Re: [FWP] Drunk Driving redux (what was he thinking?)

[Ronald J Kimball <rjk@linguist.dartmouth.edu>]

On Mon, Jun 28, 1999 at 11:20:20AM -0700, Vicki Brown wrote:
> Specifically, the line which illustrates (to me) TMTOWTDI (but some are
> wrong) is:
>     if ( index( $szPhdFile, ".phd." ) >= 0 ) {

How does this line illustrate that some ways are wrong?  This line of code
works just fine.


> My thoughts when reviewing this code ran as follows: "Now, why would
> someone who appears to understand pattern matching and substitution be
> using index here... Is there a method to the madness?
> 
> 
> I would have used
> 
>     if ($szPhdFile =~ /\.phd\./) {
> 

Why would someone who understands index use pattern matching to find a
constant substring?


#!/usr/local/bin/perl

use Benchmark;

$short = 'short (.phd.) string';
$long  = ('long ' x 100) . '(.phd.)' . (' string' x 100);

timethese(1 << shift, {
    index_s => sub { index ($short, '.phd.') >= 0 },
    index_l => sub { index ($long,  '.phd.') >= 0 },
    regex_s => sub { $short =~ /\.phd\./ },
    regex_l => sub { $long  =~ /\.phd\./ },
});

__END__

Benchmark: timing 65536 iterations of index_l, index_s, regex_l, regex_s...
   index_l:  1 secs ( 2.07 usr  0.00 sys =  2.07 cpu)
   index_s:  1 secs ( 0.92 usr  0.00 sys =  0.92 cpu)
   regex_l:  1 secs ( 1.47 usr  0.00 sys =  1.47 cpu)
   regex_s:  1 secs ( 1.21 usr  0.00 sys =  1.21 cpu)


It appears that index is faster for short target strings, but regex is
faster for long target strings.  (With perl5.004, anyway.)

I expect that the path to a file would be 'short'...


Anyway, given that the code works perfectly, and that index() is an
accepted method of finding constant substrings, I don't think this one
qualifies as a 'What was he thinking?'  (What were you thinking?  *grin*
Sorry.)

Ronald

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