Just when you thought you couldn't refactor anymore…

Presented at RubyConf, November 2017
http://rubyconf.com/program#session-218

Ruby's philosophy is to provide more than one way to do the same thing. Faced with choice, we are left wondering which methods to use.

In this talk, we will travel together on a refactoring journey. We will start from code that is easy to write but hard to read, and gradually advance to a level where the 4 C's of good code are satisfied: Correctness, Completeness, Clearness, and Compactness.

On the way, we will learn new Ruby 2.4 methods (String#match?, MatchData#named_captures) and review old methods (Enumerable#find, Regexp#===) that are more powerful than they seem at a first glance.

Transcript

1. Just when you thought you couldn’t refactor any more…
   speakerdeck.com/claudiob
   Slides available!
   

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2. String
   #start_with?
   MatchData
   #named_captures
   String
   #match?
   Enumerable
   #find
   Regexp
   #===
   break
   statement
   Regexp
   captures
   Enumerator
   .new
   

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3. What’s in a YouTube URL?
   

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4. The problem
   parse 'youtube.com/watch?v=Cx6aGMC6MjU'
   => {type: :video, id: 'Cx6aGMC6MjU'}
   parse 'not-a-youtube-url'
   => {type: :unknown}
   parse 'youtube.com/confreaks'
   => {type: :channel, name: 'confreaks'}
   Correct Complete Clear Compact
   Correct Complete Clear Compact
   & & &
   

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5. String#start_with?
   

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6. String#start_with?([prefixes]+) → true or false
   # Introduced in Ruby 1.8.7
   # Returns true if str starts with one of the prefixes given.
   'hello'.start_with? 'hell' # => true
   # Returns true if one of the prefixes matches.
   'hello'.start_with? 'heaven', 'hell' # => true
   'hello'.start_with? 'heaven', 'paradise' # => false
   

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7. parse 'youtube.com/watch?v=Cx6aGMC6MjU'
   => {type: :video, id: 'Cx6aGMC6MjU'}
   parse 'not-a-youtube-url'
   => {type: :unknown}
   parse 'youtube.com/confreaks'
   => {type: :channel, name: 'confreaks'}
   Step 1: parsing the type
   

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8. Using String#start_with?
   if text.start_with? 'youtube.com/watch?v='
   {type: :video}
   elsif text.start_with? 'youtube.com/'
   {type: :channel}
   else
   {type: :unknown}
   end
   Correct Complete Clear Compact
   Correct Complete Clear Compact
   & & &
   

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9. The problem
   parse 'youtube.com/watch?v=(11 letters, digits, _ or -)'
   => {type: :video, id: …}
   parse '(anything else)'
   => {type: :unknown}
   parse 'youtube.com/(at least 1 letter, digit, _ or -)'
   => {type: :channel, name: …}
   

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10. String#match?
    

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11. String#match?(pattern) → true or false
    # Introduced in Ruby 2.4
    # Converts pattern to a Regexp (if it isn’t already one), then
    returns true or false indicating whether the regexp is matched
    without updating $~ and other related variables.
    'Ruby'.match? %r{R...} # => true
    'Ruby'.match? %r{R..} # => false
    'Ruby'.match? %r{P...} # => false
    

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12. Using String#match?
    if text.match? %r{youtube\.com/watch\?v=[\w-]{11}}
    {type: :video}
    elsif text.match? %r{youtube\.com/[\w-]+}
    {type: :channel}
    else
    {type: :unknown}
    end
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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13. Regexp#===
    

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14. rxp === str → true or false
    # Following a regular expression literal with the === operator
    allows you to compare against a String.
    # Case Equality — Used in case statements.
    %r{R...} === 'Ruby' # => true
    case 'Ruby'
    when %r{P...} then 'Starts with P'
    when %r{R...} then 'Starts with R'
    end # => 'Starts with R'
    

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15. Using String#match?
    if text.match? %r{youtube\.com/watch\?v=[\w-]{11}}
    {type: :video}
    elsif text.match? %r{youtube\.com/[\w-]+}
    {type: :channel}
    else
    {type: :unknown}
    end
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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16. Using Regexp#=== and case statement
    case text
    when %r{youtube\.com/watch\?v=[\w-]{11}}
    {type: :video}
    when %r{youtube\.com/[\w-]+}
    {type: :channel}
    else
    {type: :unknown}
    end
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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17. Step 2: parsing everything else
    parse 'youtube.com/watch?v=Cx6aGMC6MjU'
    => {type: :video, id: 'Cx6aGMC6MjU'}
    parse 'not-a-youtube-url'
    => {type: :unknown}
    parse 'youtube.com/confreaks'
    => {type: :channel, name: 'confreaks'}
    

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18. case text
    when %r{youtube\.com/watch\?v=[\w-]{11}}
    {type: :video}
    when %r{youtube\.com/[\w-]+}
    {type: :channel}
    else
    {type: :unknown}
    end
    Using Regexp#=== and case statement
    How can we capture and name these matches?
    

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19. Regexp captures
    

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20. Regexp captures
    # Introduced in Ruby 1.9
    # Parentheses can be used for capturing. Capture groups can be
    referred to by name when defined with the (?) or (?'name')
    constructs.
    %r{\$(?\d+)\.(?\d+)}.match '$3.67'
    # => #
    $~['dollars'] # => "3"
    $~['cents'] # => "67"
    

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21. case text
    when %r{youtube\.com/watch\?v=(?[\w-]{11})}
    {type: :video, id: $~['id']}
    when %r{youtube\.com/(?[\w-]+)}
    {type: :channel, name: $~['name']}
    else
    {type: :unknown}
    end
    Using Regexp captures
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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22. MatchData#named_captures
    

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23. MatchData#named_captures → hash
    # Introduced in 2.4
    # Returns a Hash using named capture. A key of the hash is a name
    of the named captures. A value of the hash is a string of last
    successful capture of corresponding group.
    %r{\$(?\d+)\.(?\d+)}.match '$3.67'
    # => #
    $~.named_captures # => {"dollars" => "3", "cents"=> "67"}
    

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24. case text
    # e.g. "youtube.com/confreaks"
    when %r{youtube\.com/(?[\w-]+)}
    $~.named_captures
    # => {name: 'confreaks'}
    Using MatchData#named_captures
    

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25. case text
    # e.g. "youtube.com/confreaks"
    when %r{youtube\.com/(?[\w-]+)}
    $~.named_captures
    # => {name: 'confreaks'}
    $~.named_captures.merge type: :channel
    # => {id: 'confreaks', type: :channel}
    Using MatchData#named_captures
    

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26. case text
    when %r{youtube\.com/watch\?v=(?[\w-]{11})}
    $~.named_captures.merge type: :video
    when %r{youtube\.com/(?[\w-]+)}
    $~.named_captures.merge type: :channel
    else
    {type: :unknown}
    end
    Using MatchData#named_captures
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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27. Enumerable#find
    

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28. Enumerable#find(ifnone = nil) {|obj| block} → obj or nil
    # Passes each entry in enum to block. Returns the first for which
    block is not false. If no object matches, calls ifnone and
    returns its result when it is specified, or nil otherwise.
    (18..99).find {|i| i % 17 == 0} # => 34
    (18..29).find {|i| i % 17 == 0} # => nil
    (18..29).find(-> {0}) {|i| i % 17 == 0} # => 0
    

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29. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    }
    PATTERNS.find do |regex, type|
    if text.match(regex)
    …return the Regexp captures and the matched type…
    end
    end
    Using Enumerable#find
    

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30. break statement
    

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31. # Introduced before Ruby 1.8.7
    # Use break to leave a block early. break accepts a value that
    supplies the result of the expression it is "breaking" out of:
    (18..99).find {|i| i % 17 == 0}
    # => 34
    (18..99).find {|i| break("Found #{i}!") if i % 17 == 0}
    # => "Found 34!"
    break statement
    

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32. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    }
    PATTERNS.find do |regex, type|
    if text.match(regex)
    …return the Regexp captures and the matched type…
    end
    end
    Using Enumerable#find and break
    

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33. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    }
    PATTERNS.find do |regex, type|
    if text.match(regex)
    break $~.named_captures.merge(type: type)
    end
    end
    Using Enumerable#find and break
    

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34. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    }
    PATTERNS.find(-> { {type: :unknown} }) do |regex, type|
    if text.match(regex)
    break $~.named_captures.merge(type: type)
    end
    end
    Using Enumerable#find and break
    

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35. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    }
    PATTERNS.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    Using Enumerable#find and break
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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36. What’s in a YouTube URL?
    

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37. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    }
    PATTERNS.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    Using Enumerable#find and break
    

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38. PATTERNS = {
    %r{youtube\.com/watch\?v=(?[\w-]{11})} => :video,
    %r{youtu\.be/(?[\w-]{11})} => :video,
    %r{youtube\.com/channel/(?UC[\w-]{22})} => :channel,
    %r{youtube\.com/(?[\w-]+)} => :channel,
    %r{youtube\.com/playlist/\?list=(?UC[\w-]+)} => :playlist,
    }
    PATTERNS.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    Using Enumerable#find and break
    

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39. VIDEO_PATTERNS = [%r{youtube\.com/watch\?v=(?[\w-]{11})}, %r{youtu\.be/(?[\w-]{11})}]
    CHANNEL_PATTERNS = [%r{youtube\.com/channel/(?UC[\w-]{22})}, %r{youtube\.com/(?[\w-]+)}]
    PLAYLIST_PATTERNS = [%r{youtube\.com/playlist/\?list=(?UC[\w-]+)}]
    patterns = …first iterate through video patterns, then channel patterns…
    patterns.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    Using Enumerable#find and break
    

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40. Enumerator.new
    

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41. VIDEO_PATTERNS = [%r{youtube\.com/watch\?v=(?[\w-]{11})}, %r{youtu\.be/(?[\w-]{11})}]
    CHANNEL_PATTERNS = [%r{youtube\.com/channel/(?UC[\w-]{22})}, %r{youtube\.com/(?[\w-]+)}]
    PLAYLIST_PATTERNS = [%r{youtube\.com/playlist/?\?list=(?UC[\w-]+)}]
    patterns = …first iterate through video patterns, then channel patterns…
    patterns.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    Using Enumerable#find and break
    

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42. VIDEO_PATTERNS = [%r{youtube\.com/watch\?v=(?[\w-]{11})}, %r{youtu\.be/(?[\w-]{11})}]
    CHANNEL_PATTERNS = [%r{youtube\.com/channel/(?UC[\w-]{22})}, %r{youtube\.com/(?[\w-]+)}]
    PLAYLIST_PATTERNS = [%r{youtube\.com/playlist/\?list=(?UC[\w-]+)}]
    patterns = Enumerator.new do |patterns|
    VIDEO_PATTERNS.each {|regex| patterns << [regex, :video]}
    PLAYLIST_PATTERNS.each {|regex| patterns << [regex, :playlist]}
    CHANNEL_PATTERNS.each {|regex| patterns << [regex, :channel]}
    end
    patterns.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    Using Enumerator.new
    

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43. VIDEO_PATTERNS = [%r{youtube\.com/watch\?v=(?[\w-]{11})}, %r{youtu\.be/(?[\w-]{11})}]
    CHANNEL_PATTERNS = [%r{youtube\.com/channel/(?UC[\w-]{22})}, %r{youtube\.com/(?[\w-]+)}]
    PLAYLIST_PATTERNS = [%r{youtube\.com/playlist/\?list=(?UC[\w-]+)}]
    patterns = Enumerator.new do |patterns|
    VIDEO_PATTERNS.each {|regex| patterns << [regex, :video]}
    PLAYLIST_PATTERNS.each {|regex| patterns << [regex, :playlist]}
    CHANNEL_PATTERNS.each {|regex| patterns << [regex, :channel]}
    end
    patterns.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match(regex)
    end
    The final result
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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44. The final result
    VIDEO_PATTERNS = [%r{youtube\.com/watch\?v=(?[\w-]{11})}, %r{youtu\.be/(?[\w-]{11})}]
    CHANNEL_PATTERNS = [%r{youtube\.com/channel/(?UC[\w-]{22})}, %r{youtube\.com/(?[\w-]+)}]
    PLAYLIST_PATTERNS = [%r{youtube\.com/playlist/\?list=(?UC[\w-]+)}]
    patterns = Enumerator.new do |patterns|
    VIDEO_PATTERNS.each {|regex| patterns << [regex, :video]}
    PLAYLIST_PATTERNS.each {|regex| patterns << [regex, :playlist]}
    CHANNEL_PATTERNS.each {|regex| patterns << [regex, :channel]}
    end
    patterns.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match %r{\A(?:https?://)?(?:www\.)?#{regex}\Z}
    end
    Correct Complete Clear Compact
    Correct Complete Clear Compact
    & & &
    

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45. VIDEO_PATTERNS = [%r{youtube\.com/watch\?v=(?[\w-]{11})}, %r{youtu\.be/(?[\w-]{11})}]
    CHANNEL_PATTERNS = [%r{youtube\.com/channel/(?UC[\w-]{22})}, %r{youtube\.com/(?[\w-]+)}]
    PLAYLIST_PATTERNS = [%r{youtube\.com/playlist/\?list=(?UC[\w-]+)}]
    patterns = Enumerator.new do |patterns|
    VIDEO_PATTERNS.each {|regex| patterns << [regex, :video]}
    PLAYLIST_PATTERNS.each {|regex| patterns << [regex, :playlist]}
    CHANNEL_PATTERNS.each {|regex| patterns << [regex, :channel]}
    end
    patterns.find(-> { {type: :unknown} }) do |regex, type|
    break $~.named_captures.merge(type: type) if text.match %r{\A(?:https?://)?(?:www\.)?#{regex}\Z}
    end
    %r
    Regexp captures
    \w quantifiers
    Enumerator.new
    break
    Enumerable#find
    \A…\Z
    Optional captures
    $~ named_captures String#match
    <<
    The final result
    

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46. Thanks!
    speakerdeck.com/claudiob
    

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