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https://github.com/archan937/new_class

Define variable dependent classes without evalling
https://github.com/archan937/new_class

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Define variable dependent classes without evalling

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h1. NewClass "!https://secure.travis-ci.org/archan937/new_class.png!":http://travis-ci.org/archan937/new_class



Define variable dependent classes without evalling



h2. Introduction



I think we as Ruby programmers are blessed with the power of meta programming as we can program classes and instances dynamically within the Ruby language. These are just a couple of methods we can use as tools:



* eval / module_eval / class_eval / instance_eval

* class_variables / instance_variables

* class_variable_get / class_variable_set

* instance_variable_get / instance_variable_set

* define_method / undef_method / remove_method

* send

* method_missing

* Class.new



Some of the methods (such as @eval@, @class_eval@ and @instance_eval@) are often seen as evil and also, they can be very dangerous.



h3. Dynamic CarrierWave uploader classes



In my case, I had to define "CarrierWave":https://github.com/jnicklas/carrierwave uploader classes dynamically as they are dependent of certain variables. Choosing not to use @instance_eval@ for this task, I have created the @NewClass@ gem to accomplish this.



Instead of defining a CarrierWave uploader class with something like this:




  config = {

    :processor => CarrierWave::RMagick,

    :storage => :file,

    :versions => [[800, 800], {:thumb => [200, 200]}, {:icon => [100, 100]}],

    :extension_white_list => %w(jpg jpeg gif png)

  }



  avatar_uploader = Class.new(CarrierWave::Uploader::Base).tap do |klass|

    klass.instance_eval <<-RUBY

      include #{config[:processor].to_s}

      storage :#{config[:storage]}



      def store_dir

        "uploads/\#{model.class.to_s.underscore}/\#{mounted_as}/\#{model.id}"

      end



      def cache_dir

        "tmp"

      end



      def extension_white_list

        %w(#{config[:extension_white_list].join " "})

      end

    RUBY



    config[:versions].each do |v|

      case v.class.name

      when "Array"

        klass.process :resize_to_fit => v

      when "Hash"

        klass.instance_eval <<-RUBY

          version :#{v.keys.first} do

            process :resize_to_fit => [#{v.values.first[0]}, #{v.values.first[1]}]

          end

        RUBY

      end

    end

  end




I am able to define the class like this:




  config = {

    :processor => CarrierWave::RMagick,

    :storage => :file,

    :versions => [[800, 800], {:thumb => [200, 200]}, {:icon => [100, 100]}],

    :extension_white_list => %w(jpg jpeg gif png)

  }



  class Uploader < CarrierWave::Uploader::Base

    include NewClass



    def self.defined

      include config[:processor]

      storage config[:storage]



      config[:versions].each do |v|

        case v.class.name

        when "Array"

          process :resize_to_fit => v

        when "Hash"

          version v.keys.first do

            process :resize_to_fit => v.values.first

          end

        end

      end

    end



    def store_dir

      "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"

    end



    def cache_dir

      "tmp"

    end



    def extension_white_list

      config[:extension_white_list]

    end

  end



  avatar_uploader = Uploader.new_class(:config => config)




A much cleaner solution right? Try out @NewClass@ right now and spread the word if you like it! ^^



h2. Installation



h3. Using Bundler



Add NewClass in @Gemfile@ as a gem dependency:




  gem "new_class"




Run the following in your console to install with Bundler:




  bundle install




h2. Last remarks



Please check out "test/unit/test_carrierwave.rb":https://github.com/archan937/new_class/blob/master/test/unit/test_carrierwave.rb and "test/unit/test_class.rb":https://github.com/archan937/new_class/blob/master/test/unit/test_class.rb for most of the tests available. You can run the unit tests with @rake@ within the terminal.



Also, the NewClass repo is provided with @script/console@ which you can use for testing purposes.



h2. Contact me



For support, remarks and requests please mail me at "[email protected]":mailto:[email protected].



h2. License



Copyright (c) 2012 Paul Engel, released under the MIT license



"http://holder.nl":http://holder.nl – "http://codehero.es":http://codehero.es – "http://gettopup.com":http://gettopup.com – "http://github.com/archan937":http://github.com/archan937 – "http://twitter.com/archan937":http://twitter.com/archan937 – "[email protected]":mailto:[email protected]



Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:



The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.