Read existing Ruby source files into their own namespace after the fact

existing_ruby_class.rb

class A
  @counter = 0
  def self.inc
    @counter += 1
  end
end

import.rb

m1 = Module.new
m1.module_eval(File.read('existing_ruby_class.rb'))

puts "m1:"
3.times do
  puts m1::A.inc
end

m2 = Module.new
m2.module_eval(File.read('existing_ruby_class.rb'))

puts "m2:"
3.times do
  puts m2::A.inc
end

puts "m1:"
3.times do
  puts m1::A.inc
end

p A

output.txt

m1:
1
2
3
m2:
1
2
3
m1:
4
5
6
asdf.rb:22:in `<main>': uninitialized constant A (NameError)