I just rolled my own method for checking credit card digits:
def check_digits? num
odd = true
num.to_s.gsub(/\D/,'').reverse.split('').map(&:to_i).collect { |d|
d *= 2 if odd = !odd
d > 9 ? d - 9 : d
}.sum % 10 == 0
end
ADDENDUM: Rick Hull’s comments from this blog post helped me remove a dependency on map_with_index
PS: the symbol#to_proc and Enumerable#sum are Rails add-ons…
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