new to lua, but again, I learn quick. The last time I got help here, it helped me immensely, and I was able to write a better script. Now I've come to another question that I think will make my life a bit easier. I have no clue what I'm doing with functions, but I'm hoping there is a way to do what I want to do here. Below, you'll see an example of code I have to do to strip down some unneeded elements. Yeah, I realize it's not efficient in the least, so if anyone else has a better idea of how to make it much more efficient, I'm all ears. What I would like to do is create a function with it so that I can strip down whatever variable with a simple call of it (like stripdown(winds)). I appreciate any help that is offered, and any lessons given. Thanks! winds = string.gsub(winds,"%b<>","") winds = string.gsub(winds,"%c"," ") winds = string.gsub(winds," "," ") winds = string.gsub(winds," "," ") winds = string.gsub(winds,"^%s*(.-)%s*$", "%1)") winds = string.gsub(winds," ","") winds = string.gsub(winds,"/ ", "(") Josh

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How do I make a third party .jar available to my .jsp page?

- by Matthew

I'm just starting to learn JSP (and I'm pretty new to Java in general), and I'd like to use JSON-lib with it. I want to make a page something like this: <%@ page import="net.sf.json.JSONObject"%> <% String json = new JSONObject().put("hello", "world").toString(); out.println(json); %> I downloaded json-lib-2.3-jdk15.jar and put it in the same directory as the .jsp page. But I get this error org.apache.jasper.JasperException: Unable to compile class for JSP: An error occurred at line: 6 in the generated java file Only a type can be imported. net.sf.json.JSONObject resolves to a package An error occurred at line: 3 in the jsp file: /getCard.jsp JSONObject cannot be resolved to a type 1: <%@ page import="net.sf.json.JSONObject" %> 2: <% 3: String json = new JSONObject().put("hello", "world").toString(); 4: out.println(json); 5: %> 6: How do I make the JSONObject class available to my .jsp page?

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Django aggregation on a date range

- by klaut

Hi all, I have been lurking and learning in here for a while. Now i have a problem that somehow i cannot see an easy solution. In order to learn django i am bulding an app that basically keeps track of booked items. What I would like to do is to show how many days per month for a selected year one item has been booked. i have the following models: Asset(Model) BookedAsset(Model): asset = models.ForeignKey(Asset) startdate = models.DateField() enddate = models.DateField() So having the following entries: asset 1, 2010-02-11, 2010-02-13 asset 2, 2010-03-12, 2010-03-14 asset 1, 2010-04-30, 2010-05-01 I would like to get returned the following: asset 1 asset 2 ------- ------- Jan = 0 Jan = 0 Feb = 2 Feb = 0 Mar = 0 Mar = 2 Apr = 1 Apr = 0 May = 1 May = 0 Jun = 0 Jun = 0 Jul = 0 Jul = 0 Aug = 0 Aug = 0 Sep = 0 Sep = 0 Oct = 0 Oct = 0 Nov = 0 Nov = 0 Dec = 0 Dec = 0 I know i need to first get the number of days in a date range (and keep track if they fall out of the current month and into the next month) and then do an agregate on the number of days. I am just stuck on how to do it elegantly in Django. Any help (or hint in the right direction) is greatly appreciated.

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Grails or Play! for an ex-RoR developer ?

- by Kedare

Hello, I plan to begin learning a Java web framework (I love the Java API), I already used Rails and Django. I want something close to Java, but without all the complexity of J2EE. I've found 2 framework that could be good for me : Grails : Grails looks great, it use Groovy that is better than Java for web application (I think..), but it's slower, that use pure-java components (Hibernate, Strut, Spring), it looks pretty simple to deploy (send .war and it's ok !), the GSP is great ! It's a bit harder to debug (need to restart the server at each modification, and the stacktrace is a mix of Java and Groovy stack that is not always understandable..) Play! : This framework also looks great, it's faster than Grails (It's use directly Java), but I don't really like how it use Java, it modify the source code to transform the properties call as setXXX/getXXX, I'm not kind of that... The framework also have caching function that Grails don't (alreary) has. I don't really like the Template Engine. It's also easer to debug (no need to restart the server, and the stacktrace is clear) What do you recommend for ? I am looking for something easy to learn (I used a lot ruby and java, but a little bit java (But I love the Java API)), that is full featured (That's no a problem with all the Java Library availables, but if it's bundle and integrated I prefer), that scale and that is not too slow (faster than ruby), and if possible I would want something with a decent community to easily find support and answer to my questions ;) PS: No JRuby on Rails Thank you !

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How can I alter an external variable from inside my AJAX?

- by tmedge

I keep on having these same two problems. I have been trying to use Remy Sharp's wonderful tagSuggest plugin, and it works great. Until I try to use an AJAX call to get tags from my database. My setGlobalTags() works great, with my defined myTagList at the top of the function. What I want to do is set myTagList equal to the result from my AJAX. My problem is that I can neither call setGlobalTags() from inside my success or error functions, nor actually alter the original myTagList. Also, I keep on having this other issue as well. I keep this code in my Master page, and my AJAX returns 'success' on almost every page. I only (and always) get the error alert when I navigate to a page that actually contains something of id="ParentTags". I don't see why this is happening, because my $('#ParentTags').tagSuggest(); is definitely after my AJAX call. I realize that this is probably just some dumb conventions error, but I am new to this and I'm here to learn from you guys. Thanks in advance! $(function() { var myTagList = ['test', 'testMore', 'testALot']; $.ajax({ type: "POST", url: 'Admin/GetTagList', dataType: 'json', success: function(resultTags) { myTagList = resultTags; alert(myTagList[0]); setGlobalTags(myTagList); }, error: function() { alert('Error'); setGlobalTags(myTagList); } }); setGlobalTags(myTagList); $('#ParentTags').tagSuggest(); });

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backbone.js removing template from DOM upon success

- by timpone

I'm writing a simple message board app to learn backbone. It's going ok (a lot of the use of this isn't making sense) but am a little stuck in terms of how I would remove a form / html from the dom. I have included most of the code but you can see about 4 lines up from the bottom, the part that isn't working. How would I remove this from the DOM? thx in advance var MbForm=Backbone.View.extend({ events: { 'click button.add-new-post': 'savePost' }, el: $('#detail'), template:_.template($('#post-add-edit-tmpl').html()), render: function(){ var compiled_template = this.template(); this.$el.html(compiled_template); return this; }, savePost: function(e){ //var self=this; //console.log("I want you to say Hello!"); data={ header: $('#post_header').val(), detail: $('#post_detail').val(), forum_id: $('#forum_id').val(), post_id: $('#post_id').val(), parent_id: $('#parent_id').val() }; this.model.save(data, { success: function(){ alert('this saved'); //$(this.el).html('this is what i want'); this.$el.remove();// <- this is the part that isn't working /* none of these worked - error Uncaught TypeError: Cannot call method 'unbind' of undefined this.$el.unbind(); this.$el.empty(); this.el.unbind(); this.el.empty(); */ //this.unbind(); //self.append('this is appended'); } });

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Regular expression to match empty HTML tags that may contain embedded JSTL?

- by Keith Bentrup

I'm trying to construct a regular expression to look for empty html tags that may have embedded JSTL. I'm using Perl for my matching. So far I can match any empty html tag that does not contain JSTL with the following? /<\w+\b(?!:)[^<]*?>\s*<\/\w+/si The \b(?!:) will avoid matching an opening JTSL tag but that doesn't address the whether JSTL may be within the HTML tag itself (which is allowable). I only want to know if this HTML tag has no children (only whitespace or empty). So I'm looking for a pattern that would match both the following: <div id="my-id"> </div> <div class="<c:out var="${my.property}" />"></div> Currently the first div matches. The second does not. Is it doable? I tried several variations using lookahead assertions, and I'm starting to think it's not. However, I can't say for certain or articulate why it's not. Edit: I'm not writing something to interpret the code, and I'm not interested in using a parser. I'm writing a script to point out potential issues/oversights. And at this point, I'm curious, too, to see if there is something clever with lookaheads or lookbehinds that I may be missing. If it bothers you that I'm trying to "solve" a problem this way, don't think of it as looking for a solution. To me it's more of a challenge now, and an opportunity to learn more about regular expressions. Also, if it helps, you can assume that the html is xhtml strict.

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How does MVC ViewData work?

- by Matt

I am toying around with an MVC application just to learn the technology. I am mocking up a check register application that keeps track of a checking account, what has cleared the bank and what has not. I am using EF for my model and everything seems to be working correctly insofar as Edit, Create, etc. However, I have a couple of totals at the top. One to show the bank's balance and another to show the actual balance. It works most of the time but when I do Edit's it does not always accurately reflect the new total and I need it to update everytime a change is made (i.e when something clears the bank): [Authorize(Roles = "admin, checkUser")] public ActionResult Index() { var resultSet = from myChecking in chk.tblCheckings orderby myChecking.id descending select myChecking; ViewData.Model = resultSet.Take(45).ToList(); //for balances var actualBalance = from theChecking in chk.tblCheckings select theChecking.deposit - theChecking.withdrawal; var bankBalance = from theChecking in chk.tblCheckings where theChecking.cleared == true select theChecking.deposit - theChecking.withdrawal; //get bank balance ViewData["bankBalance"] = bankBalance.Sum(); //get actual balance ViewData["actualBalance"] = actualBalance.Sum(); return View(); } I am showing the actual and other balance in the Index view as follows: <td colspan="9" style="text-align: center; font-size: 11pt; color: white;"> <%= string.Format("Bank Balance: {0:c}", ViewData["bankBalance"]) %> ------ <%= string.Format("Actual Balance: {0:c}", ViewData["actualBalance"]) %> </td>

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Using JSF, PrimeFaces and JPA: Create Basic WebApp without using Generated CRUD Classes, Forms, etc

- by user2774489

I am trying to build a basic CRUD application with NetBeans 7.4, JSF, PrimeFaces and JPA using MySQL. I have successfully done this by using the NetBeans wizards. I want to do this from scratch, no wizards. There seems to be a lack of support for the combo of JSF, PrimeFaces and JPA. When I say "lack", I mean a full example (I might be asking too much), without using the CRUD auto-gen templates/classes AND shows actual queries coded and passed to the datatables(primefaces). YouTube is full of non-English speaking examples using Hibernate (not JPA) and other examples that show flashy GUI's with no code. So far I understand you need an @Entity class (provides the physical build of the tables), a Controller (serializable) and the .xhtml web page to show the datatable.. what else? Also, I'm not seeing any posts or examples where queries are using with JPA/JSF and how they are tied together (in one place). I need to connect the dots here so that I can leverage JSF/JPA to create simple queries to populate my PF DataTables. I've read the blogs and I've googled the intranets until I'm blue in the face. Sending me a list of URL's to read to learn about each product is something I've already done. I get what they do independently, but am looking for the "How do they all connect" answer with maybe some basic code examples!! :)

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Implementing a normal website inside ASP.NET MVC 2

- by cc0

I have a website consisting of an index.html, a number of style sheet files as well as some javascript files. Then I needed a way for this site to communicate efficiently with a Microsoft SQL Server, so I was recommended to use the MVC framework to facilitate that kind of communication. I created the C#.net controller code needed to output the necessary information from the database using URL parameters, so now I am trying to put the whole web-site together inside the MVC framework. I started an empty project-template in MVC 2 framework. I'm sure there must be a good way to implement the current code into this framework, but I am very uncertain as to what the best approach to this would be. Could anyone point me in the right direction here? I'm not sure whether I need to change any of the current HTML, or exactly what to add to it. I'd love to see some kind of guide or tutorial, or just any advice I can get as I try to learn this. Any help is very much appreciated!

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questions about name mangling in C++

- by Tim

I am trying to learn and understand name mangling in C++. Here are some questions: (1) From devx When a global function is overloaded, the generated mangled name for each overloaded version is unique. Name mangling is also applied to variables. Thus, a local variable and a global variable with the same user-given name still get distinct mangled names. Are there other examples that are using name mangling, besides overloading functions and same-name global and local variables ? (2) From Wiki The need arises where the language allows different entities to be named with the same identifier as long as they occupy a different namespace (where a namespace is typically defined by a module, class, or explicit namespace directive). I don't quite understand why name mangling is only applied to the cases when the identifiers belong to different namespaces, since overloading functions can be in the same namespace and same-name global and local variables can also be in the same space. How to understand this? Do variables with same name but in different scopes also use name mangling? (3) Does C have name mangling? If it does not, how can it deal with the case when some global and local variables have the same name? C does not have overloading functions, right? Thanks and regards!

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Scheme: what are the benefits of letrec?

- by Ixmatus

While reading "The Seasoned Schemer" I've begun to learn about letrec. I understand what it does (can be duplicated with a Y-Combinator) but the book is using it in lieu of recurring on the already defined function operating on arguments that remain static. An example of an old function using the defined function recurring on itself (nothing special): (define (substitute new old lat) (cond ((null? l) '()) ((eq? (car l) old) (cons new (substitute new old (cdr l)))) (else (cons (car l) (substitute new old (cdr l)))))) Now for an example of that same function but using letrec: (define (substitute new old lat) (letrec ((replace (lambda (l) (cond ((null? l) '()) ((eq? (car l) old) (cons new (replace (cdr l)))) (else (cons (car l) (replace (cdr l)))))))) (replace lat))) Aside from being slightly longer and more difficult to read I don't know why they are rewriting functions in the book to use letrec. Is there a speed enhancement when recurring over a static variable this way because you don't keep passing it?? Is this standard practice for functions with arguments that remain static but one argument that is reduced (such as recurring down the elements of a list)? Some input from more experienced Schemers/LISPers would help!

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How can I SETF an element in a tree by an accessor?

- by Willi Ballenthin

We've been using Lisp in my AI course. The assignments I've received have involved searching and generating tree-like structures. For each assignment, I've ended up writing something like: (defun initial-state () (list 0 ; score nil ; children 0 ; value 0)) ; something else and building my functions around these "states", which are really just nested lists with some loosely defined structure. To make the structure more rigid, I've tried to write accessors, such as: (defun state-score ( state ) (nth 2 state)) This works for reading the value (which should be all I need to do in a nicely functional world. However, as time crunches, and I start to madly hack, sometimes I want a mutable structure). I don't seem to be able to SETF the returned ...thing (place? value? pointer?). I get an error with something like: (setf (state-score *state*) 10) Sometimes I seem to have a little more luck writing the accessor/mutator as a macro: (defmacro state-score ( state ) `(nth 2 ,state)) However I don't know why this should be a macro, so I certainly shouldn't write it as a macro (except that sometimes it works. Programming by coincidence is bad). What is an appropriate strategy to build up such structures? More importantly, where can I learn about whats going on here (what operations affect the memory in what way)?

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Switching to WPF, the best use of time at Visual Studio Launch 2010

- by Stewbob

Yes, this is a programming-related question, if a little indirectly (that's why I marked it Community Wiki right away). For better or worse, I am switching from Winforms to WPF in April. I am also going to be in attendance at the Visual Studio Launch in Las Vegas. I have a real need to get up to speed quickly in WPF, so my question is: What sessions are going to be the best use of my time? I've got some picked out already, but I'm looking for some more advice on how to wade through all the marketing fluff and get some real educational value out of these few days. I have not been to one of these events before, so I don't really know how much is marketing hype, and how much is solid content. A couple of the workshops look interesting (VPR02 and VPS02), but I don't know enough about the actual content of these to justify the extra expense right now. Any thoughts there would be appreciated. And yes, I do have WPF learning planned other than just these few days in Vegas, but since I'm going to be there anyway, I want to learn as much as I can in the time available.

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