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• Can you explain what's going on in this Ruby code?

  - by samoz

  I'm trying to learn Ruby as well as Ruby on Rails right now. I'm following along with Learning Rails, 1st edition, but I'm having a hard time understanding some of the code. I generally do work in C, C++, or Java, so Ruby is a pretty big change for me. I'm currently stumped with the following block of code for a database migrator: def self.up create_table :entries do |t| t.string :name t.timestamps end end Where is the t variable coming from? What does it actually represent? Is it sort of like the 'i' in a for(i=0;i<5;i++) statement? Also, where is the :entries being defined at? (entries is the name of my controller, but how does this function know about that?)

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• Can someone exaplain me implicit parameters in Scala?

  - by Oscar Reyes

  And more specifically how does the BigInt works for convert int to BigInt? In the source code it reads: ... implicit def int2bigInt(i: Int): BigInt = apply(i) ... How is this code invoked? I can understand how this other sample: "Date literals" works. In. val christmas = 24 Dec 2010 Defined by: implicit def dateLiterals(date: Int) = new { import java.util.Date def Dec(year: Int) = new Date(year, 11, date) } When int get's passed the message Dec with an int as parameter, the system looks for another method that can handle the request, in this case Dec(year:Int) Q1. Am I right in my understanding of Date literals? Q2. How does it apply to BigInt? Thanks

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• Why do firefox/chrome show a different page than IE8?

  - by Edward Tanguay

  When I look at this published Google Docs document, I see the latest version with Firefox and Chrome, but an older version with IE8. Also, screen-scraping it via PHP/Curl gives me an older version. I've tried CTRL-Refresh in IE8 but I can't get it to show me the newest version. No matter what headers I try to change in PHP/Curl, I can't get it to show me the newest version. What am I not understanding about browsers/headers/caching here? How can it be that different browsers show different contents of one page?

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• ARC, worth it or not?

  - by MSK

  When I moved to Objective C (iOS) from C++ (and little Java) I had hard time understanding memory management in iOS. But now all this seems natural and I know retain, autorelease, copy and release stuff. After reading about ARC, I am wondering is there more benefits of using ARC or it is just that you dont have to worry about memory management. Before moving to ARC I wanted to know how worth is moving to ARC. XCode has "Convert to Objective C ARC" menu. Is the conversion is that simple (nothing to worry about)? Does it help me in reducing my apps memory foot-print, memory leaks etc (somehow ?) Does it has much testing impact on my apps ? What are non-obvious advantages? Any Disadvantage os moving to it?

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• car and cdr in scheme is driving me crazy ...

  - by kristian Roger

  Hi Im facing a probem with the car and cdr functions for example: first I defined a list caled it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rule (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wronge answers can any one help me in understanding this ... give me step or a way to solve it step by step thanx in advance Im really sick of scheme language.

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• [Single|Double|Or no] Quotes when using grep?

  - by Hamy

  Grep acts differently depending on what kind of quotes I surround the regex with. I can't seem to get a clear understanding of why this is. Here is an example of the problem: hamiltont$ grep -e show\( test.txt variable.show(); variable.show(a); variable.show(abc, 132); variableshow(); hamiltont$ grep -e "show\(" test.txt grep: Unmatched ( or \( hamiltont$ grep -e 'show\(' test.txt grep: Unmatched ( or \( I am just assuming there is some proper way to enclose the regex with single/double quotes. Any help? FWIW, grep --version returns grep (GNU grep) 2.5.1

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• How extensive is an Object in CakePHP model linkage?

  - by Andre

  I was hoping someone with an understanding on CakePHP could shed some light on a question I've been having. Here's my scenario, I have a User this User has a Company which in turn has many Department and many Address. If I were to get a User could I expect to have access to the Company and all models associated with that Company? So would $user['Company']['Department'][0] or $user['Company']['Address'][0] be possible? Which brings me back to the original question, how extensive is the linkage between models?

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• How to implement an ItemsControl3D which can use templates of Visual3D?

  - by Christo

  I'm looking for something like a ContainerUIElement3D which supports the ItemsSource property and an ItemTemplate property which I can use within a Viewport3D. My aim is to be able to write something like: <ItemsControl3D ItemsSource="{Binding Path=MyItems}"> <ItemsControl3D.ItemTemplate> <DataTemplate3D> <!-- My template which defines the binding to each item. --> <DataTemplate3D> </ItemsControl3D.ItemTemplate> </ItemsControl3D> I'm looking for tips on how to implement this. The first tricky part is to create a DataTemplate3D which can construct the Visual3D needed to add to the ItemsControl3D. I've been using .NET reflector to browse through the implementation of ItemsControl and DataTemplate, but I soon realised that I don't have a deep enough understanding and enough time to come up with a solution on my own.

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• how to deal with a static analyzer output

  - by Jim

  We have started using a static analyzer (Coverity) on our code base. We were promptly stupefied by the sheer amount of warnings we received (its in the hundreds of thousands) , it will take the entire team a few mounts to clear them all (obliviously impossible). the options we discussed so far are 1) hire a contractor to sort out the warning and fix them - he drawback: we will probably need very experiences people to do all these modifications, and no contractor will have required understanding of the code. 2) filter out the warning and deal only with the dangerous ones - the problem here is that our static analysis output will always be cluttered by warning making it difficult for us to isolate problems. also the filtering of the warning is also a major effort. either way, bringing our code to a state when the static analyzer can be a useful tool for us seems a monumental task. so how is it possible to work with the static analyzer without braining current development efforts into a complete stand still?

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• phing nested if conditions

  - by Matt1776

  Hello - I am having trouble understanding the Phing documentation regarding multiple conditions for a given tag. It implies you cannot have multiple conditions unless you use the tag, but there are no examples of how to use it. Consequently I nested two tags, however I feel silly doing this when I know there is a better way. Does anyone know how I can use the tag to accomplish the following: <if><equals arg1="${deployment.host.type}" arg2="unrestricted" /><then> <if><equals arg1="${db.adapter}" arg2="PDO_MYSQL"/><then> <!-- Code Here --> </then></if> </then></if>

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• Using Geo APIs to pick a random town from anywhere in the world

  - by Dan Forys

  Hi all, I'm trying to use Yahoo's excellent GeoPlanet API: http://developer.yahoo.com/geo/geoplanet/guide/api-reference.html I would like to pick a random town from anywhere in the world but can't see an easy way to do it. I have tried querying by country and asking for children of type 'town', but can't seem to do that directly. Can anyone think of a way to pluck out a random town WOEID without having to query the country, then the admin regions, then the admin 2, then the admin 3 etc. I have also experimented using YQL, but don't have enough of an understanding about the available APIs.

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• Retain, alloc, properties ... Topic to make your Obj-c life easier !

  - by gotye

  Hey everyone, The more I code, the more I get lost ... so I decided to create a topic entirely dedicated to the memory management for me (and others) not to waste hours understanding obj-c basics ... I'll update it as new questions are asked ! Okay below is some examples : // myArray is property (retain) myArray = otherArray; //myArray isn't a property myArray = otherArray; //myArray is a property (retain) myArray = [[NSArray alloc] init]; //myArray isn't a property myArray = [[NSArray alloc] init]; Could you explain to me what happens in every cases ? And especially the number 3 ;) Thanks for the time. Gotye.

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• Easy framework for OpenGL Shaders in C/C++

  - by Nils

  I just wanted to try out some shaders on a flat image. Turns out that writing a C program, which just takes a picture as a texture and applies, let's say a gaussian blur, as a fragment shader on it is not that easy: You have to initialize OpenGL which are like 100 lines of code, then understanding the GLBuffers, etc.. Also to communicate with the windowing system one has to use GLUT which is another framework.. Turns out that Nvidia's Fx composer is nice to play with shaders.. But I still would like to have a simple C or C++ program which just applies a given fragment shader to an image and displays the result. Does anybody have an example or is there a framework?

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• JavaFX - reduce() function to show how to pass functions as parameters

  - by Helper Method

  At the moment I'm writing a JavaFX guide for Java developers. In order to show how to pass a function to another funtion i adopted the reduce() function found in Effective Java: function reduce(seq: Integer[], f: function(: Integer, : Integer): Integer, init: Integer) { var result = init; for (i in seq) { result = f(i, result); } result } def nums = [1 .. 10]; println(reduce(nums, function(a: Integer, b: Integer) { a + b }, 0)); // prints 55 println(reduce(nums, function(a: Integer, b: Integer) { a * b }, 0)); // prints 3628800 Now I wonder if this example is not to hard for someone starting to learn JavaFX. The tutorial is targeted to programmers with a solid understanding of Java, yet I'm not quite sure about the usefulness of the example. Any ideas?

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• Doesn't JavaScript support closures with local variables?

  - by qollin

  I am very puzzled about this code: var closures = []; function create() { for (var i = 0; i < 5; i++) { closures[i] = function() { alert("i = " + i); }; } } function run() { for (var i = 0; i < 5; i++) { closures[i](); } } create(); run(); From my understanding it should print 0,1,2,3,4 (isn't this the concept of closures?). Instead it prints 5,5,5,5,5. I tried Rhino and Firefox. Could someone explain this behavior to me? Thx in advance.

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• MVVM where does the code to load the data belong?

  - by cody

  As I wrap my head around the mvvm thing, the view is the view, and the viewmodel is 'a modal of a view' and the model are the entities we are dealing with (or at least that is my understanding). But I'm unclear as to what and when the model entities are populated. So for example: Lets say I have app that needs to create a new record in a DB. And that record should have default values to start with. Who is responsible for the new record, and getting the default values. Does this have anything to do with MVVM or is that part of a data access layer? Who calls the the viewmodel? Or for existing records when\where are the records retrieved? And saved if altered? Thanks

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• C# regex: negative lookahead fails with the single line option

  - by Sylverdrag

  I am trying to figure out why a regex with negative look ahead fails when the "single line" option is turned on. Example (simplified): <source>Test 1</source> <source>Test 2</source> <target>Result 2</target> <source>Test 3</source> This: <source>(?!.*<source>)(.*?)</source>(?!\s*<target) will fail if the single line option is on, and will work if the single line option is off. For instance, this works (disables the single line option): (?-s:<source>(?!.*<source>)(.*?)</source>(?!\s*<target)) My understanding is that the single line mode simply allows the dot "." to match new lines, and I don't see why it would affect the expression above. Can anyone explain what I am missing here?

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• PHP namespaces and using the \ prefix in declaration

  - by Jason McCreary

  The following throws an error stating Exception can no be redeclared. namespace \NYTD\ReadingListBackend; class Exception extends \Exception { } However, removing the \ prefix in the namespace declaration does not: namespace NYTD\ReadingListBackend; I recently adopted PHP namespaces. My understanding is that namespaces prefixed with \ are a fully qualified name. So why can't I use the prefix in the namespace declaration? I can when referencing (e.g. new \NYTD\ReadingListBackend\Exception). Would appreciate a full explanation as I couldn't find anything in the docs.

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• Haskell: Pattern Matching with Lists

  - by user1670032

  I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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• Considering getting into reverse engineering/disassembly

  - by Zombies

  Assuming a decent understanding of assembly on common CPU architectures (eg: x86), how can one explore a potential path (career, fun and profit, etc) into the field of reverse engineering? There is so little educational guides out there so it is difficult to understand what potential uses this has today (eg: is searching for buffer overflow exploits still common, or do stack monitoring programs make this obselete?). I am not looking for any step by step program, just some relevant information such as tips on how to efficiently find a specific area of a program. Basic things in the trade. As well as what it is currently being used for today. So to recap, what current uses does reverse engineering yield today? And how can one find some basic information on how to learn the trade (again it doesn't have to be step-by-step, just anything which can through a clue would be helpful).

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• What resources will help me understand the fundamentals of Relational Database Design.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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• Does the number of busy worker threads in the CLR ThreadPool affect performance of I/O threads?

  - by andrej351

  We have a Windows Service which hosts a number of WCF services and, in an unrelated part of the app, makes extensive use of the TPL Task class to asynchronously do relatively short bits of work. It is my understanding that WCF uses managed I/O threads from the ThreadPool to execute requests. I noticed that after deploying a feature which significantly raised the applications use of Tasks, and as such the use of ThreadPool worker threads as well, performance of a couple of web services has become very slow. We're talking minutes instead of less than a second. The number of Tasks actually trying to run at any one time can range between 20 and 1000, which makes me think that any new (last in) work needing some CPU time could be forced to wait for quite some time. Does the (in my case extremely large) number of busy ThreadPool worker threads affect the ThreadPool's managed I/O threads? Or could these two be connected in any way? Thanks!

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• Why should I use mock objects (Java)? Do all mocking frameworks serve the same purpose?

  - by Mehmet Yesin

  I'm preparing a presentation and I need to get a better understanding of what mocking is, what is the purpose of using it, what are the common situations that I should use mock objects? I found out that there are a bunch of mocking frameworks out there. Do they all do the same thing or do I use a specific framework for specific testing purpose? What are the differences between these frameworks? Which one would you recommend for testing Java? here are some stuff that I found: 1.MockingToolkitComparisonMatrix which seems biased. 2.What are mock objects in Java? This is a year old. I thought there might be some better answer today. Thank you.

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• car and cdr in Scheme are driving me crazy ...

  - by kristian Roger

  Hi Im facing a problem with the car and cdr functions for example: first I defined a list called it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rules (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wrong answers. Can any one help me in understanding this ... give me step or a way to solve it step by step Thanks in advance. I'm really sick of Scheme.

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• Does Seaside scale?

  - by Richard Durr

  Seaside is known as "the heretical web framework". One of the points that make it heretical is that it has much shared state. That however is something which, in my current understanding, hinders easy scaling. Ruby on rails on the other hand shares as less state as possible. It has been known to scale pretty well, even if it is dog slow compared to modern smalltalk vms. flickr uses php and has scaled to an extremly big infrastructure... So has anybody some experience in the scaling of Seaside?

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