This document summarizes several useful but lesser known features in Ruby, as presented by Kazuhiro Nishiyama of Ruby Kagoshima Conference 01 in 2019. It covers string and hash methods like String#undump, Hash#transform_*, Hash#to_h with a block, and string manipulation methods such as String#prepend and String#delete. Regular expression features like Regexp.union and string matching methods like String#start_with? are also introduced.

1. あまり知られていないRuby
の便利機能
Kazuhiro NISHIYAMA
鹿児島Ruby会議01
2019/11/30
株式会社Ruby開発
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2. 自己紹介
西山 和広
Ruby のコミッター
twitter, github など: @znz
株式会社Ruby開発 www.ruby-dev.jp
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3. String#undump
String#dump ⇄ String#undump
since ruby 2.5
String#dump ≠ String#inspect
String#undump ≠ eval
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4. Hash#transform_*
convert from Hash to Hash
Hash#transform_values{|v|...}
since ruby 2.4
Hash#transform_keys{|k|...}
since ruby 2.5
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5. Hash#to_h with block
Hash#to_h{|k,v|...}
with block since ruby 2.6
without block since ruby 2.0.0
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6. warn with uplevel:
old: warn "#{caller(1, 1)[0]}:
warning: message"
new: warn "message", uplevel: 1
since ruby 2.5
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7. abort(message)
abort("failed message")
≒ warn("failed message");
exit(false)
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8. rand(range)
rand(range)
rand(1..6)
since ruby 1.9.3
NG: rand(endless_range)
rand(1..)
Errno::EDOM (Numerical argument out
of domain)
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9. String.new
String.new.encoding → ASCII-8BIT
String.new(encoding: 'euc-
jp').encoding → EUC-JP
''.dup → UTF-8 (script encoding)
+'' → UTF-8 (script encoding)
''.+@ (for method chain)
(useful with frozen string literal)
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10. String#gsub(pattern,
hash)
string.gsub(/['&"<>]/, {
"'" => '&#39;',
'&' => '&amp;',
'"' => '&quot;',
'<' => '&lt;',
'>' => '&gt;',
})
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11. Regexp.union
Regexp.union #=> /(?!)/
Regexp.union("penzance") #=> /penzance/
Regexp.union("a+b*c") #=> /a+b*c/
Regexp.union("skiing", "sledding")
Regexp.union(["skiing", "sledding"])
#=> /skiing|sledding/
Regexp.union(/dogs/, /cats/i)
#=> /(?-mix:dogs)|(?i-mx:cats)/
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12. String#*_with?
"hello".start_with?("hell") #=> true
"hello".start_with?(/H/i) #=> true
# returns true if one of the prefixes matches.
"hello".start_with?("heaven", "hell") #=> true
"hello".start_with?("heaven", "paradise") #=> false
"hello".end_with?("ello") #=> true
# returns true if one of the +suffixes+ matches.
"hello".end_with?("heaven", "ello") #=> true
"hello".end_with?("heaven", "paradise") #=> false
NG: starts_with?, ends_with?
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13. String#{prepend,delet
e_prefix,delete_suffix,c
homp,chop}
"end".prepend("prep") #=> "prepend"
"prefix".delete_prefix("pre") #=> "fix"
"suffix".delete_suffix("fix") #=> "suf"
"suffix".chomp("fix") #=> "fix"
"hellorn".chomp #=> "hello"
"hellorn".chop #=> "hello"
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14. String#{delete,tr}
"hello".delete "l","lo" #=> "heo"
"hello".delete "lo" #=> "he"
"hello".delete "aeiou", "^e" #=> "hell"
"hello".delete "ej-m" #=> "ho"
"hello".tr('el', 'ip') #=> "hippo"
"hello".tr('a-y', 'b-z') #=> "ifmmp"
"hello".tr('^aeiou', '*') #=> "*e**o"
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15. 参考文献
リファレンスマニュアル
https://docs.ruby-lang.org/ja/
間違いなどを見つけたら
https://github.com/rurema/doctree
もっと気軽に確認したいなら
https://ruby-jp.github.io/
ruby-jp Slack の #rurema など
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