The trouble with dispatch tables in Perl is that the conditions need to be exact keys. In other words, if you want any value in the range 1-999 to do the same thing, you need to create keys for each of those integers.

If you need integers in a range, you've still got a discrete set of values and mapping that to the dispatch table isn't hard. 

use strict;
use warnings;

sub action_1_to_999 {
    print "1 to 999\n";
}

my %dispatch = (
    0 => sub { print "Zero\n" },
    map { $_ => \&action_1_to_999 } ( 1 .. 999 ),
    1000 => sub { print "1e3\n" },
);

$dispatch{0}->();
$dispatch{23}->();

[download]

The challenge is for non-integer conditions or non-bounded ones. What if N > 1000? What if N = 3.14159265358979323? What if N = 'PI'? In that case, you still need to have the advance logic, if/else or otherwise, to convert inputs to a smaller number of well-defined cases.

My advice in that case is keep the case logic in one place and the actions all somewhere else via subroutines. Dispatch tables probably don't help unless you're already starting with a discrete, bounded set of inputs (or need to dynamically add cases as your program runs).

-xdg

Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

In reply to Re^2: Avoiding if/else knots by xdg
in thread Avoiding if/else knots by loris

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.