if ($foo){...}

##</code><code>##

if ($myHash{"unknown_if_this_key_exists_yet_or_not"}){...}

##</code><code>##

if ($myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}{not}){...}

##</code><code>##

my %myHash = ();
if ($myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}{not}){print "Nothing prints here; Good!"}
if ($myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}     ){print "This will print, although we'd like it not to...";}

##</code><code>##

if (exists($myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}{not}) and $myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}{not}){...}

##</code><code>##

if ($myHash{"this_key_does_not_exist"){...}

##</code><code>##

Readonly::Hash $myHash => ("key1" = "val1",); 
$myTempValue = $myHash{"this_key_does_not_exist"};

##</code><code>##

no autovivification;
my %myHash = ();
if ($myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}{not}){print "Nothing prints here; Good!"}
if ($myHash{unknown}{if}{this}{key}{combination}{exists}{yet}{or}     ){print "This will NOT print! That is exactly what we want!";}

##</code><code>##

cpan
> notest install autovivification
> q