I can think of two reasons to not use die/eval for (normal) control flow:

(1) Clarity. An exception is supposed to indicate — well, an exceptional condition: either an error, or a resource failure. Throwing an exception as a part of normal execution is liable to mislead maintainers of the code when they try to understand what’s going on. So, at the very least, it’s poor style.

(2) Efficiency. Consider the following code:

#! perl
use strict;
use warnings;
use Benchmark qw(cmpthese);

cmpthese(1_000_000, {
    'bare_loop' => \&bare_loop,
    'eval_loop' => \&eval_loop,
});

sub bare_loop
{
    my ($count, $evens, $flag) = (100, 0, 0);

    while ($count--)
    {
        next if $count % 2;     # odd

        if ($count == 50)
        {
            $flag = 1;
            last;
        }

        ++$evens;
    }

    print "Normal loop exit\n" unless $flag;
}

sub eval_loop
{
    my ($count, $evens) = (100, 0);

    eval
    {
        while ($count--)
        {
            next if $count % 2;     # odd
            die  if $count == 50;
            ++$evens;
        }
    };

    print "Normal loop exit\n" unless $@;
}

[download]

Typical output (on my machine):

             Rate eval_loop bare_loop
eval_loop 71541/s        --      -23%
bare_loop 92362/s       29%        --

[download]

So, there is a definite performance penalty for throwing and then catching the exception. Not nearly as great a penalty as in a language like C++, but still — why opt for a less efficient method when the more efficient methods are just as easy to use?

Athanasius <°(((>< contra mundum

In reply to Re^2: while loop question by Athanasius
in thread while loop question by Freezer

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.