set_instance_variable.rb

require 'yaml'

s = "a string"
a = %w(a array)

puts "Before setting instance variable:\n#{s.to_yaml}\n#{a.to_yaml}\n"

s.instance_variable_set(:@test, 'test')
a.instance_variable_set(:@test, 'test')

puts "After setting instance variable:\n#{s.to_yaml}\n#{a.to_yaml}\n"

# Before setting instance variable:
# --- a string

# --- 
# - a
# - array

# After setting instance variable:
# --- !str 
# str: a string
# :@test: test

# --- 
# - a
# - array