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Ruby で無限 Range

Ruby

Last updated at 2012-12-26Posted at 2012-07-06

Ruby の Range は無限大を扱うことができます．

(-Float::INFINITY..Float::INFINITY) #=> -Infinity..Infinity

(0..Float::INFINITY) === 817049871230948719384719274389123874198741 #=> true
(0..Float::INFINITY) === -1 #=> false

# 負の無限大も OK
(-Float::INFINITY..0) === -841794879213748747847321751947365 #=> true

どういう時に使うのかというと，case 文の when 節では === でマッチングを行うので，そこで使えます．

a = 10000

case a
when 0 ... 100
  "0 〜 99"
when 100 ... 1000
  "100 〜 999"
when 1000 .. Float::INFINITY
  "1000以上"
else
  "負数"
end

#=> "1000以上"

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