From: "Guy N. Hurst" <gnhurst@...>
Date: 2002-04-21T07:58:57+09:00
Subject: Re: RCR: key value mapping for sprintf/%

Carlo Teubner wrote:
> ...
> 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.
> 

I don't like complaints ;-)
However, I will incorporate this change and see how it goes.

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

Ok, sounds fair enough, since I never ended up using them like I first thought I would,
and if in the future I need to, I can always put them in explicitly.
 
> [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?
>

I liked it absorbing all errors. However, I will take it out. The coder can
put his own exception block in, I guess.
 
> [4] Thanks to [2], we don't need to remove the parentheses from $1 and can directly use $1.
>

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

True. But you have actually uncovered a tiny bug here. I have modified
it to use vars.key?$1 instead.
 
> 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

Thanks for the input!

I am also incorporating some input from Paul Brannon.


Guy N. Hurst