Re: Dualvar via table

[roboticus]

Dirk80:

It appears (from my casual reading) that each tie would create a new copy of the table, so extensive use may cost more time and memory than needed. So you might want to have a function in My::DualVar that creates the table, and then you can tie the table to variables as necessary. I haven't played with tying variables (much or recently), so I'm sure my syntax is (likely to be) wrong, but what I'm thinking is something that would give you usage something like:

my %directions = ( 1=>'NORTH', 2=>'SOUTH', 3=>'EAST', 4=>'WEST' );

my $table_fwd = My::DualVar->new(%directions);
my $table_rev = My::DualVar->new(reverse %directions);

tie $direction, \$table_fwd;

my ($dir, $dir2) = (4, 1);
tie $dir,  \$table_fwd;
tie $dir2, \$table_fwd;

print_dualvar($dir);
++$dir2;
print_dualvar($dir2);

tie $dir2, \$table_rev;
for $dir2 (qw(SOUTH WEST EAST)) {
    $dir = $dir2 + 0;
    print_dualvar($dir);
}

I've thought a little about using the dual nature of variables in some perl code, but haven't actually taken the plunge. (What I was thinking was along the lines of parsing a file, and keeping the original representation of a number in the string section so that if calculations are unexpected, I can see what string led to the fault. As a terrible example, suppose I was reading the number part of a street address into a variable (using a stupid technique):

use strict;
no warnings;  # !!!

my @addresses = (
    "1141 Tennessee Avenue",
    "12E10th Street"
);

for (@addresses) {
    my $house_number = $_+0;
    print "House# across the street is ", $house_number+1, "\n";
    print "DEBUG: Original house number '$house_number'\n\n";
}

Which prints:

$ perl t.pl
House# across the street is 1142
DEBUG: Original house number '1141'

House# across the street is 120000000001
DEBUG: Original house number '120000000000'

Where I would want to see:

House# across the street is 1142
DEBUG: Original house number '1141 Tennessee Avenue'

House# across the street is 120000000001
DEBUG: Original house number '12E10th Street'

...roboticus

When your only tool is a hammer, all problems look like your thumb.