あまり知られていないRubyの便利機能

[鹿児島Ruby会議01](https://k-ruby.github.io/kagoshima-rubykaigi01/)での発表資料です。

Transcript

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(/['&"<>]/, {
    "'" => ''',
    '&' => '&',
    '"' => '"',
    '<' => '<',
    '>' => '>',
    })
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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"
    "hello\r\n".chomp #=> "hello"
    "hello\r\n".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
    14/14
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