Hash::NoVivify 0.01

Hash::NoVivify is a Perl extension for non-vivifying exists and defined functions.

SYNOPSIS

use Hash::NoVivify qw(Defined Exists);

...

if (Exists(%hash, qw(key1 key2 ... keyn ))) {
...
}

if (Defined(%hash, qw(key1 key2 ... keyn))) {
...
}

When used on a hash, the exists() and defined() functions will create entries in a hash in order to evaluate the function.

For instance, the code:

%a = (a => 1, b=> 2);
print "Doesnt existn" unless exists($a{c});
print "Also Doesnt existn" unless exists($a{c}->{d});
print "Oh, my, not goodn" if exists($a{c});

will print out:

Doesnt exist
Also Doesnt exist
Oh, my, not good

The Hash::NoVivify module provides two functions, Defined() and Exists(), which avoid this, at the cost of a slightly convoluted syntax. Both functions take a reference to a hash, followed by a list of descending keys defining the hash entry to be investigated.