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PODefine meta class methods using modules
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  1. PODefine meta class methods using modules
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    copied!<p>I want to be able to create meta class method. For exemple, I have an autocomplete mechanisme on my website working with select_tags.</p> <p>Here is how I would like to build my select options:</p> <pre><code>f.select(:subjects, options_from_collection_for_select(Subject.autocomplete_for_subject_title, :id, :title)) </code></pre> <p>So my autocomplete_for_subject_title class method could return for now Subject.all</p> <p>I was thinking about a module than defines a class method for a given model, something like this :</p> <p>Subject.rb</p> <pre><code>class Subject include SimpleAutocomplete field :title, :type =&gt; String autocomplete_for :subject, :title end </code></pre> <p>lib/simple_autocomplete.rb</p> <pre><code>module SimpleAutocomplete def self.included(base) base.class_eval do |klass| extend ClassMethods end end module ClassMethods def autocomplete_for(object, method, options = {}, &amp;block) (class &lt;&lt; object; object; end).instance_eval { define_method "autocomplete_for_#{object}_#{method}" do puts "It works!" end } end end end </code></pre> <p>But when I launch rails server, here is what I've got :</p> <pre><code>simple_autocomplete.rb:13:in `autocomplete_for': can't define singleton (TypeError) from /Users/pierrelouisgottfrois/Work/teamento_beta_git/app/models/subject.rb:20:in `&lt;class:Subject&gt;' from /Users/pierrelouisgottfrois/Work/teamento_beta_git/app/models/subject.rb:1:in `&lt;top (required)&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:454:in `load' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:454:in `block in load_file' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:596:in `new_constants_in' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:453:in `load_file' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:340:in `require_or_load' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:300:in `depend_on' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:216:in `require_dependency' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/rails/mongoid.rb:55:in `load_model' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/rails/mongoid.rb:18:in `block (2 levels) in load_models' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/rails/mongoid.rb:17:in `each' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/rails/mongoid.rb:17:in `block in load_models' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/paths.rb:102:in `block in each' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/paths.rb:102:in `each' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/paths.rb:102:in `each' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/rails/mongoid.rb:16:in `load_models' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/mongoid-2.0.2/lib/mongoid/railtie.rb:86:in `block (2 levels) in &lt;class:Railtie&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/callbacks.rb:419:in `_run_prepare_callbacks' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/callbacks.rb:40:in `initialize' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/stack.rb:33:in `new' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/stack.rb:33:in `build' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/stack.rb:79:in `block in build' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/stack.rb:79:in `each' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/stack.rb:79:in `inject' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/actionpack-3.0.4/lib/action_dispatch/middleware/stack.rb:79:in `build' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/application.rb:162:in `app' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/application/finisher.rb:35:in `block in &lt;module:Finisher&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/initializable.rb:25:in `instance_exec' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/initializable.rb:25:in `run' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/initializable.rb:50:in `block in run_initializers' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/initializable.rb:49:in `each' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/initializable.rb:49:in `run_initializers' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/application.rb:134:in `initialize!' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/application.rb:77:in `method_missing' from /Users/pierrelouisgottfrois/Work/teamento_beta_git/config/environment.rb:10:in `&lt;top (required)&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:239:in `require' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:239:in `block in require' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:225:in `block in load_dependency' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:596:in `new_constants_in' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:225:in `load_dependency' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:239:in `require' from /Users/pierrelouisgottfrois/Work/teamento_beta_git/config.ru:3:in `block in &lt;main&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/builder.rb:46:in `instance_eval' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/builder.rb:46:in `initialize' from /Users/pierrelouisgottfrois/Work/teamento_beta_git/config.ru:1:in `new' from /Users/pierrelouisgottfrois/Work/teamento_beta_git/config.ru:1:in `&lt;main&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/builder.rb:35:in `eval' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/builder.rb:35:in `parse_file' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/server.rb:162:in `app' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/server.rb:248:in `wrapped_app' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/rack-1.2.1/lib/rack/server.rb:213:in `start' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands/server.rb:65:in `start' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands.rb:30:in `block in &lt;top (required)&gt;' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands.rb:27:in `tap' from /Users/pierrelouisgottfrois/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands.rb:27:in `&lt;top (required)&gt;' from script/rails:6:in `require' from script/rails:6:in `&lt;main&gt;' </code></pre> <p>I've read this blog post to start: <a href="http://blog.jayfields.com/2007/10/ruby-defining-class-methods.html" rel="nofollow">http://blog.jayfields.com/2007/10/ruby-defining-class-methods.html</a></p> <p>Do you have any idea ?</p>
 

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