Creating a class dynamically

Question

I\'m trying to create a new class, without knowing the name of the class until it\'s supposed to på created.

Something like this;

    variable = \"V         


        

Answer 1

Your code would look something akin to this:

variable = "SomeClassName"
klass = Class.new(ParentClass)
# ...maybe evaluate some code in the context of the new, anonymous class
klass.class_eval {  }
# ...or define some methods
klass.send(:title, :Person)
klass.send(:attribute, :name, String)
# Finally, name that class!
ParentClass.send(:const_set, variable, klass)

...or you could just use eval:

eval <<DYNAMIC
  class #{name}
    title :Person
    attribute :name, String
    # ...or substitute other stuff in here.
  end
DYNAMIC

Answer 2

A class gains its name when it is assigned to a constant. So It's easy to do in a generic fashion with const_set.

For example, let's say you want to use Struct to build a class with some attributes, you can:

name = "Person"
attributes = [:name, :age]

klass = Object.const_set name, Struct.new(*attributes)
# Now use klass or Person or const_get(name) to refer to your class:
Person.new("John Doe", 42) # => #<struct Person name="John Doe", age=42>

To inherit from another class, replace the Struct.new by Class.new(MyBaseClass), say:

class MyBaseClass; end

klass = Class.new(MyBaseClass) do
  ATTRIBUTES = attributes
  attr_accessor *ATTRIBUTES
  def initialize(*args)
    raise ArgumentError, "Too many arguments" if args.size > ATTRIBUTES.size
    ATTRIBUTES.zip(args) do |attr, val|
      send "#{attr}=", val
    end
  end
end
Object.const_set name, klass
Person.new("John Doe", 42) # => #<Person:0x007f934a975830 @name="John Doe", @age=42>