From: Kirk Haines <khaines@...>
Date: 2004-04-03T03:54:08+09:00
Subject: Re: parent of TrueClass, FalseClass, continued

On Sat, 3 Apr 2004, Daniel Berger wrote:

> You're joking a little, I know, but consider the case of Oracle. 
> Well, ok, Oracle PL/SQL.  In Ruby, nil is false.  However, in Oracle
> PL/SQL you have a Boolean data type that is either true, false or null
> (i.e. unknown).
> 
> Having a Boolean parent class could make object-relational mapping
> layer packages, like Kansas, a bit easier (though I admit, I'm
> guessing here).  It could also be useful in DBI itself, where I could
> retrieve data from a column with a NULL value as nil, but which
> wouldn't equate to false.  From there I can perform tri-state code
> logic, ala PL/SQL.
> 
> For example, consider a table with a VARCHAR2(1) column called
> "is_deceased" for a list of movie actors and actresses.  I could
> either have 'Y' or 'N' to indicate true or false.  But if there's no
> constraint on that column *it could also be NULL*, which is NOT the
> same as false.  See what I mean?

Heh.  I skipped a lot of the middle of this thread.  Now I am going to 
have to go back and read it all.  I can see for my own use where exactly 
what you describe would be very useful.  I have code right now that deals 
with precisely what you describe, with a 1 char field that can be 'y' or 
'n' or null.

I like the way that you think, Mr. Berger.  I'm glad I decided to read 
what you had to say.  :)


Thanks,

Kirk Haines