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scanf(str,&b) click to toggle source

The trick here is doing a match where you grab one line of input at a time. The linebreak may or may not occur at the boundary where the string matches a format specifier. And if it does, some rule about whitespace may or may not be in effect…

That’s why this is much more elaborate than the string version.

For each line: Match succeeds (non-emptily) and the last attempted spec/string sub-match succeeded:

could the last spec keep matching?
  yes: save interim results and continue (next line)

The last attempted spec/string did not match:

are we on the next-to-last spec in the string?

yes:
  is fmt_string.string_left all spaces?
    yes: does current spec care about input space?
      yes: fatal failure
      no: save interim results and continue
no: continue  [this state could be analyzed further]
 
               # File scanf.rb, line 607
def scanf(str,&b)
  return block_scanf(str,&b) if b
  return [] unless str.size > 0

  start_position = pos rescue 0
  matched_so_far = 0
  source_buffer = ""
  result_buffer = []
  final_result = []

  fstr = Scanf::FormatString.new(str)

  loop do
    if eof || (tty? &&! fstr.match(source_buffer))
      final_result.concat(result_buffer)
      break
    end

    source_buffer << gets

    current_match = fstr.match(source_buffer)

    spec = fstr.last_spec_tried

    if spec.matched
      if spec.mid_match?
        result_buffer.replace(current_match)
        next
      end

    elsif (fstr.matched_count == fstr.spec_count - 1)
      if /\A\s*\z/.match(fstr.string_left)
        break if spec.count_space?
        result_buffer.replace(current_match)
        next
      end
    end

    final_result.concat(current_match)

    matched_so_far += source_buffer.size
    source_buffer.replace(fstr.string_left)
    matched_so_far -= source_buffer.size
    break if fstr.last_spec
    fstr.prune
  end
  seek(start_position + matched_so_far, IO::SEEK_SET) rescue Errno::ESPIPE
  soak_up_spaces if fstr.last_spec && fstr.space

  return final_result
end
            

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