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• Computer science textbooks

  - by Barrett Conrad

  I would like to try the book question a little bit differently. My goal is to know what the community thinks are the quintessential computer science textbooks. <beginsadstory>I lost all of my computer science and math books from college in Hurricane Katrina in 2005. I greatly miss having my familiar tomes to refer to when topics and problems come up, so I am looking to rebuild my library.<endsadstory> What are your recommendations for the best examples of academic caliber books for the field of computer science and its associated mathematics? I am looking for books on subjects like computational theory, programming languages, compilers, operating systems, algorithms and so on. Don't limit your suggestions to your textbooks only. If there is a book you have read that covers computer science or a related math in a formal way, but is not strictly a textbook, I would be love to hear about them as well. Finally, for the sake of creating a good reference for all of us, may I suggest posting one book per answer so they can be rated individually.

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• javascript using 'this' in global object

  - by Marco Demaio

  What does 'this' keyword refer to when used in gloabl object? Let's say for instance we have: var SomeGlobalObject = { rendered: true, show: function() { /* I should use 'SomeGlobalObject.rendered' below, otherwise it won't work when called from event scope. But it works when called from timer scope!! How can this be? */ if(this.rendered) alert("hello"); } } Now if we call in an inline script in the HTML page: SomeGlobalObject.show(); window.setTimeout("Msg.show()", 1000); everything work ok. But if we do something like AppendEvent(window, 'load', Msg.show); we get an error because this.rendered is undefined when called from the event scope. Do you know why this happens? Could you explain then if there is another smarter way to do this without having to rewrite every time "SomeGlobalObject.someProperty" into the the SomeGlobalObject code? Thanks! AppendEvent is just a simple cross-browser function to append an event, code below, but it does not matter in order to answer the above questions. function AppendEvent(html_element, event_name, event_function) { if(html_element.attachEvent) //IE return html_element.attachEvent("on" + event_name, event_function); else if(html_element.addEventListener) //FF html_element.addEventListener(event_name, event_function, false); }

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• CSS Caching and User-CUstomized CSS - Any Suggestions?

  - by Joe

  I'm just trying to figure out the best approach here... my consideration is that I'd like my users to be able to customize the colors of certain elements on the page. These are not pre-made css they can choose from, but rather styles that can be edited using javascript to change the style, so they cannot be "pre-made" into separate style sheets. I am also generating the css into a cache directory since I am generating the css through a PHP script. I am thinking that, perhaps I should: 1) If cached css file doesn't exist, create css file using the website default style settings. 2) If cached css file does exist, check if user has custom settings, if so, edit the cache file before displaying it. Btw, when I refer to "cached file" I mean the PHP generated css document. My goal is to prevent the need to have PHP re-generate the css file each time, whilst still allowing users, when logged in, to have their customized css settings applied. I will store these settings in a database most likely so when they return it is saved for them when they login.

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• SQL 2005 indexed queries slower than unindexed queries

  - by uos??

  Adding a seemingly perfectly index is having an unexpectedly adverse affect on a query performance... -- [Data] has a predictable structure and a simple clustered index of the primary key: ALTER TABLE [dbo].[Data] ADD PRIMARY KEY CLUSTERED ( [ID] ) -- My query, joins on itself looking for a certain kind of "overlapping" records SELECT DISTINCT [Data].ID AS [ID] FROM dbo.[Data] AS [Data] JOIN dbo.[Data] AS [Compared] ON [Data].[A] = [Compared].[A] AND [Data].[B] = [Compared].[B] AND [Data].[C] = [Compared].[C] AND ([Data].[D] = [Compared].[D] OR [Data].[E] = [Compared].[E]) AND [Data].[F] <> [Compared].[F] WHERE 1=1 AND [Data].[A] = @A AND @CS <= [Data].[C] AND [Data].[C] < @CE -- Between a range [Data] has about a quarter-million records so far, 10% to 50% of the data satisfies the where clause depending on @A, @CS, and @CE. As is, the query takes 1 second to return about 300 rows when querying 10%, and 30 seconds to return 3000 rows when querying 50% of the data. Curiously, the estimated/actual execution plan indicates two parallel Clustered Index Scans, but the clustered index is only of the ID, which isn't part of the conditions of the query, only the output. ?? If I add this hand-crafted [IDX_A_B_C_D_E_F] index which I fully expected to improve performance, the query slows down by a factor of 8 (8 seconds for 10% & 4 minutes for 50%). The estimated/actual execution plans show an Index Seek, which seems like the right thing to be doing, but why so slow?? CREATE UNIQUE INDEX [IDX_A_B_C_D_E_F] ON [dbo].[Data] ([A], [B], [C], [D], [E], [F]) INCLUDE ([ID], [X], [Y], [Z]); The Data Engine Tuning wizard suggests a similar index with no noticeable difference in performance from this one. Moving AND [Data].[F] <> [Compared].[F] from the join condition to the where clause makes no difference in performance. I need these and other indexes for other queries. I'm sure I could hint that the query should refer to the Clustered Index, since that's currently winning - but we all know it is not as optimized as it could be, and without a proper index, I can expect the performance will get much worse with additional data. What gives?

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• Using T4 templates to add custom code to EF4 generated entities?

  - by David Veeneman

  I am getting started with Entity Framework 4, using model-first development. I am building a simple WPF demo app to learn the framework. My app has two entities, Topic and Note. A Topic is a discussion topic; it has Title, Text, and DateRevised properties. Topic also has a Notes collection property. a Note has DateCreated and Text properties. I have used EF4 to create an EDM and data store for the app. Now I need to add just a bit of intelligence to the entities. For example, the property setter for the Topic.Text property needs to update the Topic.DateRevised property, and a Note needs to set its DateCreated property when it is instantiated--pretty simple stuff. I assume that I can't modify the generated classes directly, because my code would be lost if the entities are re-generated. Is this the sort of thing that I can implement by modifying the T4 template that EF4 uses to generate the entities? In other words, can a T4 template be modified to add my code for performing these tasks to the entities that it generates? Can you refer me to a good tutorial or explanation of how to get started? Most of what I have found so far talks about how to add a tt file to an EDM, so I can do that. What I am looking for is a resource that I can use to get to the next level, assuming that a T4 template can be used to customize generated entities as I have described. Thanks for your help.

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• New to Linux Kernel/Driver development...

  - by CVS-2600Hertz-wordpress-com

  Recently, i began developing a driver of an embedded device running linux. Until now i have only read about linux internals. Having no prior experience in driver devlopment, i am finding it a tad difficult to land my first step. I have downloaded the kernel source-code (v2.6.32). I have read (skimped) Linux Device Drivers (3e) I read a few related posts here on StackOverflow. I understand that linux has a "monolithic" approach. I have built kernel (included existing driver in menuconfig etc.) I know the basics of kconfig and makefile files so that should not be a problem. Can someone describe the structure (i.e. the inter-links) of the various folders in the kernel-source code. In other words given a source-code file, which other files would it refer to for related code (The "#include"-s provide a partial idea) Could someone please help me in getting a better idea? Any help will be greatly appreciated Thank You.

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• CSS animated menu

  - by Andrea

  I am trying to obtain something similar to the "share this on..." menu here but I don't quite understand how they are doing this, even after a look at their CSS. I refer to the fact that the images show up on hover. My first attempt would be something like <div id="share_on"> <ul> <li><a href="#"><img src="shareon-digg.png" /></a></li> <li><a href="#"><img src="shareon-reddit.png" /></a></li> ... <li><a href="#"><img src="shareon-stumbleupon.png" /></a></li> </ul> </div> and the CSS: #share_on {overflow: hidden} #share_on ul {margin-bottom: -16px} #share_on li {display: inline} #share_on li:hover {margin-top: -16px} Of course this does not work, which is why I am asking here. In the inactive state, only half of the icon shows up, which is the expected behaviour. But on hover, nothing changes. I also have tried some variations, like #share_on li:hover {margin-bottom: 16px} or #share_on li:hover {padding-bottom: 16px} but none of these works. Any ideas?

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• C#, Asp.net Uploading files to file server...

  - by Imcl

  Using the link below, I wrote a code for my application. I am not able to get it right though, Please refer the link and help me ot with it... http://stackoverflow.com/questions/263518/c-uploading-files-to-file-server The following is my code:- protected void Button1_Click(object sender, EventArgs e) { filePath = FileUpload1.FileName; try { WebClient client = new WebClient(); NetworkCredential nc = new NetworkCredential(uName, password); Uri addy = new Uri("\\\\192.168.1.3\\upload\\"); client.Credentials = nc; byte[] arrReturn = client.UploadFile(addy, filePath); arrReturn = client.UploadFile(addy, filePath); Console.WriteLine(arrReturn.ToString()); } catch (Exception ex) { Console.WriteLine(ex.Message); } } I also used:- File.Copy(filePath, "\\192.168.1.3\upload\"); The following line doesnt execute... byte[] arrReturn = client.UploadFile(addy, filePath); tried changing it to:- byte[] arrReturn = client.UploadFile("\\192.168.1.3\upload\", filePath); IT still doesnt work...Any solution to it?? I basically want to transfer a file from the client to the file storage server without actually loggin into the server so that the client cannot access the storage location on the server directly...

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• Use Maven to trigger a wsgen & wsimport in a row, using wsdlLocation

  - by ben

  I have hard times using maven to generate my client. So Please refer to http://stackoverflow.com/questions/2131001/creating-a-web-service-client-directly-from-the-source for the first part of my question. To keep it simple and short, I want to go from here (a file in src/main/java) : package com.example.maven.jaxws.helloservice; import javax.jws.WebService; @WebService public class Hello { public String sayHello(String param) { ; return "Hello " + param; } } to there : /** * This class was generated by the JAX-WS RI. * JAX-WS RI 2.1.7-b01- * Generated source version: 2.1 * */ @WebServiceClient(name = "HelloService", targetNamespace = "http://helloservice.jaxws.maven.example.com/", wsdlLocation = "http://localhost:8080/test/") public class HelloService extends Service { private final static URL HELLOSERVICE_WSDL_LOCATION; private final static Logger logger = Logger.getLogger(com.example.wsimport.HelloService.class.getName()); ...etc using only 1 pom.xml file. Please note the wsdlLocation set on the end. The pom.xml file will probably use both maven-jaxws-plugin wsgen AND wsimport with some tricky configuration to achieve this.

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• VS2010 compiles solution without errors, msbuild fails: "fatal error CS0002: Unable to load message string from resources"

  - by Nathan Ridley

  I'm having a lot of trouble trying to track down the cause of this error message. I have a large Visual Studio 2010 solution which compiles without error on my local machine but on the build server, msbuild fails on one of the projects with the error: fatal error CS0002: Unable to load message string from resources Here's the red error section at the end: Build FAILED. "C:\TeamCity\buildAgent\work\85eff164854b9e67\Libraries\Domainface.Proxy.Common\Domainface.Proxy.Common.csproj" (default target) (9) -> (CoreCompile target) -> CSC : fatal error CS0002: Unable to load message string from resources. [C:\TeamCity\buildAgent\work\85eff164854b9e67\Libraries\Domainface.Proxy.Common\Domainface.Proxy.Common.csproj] 0 Warning(s) 1 Error(s) The entire msbuild output from the build server is here: http://pastie.org/3660842 What does the error generally refer to, that would cause it to build locally but not on the build server? UPDATE I have just run msbuild /version on both machines and it turns out the .net framework versions are very slightly different. Local machine is 4.0.30319.488 and build server is 4.0.30319.1. I'm about to run windows update on the server to allow it to install some updates, as several seem to be .net framework-related, so I'll see if that makes a difference. UPDATE Installing the updates didn't help. Just remembered I copied up csc.exe from the async preview a little while ago in order to facilitate async compilation (the actual async preview had failed to install on the server due to visual studio not being there, but installing visual studio team viewer seems to have fixed that, so i've just run the proper async ctp3 installer to see if that makes a difference.

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• QT- QImage and multi-threading problem.

  - by umanga

  Greetings all, Please refer to image at : http://i48.tinypic.com/316qb78.jpg We are developing an application to extract cell edges from MRC images from electron microscope. MRC file format stores volumetric pixel data (http://en.wikipedia.org/wiki/Voxel) and we simply use 3D char array(char***) to load and store data (gray scale values) from a MRC file. As shown in the image,there are 3 viewers to display XY,YZ and ZX planes respectively. Scrollbars on the top of the viewers use to change the image slice along an axis. Here is the steps we do when user changes the scrollbar position. 1) get the new scrollbar value.(this is the selected slice) 2) for the relavant plane (YZ,XY or ZX), generate (char* slice;) array for the selected slice by reading 3D char array (char***) 3) Create a new QImage* (Format_RGB888) and set pixel values by reading 'slice' (using img-setPixel(x,y,c);) 4) This new QImage* is painted in the paintEvent() method. We are going to execute "edge-detection" process in a seperate thread since it is an intensive process.During this process we need to draw detected curve (set of pixels) on top of above QImage*.(as a layer).This means we need to call drawPoint() methods outside the QT thread. Is it the best wayto use QImage for this case? What is the best way to execute QT drawing methods from another thread? thanks in advance,

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• Using jQuery delay() with separate elements

  - by boomturn

  I want to fake a simple animation on page load by sequentially revealing several pngs, each appearing instantly but with unique, precisely timed delay before the next one. Using the latest version of jQuery (1.4.2 at writing), which provides a delay method. My first (braindead) impulse was: $('#image1').show('fast').delay(800); $('#image2').show('fast').delay(1200); $('#image3').show('fast'); Of course all come up simultaneously. jQuery doc examples refer to a single item being chained, not handling multiple items. OK... try again using nested callbacks from show(): $('#image1').show('fast', function() { $('#image2').show('fast', function() { $('#image3').show('fast', function() { }); }); }); Looks ugly (imagine doing 10, also wonder what processor hit would be) but hey, it works sequentially! Without delay though. So... chain delay() after show() using a callback function from it (not even sure if it supports one): $('#image1').show('fast').delay(800, function() { $('#image2').show('fast').delay(1200, function() { $('#image3').show('fast'); }); }); Hm. Opposite result of what I thought might happen: the callback works, but still no delay. So... should I be using some combination of queue and delay instead of nested callbacks? jQuery doc examples for queue again only use one element for example. Guessing this would involve using a custom queue, but am uncertain how to implement this. Or maybe I'm missing a simple way? (For a simple problem!)

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• Using Doctype in Nhibernate

  - by sukh

  Hi I am trying to keep common properties of base class in one location and use XML ENTITY to refer in Nhibernate mapping file. Mapping file <?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE hibernate-mapping [ <!ENTITY BasePropertyList SYSTEM "BasePropertyList.xml"> ]> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Model" namespace= "Model" default-lazy="false"> <class name="DerivedClass"> &BasePropertyList; </class> </hibernate-mapping> BasePropertyList.xml <id name="ID" column="ID" type="Int32" unsaved-value="0"> <generator class="native"></generator> </id> <property name="CreatedDate" update="false" /> <property name="CreatedBy" update="false" /> <property name="LastModifiedDate" /> <property name="LastModifiedBy" /> I am getting following exception System.Xml.XmlException : DTD is prohibited in this XML document. at NHibernate.Cfg.Configuration.LogAndThrow(Exception exception) Am I missing anything here? How DOCTYPE works in Nhibernate mapping file??

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• Need advice on OOP philosophy

  - by David Jenings

  I'm trying to get the wheels turning on a large project in C#. My previous experience is in Delphi, where by default every form was created at applicaton startup and form references where held in (gasp) global variables. So I'm trying to adapt my thinking to a 100% object oriented environment, and my head is spinning just a little. My app will have a large collection of classes Most of these classes will only really need one instance. So I was thinking: static classes. I'm not really sure why, but much of what I've read here says that if my class is going to hold a state, which I take to mean any property values at all, I should use a singleton structure instead. Okay. But there are people out there who for reasons that escape me, think that singletons are evil too. None of these classes is in danger of being used anywhere except in this program. So they could certainly work fine as regular objects (vs singletons or static classes) Then there's the issue of interaction between objects. I'm tempted to create a Global class full of public static properties referencing the single instances of many of these classes. I've also considered just making them properties (static or instance, not sure which) of the MainForm. Then I'd have each of my classes be aware of the MainForm as Owner. Then the various objects could refer to each other as Owner.Object1, Owner.Object2, etc. I fear I'm running out of electronic ink, or at least taxing the patience of anyone kind enough to have stuck with me this long. I hope I have clearly explained my state of utter confusion. I'm just looking for some advice on best practices in my situation. All input is welcome and appreciated. Thanks in advance, David Jennings

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• Nested URLs and Rewrite rules in Apache2

  - by Radha Krishna. S.

  Hi, I need some help with rewrite rules and nested URLs. I am using TikiWiki for my website and am in the process of setting up SE friendly URLs for my projects. Specifically, I have the following rewrite rule for www.example.com/projects to point to a page that lists out all the projects hosted in example. RewriteRule ^Projects$ articles?type=Project [L] This works fine. Now, I would like to point www.example.com/projects/project1 to point to a specific project. I have this rewrite rule RewriteRule ^(Projects/Project1)$ tiki-read_article.php?articleId=6 This works, but partially. The content is all rendered as text but the theme - images/ css etc all go for a toss - the page is completely in text. I understand that this happens 'cause the relative paths in the theme/ css/ images all refer to Projects as the base folder instead of the root of the website. I don't want to touch the CMS portion - change the theme/ css/ image paths in the files, more for reasons of upgradability. Can someone help me understand and write a rule so that the above nested URL works? Regards, Radha

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• Windows could not start the Apache2 on Local Computer - problem

  - by vaske

  During the installation of Apache2 I got the following message into cmd window: Installing the Apache2.2 service The Apache2.2 service is successfully installed. Testing httpd.conf.... Errors reported here must be corrected before the service can be started. httpd.exe: Could not reliably determine the server's fully qualified domain name , using 192.168.1.3 for ServerName (OS 10048)Only one usage of each socket address (protocol/network address/port) is normally permitted. : make_sock: could not bind to address 0.0.0.0:80 no listening sockets available, shutting down Unable to open logs Note the errors or messages above, and press the key to exit. 24... and after installing everything look fine, but it isn't. If I try to start service I got the following message: Windows could not start the Apache2 on Local Computer. For more information, review the System Event Log. If this is a non-Micorsoft service, contact the service vendor, and refer to service-specific error code 1. Apach2 version is 2.2.9 Does anyone have the same problem, or could help me.

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• How do you word wrap a RichTextField for Blackberry

  - by Kai

  I've been trying to modify a rich text field to display correctly in its half of the horizontal field. The goal is this: --------------------------- | address is | ***********| | very long | ** IMAGE **| | state, zip | ***********| --------------------------- Where address is a single string separate from the city and zip. I am modifying the address field like this: RichTextField addrField = new RichTextField(address) { public int getPreferredWidth() { return 200; } protected void layout(int maxWidth,int maxHeight) { super.layout(getPreferredWidth(),maxHeight); setExtent(getPreferredWidth(), getHeight()); } }; The results look like this: ----------------------------- | address is ve| ***********| | state, zip | ** IMAGE **| | | ***********| ----------------------------- where clearly the address is just going under the image. Both horizontal fields are static 200 pixels wide. It's not like the system wouldn't know where to wrap the address. However, I have heard it is not easy to do this and is not done automatically. I have had no success finding a direct answer online. I have found people saying you need to do it in a custom layout manager, some refer to the RichTextField API, which is of no use. But nobody actually mentions how to do it. I understand that I may need to read character by character and set where the line breaks should happen. What I don't know is how exactly to do any of this. You can't just count characters and assume each is worth 5 pixels, and you shouldn't have to. Surely there must be some way to achieve this in a way that makes sense. Any suggestions?

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• RESTful API design question - how should one allow users to create new resource instances?

  - by Tamás

  I'm working in a research group where we intend to publish implementations of some of the algorithms we develop on the web via a RESTful API. Most of these algorithms work on small to medium size datasets, and in many cases, a user of our services might want to run multiple queries (with different parameters) on the same dataset, so for me it seems reasonable to allow users to upload their datasets in advance and refer to them in their queries later. In this sense, a dataset could be a resource in my API, and an algorithm could be another. My question is: how should I let the users upload their own datasets? I cannot simply let users upload their data to /dataset/dataset_id as letting the users invent their own dataset_ids might result in ID collision and users overwriting each other's datasets by accident. (I believe one of the most frequently used dataset ID would be test). I think an ideal way would be to have a dedicated URL (like /dataset/upload) where users can POST their datasets and the response would contain a unique ID under which the dataset was stored, but I'm not sure that it does not violate the basic principles of REST. What is the preferred way of dealing with such scenarios?

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• Facebook like and share create a fanpage

  - by nblumoe

  We are using the facebook like plugin with the share button. The URL points to a resource of our app. For example http://apps.facebook.com/appname/resources/id The first time this resource/url is shared or liked, everything works fine. The share for example holds the URL given above. But if the same resource/url is shared again, an error occurs. Facebook did create a fanpage for that resource like http://www.facebook.com/pages/appname So from now on, share/likes refer to that page instead of the resource/url of our app. The URL we use for the like plugin is correct and always points to the app resource URL. The fbappid in there is correct, too. Furthermore the page of the resource holds open graph meta tags like og:url, also pointing to the correct URL. The facebook linter/debugger returns URLs to the correct app resource URLs, when checking the liked/shared resource. Why is a fanpage created instead and the URL exchanged in shares/likes? How to fix it? We want the share to include the URL of the app resource and to increase the like count for that open graph object.

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• User roles - why not store in session?

  - by Phil

  I'm porting an ASP.NET application to MVC and need to store two items relating to an authenitcated user: a list of roles and a list of visible item IDs, to determine what the user can or cannot see. We've used WSE with a web service in the past and this made things unbelievably complex and impossible to debug properly. Now we're ditching the web service I was looking foward to drastically simplifying the solution simply to store these things in the session. A colleague suggested using the roles and membership providers but on looking into this I've found a number of problems: a) It suffers from similar but different problems to WSE in that it has to be used in a very constrained way maing it tricky even to write tests; b) The only caching option for the RolesProvider is based on cookies which we've rejected on security grounds; c) It introduces no end of complications and extra unwanted baggage; All we want to do, in a nutshell, is store two string variables in a user's session or something equivalent in a secure way and refer to them when we need to. What seems to be a ten minute job has so far taken several days of investigation and to compound the problem we have now discovered that session IDs can apparently be faked, see http://blogs.sans.org/appsecstreetfighter/2009/06/14/session-attacks-and-aspnet-part-1/ I'm left thinking there is no easy way to do this very simple job, but I find that impossible to believe. Could anyone: a) provide simple information on how to make ASP.NET MVC sessions secure as I always believed they were? b) suggest another simple way to store these two string variables for a logged in user's roles etc. without having to replace one complex nightmare with another as described above? Thank you.

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• How does one properly redefine self while avoiding the "Multiple methods named ..." warning?

  - by Elise van Looij

  In Apple's The Objective-C Programming Language: Defining a Class the section named "Redifining self" recommends that that class methods allocate and return instances use 'self' only to allocate an instance and then refer only to that instance. Thus, I have a number of subclasses, that have class methods along the lines of: + (id)scrollViewWithFrame: (NSRect)rectFrame { id newInstance = [[[self alloc] initWithFrame:rectFrame] autorelease]; [newInstance setHasHorizontalScroller: YES]; [newInstance setHasVerticalScroller: YES]; [newInstance setBorderType: NSNoBorder]; [newInstance setAutoresizingMask: (NSViewWidthSizable | NSViewHeightSizable)]; return newInstance; } The above is, of course, a subclass of NSScrollView. Unfortunately, Xcode 3.x all these NSView subclasses now raise warnings: "Warning: Multiple methods named '-setAutoresizingMask' found". I believe it has something to do with GCC 4.2, the settings of which I have not changed. The warning is correct, of course, since NSView and its various subclasses all implement setAutoresizingMask, but it is also unnecessary. Since they're only warnings, I ignore them but there is a risk that in between the thirty or so unnecessary ones, a really useful warning lurks which I simply don't see. So, what to do? I do want to adhere to good coding practices and I want to build warning-free apps -- how can I do both?

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• Can't operator == be applied to generic types in C#?

  - by Hosam Aly

  According to the documentation of the == operator in MSDN, For predefined value types, the equality operator (==) returns true if the values of its operands are equal, false otherwise. For reference types other than string, == returns true if its two operands refer to the same object. For the string type, == compares the values of the strings. User-defined value types can overload the == operator (see operator). So can user-defined reference types, although by default == behaves as described above for both predefined and user-defined reference types. So why does this code snippet fail to compile? void Compare<T>(T x, T y) { return x == y; } I get the error Operator '==' cannot be applied to operands of type 'T' and 'T'. I wonder why, since as far as I understand the == operator is predefined for all types? Edit: Thanks everybody. I didn't notice at first that the statement was about reference types only. I also thought that bit-by-bit comparison is provided for all value types, which I now know is not correct. But, in case I'm using a reference type, would the the == operator use the predefined reference comparison, or would it use the overloaded version of the operator if a type defined one? Edit 2: Through trial and error, we learned that the == operator will use the predefined reference comparison when using an unrestricted generic type. Actually, the compiler will use the best method it can find for the restricted type argument, but will look no further. For example, the code below will always print true, even when Test.test<B>(new B(), new B()) is called: class A { public static bool operator==(A x, A y) { return true; } } class B : A { public static bool operator==(B x, B y) { return false; } } class Test { void test<T>(T a, T b) where T : A { Console.WriteLine(a == b); } }

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• C# - Help with LINQ

  - by cmaduro

  I need to check if a certain property exists within a class. Please refer to the LINQ query in question. For the life of me I cannot make the compiler happy. class Program { static void Main(string[] args) { ModuleManager m = new ModuleManager(); IModule module = m.FindModuleForView(typeof(HomeView)); Console.WriteLine(module.GetType().ToString()); Console.ReadLine(); } } public class ModuleManager { [ImportMany] public IEnumerable<Lazy<IModule>> Modules { get; set; } [ImportMany] public IEnumerable<Lazy<View>> Views { get; set; } public ModuleManager() { //An aggregate catalog that combines multiple catalogs var catalog = new AggregateCatalog(); //Adds all the parts found in the same assembly as the Program class catalog.Catalogs.Add(new AssemblyCatalog(typeof(Program).Assembly)); //Create the CompositionContainer with the parts in the catalog _container = new CompositionContainer(catalog); //Fill the imports of this object try { this._container.ComposeParts(this); } catch (CompositionException compositionException) { Console.WriteLine(compositionException.ToString()); } } public IModule FindModuleForView(Type view) { //THIS IS THE PROBLEM var module = from m in Modules where ( from p in m.Value.GetType().GetProperties() where p.GetType().Equals(view) select p ) select m; } public CompositionContainer _container { get; set; } } public interface IModule { } [Export] public class HomeModule : IModule { public HomeModule() { } [Export] public HomeView MyHomeView { get { return new HomeView(); } set { } } } public class HomeView : View { } public class View { }

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• Where my memory is alloced, Stack or Heap, Can I find it at Run-time?

  - by AKN

  I know that memory alloced using new, gets its space in heap, and so we need to delete it before program ends, to avoid memory leak. Let's look at this program... Case 1: char *MyData = new char[20]; _tcscpy(MyData,"Value"); . . . delete[] MyData; MyData = NULL; Case 2: char *MyData = new char[20]; MyData = "Value"; . . . delete[] MyData; MyData = NULL; In case 2, instead of allocating value to the heap memory, it is pointing to a string literal. Now when we do a delete it would crash, AS EXPECTED, since it is not trying to delete a heap memory. Is there a way to know where the pointer is pointing to heap or stack? By this the programmer Will not try to delete any stack memory He can investigate why does this ponter, that was pointing to a heap memory initially, is made to refer local literals? What happened to the heap memory in the middle? Is it being made to point by another pointer and delete elsewhere and all that?

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• Using Scala structural types with abstract types

  - by Joshua Hartman

  I'm trying to define a structural type defining anything that has an "add" method (for instance, a java collection or a java map). Using this, I want to define a few higher order functions that operate on a certain collection object GenericTypes { type GenericCollection[T] = { def add(value: T): java.lang.Boolean} } import GenericTypes._ trait HigherOrderFunctions[T, CollectionType[X] <: GenericCollection[X]] { def map[V](fn: (T) => V): CollectionType[V] .... } class RichJList[T](list: List[T]) extends HigherOrderFunctions[T, java.util.List] This does not compile with the following error error: Parameter type in structural refinement may not refer to abstract type defined outside that same refinement I tried removing the parameter on GenericCollection and putting it on the method: object GenericTypes { type GenericCollection = { def add[T](value: T): java.lang.Boolean} } import GenericTypes._ trait HigherOrderFunctions[T, CollectionType[X] <: GenericCollection] class RichJList[T](list: List[T]) extends HigherOrderFunctions[T, java.util.List] but I get another error: error: type arguments [T,java.util.List] do not conform to trait HigherOrderFunctions's type parameter bounds [T,CollectionType[X] <: org.scala_tools.javautils.j2s.GenericTypes.GenericCollection] Can anyone give me some advice on how to use structural typing with abstract typed parameters in Scala? Or how to achieve what I'm looking to accomplish? Thanks so much!

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