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• How do I bind to a custom view in Cocoa using Xcode 4?

  - by Newt

  I'm a beginner when it comes to writing Mac apps and working with Cocoa, so please forgive my ignorance. I'm looking to create a custom view, that exposes some properties, which I can then bind to an NSObjectController. Since it's a custom view, the Bindings Inspector obviously doesn't list any of the properties I've added to the view that I can then bind to using Interface Builder. After turning to the Stackoverflow/Google for help, I've stumbled across a couple of possible solutions, but neither seem to be quite right for my situation. The first suggested creating an IBPlugin, which would then mean my bindings would be available in the Bindings Inspector. I could then bind the view to the controller using IB. Apparently IBPlugins aren't supported in Xcode 4, so that one's out the window. I'm also assuming (maybe wrongly) that IBPlugins are no longer supported because there's a better way of doing such things these days? The second option was to bind the controller to the view programmatically. I'm a bit confused as to exactly how I would achieve this. Would it require subclassing NSObjectController so I can add the calls to bind to the view? Would I need to add anything to the view to support this? Some examples I've seen say you'd need to override the bind method, and others say you don't. Also, I've noticed that some example custom views call [self exposeBinding:@"bindingName"] in the initializer. From what I gather from various sources, this is something that's related to IBPlugins and isn't something I need to do if I'm not using them. Is that correct? I've found a post on Stackoverflow here which seems to discuss something very similar to my problem, but there wasn't any clear winner as to the best answer. The last comment by noa on 12th Sept seems interesting, although they mention you should be calling exposeBinding:. Is this comment along the right track? Is the call to exposeBinding really necessary? Apologies for any dumb questions. Any help greatly appreciated.

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• Unity: Replace registered type with another type at runtime

  - by gehho

  We have a scenario where the user can choose between different hardware at runtime. In the background we have several different hardware classes which all implement an IHardware interface. We would like to use Unity to register the currently selected hardware instance for this interface. However, when the user selects another hardware, this would require us to replace this registration at runtime. The following example might make this clearer: public interface IHardware { // some methods... } public class HardwareA : IHardware { // ... } public class HardwareB : IHardware { // ... } container.RegisterInstance<IHardware>(new HardwareA()); // user selects new hardware somewhere in the configuration... // the following is invalid code, but can it be achieved another way? container.ReplaceInstance<IHardware>(new HardwareB()); Can this behavior be achieved somehow? BTW: I am completely aware that instances which have already been resolved from the container will not be replaced with the new instances, of course. We would take care of that ourselves by forcing them to resolve the instance once again.

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• Rails upload file to ftp server

  - by Bob

  I'm on Rails 2.3.5 and Ruby 1.8.6 and trying to figure out how to let a user upload a file to a FTP server on a different machine than my Rails app. Also my Rails app will be hosted on Heroku which doesn't facilitate the writing of files to the local filesystem. index.html.erb <% form_tag '/ftp/upload', :method => :post, :multipart => true do %> <label for="file">File to Upload</label> <%= file_field_tag "file" %> <%= submit_tag 'Upload' %> <% end %> ftp_controller.rb require 'net/ftp' class FtpController < ApplicationController def upload file = params[:file] ftp = Net::FTP.new('remote-ftp-server') ftp.login(user = "***", passwd = "***") ftp.puttextfile(file.read, File.basename(file.original_filename)) ftp.quit() end def index end end Currently I'm just trying to get the Rails app to work on my Windows laptop. With the above code, I'm getting this error Errno::ENOENT in FtpController#upload No such file or directory -.... followed by a dump of the file contents Anyone knows what's going on?

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• Java: using generic wildcards with subclassing

  - by gibberish

  Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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• Are .NET's regular expressions Turing complete?

  - by Robert

  Regular expressions are often pointed to as the classical example of a language that is not Turning complete. For example "regular expressions" is given in as the answer to this SO question looking for languages that are not Turing complete. In my, perhaps somewhat basic, understanding of the notion of Turning completeness, this means that regular expressions cannot be used check for patterns that are "balanced". Balanced meaning have an equal number of opening characters as closing characters. This is because to do this would require you to have some kind of state, to allow you to match the opening and closing characters. However the .NET implementation of regular expressions introduces the notion of a balanced group. This construct is designed to let you backtrack and see if a previous group was matched. This means that a .NET regular expressions: ^(?<p>a)*(?<-p>b)*(?(p)(?!))$ Could match a pattern that: ab aabb aaabbb aaaabbbb ... etc. ... Does this means .NET's regular expressions are Turing complete? Or are there other things that are missing that would be required for the language to be Turing complete?

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• What's the best Linux backup solution?

  - by Jon Bright

  We have a four Linux boxes (all running Debian or Ubuntu) on our office network. None of these boxes are especially critical and they're all using RAID. To date, I've therefore been doing backups of the boxes by having a cron job upload tarballs containing the contents of /etc, MySQL dumps and other such changing, non-packaged data to a box at our geographically separate hosting centre. I've realised, however that the tarballs are sufficient to rebuild from, but it's certainly not a painless process to do so (I recently tried this out as part of a hardware upgrade of one of the boxes) long-term, the process isn't sustainable. Each of the boxes is currently producing a tarball of a couple of hundred MB each day, 99% of which is the same as the previous day partly due to the size issue, the backup process requires more manual intervention than I want (to find whatever 5GB file is inflating the size of the tarball and kill it) again due to the size issue, I'm leaving stuff out which it would be nice to include - the contents of users' home directories, for example. There's almost nothing of value there that isn't in source control (and these aren't our main dev boxes), but it would be nice to keep them anyway. there must be a better way So, my question is, how should I be doing this properly? The requirements are: needs to be an offsite backup (one of the main things I'm doing here is protecting against fire/whatever) should require as little manual intervention as possible (I'm lazy, and box-herding isn't my main job) should continue to scale with a couple more boxes, slightly more data, etc. preferably free/open source (cost isn't the issue, but especially for backups, openness seems like a good thing) an option to produce some kind of DVD/Blu-Ray/whatever backup from time to time wouldn't be bad My first thought was that this kind of incremental backup was what tar was created for - create a tar file once each month, add incrementally to it. rsync results to remote box. But others probably have better suggestions.

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• Database schema for Product Properties

  - by Chemosh

  As so many people I'm looking for a Products /Product Properties database schema. I'm using Ruby on Rails and (Thinking) Sphinx for faceted searches. Requirements: Adding new product types and their options should not require a change to the database schema Support faceted searches using Sphinx. Solutions I've come across: (See Bill Karwin's answer) Option 1: Single Table Inheritance Not an option really. The table would contain way to many columns. Option 2: Class Table Inheritance Ruby on Rails caches the database schema on start-up which means a restart whenever a new type of product is introduced. If you have a size able product catalog this could mean hundreds of tables. Option 3: Serialized LOB Kills being able to do faceted searches without heavy application logic. Option 4: Entity-Attribute-Value For testing purposes, EAV worked fine. However it could quickly become a mess and a maintenance hell as you add more and more options (e.g. when an option increase the prices or delivery time). What option should I go with? What other solutions are out there? Is there a silver bullet (ha) I overlooked?

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• Inserting default "admin" user into database during Rails App startup

  - by gbc

  I'm building my first real rails application for a little in-house task. Most of the application tasks require authentication/authorization. The first time the app starts up (or starts with a wiped db), I'd like the process to be: User logs into the admin panel using "admin" & "admin" for authentication info. User navigates to admin credentials editing page and changes name and password to something safer so that "admin" & "admin" is no longer a valid login. To achieve this result, I'd like to stuff a default username & password combination into the database on if the application starts up and detects that there are no user credentials in the 'users' table. For example: if User.count == 0 User.create(:name => "admin", :password => "admin") end However, I'm unsure where to place that code. I tried adding an initializer script in the config/initializers, but the error I received appeared to indicate that the model classes weren't yet loaded into the application. So I'm curious to know at what point I can hook into the application startup cycle and insert data into the database through ActiveRecord before requests are dispatched.

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• How to combine two separate unrelated Git repositories into one with single history timeline

  - by Antony

  I have two unrelated (not sharing any ancestor check in) Git repositories, one is a super repository which consists a number of smaller projects (Lets call it repository A). Another one is just a makeshift local Git repository for a smaller project (lets call it repository B). Graphically, it would look like this A0-B0-C0-D0-E0-F0-G0-HEAD (repo A) A0-B0-C0-D0-E0-F0-G0-HEAD (remote/master bare repo pulled & pushed from repo A) A1-B1-C1-D1-E1-HEAD (repo B) Ideally, I would really like to merge repo B into repo A with a single history timeline. So it would appear that I originally started project in repo A. Graphically, this would be the ideal end result A0-A1-B1-B0-D1-C0-D0-E0-F0-G0-E1-H(from repo B)-HEAD (new repo A) A0-A1-B1-B0-D1-C0-D0-E0-F0-G0-E1-H(from repo B)-HEAD (remote/master bare repo pulled & pushed from repo A) I have been doing some reading with submodules and subtree (Pro Git is a pretty good book by the way), but both of them seem to cater solution towards maintaining two separate branch with sub module being able to pull changes from upstream and subtree being slightly less headache. Both solution require additional and specialized git commands to handle check ins and sync between master and sub tree/module branch. Both solution also result in multiple time-lines (with --squash you even get 3 timelines with subtree). The closest solution from SO seems to talk about "graft", but is that really it? The goal is to have a single unified repository where I can pull/push check-ins, so that there are no more repo B, just repo A in the end.

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• typedef struct, circular dependency, forward definitions

  - by BlueChip

  The problem I have is a circular dependency issue in C header files ...Having looked around I suspect the solution will have something to do with Forward Definitions, but although there are many similar problems listed, none seem to offer the information I require to resolve this one... I have the following 5 source files: // fwd1.h #ifndef __FWD1_H #define __FWD1_H #include "fwd2.h" typedef struct Fwd1 { Fwd2 *f; } Fwd1; void fwd1 (Fwd1 *f1, Fwd2 *f2) ; #endif // __FWD1_H . // fwd1.c #include "fwd1.h" #include "fwd2.h" void fwd1 (Fwd1 *f1, Fwd2 *f2) { return; } . // fwd2.h #ifndef __FWD2_H #define __FWD2_H #include "fwd1.h" typedef struct Fwd2 { Fwd1 *f; } Fwd2; void fwd2 (Fwd1 *f1, Fwd2 *f2) ; #endif // __FWD2_H . // fwd2.c #include "fwd1.h" #include "fwd2.h" void fwd2 (Fwd1 *f1, Fwd2 *f2) { return; } . // fwdMain.c #include "fwd1.h" #include "fwd2.h" int main (int argc, char** argv, char** env) { Fwd1 *f1 = (Fwd1*)0; Fwd2 *f2 = (Fwd2*)0; fwd1(f1, f2); fwd2(f1, f2); return 0; } Which I am compiling with the command: gcc fwdMain.c fwd1.c fwd2.c -o fwd -Wall I have tried several ideas to resolve the compile errors, but have only managed to replace the errors with other errors ...How do I resolve the circular dependency issue with the least changes to my code? ...Ideally, as a matter of coding style, I would like to avoid putting the word "struct" all over my code.

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• Avoid an "out of memory error" in Java(eclipse), when using large data structure?

  - by gnomed

  OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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• calculating the index of an array C#

  - by Kerry G

  I want to display a list of the answers a student entered incorrectly. How do I identify the index of these questions? I am hoping to change the contents of a textbox to a list of the questions answered incorrectly, which would require calculating the index of each incorrect question. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace WindowsFormsApplication5 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } //return a pass/fail //return number of correct answers //return number of incorrect answers //return index figures of incorrect values public void examResults () { string[] correctAnswers = {B,D,A,A,C,A,B,A,C,D,B,C,D,A,D,C,C,B,D,A}; string[] studentResults = File.ReadAllLines("studentResults.txt"); var c = correctAnswers.Where((x, i) => x.Equals(studentResults[i])).Count(); if ( c <= 14) passFailBox.Text = "Student has failed the exam"; else passFailBox.Text = "Student has passed the exam"; numberCorrectBox.Text = "Student has answered" + c + "answers correctly"; int f; f= 21-c; numberIncorrectBox.Text = "Student has answered" + f + "answers incorrectly"; } } }

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• Restoring dev db from production: Running a set of SQL scripts based on a list stored in a table?

  - by mattley

  I need to restore a backup from a production database and then automatically reapply SQL scripts (e.g. ALTER TABLE, INSERT, etc) to bring that db schema back to what was under development. There will be lots of scripts, from a handful of different developers. They won't all be in the same directory. My current plan is to list the scripts with the full filesystem path in table in a psuedo-system database. Then create a stored procedure in this database which will first run RESTORE DATABASE and then run a cursor over the list of scripts, creating a command string for SQLCMD for each script, and then executing that SQLCMD string for each script using xp_cmdshell. The sequence of cursor-sqlstring-xp_cmdshell-sqlcmd feels clumsy to me. Also, it requires turning on xp_cmdshell. I can't be the only one who has done something like this. Is there a cleaner way to run a set of scripts that are scattered around the filesystem on the server? Especially, a way that doesn't require xp_cmdshell?

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• SELECT Statement without duplicate rows on the multiple join tables

  - by theBo

  I have 4 tables built with JOINS and I would like to SELECT DISTINCT rows on the setsTbl.s_id so they always show regardless if there's relational data against them or not!. This is what I have at present which displays the data but doesn't display all of but not the entire distinct row! SELECT setsTbl.s_id, setsTbl.setName, userProfilesTbl.no + ' ' + userProfilesTbl.surname AS Name, trainingTbl.t_date, userAssessmentTbl.o_id FROM userProfilesTbl LEFT OUTER JOIN userAssessmentTbl ON userProfilesTbl.UserId = userAssessmentTbl.UserId FULL OUTER JOIN trainingTbl ON userAssessmentTbl.tt_id = trainingTbl.tt_id RIGHT OUTER JOIN setsTbl ON trainingTbl.s_id = setsTbl.s_id WHERE (userProfilesTbl.st_id=@st_id AND userProfilesTbl.sh_id=@sh_id) AND (DATEPART(yyyy,t_date) = @y_date ) OR (userAssessmentTbl.o_id IS NULL) ORDER BY setName ASC, t_date ASC With this statement I get some of the rows (the ones with data against them) but as stated the s_id field does not return distinct. This following inner select statement works in part when used in SQL Query analyzer and returns pretty much the data i require s_id setName Name o_id ----- ----- ----- ------ 1 100 Barnes 2 2 100 Beardsley 3 3 101 Aldridge 1 4 102 Molby 2 5 102 Whelan 3 but not when used outside of that environment. select * from ( SELECT userProfilesTbl.serviceNo + ' ' + userProfilesTbl.surname AS Name, userProfilesTbl.st_id, userProfilesTbl.sh_id, userAssessmentTbl.o_id, setsTbl.s_id, setsTbl.setName, row_number() over ( partition by setsTbl.s_id order by setsTbl.s_id ) r FROM userProfilesTbl LEFT OUTER JOIN userAssessmentTbl ON userProfilesTbl.UserId = userAssessmentTbl.UserId FULL OUTER JOIN trainingTbl ON userAssessmentTbl.tt_id = trainingTbl.tt_id RIGHT OUTER JOIN setsTbl ON trainingTbl.s_id = setsTbl.s_id ) x where x.r = 1 Not receiving any errors just not displaying the data?

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• what's the performance difference between int and varchar for primary keys

  - by user568576

  I need to create a primary key scheme for a system that will need peer to peer replication. So I'm planning to combine a unique system ID and a sequential number in some way to come up with unique ID's. I want to make sure I'll never run out of ID's, so I'm thinking about using a varchar field, since I could always add another character if I start running out. But I've read that integers are better optimized for this. So I have some questions... 1) Are integers really better optimized? And if they are, how much of a performance difference is there between varchars and integers? I'm going to use firebird for now. But I may switch later. Or possibly support multiple db's. So I'm looking for generalizations, if that's possible. 2) If integers are significantly better optimized, why is that? And is it likely that varchars will catch up in the future, so eventually it won't matter anyway? My varchar keys won't have any meaning, except for the unique system ID part. But I may want to obscure that somehow. Also, I plan to efficiently use all the bits of each character. I don't, for example, plan to code the integer 123 as the character string "123". So I don't think varchars will require more space than integers.

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• Recommended/Standard image thumbnails sizes

  - by Rakan

  Hello, Based on my experience in web development, HTML page designs for every website may have different < img tags showing the same image in different sizes. i.e: the website's main page might show the image in 500*500, the listing page might show it in 200*150 and other sections of the website will use different sizes. As you can see the ratios of the images to be displayed to the user are different and therefore will cause a problem in having the image stretched, pixelated and/or other quality problems. How i currently handle this issue is by using a jQuery cropping tool to make the user select the area to crop the thumbnail from. the cropped image is then resized using imagick to fit every position in the page design. However, although i can force the user to crop an image based on a pre-defined ratio, the HTML will still contain image placeholders which require a different ratio for its thumbnail. So for every image, i will have to force the user to crop the uploaded image based on every possible ratio my site requires. I don't think this is a friendly solution, how would you do it? is there a standard/recommended ratio for the web? Thanks

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• Design pattern to integrate Rails with a Comet server

  - by empire29

  I have a Ruby on Rails (2.3.5) application and an APE (Ajax Push Engine) server. When records are created within the Rails application, i need to push the new record out on applicable channels to the APE server. Records can be created in the rails app by the traditional path through the controller's create action, or it can be created by several event machines that are constantly monitoring various inputstream and creating records when they see data that meets a certain criteria. It seems to me that the best/right place to put the code that pushes the data out to the APE server (which in turn pushes it out to the clients) is in the Model's after_create hook (since not all record creations will flow through the controller's create action). The final caveat is I want to push a piece of formatted HTML out to the APE server (rather than a JSON representation of the data). The reason I want to do this is 1) I already have logic to produce the desired layout in existing partials 2) I don't want to create a javascript implementation of the partials (javascript that takes a JSON object and creates all the HTML around it for presentation). This would quickly become a maintenance nightmare. The problem with this is it would require "rendering" partials from within the Model (which im having trouble doing anyhow because they don't seem to have access to Helpers when they're rendered in this manner). Anyhow - Just wondering what the right way to go about organizing all of this is. Thanks

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• how to allow unamed user in svn authz file?

  - by dtrosset

  I have a subversion server running with apache. It authenticates users using LDAP in apache configuration and uses SVN authorizations to limit user access to certain repositories. This works perfectly. Apache DAV svn SVNParentPath /srv/svn SVNListParentPath Off SVNPathAuthz Off AuthType Basic AuthName "Subversion Repository" AuthBasicProvider ldap AuthLDAPBindDN # private stuff AuthLDAPBindPassword # private stuff AuthLDAPURL # private stuff Require valid-user AuthzSVNAccessFile /etc/apache2/dav_svn.authz Subversion [groups] soft = me, and, all, other, developpers Adding anonymous access from one machine Now, I have a service I want to setup (rietveld, for code reviews) that needs to have an anonymous access to the repository. As this is a web service, accesses are always done from the same server. Thus I added apache configuration to allow all accesses from this machine. This did not work until I add an additional line in the authorization file to allow read access to user -. Apache <Limit GET PROPFIND OPTIONS REPORT> Order allow,deny Allow from # private IP address Satisfy Any </Limit> Subversion [Software:/] @soft = rw - = r # <-- This is the added line For instance, before I add this, all users were authenticated, and thus had a name. Now, some accesses are done without a user name! I found this - user name in the apache log files. But does this line equals to * = r that I absolutely do not want to enable, or does it only allows the anonymous unnamed user (that is allowed access only from the rietveld server)?

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• Rails : can't write unknown attribute `url'

  - by user2954789

  I am new to ruby on rails,and I am learning by creating a blog. I am not able to save to my blogs table and I get this error "can't write unknown attribute url" Blogs migration :db/migrate/ class CreateBlogs < ActiveRecord::Migration --def change --- create_table :blogs do |t| ---- t.string :title ---- t.text :description ---- t.string :slug ---- t.timestamps --- end --end end Blogs Model :/app/models/blogs.rb class Blogs < ActiveRecord::Base --acts_as_url :title --def to_param ---url --end --validates :title, presence:true end Blogs Controller : /app/controllers/blogs_controller.rb class BlogsController < ApplicationController before_action :require_login --def new --- @blogs = Blogs.new --end --def show ---@blogs = Blogs.find(params[:id]) --end --def create ---@blogs = Blogs.new(blogs_params) --if @blogs.save ---flash[:success] = "Your Blog has been created." ---redirect_to home_path --else ---render 'new' --end -end --def blogs_params ---params.require(:blogs).permit(:title,:description) --end private --def require_login ---unless signed_in? ----flash[:error] = "You must be logged in to create a new Blog" ----redirect_to signin_path ---end --end end Blogs Form:/app/views/blogs/new.html.erb Blockquote <%= form_for @blogs, url: blogs_path do |f| %><br/> <%= render 'shared/error_messages_blogs' %><br/> <%= f.label :title %><br/> <%= f.text_field :title %><br/> <%= f.label :description %><br/> <%= f.text_area :description %><br/> <%= f.submit "Submit Blog", class: "btn btn-large btn-primary" %><br/> <% end %><br/> and I have also added "resources :blogs" to my routes.rb file. I get this error in controller at if @blogs.save

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• Where in the standard is forwarding to a base class required in these situations?

  - by pgast

  Maybe even better is: Why does the standard require forwarding to a base class in these situations? (yeah yeah yeah - Why? - Because.) class B1 { public: virtual void f()=0; }; class B2 { public: virtual void f(){} }; class D : public B1,public B2{ }; class D2 : public B1,public B2{ public: using B2::f; }; class D3 : public B1,public B2{ public: void f(){ B2::f(); } }; D d; D2 d2; D3 d3; EDG gives: sourceFile.cpp sourceFile.cpp(24) : error C2259: 'D' : cannot instantiate abstract class due to following members: 'void B1::f(void)' : is abstract sourceFile.cpp(6) : see declaration of 'B1::f' sourceFile.cpp(25) : error C2259: 'D2' : cannot instantiate abstract class due to following members: 'void B1::f(void)' : is abstract sourceFile.cpp(6) : see declaration of 'B and similarly for the MS compiler. I might buy the first case,D. But in D2 - f is unambiguously defined by the using declaration, why is that not enough for the compiler to be required to fill out the vtable? Where in the standard is this situation defined?

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• Using list() to extract a data.table inside of a function

  - by Nathan VanHoudnos

  I must admit that the data.table J syntax confuses me. I am attempting to use list() to extract a subset of a data.table as a data.table object as described in Section 1.4 of the data.table FAQ, but I can't get this behavior to work inside of a function. An example: require(data.table) ## Setup some test data set.seed(1) test.data <- data.table( X = rnorm(10), Y = rnorm(10), Z = rnorm(10) ) setkey(test.data, X) ## Notice that I can subset the data table easily with literal names test.data[, list(X,Y)] ## X Y ## 1: -0.8356286 -0.62124058 ## 2: -0.8204684 -0.04493361 ## 3: -0.6264538 1.51178117 ## 4: -0.3053884 0.59390132 ## 5: 0.1836433 0.38984324 ## 6: 0.3295078 1.12493092 ## 7: 0.4874291 -0.01619026 ## 8: 0.5757814 0.82122120 ## 9: 0.7383247 0.94383621 ## 10: 1.5952808 -2.21469989 I can even write a function that will return a column of the data.table as a vector when passed the name of a column as a character vector: get.a.vector <- function( my.dt, my.column ) { ## Step 1: Convert my.column to an expression column.exp <- parse(text=my.column) ## Step 2: Return the vector return( my.dt[, eval(column.exp)] ) } get.a.vector( test.data, 'X') ## [1] -0.8356286 -0.8204684 -0.6264538 -0.3053884 0.1836433 0.3295078 ## [7] 0.4874291 0.5757814 0.7383247 1.5952808 But I cannot pull a similar trick for list(). The inline comments are the output from the interactive browser() session. get.a.dt <- function( my.dt, my.column ) { ## Step 1: Convert my.column to an expression column.exp <- parse(text=my.column) ## Step 2: Enter the browser to play around browser() ## Step 3: Verity that a literal X works: my.dt[, list(X)] ## << not shown >> ## Step 4: Attempt to evaluate the parsed experssion my.dt[, list( eval(column.exp)] ## Error in `rownames<-`(`*tmp*`, value = paste(format(rn, right = TRUE), (from data.table.example.R@1032mCJ#7) : ## length of 'dimnames' [1] not equal to array extent return( my.dt[, list(eval(column.exp))] ) } get.a.dt( test.data, "X" ) What am I missing? Update: Due to some confusion as to why I would want to do this I wanted to clarify. My use case is when I need to access a data.table column when when I generate the name. Something like this: set.seed(2) test.data[, X.1 := rnorm(10)] which.column <- 'X' new.column <- paste(which.column, '.1', sep="") get.a.dt( test.data, new.column ) Hopefully that helps.

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• What's the best way of accessing a DRb object (e.g. Ruby Queue) from Scala (and Java)?

  - by Tom Morris

  I have built a variety of little scripts using Ruby's very simple Queue class, and share the Queue between Ruby and JRuby processes using DRb. It would be nice to be able to access these from Scala (and maybe Java) using JRuby. I've put together something Scala and the JSR-223 interface to access jruby-complete.jar. import javax.script._ class DRbQueue(host: String, port: Int) { private var engine = DRbQueue.factory.getEngineByName("jruby") private var invoker = engine.asInstanceOf[Invocable] engine.eval("require \"drb\" ") private var queue = engine.eval("DRbObject.new(nil, \"druby://" + host + ":" + port.toString + "\")") def isEmpty(): Boolean = invoker.invokeMethod(this.queue, "empty?").asInstanceOf[Boolean] def size(): Long = invoker.invokeMethod(this.queue, "length").asInstanceOf[Long] def threadsWaiting: Long = invoker.invokeMethod(this.queue, "num_waiting").asInstanceOf[Long] def offer(obj: Any) = invoker.invokeMethod(this.queue, "push", obj.asInstanceOf[java.lang.Object]) def poll(): Any = invoker.invokeMethod(this.queue, "pop") def clear(): Unit = { invoker.invokeMethod(this.queue, "clear") } } object DRbQueue { var factory = new ScriptEngineManager() } (It conforms roughly to java.util.Queue interface, but I haven't declared the interface because it doesn't implement the element and peek methods because the Ruby class doesn't offer them.) The problem with this is the type conversion. JRuby is fine with Scala's Strings - because they are Java strings. But if I give it a Scala Int or Long, or one of the other Scala types (List, Set, RichString, Array, Symbol) or some other custom type. This seems unnecessarily hacky: surely there has got to be a better way of doing RMI/DRb interop without having to use JSR-223 API. I could either make it so that the offer method serializes the object to, say, a JSON string and takes a structural type of only objects that have a toJson method. I could then write a Ruby wrapper class (or just monkeypatch Queue) to would parse the JSON. Is there any point in carrying on with trying to access DRb from Java/Scala? Might it just be easier to install a real message queue? (If so, any suggestions for a lightweight JVM-based MQ?)

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• JQuery Delegate and using traveral options in function

  - by Brian

  I am having trouble figuring out how to use the JQuery delegate function to do what I require. Basically, I need to allow users to add Panels (i.e. divs) to a form dynamically by selecting a button. Then when a user clicks a button within a given Panel, I want to be able to to something to that Panel (like change the color in this example). Unfortunately, it seems that references to the JQuery traversing functions don't work in this instance. Can anybody explain how to achieve this effect? Is there anyway to bind a different delegate to the each panel as its added. $('.addPanels').delegate('*', 'click', function() { $(this).parent.css('background-color', 'black'); $('.placeholder').append('Add item'); }); <div class="addPanels"> <div class="panel"> <a href="#" class="addLink">Add item</a> text</div> <div class="placeholder"/> </div> </div>

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• In Django, how to define a "location path" in order to display it to the users?

  - by naw

  I want to put a "location path" in my pages showing where the user is. Supposing that the user is watching one product, it could be Index > Products > ProductName where each word is also a link to other pages. I was thinking on passing to the template a variable with the path like [(_('Index'), 'index_url_name'), (_('Products'), 'products_list_url_name'), (_('ProductName'), 'product_url_name')] But then I wonder where and how would you define the hierarchy without repeating myself (DRY)? As far I know I have seen two options To define the hierarchy in the urlconf. It could be a good place since the URL hierarchy should be similar to the "location path", but I will end repeating fragments of the paths. To write a context processor that guesses the location path from the url and includes the variable in the context. But this would imply to maintain a independient hierarchy wich will need to be kept in sync with the urls everytime I modify them. Also, I'm not sure about how to handle the urls that require parameters. Do you have any tip or advice about this? Is there any canonical way to do this?

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• How do I change the viewport of a window in win32?

  - by Colen

  Hi, I have a window with child windows inside in it. The child windows take up about 1000 pixels of vertical space. However, our users don't always have 1000 pixels of vertical space available - they might have as little as 500 or 600 pixels. I want to be able to display this window at a size of 500 pixels high, and have the user "scroll" up and down the window to see the full contents. The window should always be 500 pixels high, but the view within it should change. Assume I can add a scroll bar somewhere so the user can choose which part of the window he wants to see. Windows will normally paint the window contents from height 0 to height 500; how do I tell it instead to "paint from height 250 to height 750", for example? I know that I can set the viewport with functions like SetViewportOrgEx etc, but those functions require a device context - when do I call them if I want them to be "permanent"? Do I call them when I get the WM_PAINT message from windows? Or at some other time? And which functions from that family do I want to use? Thanks.

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