Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!sundc!texsun!convex!convex.COM
From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: The best way to search an array ?
Keywords: detab
Message-ID: <109494@convex.convex.com>
Date: 29 Nov 90 16:08:20 GMT
References: <443@stephsf.stephsf.com> <1990Nov28.160822.21351@utgard.uucp>
Sender: news@convex.com
Reply-To: tchrist@convex.COM (Tom Christiansen)
Distribution: na
Organization: CONVEX Software Development, Richardson, TX
Lines: 58

In article <1990Nov28.160822.21351@utgard.uucp> chris@utgard.uucp (Chris Anderson) writes:
>			undef %states;
>			@states{@all_the_states} = ();
>
>Either way, you don't have the baggage and you can find the name
>easily and quickly.  Associative arrays are great!

Yes, they're great, but the recent patches have made the quoted usage of
questionable utility.  This I find highly unfortunate, since it's so very
useful.

The problem is Larry made it so you can have a key defined, but whose
value is undefined.  This means strange things like this happen:

    @colors = ( 'red', 'blue', 'green' );
    @seen{@colors} = ();
    print "defined\n" 		if defined $seen{'blue'};
    print "undefined\n" 	unless defined $seen{'blue'};

That now prints undefined, although it used to print defined.

You can still say 
    for (@seen) { $colors{$_}++; }
with an explicit loop, but I really like the @foo{@bar} = () usage.

I can't figure out WHY you want entries in an associative arrays
with undefined values.  Does doing that really make sense??

Larry addressed this in <10334@jpl-devvax.JPL.NASA.GOV> on 12 Nov 90
19:22:14 GMT, in a message entitled "Re: defined() on an undef array
element created via slice."  After granting that correct interpretation
of this is a judgment call, he pointed out that it's nice to distinguish
between

    @foo{"bar"} = ();

and

    @foo{"bar"} = ('');

(I still get nervous with that usage because despite the parens, 
 novices will think it a scalar assignment as there's only one element
 in the slice.)

But what really bothers me is that 

    @seen{@colors} = ('');

makes red defined and blue not, but they're both valid keys, and this
isn't what I call following the principle the least surprise.

    @seen{@colors} = (1..$#colors);

is a hack that will get you by, but I still prefer the prior behavior.
Maybe I just got too used to it.


--tom