instance method CSV::FieldInfo#line

行番号を返します。

例

require 'csv'

csv = CSV.new("date1,date2,date3\n2018-07-09,2018-07-10\n2018-08-09,2018-08-10", headers: true)
csv.convert do |field,field_info|
  p field_info.line
  Date.parse(field)
end
p csv.to_a

# => 2
# => 2
# => 3
# => 3
# => [#<CSV::Row "date1":#<Date: 2018-07-09 ((2458309j,0s,0n),+0s,2299161j)> "date2":#<Date: 2018-07-10 ((2458310j,0s,0n),+0s,2299161j)> "date3":nil>, ...]