Re: Re: Making a failed hash lookup return something other than undef

[thelenm]

in reply to Re: Making a failed hash lookup return something other than undef
in thread Making a failed hash lookup return something other than undef

Actually, auto-vivification of hash entries doesn't happen unless you do something like take a reference to the hash entry... for example by referring to something more deeply nested in the non-existent hash entry:

#!/usr/bin/perl -l
my %hash;

my $foo = $hash{'foo'};
print exists $hash{'foo'} ? "yes" : "no";  # prints "no"

my $bar = $hash{'bar'}->{'xxx'};
print exists $hash{'bar'} ? "yes" : "no";  # prints "yes"

my $baz = \$hash{'baz'};
print exists $hash{'baz'} ? "yes" : "no";  # prints "yes"

[shenme]

However, the hash itself may be auto-vivified in spite of using exists().   In fact, the hash will be auto-vivified by the use in exists()!   This may be what davido was thinking about.   Check perlref for examples of how the end-point (the hash element) is protected from auto-vivification by the above constructs, by the leading components of the hash expression are not.