From: Dossy <dossy@...>
Date: 2002-05-15T19:43:56+09:00
Subject: Re: cgi params api

On 2002.05.15, Patrick May <patrick-may@monmouth.com> wrote:
> Dossy <dossy@panoptic.com> wrote in message news:<20020514172939.GL14145@panoptic.com>...
> > On 2002.05.15, Wakou Aoyama <wakou@fsinet.or.jp> wrote:
> > > problem is this:
> > > 
> > >   cgi["key"].each{|value| foo(value) }
> > > 
> > > Will this be necessary?
> > 
> > This is my preferred idiom, personally.  I don't know about
> > others.
> 
> even if you aren't looking for multiple params?

Yes.  Because this way the code works if there's only one value
OR if there's multiple values -- I don't have to have special
conditional code which I think violates OAOO and forces
duplication.

If I ONLY want one value regardless of if there's more than one
value available, then just operating on cgi["key"] gives it to
me.  I don't have to worry if there's more than one value or
not.  If I really care to find out, I can test for multiple
values by asking cgi["key"].size ...

But normally, if I'm willing to tolerate multiple values at
all, I don't want to have to write:

if cgi.params("key").size > 1
  cgi.params("key").each { |value| ... do some stuff ... }
else
  ... do some stuff with cgi["key"] ...
end

This was suggested by some folks (Matz included).  The
premise is that more often than not, when dealing with
CGI parameter values, you're dealing with a single value
per key.  So, making the programmer access a full array
of multiple values with a new method isn't really
"inconveniencing" since it's infrequent enough that it
shouldn't matter.  However, I think this perception is
only true if you don't write a lot of CGI's -- the
more you write, the more frequently you use multiple
values.

The trade-off is to make CGI#[] _always_ return an array
of params, and do something like this:

cgi["key"].each { |value|
  ... do some stuff for multiple values...
}

OR, if you only want the single value regardless:

... do some stuff with cgi["key"][0] ...

However, this gets dangerous if cgi["key"] has no values and
thus returns nil, NilClass#[] isn't defined, is it.  So,
we have to guard references to cgi["key"][0] with cgi["key"].nil?
tests?  Yuck.

I like what I've come up with (and Wakou's code will help me
improve mine) -- I'll keep it under Panoptic::CGI and use
it myself, perhaps wrap cgi.rb with it.  It'll certainly make
writing CGI's in Ruby a lot easier for me.

-- Dossy

-- 
Dossy Shiobara                       mail: dossy@panoptic.com 
Panoptic Computer Network             web: http://www.panoptic.com/ 
  "He realized the fastest way to change is to laugh at your own
    folly -- then you can let go and quickly move on." (p. 70)