The hardest thing for me to grok in Ruby

the_hardest_thing_for_me_to_grok_in_ruby.rb

colors = ["red"]   #=> ["red"]
colors_2 = colors  #=> ["red"]
colors_2 << "blue" #=> ["red", "blue"]
colors             #=> ["red", "blue"]

def add_white (original_colors)
  original_colors << "white"
end

add_white colors   #=> ["red", "blue", "white"]
colors_2           #=> ["red", "blue", "white"]

• https://rosettacode.org/wiki/Address_of_a_variable#Ruby
• https://launchschool.com/blog/mutating-and-non-mutating-methods
• https://launchschool.com/blog/references-and-mutability-in-ruby
• http://rubyblog.pro/2017/09/pass-by-value-or-pass-by-reference
• http://nicholasjohnson.com/ruby/ruby-course/exercises/hashes-and-symbols/