Re: [MacPerl] crazy hoops to do something that seems so simple?

["Scott R. Godin" <mactech@webdragon.net>]

on 11/11/2000 05:54 PM, Bart Lateur at bart.lateur@skynet.be wrote:

> On Sat, 11 Nov 2000 04:30:26 -0500, Scott R. Godin wrote:
> 
>> perl 5.004 doesn't understand the sort of
>> my $forwards .= for ('a'..'z');
>> context (sigh) that you later version users have,
> 
> Nope. You must be referring to:
> 
> my $forwards .= $_ for ('a' .. 'z');

yeah, but it was my (perhaps foolish) understanding that the $_ would be
'understood' in this context, as it is in several others. *shrug* :) live
and learn, always.

Is there any listing anywhere of places where $_ is most decidedly NOT
'understood' in places where you might think it would be, (so that I can
stuff the space between my ears with more useful info)? (:

>> and if I use
>> my $forwards = 'a'..'z';
>> I get non-numeric errors in 'flip' and 'flop' whatever they are.
> 
> The '..' operator in a scalar context is a logical test, but with
> built-in memory. For example:
> 
> for my $i (1 .. 10) {
> print "$i\n" if $i==5 .. $i==8
> }
> -->
> 5
> 6
> 7
> 8
> 
> Now, what does this do? Well,  first it attempts to do a test on the
> left side of the '..'. Until this succeeds, the result is false. As soon
> as this succeeds, *once*, the right side is being the crucial test. The
> whole expression is true (that's the memory part), until the right side
> becomes true, which is the final case. After that, the memory is
> cleared. after that, it's the left side again that matters.
> 
> So, as a whole, the condition is false until $i==5, and then it stays
> true until (and including) $i==8.

AHhhhhhh, okay, I understand that.. thank you for the detailed explanation..
NOW I see how that works, and damn, that's a nice short-circuit. I'll
definitely have to remember that little trick. :)

> As for your problem, I think I'd do:
> 
> my %replace;
> @replace{'a' .. 'z'} = reverse 'a' .. 'z';
> s/([a-z])/$replace{$1}/g;

works for me, definitely, although I wound up doing it more like this, due
to what I wanted:

    my %replace;
    @replace{'a' .. 'z'} = reverse 'a' .. 'z';
    @replace{'0' .. '9'} = reverse '0' .. '9';
#elsewhere
    $coercename =~ s/([a-z]|[0-9])/$replace{$1}/g;

the resultant yield again sorts properly, although It has been my
understanding that tr/// was a great deal faster than s///

I'd have to run some benchmarking to be sure, but I get the impression that
I'm still losing out here time-wise. if the CGI takes a lot of hits, the
time can potentially stack up against me, at least in my understanding.

any thoughts? 


-- 
Scott R. Godin            | e-mail : mactech@webdragon.net
Laughing Dragon Services  |    web : http://www.webdragon.net/



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