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[Ruby]あまり見ないけどたまに便利なメソッド[String編]

sprintfのフォーマット文字列として扱う

"ID: %05d" % 321
# => "ID: 00321"

足したり掛けたりする

"ventra " * 2 + "space people"
# => "ventra ventra space people"

中央寄せ文字列を作る

"title".center(20)
# => "       title        "

" title ".center(20, "#")
# => "###### title #######"

左寄せ、右寄せも

"title".ljust(20, ".")
# => "title..............."

"title".rjust(20, ".")
# => "...............title"

一行毎に処理する

"abc\ndef\nxyz".each_line do |line|
  puts line
end

.linesでもいける。

"abc\ndef\nxyz".lines do |line|
  puts line
end

.split("\n").eachより手軽だけど、.each_line.linesに渡される行は改行コードが入ったままなのに注意。

IDをインクリメントする

"X1001".succ
# => "X1002"
"X9999".succ
# => "Y0000"

"A".succ
# => "B"
"Z".succ
# => "AA"

なんとなく、こうしたいんだろうなと思えるIDを作ってくれて便利。

連続した文字を縮める

"Woooooooooooow!".squeeze
# => "Wow!"

先頭の文字列が一致するかどうかを調べる

%w(F-14 A-10 F-18).each do |jet|
  puts "#{jet} is Fighter" if jet.start_with?("F-")
end
# => "F-14 is Fighter" "F-18 is Fighter"
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Help us understand the problem. What are the problem?