package MyPackage;
use strict;
use Exporter qw( import );
our @EXPORT_OK = qw( print_columns );

sub char_width { ... }

my $cache = [];

sub print_columns {
    my ( $str ) = @_;
    my $width = 0;
    for my $i ( 0 .. ( length( $str ) - 1 ) ) {
        my $c = ord substr $str, $i, 1;
        if ( ! defined $cache->[$c] ) {
            $cache->[$c] = char_width( $c )
        }
        $width = $width + $cache->[$c];
    }
    return $width;
}

1;