metaprogramming but inspectable

@class_generator = ->(name, attrs) {
  file = "tmp/meta_classes/#{name.underscore}.rb"
  FileUtils.mkdir_p(File.dirname(file))
  template = File.write(file, ERB.new(<<TEMP, nil, "%").result(binding))
class <%= name %>
  attr_accessor <%= attrs.map(&:inspect).join(', ') %>

  def initialize(<%= attrs.join(", ") %>)
% attrs.each do |attr|
    @<%= attr %> = <%= attr %>
% end
  end
end
TEMP
  load file
} 

@class_generator.call("Foo", :key1, :key2)
Foo.new("hello").key1
=> hello
show-source Foo

From: tmp/meta_classes/foo.rb @ line 1:
Class name: Foo
Number of lines: 8

class Foo
  attr_accessor :key1, :key2

  def initialize(key1, key2)
    @key1 = key1
    @key2 = key2
  end
end