Roman to integers in ruby

gistfile1.rb

def solution(roman)
  roman.scan(/IV|IX|CM|XC|I|V|L|X|C|M|D/).inject(0) do |final, current|
    final += case current
               when 'IV' then 4
               when 'IX' then 9
               when 'XC' then 90
               when 'CM' then 900
               when 'I' then 1
               when 'V' then 5
               when 'X' then 10
               when 'L' then 50
               when 'C' then 100
               when 'D' then 500
               when 'M'then 1000
               else 0 
             end
    final
  end
end