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  • Trying to understand the usage of class_eval

    - by eMxyzptlk
    Hello everyone, I'm using the rails-settings gem, and I'm trying to understand how you add functions to ActiveRecord classes (I'm building my own library for card games), and I noticed that this gem uses one of the Meta-programming techniques to add the function to the ActiveRecord::Base class (I'm far from Meta-programming master in ruby, but I'm trying to learn it) module RailsSettings class Railtie < Rails::Railtie initializer 'rails_settings.initialize', :after => :after_initialize do Railtie.extend_active_record end end class Railtie def self.extend_active_record ActiveRecord::Base.class_eval do def self.has_settings class_eval do def settings RailsSettings::ScopedSettings.for_thing(self) end scope :with_settings, :joins => "JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}')", :select => "DISTINCT #{self.table_name}.*" scope :with_settings_for, lambda { |var| { :joins => "JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}') AND settings.var = '#{var}'" } } scope :without_settings, :joins => "LEFT JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}')", :conditions => 'settings.id IS NULL' scope :without_settings_for, lambda { |var| { :joins => "LEFT JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}') AND settings.var = '#{var}'", :conditions => 'settings.id IS NULL' } } end end end end end end What I don't understand is why he uses class_eval on ActiveRecord::Base, wasn't it easier if he just open the ActiveRecord::Base class and define the functions? Specially that there's nothing dynamic in the block (What I mean by dynamic is when you do class_eval or instance_eval on a string containing variables) something like this: module ActiveRecord class Base def self.has_settings class_eval do def settings RailsSettings::ScopedSettings.for_thing(self) end scope :with_settings, :joins => "JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}')", :select => "DISTINCT #{self.table_name}.*" scope :with_settings_for, lambda { |var| { :joins => "JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}') AND settings.var = '#{var}'" } } scope :without_settings, :joins => "LEFT JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}')", :conditions => 'settings.id IS NULL' scope :without_settings_for, lambda { |var| { :joins => "LEFT JOIN settings ON (settings.thing_id = #{self.table_name}.#{self.primary_key} AND settings.thing_type = '#{self.base_class.name}') AND settings.var = '#{var}'", :conditions => 'settings.id IS NULL' } } end end end end I understand the second class_eval (before the def settings) is to define functions on the fly on every class that 'has_settings' right ? Same question here, I think he could use "def self.settings" instead of "class_eval.... def settings", no ?

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  • should we use a captcha for Sign Up ?

    - by fabrice
    Hello, I know it's not really a programming question but I don't know where to ask it. Should i use a captcha in my sign up form ? Facebook, twitter, foursquare, gowalla etc... don't use one (or not a visible one). Is there an invisible catpcha on theses sites ? Thank you

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  • how to build good python web application

    - by Moayyad Yaghi
    hello i never worked with web programming and i've been asked lately to write a web-based software to manage assets and tasks. to be used by more than 900 persons what are the recommended modules , frameworks , libraries for this task. and it will be highly appreciated if you guyz recommend some books and articles that might help me. thanks in advance

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  • php dom problem

    - by Guru
    hello I'm new to PHP programming and I migrated from ASP .net to PHP.. I have a div just like below <div id="mydiv"></div> what I wanted to do is just to change the text and html content(like some name or any data in it) in it. What I imagine is just like mydiv=innertext="some value"; Thanks, GURU

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  • PHP click event handlers.

    - by Guru
    Hello, I'm new to PHP programming and I wanted to know that is it possible to handle PHP events as we do in ASP.NET I mean I've got a img and I want to perform some task on click event of this img. I know how to do it in ASP.NET but please help me in context of PHP Thanks, GURU

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  • How do I randomly select from a list in Python?

    - by Liam Block
    Basically, I've got a homework task of programming a text based battle simulator in Python. Obviously I've gone with pokémon... I would like the enemy to be randomly selected, however I don't know how to randomly select from a list... foo = ['a', 'b', 'c', 'd', 'e'] from random import choice print choice(foo) This is what I've been told to try but I've got no modules or anything imported... How can I make this work, appreciated.

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  • iPhone memory management

    - by Prazi
    I am newbie to iPhone programming. I am not using Interface Builder in my programming. I have some doubt about memory management, @property topics in iPhone. Consider the following code @interface LoadFlag : UIViewController { UIImage *flag; UIImageView *preview; } @property (nonatomic, retain) UIImageView *preview; @property (nonatomic, retain) UIImage *flag; @implementation @synthesize preview; @synthesize flag; - (void)viewDidLoad { flag = [UIImage imageNamed:@"myImage.png"]]; NSLog(@"Preview: %d\n",[preview retainCount]); //Count: 0 but shouldn't it be 1 as I am retaining it in @property in interface file preview=[[UIImageView alloc]init]; NSLog(@"Count: %d\n",[preview retainCount]); //Count: 1 preview.frame=CGRectMake(0.0f, 0.0f, 100.0f, 100.0f); preview.image = flag; [self.view addSubview:preview]; NSLog(@"Count: %d\n",[preview retainCount]); //Count: 2 [preview release]; NSLog(@"Count: %d\n",[preview retainCount]); //Count: 1 } When & Why(what is the need) do I have to set @property with retain (in above case for UIImage & UIImageView) ? I saw this statement in many sample programs but didn't understood the need of it. When I declare @property (nonatomic, retain) UIImageView *preview; statement the retain Count is 0. Why doesn't it increase by 1 inspite of retaining it in @property. Also when I declare [self.view addSubview:preview]; then retain Count increments by 1 again. In this case does the "Autorelease pool" releases for us later or we have to take care of releasing it. I am not sure but I think that the Autorelease should handle it as we didn't explicitly retained it so why should we worry of releasing it. Now, after the [preview release]; statement my count is 1. Now I don't need UIImageView anymore in my program so when and where should I release it so that the count becomes 0 and the memory gets deallocated. Again, I am not sure but I think that the Autorelease should handle it as we didn't explicitly retained it so why should we worry of releasing it. What will happen if I release it in -(void) dealloc method In the statement - flag = [UIImage imageNamed:@"myImage.png"]]; I haven't allocated any memory to flag but how can I still use it in my program. In this case if I do not allocate memory then who allocates & deallocates memory to it or is the "flag" just a reference pointing to - [UIImage imageNamed:@"myImage.png"]];. If it is a reference only then do i need to release it. Thanks in advance.

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  • Horrible VMware keyboard shortcuts

    - by rshimoda
    Hello, I'm a VMware user and far too often I use keyboard shortcuts while programming. However, this has proved to be quite distressing as sometimes the VMware gets hold of it and turns off / pauses (ctrl+Z) the virtual machine. Is there a way to disable keyboard shortcuts on VMware? Has anyone here ever found a workaround?

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  • c++ try catch practices

    - by Tony
    Is this considered good programming practise in C++: try { // some code } catch(someException) { // do something } catch (...) { // left empty <-- Good Practise??? }

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  • What is the relationship between domNode and htmlelement?

    - by Turtle
    Hello, I am confused about the two terms. What is the difference in browser-side javascript programming? I use dojo as framework. And there is only the concept of domNode. But browser debugger always told me something as htmlelement. Are they just the same thing with different names, or with some subtle differences? Thanks.

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  • Removing the transperancy from image while keeping the actual image

    - by KPL
    Hello people, I have three images,and , they are not square or rectangular in shape. They are just like face of anyone. So,basically, my images are in the size 196x196 or anything like that, but complete square or rectangle with the face in the middle and transperant background in the rest of the portion. Now, I want to remove the transperant background too and just keep the faces. Don't know if this is possible and mind you, this isn't a programming question.

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  • Nhibernate 3.0 and FluentNHibernate

    - by Keith Nicholas
    is anyone building the truck NHibernate and FluentNhibernate together? How's it working? are you using it for production systems? How is the Linq support? Is it nearly ready for release? Is there a nice and concise way to keep up to date with what is going on in the world of NHibernate? (ie, without having to read lots of blogs, and mailing lists )

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  • Task managment for team

    - by Kartoch
    I'm looking for a web application to manage tasks (not necessary programming-oriented) for a small team. It must be easy to setup and maintain. It must offer file upload and mail users in case of a change. There is hundred of solutions available but most are too complex for what we want or are not "stable" (not updated since a long time, not very well programmed). i was wondering if stack overflow's folks have some recommendations...

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  • Maximum size of email X-Headers

    - by Spike Williams
    We are looking at sticking some metadata into the X-Headers of email messages. These emails are for consumption by internal systems, and will be hosted on an Exchange server. Is there a maximum size for the ammount of data that we can store in an X-Header? Are there any limitations, such as special characters, that I should know about?

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  • AOP support in Delphi

    - by Miel
    Hi, Is it possible to do Aspect Oriented Programming in Delphi? I would be interested in native support as well as third party solutions. I don't have a specific problem I want to solve with AOP, but am simply interested in studying AOP. Thanks, Miel Bronneberg.

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  • Anyone have a database of file extensions & icons to go with the extensions?

    - by neddy
    Ok, im developing some software which requires file icons to display lists of files on a computer... i don't want to use the system ExtractAssociatedIcon api's i'd rather load the icons for the file extensions out of a database... (as some systems may not have certain files associated etc)... Does anyone have a database of file extensions & icons to go with the extensions that i can use? Cheers in advance,

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  • Upgrading PHP 5.1 to 5.3 on Linux Server

    - by nicorellius
    I trying to find the best way to upgrade from PHP 5.1 to 5.3. The CRM software I am running on this server requires this upgrade or else I probably wouldn't even perform it, because it seems like it's going to be perhaps trickier than I hoped it would be. Being still new to the programming world, these routine upgrades are still worrisome to me. I am running apache 2.2.6 (Fedora), PHP 5.1.6 and MySQL 5.0.27 on this server.

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