From: Brian Candler <B.Candler@...>
Date: 2003-08-05T18:14:12+09:00
Subject: Re: Incompatible changes to cgi.rb in 1.8.0

On Tue, Aug 05, 2003 at 07:37:19AM +0900, Dan Doel wrote:
> What about:
> 
>   if @cgi.has_key? 'foo'
>     ... do stuff
>   end

Thanks for the suggestion; that does work but unfortunately I
over-simplified my example so it's not directly applicable.

(1) My code passes cgi variables to functions, e.g.

      database_fetch(@cgi['mykey'][0])

That function uses 'nil' to mean 'no parameter provided, fetch the default
row'.

So either I have to change database_fetch to do a "nil_or_empty?" test as
discussed a few weeks ago, or change the code to

      database_fetch(@cgi.params['mykey'][0])
or
      database_fetch(@cgi.has_key?('mykey') ? @cgi['mykey'] : nil)

(2) My code binds CGI parameters to Amrita templates to preserve state
through hidden variables in HTML pages:

      require 'amrita/template'

      tmpl = Amrita::TemplateText.new <<EOS
        <input id="mykey" type="hidden" name="mykey" value="">
      EOS

      tmpl.expand($stdout, {   
              :mykey => Amrita::a(:value => @cgi['mykey'][0]),
      })

Amrita interprets :value => nil as 'strip out attribute "value" completely'.
So if the parameter was unset (nil) on entry, it will not be carried forward
in the generated HTML either, and will remain nil when the page is next
loaded. After this change, the HTML always carries forwards a value of
empty-string for mykey.

This change seems very un-Rubylike to me. If I access myhash['foo'] then I
expect to get back nil if there is no key 'foo'. (Having said that, you
*can* define a hash to have a default value of empty-string)

I checked the source code and found the following example:

  value = cgi['field_name']   # <== value string for 'field_name'
    # if not 'field_name' included, then return "".

so it does seem this is an intentional change, not a bug.

I would suggest updating doc/NEWS as follows:

: lib/cgi.rb

  cgi[name] returns CGI::QueryExtension::Value that wraps string
  value, no longer array.
  If parameter <name> is not present then an empty string is returned,
  rather than nil.

Regards,

Brian.