ActionView module declared several times

The ActionView module is declared several times in the Rails source:

asset_paths.rb, and the list goes on and on.

How is it able to be declared like this in multiple files without the
previous definition of it being overwritten?

It is a basic feature of Ruby that you can re-open a class definition
and add or redefine methods.


It’s kind of “metaprogramming—creating code at runtime that defines new methods. In fact, in a sense all Ruby programming is metaprogramming, since even a class definition is not a declaration as it is in Java but actually code that is executed at runtime. Given that this is true, you might wonder whether you can modify a class at runtime. In fact you can, by adding or changing instance methods or class methods, even for Ruby’s built-in classes”.

This is citation from book Engineering Long-Lasting Software: An Agile Approach Using SaaS and Cloud Computing

Yes, it is a basic feature of ruby that you can reopen a class
definition. I forgot about that.

The metaprogramming nature of ruby is the most advantage feature of ruby.

Thank You,

Uma Mahesh.