Extract from pickle gem which adds capture_fields and parse_fields helpers

capture_fields.rb

module CaptureFields
  class Matcher
    class << self
      def match_quoted
        '(?:\\\\"|[^\\"]|\\.)*'
      end

      def match_label
        "(?::? \"#{match_quoted}\")"
      end

      def match_value
        "(?:\"#{match_quoted}\"|nil|true|false|[+-]?[0-9_]+(?:\\.\\d+)?)"
      end

      def match_field
        "(?:\\w+: #{match_value})"
      end

      def match_fields
        "(?:#{match_field}, )*#{match_field}"
      end

      def capture_key_and_value_in_field
        "(?:(\\w+): (#{match_value}))"
      end
    end
  end

  module Parser
    # given a string like 'foo: expr' returns {key => value}
    def parse_field(field)
      if field =~ /^#{Matcher.capture_key_and_value_in_field}$/
        { $1 => eval($2) }
      else
        raise ArgumentError, "The field argument is not in the correct format.\n\n'#{field}' did not match: #{match_field}"
      end
    end

    # given a string like 'foo: "bar", bar: "baz"' returns {"foo" => "bar", "bar" => "baz"}
    def parse_fields(fields)
      if fields.blank?
        {}
      elsif fields =~ /^#{Matcher.match_fields}$/
        fields.scan(/(#{Matcher.match_field})(?:,|$)/).inject({}) do |m, match|
          m.merge(parse_field(match[0]))
        end
      else
        raise ArgumentError, "The fields string is not in the correct format.\n\n'#{fields}' did not match: #{match_fields}" 
      end
    end
  end
end

World CaptureFields::Parser

def self.capture_fields
  "(#{CaptureFields::Matcher.match_fields})"
end