From: Carlo Teubner <C.Teubner@...>
Date: 2002-04-14T22:00:35+09:00
Subject: Re: RCR: key value mapping for sprintf/%

Hi,

[snip]
> I wrote a substitute method for String#% which treats a Hash argument
> as described above. It seems to be working fine, and I even posted
> it to the RAA ("TextFormatTemplate").
[snip]

Wow, what a cool idea.
Dissecting your code, I found some very minor things I would have done slightly differently. Annotations below.

class String
  alias old_sf %
  def %(vars)   # [1]
    re = /%\((\w*?)\)([-#0\s+']*\d*(?:\.\d*)?[bcdeEfgGiosxXu])/  # [2]
    case vars
      when Hash
          gsub(re) { |m|
            if vars[$1].nil?  # [3], [4]
              m  # [5]
            else
              "%#$2" % vars[$1]  # [4]
            end
          }
      else
        old_sf vars
    end
  end
end

Annotations:

[1] Why the default value, {}? Normally, String#% complains if you give it too many or too little arguments (or none at all). I think this behaviour should be kept.

[2] I changed (\([\w]*?\)) to \((\w*?)\). That way, the parentheses won't become part of $1.

[3] I removed the begin..rescue construct, because I think that an ArgumentError thrown by old_sf should just be passed on to the caller. Or did you think of other kinds of exceptions?

[4] Thanks to [2], we don't need to remove the parentheses from $1 and can directly use $1.

[5] if vars[$1].nil?, then vars.default will also be nil.


Sorry for the nitpicking... probably I am even wrong in some places. But I found your code so intriguing that I had to play around with it a bit :)

-Carlo