From: matz@... (Yukihiro Matsumoto)
Date: 2003-02-18T00:55:37+09:00
Subject: Re: class of $1, $2 in 1.8.0

Hi,

In message "class of $1, $2 in 1.8.0"
    on 03/02/07, dblack@candle.superlink.net <dblack@candle.superlink.net> writes:

|Just wondering about this:
|
|Fri Dec 20 00:16:06 2002  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
|
|   * re.c (rb_reg_match_pre, rb_reg_match_post, match_to_a,
|     match_select): return instances of same class as the original
|     string.  [ruby-dev:19119]
|
|which applies to the $1, $2... sub-matches.  It caused scanf to blow
|up, and while I can fix it with a bunch of String.new() calls, I'm
|still left wondering what was wrong with having $1, $2... just be
|String objects.

First of all, I examined scanf-1.0.0, and had a conclusion that the
design was plain wrong in making subclass.  Attached was my
modification.

Besides that, class of subrange (both arrays and strings) are
interesting issue, and I continue working on it.

							matz.

----
# scanf for Ruby, v.1.0.0
#
# August 21, 2002
#
# A product of the Austin Ruby Codefest (Austin, Texas, August 2002)
#
# Copyright (c) 2002, David Alan Black
# Released under the same licensing terms as Ruby itself.
#
# See README for information on usage and details of license.
#
#

module Scanf

  class FormatSpecifier

    attr_reader :re_string

    private

    def skip;  /^%\*/.match(@spec); end
    def to_i(s); s.to_i if s &&! skip; end
    def to_f(s); s.to_f if s &&! skip; end
    def to_h(s); s.hex if s &&! skip; end
    def to_o(s); s.oct if s &&! skip; end
    def to_n(s); Integer(s) if s &&! skip; end
    def keep(s); s unless skip; end
    def nil_proc(s); nil; end

    def count_spec_space?
      /%\*?\d*c/.match(@spec)
    end

    def count_input_space?
      /(?:\A|\S)%\*?\d*c|\[/.match(@spec)
    end

    public

    def initialize(spec)
      @spec = spec

      @spec.sub!(/\A\s+/, '') unless count_spec_space?

      h = '[A-Fa-f0-9]'

      @re_string, @handler = 
	case @spec

	  # %[[:...:]]
	when /%\*?(\[\[:[a-z]+:\]\])/
	  ["(#{$1}+)", :keep]

	  # %5[[:...:]]
	when /%\*?(\d+)(\[\[:[a-z]+:\]\])/
	  ["(#{$2}{1,#{$1}})", :keep]

	  # %[...]
	when /%\*?(\[[^\]]*\])/
	  ["(#{$1}+)", :keep]

	  # %5[...]
	when /%\*?(\d+)(\[[^\]]*\])/
	  ["(#{$2}{1,#{$1}})", :keep]

	  # %i
	when /%\*?i/
	  ["([-+]?(?:(?:0[0-7]+)|(?:0[Xx]#{h}+)|(?:[1-9]\\d+)))", :to_n]

	  # %5i
	when /%\*?(\d+)i/
	  n = $1.to_i
	  s = "("
	  if n > 1 then s += "[1-9]\\d{1,#{n-1}}|" end
	  if n > 1 then s += "0[0-7]{1,#{n-1}}|" end
	  if n > 2 then s += "[-+]0[0-7]{1,#{n-2}}|" end
	  if n > 2 then s += "[-+][1-9]\\d{1,#{n-2}}|" end
	  if n > 2 then s += "0[Xx]#{h}{1,#{n-2}}|" end
	  if n > 3 then s += "[-+]0[Xx]#{h}{1,#{n-3}}|" end
	  s += "\\d"
	  s += ")"
	  [s, :to_n]

	  # %d, %u
	when /%\*?[du]/
	  ['([-+]?\d+)', :to_i]

	  # %5d, %5u
	when /%\*?(\d+)[du]/
	  n = $1.to_i
	  s = "("
	  if n > 1 then s += "[-+]\\d{1,#{n-1}}|" end
	  s += "\\d{1,#{$1}})"
	  [s, :to_i]

	  # %x
	when /%\*?[Xx]/
	  ["([-+]?(?:0[Xx])?#{h}+)", :to_h]

	  # %5x
	when /%\*?(\d+)[Xx]/
	  n = $1.to_i
	  s = "("
	  if n > 3 then s += "[-+]0[Xx]#{h}{1,#{n-3}}|" end
	  if n > 2 then s += "0[Xx]#{h}{1,#{n-2}}|" end
	  if n > 1 then s += "[-+]#{h}{1,#{n-1}}|" end
	  s += "#{h}{1,#{n}}"
	  s += ")"
	  [s, :to_h]

	  # %o
	when /%\*?o/
	  ['([-+]?[0-7]+)', :to_o]

	  # %5o
	when /%\*?(\d+)o/
	  ["([-+][0-7]{1,#{$1.to_i-1}}|[0-7]{1,#{$1}})", :to_o]

	  # %f
	when /%\*?f/
	  ['([-+]?((\d+(?>(?=[^\d.]|$)))|(\d*(\.(\d*([eE][-+]?\d+)?)))))', :to_f]

	  # %5f
	when /%\*?(\d+)f/
	  ["(\\S{1,#{$1}})", :to_f]

	  # %5s
	when /%\*?(\d+)s/
	  ["(\\S{1,#{$1}})", :keep]

	  # %s
	when /%\*?s/
	  ['(\S+)', :keep]

	  # %c
	when /\s%\*?c/
	  ["\\s*(.)", :keep]

	  # %c
	when /%\*?c/
	  ["(.)", :keep]

	  # %5c (whitespace issues are handled by the count_*_space? methods)
	when /%\*?(\d+)c/
	  ["(.{1,#{$1}})", :keep]

	  # %%
	when /%%/
	  ['(\s*%)', :nil_proc]

	  # literal characters
	else
	  ["(#{Regexp.escape(@spec)})", :nil_proc]
	end

      @re_string = '\A' + @re_string
    end

    def cook(str)
      send(@handler, str)
    end

    def to_re
      Regexp.new(@re_string,Regexp::MULTILINE)
    end

    def match(str)
      s = str.dup
      s.sub!(/^\s+/,'') unless count_input_space?
      to_re.match(s)
    end

    def letter
      /%\*?\d*([a-z])/.match(@spec).to_a[1]
    end

    def width
      /%\*?(\d+)/.to_a[1]
    end
  end

  class FormatString

    attr_reader :pos, :last, :space

    def done?; @done; end
    def failed?; @failed; end
    def fatal?; @fatal; end

    SPECIFIERS = 'diuXxofeEgsc'
    REGEX = /
        # possible space, followed by...
          (?:\s*
          # percent sign, followed by...
	    %
	    # another percent sign, or...
	      (?:%|
		 # optional assignment suppression flag
		 \*?
		 # optional maximum field width
		 \d*
		   # named character class, ...
		   (?:\[\[:\w+:\]\]|
		   # traditional character class, or...
		      \[[^\]]*\]|
		   # specifier letter.
		      [#{SPECIFIERS}])))|
	    # or miscellaneous characters
	      [^%\s]+/ix

    def initialize(str)
      unless /\S/.match(str)
	@specs = []
      else
	@space = true if /\s\z/.match(str)
	@specs = str.scan(REGEX).map {|spec| FormatSpecifier.new(spec)}
      end
    end

    private

    def fatal_error(spec, str)
      /\S/.match(str)
    end

    public

    def shift
      @specs.shift
    end

    def match(str)
      acc = []
      @pos = 0
      @specs.each_with_index do |spec,i|
	@last = i
	@fatal = false
	m = spec.match(str)
	@failed = !m
	if @failed
	  @fatal = fatal_error(spec,str)
	  break
	end
	acc << spec.cook(m[1])
	s = str.size
	str = m.post_match
	if @space && i == @specs.size - 1
	  str = str.sub(/(\s*)\z/,'')
	  @pos += $1.size if $1
	end
	@pos += s - str.size
      end
      @done = !@failed
      acc
    end
  end
end

class IO
  def scanf(fstr)
    start = pos
    fs = Scanf::FormatString.new(fstr)
    buffer = ""
    matched = 0
    m = []

    loop do
      break if eof
      buffer << gets
      m.concat fs.match(buffer).compact
      s = buffer.size
      buffer = buffer[fs.pos..-1] || ""
      matched += s - buffer.size if buffer
      break if fs.done? || fs.fatal?
      fs.last.times do fs.shift end
    end
    seek(matched + start, IO::SEEK_SET) rescue Errno::ESPIPE
    m
  end
end

class String
  def scanf(fs)
    Scanf::FormatString.new(fs).match(self).compact
  end
end

module Kernel
  def scanf(fs)
    STDIN.scanf(fs)
  end
end