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• What is the most elegant way to access current_user from the models? or why is it a bad idea?

  - by TheLindyHop

  So, I've implemented some permissions between my users and the objects the users modify.. and I would like to lessen the coupling between the views/controllers with the models (calling said permissions). To do that, I had an idea: Implementing some of the permission functionality in the before_save / before_create / before_destroy callbacks. But since the permissions are tied to users (current_user.can_do_whatever?), I didn't know what to do. This idea may even increase coupling, as current_user is specifically controller-level. The reason why I initially wanted to do this is: All over my controllers, I'm having to check if a user has the ability to save / create / destroy. So, why not just return false upon save / create / destroy like rails' .save already does, and add an error to the model object and return false, just like rails' validations? Idk, is this good or bad? is there a better way to do this?

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• Getting a user's Facebook pic

  - by Newy

  Can I get a users Facebook picture in a Rails app without fully integrating Facebook Connect into Authlogic?

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• Are `return` and `break` useless inside a Ruby block when used as a callback?

  - by Skilldrick

  In Rails, blocks can be used as callbacks, e.g.: class User < ActiveRecord::Base validates_presence_of :login, :email before_create {|user| user.name = user.login.capitalize if user.name.blank?} end When a block is used like this, is there any use for break and return? I'm asking because normally in a block, break will break out of the loop, and return will return from the enclosing method. But in a callback context, I can't get my head round what that means. The Ruby Programming Language suggests that return could cause a LocalJumpError but I haven't been able to reproduce this in a Rails callback. Edit: with the following code I'd expect a LocalJumpError, but all the return does is stop the rest of the callback executing. class User < ActiveRecord::Base validates_presence_of :login, :email before_create do |user| return user.name = user.login.capitalize end

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• Is there a webservice I can use to compare 2 audio clips for similarity?

  - by wgpubs

  Just wondering if something like this exists ... or if there is something I can plug into a Rails or ASP.NET webapplication

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• minifying patched javascript files

  - by Stacia

  I'm writing a Rails app and I've partially integrated in this nice little patch to the in line ajax editor: http://inplacericheditor.box.re/ The problem is, on that page I have tinymce, prototype and scriptaculous included. In Firefox at least there's a big lag when all this stuff is loading. I was hoping to fix it by compressing the files so I checked out a plugin for rails called Smurf. It seemed to do what it was supposed to do nicely, but it choked on the little patch files that are included with the Ajax editor thing. THe patch files look like this: Object.extend(Ajax.InPlaceEditor.prototype, { handleAJAXFailure: function(transport) Alternatively, should I just be catching them instead of worrying about minfying them? I know I'm running on development and that Apache would maybe be handling serving the js files differently..It just seems like a lot of things to serve on one page.

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• Are there any Simple and Clean Methods to implement Maps (Google or otherwise) in RoR 3?

  - by Port3M5

  I'm looking into building a group work app for my final year project next year. One of the core parts is organising group meetings. I plan to make this as powerful as possible and adding a map can help get rid of excuses such as "I didn't know where it was". I have been unable to find any simple solutions to embed maps into my Rails apps so far. An important issue is I need Rails 3 Compatibility. What are your suggestions? Gems, plugins or even something totally different?

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• DB fields not showing up in association custom queries?

  - by Kevin

  I have a notification list that the user can select different show options for different kinds of notifications along with how many results are returned. I'm keeping them in the user model because I want the custom sort to stay with the user between sessions. Here is the association in my user model: has_many :notifications, :class_name => "Notification", :foreign_key => "user_id", :conditions => ["won = ? and lost = ? and paid = ?", self.prefs_won, self.prefs_lost, self.prefs_paid], :limit => self.prefs_results.to_s But when I use the above code, Rails throws me an "unknown method" error for self.prefs_won. It is definitely a field in my database and set as a boolean value, but Rails can't find it... what's the problem?

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• :from parameter in active record find not well designed?

  - by potlee

  i got this error: SQLite3::SQLException: no such column: apis.name: SELECT * FROM examples WHERE ("apis"."name" = 'deep') my code Api.find :all, :from => params[:table_name], :conditions => {:name => 'deep' } I need to make a back end rails application which will be used by a silverlight application. one of the requirements is to fetch simple data from the database. i need to be able to query different tables with the same code.(my app has 2000 tables!) i think it does not make sense for rails to put in "apis" in the WHERE clause. is there any speciic reason for this?

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• How can I get a set of radio buttons to accept NULL (nothing checked)?

  - by Ethan

  I'm working on a Rails application where I have some a set of two radio buttons where users can click "yes" or "no". The MySQL DB column created by the ActiveRecord migration is a tinyint. If the user doesn't click either radio button I want MySQL to store NULL. (The column allows NULL.) And when they come back to edit the data, neither button should be checked. What's happening is that ActiveRecord is storing 0 and then when I come back the "No" button is checked. Rails 2.3.5 Form code (I'm using Haml): = f.radio_button( :model_attribute, true ) Yes = f.radio_button( :model_attribute, false ) No (In retrospect it probably would have been better to use a single checkbox, but it would be difficult to change that now.)

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• How to version SQL Server schema using VS 2005?

  - by Mike

  I am new to C# programming and am coming to it most recently from working with Ruby on Rails. In RoR, I am used to being able to write schema migrations for the database. I would like to be able to do something similar for my C#/SQLServer projects. Does such a tool exist for the VS 2005 toolset? Would it be wise to use RoR migrations with SQL Server directly outside of VS 2005? In other words, I would handle all schema versioning using ActiveRecord:Migration from Rails but nothing else. If I do handle migrations outside of C# and VS 2005 with another tool, is RoR ActiveRecord:Migration the best thing to use or is there something which is a better fit?

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• rolling up text method

  - by small

  i am stacked i want the method of rolling up text in ruby on rails please help me

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• No route matches - after login attempt - even though the route exists?

  - by datorum

  I am working on a rails application and added a simple login system according to a book. I created the controller admin: rails generate controller admin login logout index It added the following routes to routes.db get "admin/login" get "admin/logout" get "admin/index" I can got to http://localhost:3000/admin/login there is no problem at all. But when I try to login I get: No route matches "/admin/login"! Now, the first confusing part is that the "login" method of my AdminController is not executed at all. The second confusing part is that this code works like a charm - redirects everything to /admin/login: def authorize unless User.find_by_id(session[:user_id]) flash[:notice] = "you need to login" redirect_to :controller => 'admin', :action => 'login' end end Sidenotes: I restarted the server several times. I tried a different browser - to be sure there is no caching problem.

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• nested has_many

  - by Nick Vanderbilt

  I am using Rails 2.3.5. Class User < ActiveRecord::Base has_many :phones end class Phone < ActiveRecord::Base has_many :frequency_bands end I want to get all the frequency_bands for a user. I know I can write a method def freq_bands for User but I would like to know if it is possible to have has_many freq_bands for a User. In this way I can chain the call. What I would like to have is class User < ActiveRecor::Base has_many :frequence_bands, :through => phones end I think it is possible to have nested has_many using this plugin http://github.com/ianwhite/nested_has_many_through However if possible I would like to avoid using another plugin and rely solely on rails.

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• nested has_many

  - by dorelal

  I am using Rails 2.3.5. Class User < ActiveRecord::Base has_many :phones end class Phone < ActiveRecord::Base has_many :frequency_bands end I want to get all the frequency_bands for a user. I know I can write a method def freq_bands for User but I would like to know if it is possible to have has_many freq_bands for a User. In this way I can chain the call. What I would like to have is class User < ActiveRecor::Base has_many :frequence_bands, :through => phones end I think it is possible to have nested has_many using this plugin http://github.com/ianwhite/nested_has_many_through However if possible I would like to avoid using another plugin and rely solely on rails.

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• Module.new with class_eval

  - by dorelal

  This is a large commit. But I want you to concentrate on this change block. http://github.com/rails/rails/commit/d916c62cfc7c59ab6411407a05b946d3dd7535e9#L2L1304 Even without understanding the full context of the code I am not able to think of a scenario where I would use include Modue.new { class_eval <<-RUBY def foo puts 'foo' end RUBY } Then end result is that in the root context (self just before include Moduel.new) a method call foo has been added. If I take out the Module.new code and if I only leave class_eval in that case also I will have a method called foo in self. What am I missing.

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• Impossible to do POSTs with appengine-jruby/RoR: Reflection is not allowed

  - by Joel Cuevas

  I'm trying to build a site with RoR on Google App Engine. I'm using the google-appengine gem (http://appengine-jruby.googlecode.com) and following the instructions in (http://gist.github.com/268192). The problem is that I can't submit ANY form! I've already tried this in two diferent clean Win 7 Pro envs and the result is the same. After install Ruby 1.8.6 (One-Click Installer): 1. gem update --system 2. gem install rails 3. gem install google-appengine 4. gem install rails_dm_datastore 5. gem install activerecord-nulldb-adapter 6. curl -O http://appengine-jruby.googlecode.com/hg/demos/rails2/rails2_appengine.rb 7. ruby rails2_appengine.rb (previously downloaded) 8. rails myproj 9. chmod myproj 10. ruby script/generate dd_model MyModel f1:string f2:float f3:float f4:float f5:integer f6:integer f7:integer -f 11. ruby script/generate scaffold MyModel f1:string f2:float f3:float f4:float f5:integer f6:integer f7:integer -f --skip-migration 12. dev_appserver.rb -p 3000 . At this point, I manually test the scaffold in (http://localhost:3000/my_models). The index is OK, then I create a new registry with the generated form, everything's fine, but when I try to create a second one, I get a "java.lang.RuntimeException: DummyDynamicScope should never be used for backref storage" in the console. As far as I read this is a won't-fix behavior in JRuby 1.4.1, but it's converted to a debug only warning in 1.5.0, so I proceed to install the pre release. 13. gem install appengine-jruby-jars --pre With this, that exception is solved and everything works great... until I move the project to the GAE server. 14. ruby appcfg.rb update . And now, in (http://myproj.appspot.com/my_models), again, the index is fine, also the new form, but in the moment that I submit it with valid data, I get a 500 error: "java.lang.IllegalAccessException: Reflection is not allowed on public int". As I said, this behavior is not present in the local SDK. In both cases, I'm completely unable to post anything. This is what I have right now in the GAE environment: Ruby version 1.8.7 (java) RubyGems disabled Rack version 1.1 Rails version 2.3.5 Action Pack version 2.3.5 Active Support version 2.3.5 DataMapper version 0.10.2 Environment production JRuby Runtime version 1.5.0.pre JRuby-Rack version 0.9.7 AppEngine SDK version Google App Engine/1.3.3 AppEngine APIs version 0.0.15 And this are my intalled gems: actionmailer (2.3.5) actionpack (2.3.5) activerecord (2.3.5) activerecord-nulldb-adapter (0.2.0) activeresource (2.3.5) activesupport (2.3.5) addressable (2.1.2) appengine-apis (0.0.15) appengine-jruby-jars (0.0.8.pre, 0.0.7) appengine-rack (0.0.8) appengine-sdk (1.3.3.1) appengine-tools (0.0.12) bundler08 (0.8.5) dm-appengine (0.0.8) dm-ar-finders (0.10.2) dm-core (0.10.2) dm-timestamps (0.10.2) dm-validations (0.10.2) extlib (0.9.14) fxri (0.3.7, 0.3.6) google-appengine (0.0.12) hpricot (0.8.2 x86-mswin32, 0.6 mswin32) jruby-rack (0.9.8, 0.9.7) log4r (1.1.7, 1.0.5) rack (1.1.0, 1.0.1) rails (2.3.5) rails_appengine (0.0.3) rails_dm_datastore (0.2.9) rake (0.8.7, 0.7.3) rubygems-update (1.3.7, 1.3.6) rubyzip (0.9.4) sources (0.0.1) win32-api (1.4.6 x86-mswin32-60, 1.0.4 mswin32) win32-clipboard (0.5.2, 0.4.3) win32-dir (0.3.6, 0.3.2) win32-eventlog (0.5.2, 0.4.6) win32-file (0.6.3, 0.5.4) win32-file-stat (1.3.4, 1.2.7) win32-process (0.6.2, 0.5.3) win32-sapi (0.1.5, 0.1.4) win32-sound (0.4.2, 0.4.1) windows-api (0.4.0, 0.2.0) windows-pr (1.0.9, 0.7.2) I'm unable to attach the full logs of the exceptions because of the character limits, but I can provide them under request. Here's an abstract of them: DummyDynamicScope (dev and prod envs): 14-may-2010 7:18:40 com.google.appengine.tools.development.ApiProxyLocalImpl log SEVERE: [1273821520195000] javax.servlet.ServletContext log: Application Error java.lang.RuntimeException: DummyDynamicScope should never be used for backref storage at org.jruby.runtime.scope.DummyDynamicScope.getBackRef(DummyDynamicScope.java:49) at org.jruby.RubyRegexp.updateBackRef(RubyRegexp.java:1404) at org.jruby.RubyRegexp.updateBackRef(RubyRegexp.java:1396) at org.jruby.RubyRegexp.search(RubyRegexp.java:1386) at org.jruby.RubyRegexp.op_match(RubyRegexp.java:1301) at org.jruby.RubyString.op_match(RubyString.java:1446) at org.jruby.RubyString$i_method_1_0$RUBYINVOKER$op_match.call(org/jruby/RubyString$i_method_1_0$RUBYINVOKER$op_match.gen) at org.jruby.internal.runtime.methods.JavaMethod$JavaMethodOneOrN.call(JavaMethod.java:721) at org.jruby.RubyClass.finvoke(RubyClass.java:472) at org.jruby.RubyObject.send(RubyObject.java:1442) at org.jruby.RubyObject$i_method_multi$RUBYINVOKER$send.call(org/jruby/RubyObject$i_method_multi$RUBYINVOKER$send.gen) at org.jruby.internal.runtime.methods.JavaMethod$JavaMethodZeroOrOneOrTwoOrNBlock.call(JavaMethod.java:276) at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:330) at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:189) at ruby.jit.ruby.C_3a_.Desarrollo.AppEngine.gorgory.WEB_minus_INF.lib.gems_dot_jar.bundler_gems.jruby.$1_dot_8.gems.dm_minus_validations_minus_0_dot_10_dot_2.lib.dm_minus_validations.validators.numeric_validator.validate_with_comparison at ruby.jit.ruby.C_3a_.Desarrollo.AppEngine.gorgory.WEB_minus_INF.lib.gems_dot_jar.bundler_gems.jruby.$1_dot_8.gems.dm_minus_validations_minus_0_dot_10_dot_2.lib.dm_minus_validations.validators.numeric_validator.validate_with_comparison at org.jruby.internal.runtime.methods.JittedMethod.call(JittedMethod.java:102) at org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:144) at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:280) at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:69) at org.jruby.ast.FCallManyArgsNode.interpret(FCallManyArgsNode.java:60) at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104) at org.jruby.internal.runtime.methods.InterpretedMethod.call(InterpretedMethod.java:229) at org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:193) at org.jruby.RubyClass.finvoke(RubyClass.java:491) at org.jruby.RubyObject.send(RubyObject.java:1448) at org.jruby.RubyObject$i_method_multi$RUBYINVOKER$send.call(org/jruby/RubyObject$i_method_multi$RUBYINVOKER$send.gen) at org.jruby.internal.runtime.methods.JavaMethod$JavaMethodZeroOrOneOrTwoOrThreeOrNBlock.call(JavaMethod.java:293) at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:350) at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:229) at ruby.jit.ruby.C_3a_.Desarrollo.AppEngine.gorgory.WEB_minus_INF.lib.gems_dot_jar.bundler_gems.jruby.$1_dot_8.gems.dm_minus_validations_minus_0_dot_10_dot_2.lib.dm_minus_validations.validators.numeric_validator.validate_with28985350_50 at ruby.jit.ruby.C_3a_.Desarrollo.AppEngine.gorgory.WEB_minus_INF.lib.gems_dot_jar.bundler_gems.jruby.$1_dot_8.gems.dm_minus_validations_minus_0_dot_10_dot_2.lib.dm_minus_validations.validators.numeric_validator.validate_with28985350_50 at org.jruby.internal.runtime.methods.JittedMethod.call(JittedMethod.java:221) at org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:201) at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:227) at org.jruby.ast.FCallThreeArgNode.interpret(FCallThreeArgNode.java:40) Reflection (only prod env): Java::JavaLang::SecurityException (java.lang.IllegalAccessException: Reflection is not allowed on public int java.lang.String$CaseInsensitiveComparator.compare(java.lang.String,java.lang.String)): com.google.appengine.runtime.Request.process-92563a0605f433ea(Request.java) java.lang.reflect.AccessibleObject.setAccessible(AccessibleObject.java:40) org.jruby.javasupport.JavaMethod.<init>(JavaMethod.java:176) org.jruby.javasupport.JavaMethod.create(JavaMethod.java:183) org.jruby.java.invokers.MethodInvoker.createCallable(MethodInvoker.java:23) org.jruby.java.invokers.RubyToJavaInvoker.<init>(RubyToJavaInvoker.java:63) org.jruby.java.invokers.MethodInvoker.<init>(MethodInvoker.java:13) org.jruby.java.invokers.InstanceMethodInvoker.<init>(InstanceMethodInvoker.java:15) org.jruby.javasupport.JavaClass$InstanceMethodInvokerInstaller.install(JavaClass.java:339) org.jruby.javasupport.JavaClass.installClassMethods(JavaClass.java:723) org.jruby.javasupport.JavaClass.setupProxy(JavaClass.java:586) org.jruby.javasupport.Java.createProxyClass(Java.java:506) org.jruby.javasupport.Java.getProxyClass(Java.java:445) org.jruby.javasupport.Java.getInstance(Java.java:354) org.jruby.javasupport.JavaUtil.convertJavaToUsableRubyObject(JavaUtil.java:143) org.jruby.javasupport.JavaClass$ConstantField.install(JavaClass.java:360) org.jruby.javasupport.JavaClass.installClassFields(JavaClass.java:711) org.jruby.javasupport.JavaClass.setupProxy(JavaClass.java:585) org.jruby.javasupport.Java.createProxyClass(Java.java:506) org.jruby.javasupport.Java.getProxyClass(Java.java:445) org.jruby.javasupport.Java.getProxyOrPackageUnderPackage(Java.java:885) org.jruby.javasupport.Java.get_proxy_or_package_under_package(Java.java:918) org.jruby.javasupport.JavaUtilities.get_proxy_or_package_under_package(JavaUtilities.java:54) org.jruby.javasupport.JavaUtilities$s_method_2_0$RUBYINVOKER$get_proxy_or_package_under_package.call(org/jruby/javasupport/JavaUtilities$s_method_2_0$RUBYINVOKER$get_proxy_or_package_under_package.gen:65535) org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:329) org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:188) org.jruby.ast.CallTwoArgNode.interpret(CallTwoArgNode.java:59) org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104) org.jruby.ast.BlockNode.interpret(BlockNode.java:71) org.jruby.internal.runtime.methods.InterpretedMethod.call(InterpretedMethod.java:113) org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:138) org.jruby.javasupport.util.RuntimeHelpers$MethodMissingMethod.call(RuntimeHelpers.java:389) org.jruby.internal.runtime.methods.DynamicMethod.call(DynamicMethod.java:182) What should I do now? Any hint would be wellcome. Thanks!

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• Extending Programming Languages [closed]

  - by chpwn

  I'm a fan of clean code.

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• Algorithm for creating a school timetable.

  - by cand

  Hello all. I've been wondering if there are known solutions for algorithm of creating a school timetable. Basically, it's about optimizing "hour-dispersion" (both in teachers and classes case) for given class-subject-teacher associations. We can assume that we have sets of classes, lesson subjects and teachers associated with each other at the input and that timetable should fit between 8AM and 4PM. I guess that there is probably no accurate algorithm for that, but maybe someone knows a good approximation or hints for developing it. P.S. I know, there was http://stackoverflow.com/questions/1259686/school-timetable-generation-algorithm-closed , but unlike in that case, I'm not looking for actual implementation, rather for thoughts on how to do it or why it's impossible.

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• Stack data storage order

  - by Jamie Dixon

  When talking about a stack in either computing or "real" life we usually assume a "first on, last off" type of functionality. Because the idea of a stack is based around something in the physical world, does it matter how the data in the stack is stored? I notice in a lot of examples that the storage of the stack data is quite often done using an array and the newest item added to the stack is placed at the bottom of the array. (like adding a new plate to an existing stack of plates except putting it underneath the other plates rather than on top). As a paradigm, does it matter in what order the data is stored within the stack as long as the operation of the stack acts as expected?

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• Ball to Ball Collision - Detection and Handling

  - by Simucal

  With the help of the Stack Overflow community I've written a pretty basic-but fun physics simulator. You click and drag the mouse to launch a ball. It will bounce around and eventually stop on the "floor". My next big feature I want to add in is ball to ball collision. The ball's movement is broken up into a x and y speed vector. I have gravity (small reduction of the y vector each step), I have friction (small reduction of both vectors each collision with a wall). The balls honestly move around in a surprisingly realistic way. I guess my question has two parts: What is the best method to detect ball to ball collision? Do I just have an O(n^2) loop that iterates over each ball and checks every other ball to see if it's radius overlaps? What equations do I use to handle the ball to ball collisions? Physics 101 How does it effect the two balls speed x/y vectors? What is the resulting direction the two balls head off in? How do I apply this to each ball? Handling the collision detection of the "walls" and the resulting vector changes were easy but I see more complications with ball-ball collisions. With walls I simply had to take the negative of the appropriate x or y vector and off it would go in the correct direction. With balls I don't think it is that way. Some quick clarifications: for simplicity I'm ok with a perfectly elastic collision for now, also all my balls have the same mass right now, but I might change that in the future. In case anyone is interested in playing with the simulator I have made so far, I've uploaded the source here (EDIT: Check the updated source below). Edit: Resources I have found useful 2d Ball physics with vectors: 2-Dimensional Collisions Without Trigonometry.pdf 2d Ball collision detection example: Adding Collision Detection Success! I have the ball collision detection and response working great! Relevant code: Collision Detection: for (int i = 0; i < ballCount; i++) { for (int j = i + 1; j < ballCount; j++) { if (balls[i].colliding(balls[j])) { balls[i].resolveCollision(balls[j]); } } } This will check for collisions between every ball but skip redundant checks (if you have to check if ball 1 collides with ball 2 then you don't need to check if ball 2 collides with ball 1. Also, it skips checking for collisions with itself). Then, in my ball class I have my colliding() and resolveCollision() methods: public boolean colliding(Ball ball) { float xd = position.getX() - ball.position.getX(); float yd = position.getY() - ball.position.getY(); float sumRadius = getRadius() + ball.getRadius(); float sqrRadius = sumRadius * sumRadius; float distSqr = (xd * xd) + (yd * yd); if (distSqr <= sqrRadius) { return true; } return false; } public void resolveCollision(Ball ball) { // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); // impact speed Vector2d v = (this.velocity.subtract(ball.velocity)); float vn = v.dot(mtd.normalize()); // sphere intersecting but moving away from each other already if (vn > 0.0f) return; // collision impulse float i = (-(1.0f + Constants.restitution) * vn) / (im1 + im2); Vector2d impulse = mtd.multiply(i); // change in momentum this.velocity = this.velocity.add(impulse.multiply(im1)); ball.velocity = ball.velocity.subtract(impulse.multiply(im2)); } Source Code: Complete source for ball to ball collider. Binary: Compiled binary in case you just want to try bouncing some balls around. If anyone has some suggestions for how to improve this basic physics simulator let me know! One thing I have yet to add is angular momentum so the balls will roll more realistically. Any other suggestions? Leave a comment!

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• What makes a good software developer? [closed]

  - by David Johnstone

  Previously there have been questions on what makes a good team lead and what makes a good programming team, but I can't find any questions on what makes a good programmer. I believe the answer to this question is especially important in the context of hiring. Hiring the best people you can afford only works when you are able to identify who the best people are. Being able to consistently identify the best people is only possible when you know what makes the best people the best people. The easy answer is "smart and gets things done" (see "Done, and Gets Things Smart" for an interesting response). But surely there is more to being a good software developer than this aphorism. So, what makes a good software developer a good software developer? (Note: For the purposes of this question, I'm not interested in how to actually tell if somebody is a good software developer.)

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• What is the difference between these two nloglog(n) sorting algorithms? (Andersson et al., 1995 vs.

  - by Yktula

  Swanepoel's comment here lead me to this paper. Then, searching for an implementation in C, I came across this, which referenced another paper on an algorithm described here. Both papers describe integer sorting algorithms that run in O(nloglog(n)) time. What is the difference between the two? Have there been any more recent findings about this topic? Andersson et al., 1995 Han, 2004

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• Using a Mac for cross platform development?

  - by mdec

  Who uses Macs for cross-platform development? By cross platform I essentially mean you can compile to target Windows or Unix (not necessarily both at the same time). I understand that this also has a lot to do with writing portable code, but I am more interested in people's experience with Mac OS X to develop software. I understand that there are a range of IDEs to choose from, I would probably use Eclipse (I like the GCC toolchain) however Xcode seems to be quite popular. Could it be used as described above? At a pinch I could always virtualise with VirtualBox or VMware Player or parallels to use Visual Studio (or dual boot for that matter). Having said that I am open to any other suggested compilers (with preferably an IDE that uses GCC.) Also with the range of Macs available, which one would you recommend? I would prefer a laptop (as I already have a desktop) but am unsure of reasonable specifications. If you are currently using a Mac to do development, I would love to hear what you develop on your Mac and what you like and don't like about it. I would primarily be developing in C/C++/Java. I am also looking to experiment with Boost and Qt, so I'm interested in hearing about any (potential) compatibility issues. If you have any other tips I'd love you hear what you have to say.

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• Have you ever bought a commercial implementation of a programming language for personal programming

  - by Nelson

  Commercial products are often a source of ideas and inspiration for open source projects. There are free and open source implementations of almost every programming language ever devised, and a lot of them are very good. For non-work related personal programming projects, have you ever bought an expensive commerical implementation of a programming language and found it well worth the investment? If so, which one and why?

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• Code Golf: Collatz Conjecture

  - by Earlz

  Inspired by http://xkcd.com/710/ here is a code golf for it. The Challenge Given a positive integer greater than 0, print out the hailstone sequence for that number. The Hailstone Sequence See Wikipedia for more detail.. If the number is even, divide it by two. If the number is odd, triple it and add one. Repeat this with the number produced until it reaches 1. (if it continues after 1, it will go in an infinite loop of 1 -> 4 -> 2 -> 1...) Sometimes code is the best way to explain, so here is some from Wikipedia function collatz(n) show n if n > 1 if n is odd call collatz(3n + 1) else call collatz(n / 2) This code works, but I am adding on an extra challenge. The program must not be vulnerable to stack overflows. So it must either use iteration or tail recursion. Also, bonus points for if it can calculate big numbers and the language does not already have it implemented. (or if you reimplement big number support using fixed-length integers) Test case Number: 21 Results: 21 -> 64 -> 32 -> 16 -> 8 -> 4 -> 2 -> 1 Number: 3 Results: 3 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1 Also, the code golf must include full user input and output.

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