Meta programming example with currency expert

meta_currency.rb

currency = {usd: 1, baht: 30.73, yen: 83.447, rupee: 50.21}

[Float, Fixnum].each do |number|
  currency.each do |key, value|
    number.class_eval "def #{key}; 
      return self/#{value}; 
    end"
    number.class_eval %{def #{key}_string; 
      return (self * #{value}).to_s+" #{key.upcase}"; 
    end}
  end
end

puts 3.methods.grep(/usd/)

puts (3.usd + 20.baht).usd_string
puts (3.usd + 20.baht).baht_string