Generate dynamic classes and instances methods in Ruby

Question

I would like to generate complete classes in Ruby, that extend other classes. For example, I have my function:

def generator(classname, methodname, ModelClass)
  # make the class
  # now make the instance method on the class
end

and calling it generates a class like below:

generator 'ArticlesController' 'save' 'Article'

class ArticlesController < ApplicationController
  def save 
    @generated_params = # generate params from Article
    @item = Article.new(@generated_params)
    @item.save
  end
end

except that I can make new classes based on some input.

Define "fast". Define "many". Can you give a better example? — tadman
– tadman, Commented May 19, 2017 at 1:56

Ilya Lavrov · Accepted Answer · 2017-05-19 02:26:02Z

2

For your case code will be like this:

def generator(classname, methodname, arbitrary_class = ArbitraryClass)
  klass = Class.new(Parent) do
    define_method(methodname) do |*args, &block|
      @generated_params = # generate params from method_arg
      @item = arbitrary_class.new(@generated_params)
      @item.save
    end
  end
  Object.const_set classname, klass
end

This code do three things:

creates an anonymous class
adds a method to the new class
associate the new class with classname constant

Also this code does not receive a parent class for the generated class, I hope it will be easy to add. The generated method may receive any number of argument, they available through args.

Update: I will add here a way how to receive a class constant from a string for arbitrary_class:

"Article".constantize # Article

edited May 19, 2017 at 2:26

answered May 19, 2017 at 2:05

Ilya Lavrov

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4 Comments

Ilya Lavrov Over a year ago

Also this code expects to receive arbitrary_class as a constant, not as a string. A call should be like generator 'ArticlesController', 'save', Article. Notice that the last argument is not a string here.

codyc4321 Over a year ago

awesome. I just found stackoverflow.com/questions/3163641/get-a-class-by-name-in-ruby for that anyway. Thanks Ilya

codyc4321 Over a year ago

uh oh it didnt work: NoMethodError: undefined method constantize' for "ClassName":String`

Ilya Lavrov Over a year ago

constantize comes from Rails and it does not work in plain Ruby (without Rails). Are you sure you are trying in Rails environment?

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