From: timr <timrandg@...>
Date: 2010-08-29T23:48:01+09:00
Subject: Re: require from a method

On Aug 29, 3:25 am, Ammar Ali <ammarabu...@gmail.com> wrote:
> Hello,
>
> Are there any gotchas in requiring files from within a method? It
> seems to work, but I have a sinking feeling that I'm missing something
> here.
>
> def require_relative(start, path)
>   require File.expand_path( File.join( File.dirname(start), path ) )
> end
>
> require_relative __FILE__, %w{.. tests tester.rb}
>
> 1.upto(3) {|i|
>   Tester.run i, "some", [3,6,9], :foo => :bar
>
> }
>
> Thanks,
> Ammar

Hi Ammar,
I recently wrote a script to graph out (using a .dot file and Graphviz
for visualization) what files load when a given gem is loaded. When I
started looking at gems this way I realized that it was not uncommon
for one file to require a second more than once. When I inspect in the
code, there is usually two require statement within separate method
calls. The logic is just as Robert explained, better efficiency by
only loading something when you need it. I can give you a quick
example from the yadis gem. requiring 'yadis' causes a chain reaction
of file loading resulting in 73 files loading! One of those is a
'cgi.rb' file, which itself loads tempfile twice. Looking in cgi.rb
shows the following def for the read_multipart method definition. Note
the two require 'tempfile' statements in one method definition.
Regards,
Tim

    def read_multipart(boundary, content_length)
      params = Hash.new([])
      boundary = "--" + boundary
      quoted_boundary = Regexp.quote(boundary, "n")
      buf = ""
      bufsize = 10 * 1024
      boundary_end=""

      # start multipart/form-data
      stdinput.binmode if defined? stdinput.binmode
      boundary_size = boundary.size + EOL.size
      content_length -= boundary_size
      status = stdinput.read(boundary_size)
      if nil == status
        raise EOFError, "no content body"
      elsif boundary + EOL != status
        raise EOFError, "bad content body"
      end

      loop do
        head = nil
        if 10240 < content_length
          require "tempfile"
          body = Tempfile.new("CGI")
        else
          begin
            require "stringio"
            body = StringIO.new
          rescue LoadError
            require "tempfile"
            body = Tempfile.new("CGI")
          end
        end
        body.binmode if defined? body.binmode

        until head and /#{quoted_boundary}(?:#{EOL}|--)/n.match(buf)

          if (not head) and /#{EOL}#{EOL}/n.match(buf)
            buf = buf.sub(/\A((?:.|\n)*?#{EOL})#{EOL}/n) do
              head = $1.dup
              ""
            end
            next
          end

          if head and ( (EOL + boundary + EOL).size < buf.size )
            body.print buf[0 ... (buf.size - (EOL + boundary +
EOL).size)]
            buf[0 ... (buf.size - (EOL + boundary + EOL).size)] = ""
          end

          c = if bufsize < content_length
                stdinput.read(bufsize)
              else
                stdinput.read(content_length)
              end
          if c.nil? || c.empty?
            raise EOFError, "bad content body"
          end
          buf.concat(c)
          content_length -= c.size
        end

        buf = buf.sub(/\A((?:.|\n)*?)(?:[\r\n]{1,2})?#{quoted_boundary}
([\r\n]{1,2}|--)/n) do
          body.print $1
          if "--" == $2
            content_length = -1
          end
          boundary_end = $2.dup
          ""
        end

        body.rewind

        /Content-Disposition:.* filename=(?:"((?:\\.|[^\"])*)"|([^;
\s]*))/ni.match(head)
	filename = ($1 or $2 or "")
	if /Mac/ni.match(env_table['HTTP_USER_AGENT']) and
	    /Mozilla/ni.match(env_table['HTTP_USER_AGENT']) and
	    (not /MSIE/ni.match(env_table['HTTP_USER_AGENT']))
	  filename = CGI::unescape(filename)
	end

        /Content-Type: ([^\s]*)/ni.match(head)
        content_type = ($1 or "")

        (class << body; self; end).class_eval do
          alias local_path path
          define_method(:original_filename) {filename.dup.taint}
          define_method(:content_type) {content_type.dup.taint}
        end

        /Content-Disposition:.* name="?([^\";\s]*)"?/ni.match(head)
        name = $1.dup

        if params.has_key?(name)
          params[name].push(body)
        else
          params[name] = [body]
        end
        break if buf.size == 0
        break if content_length == -1
      end
      raise EOFError, "bad boundary end of body part" unless
boundary_end=~/--/

      params
    end # read_multipart