Re: Are defined or // garantee not to autovivify?

[perlfan]

I don't use exists $hashtest{abc} and defined $hashtest{abc} because defined can handle undef. However, sometimes I do defined $hashtest{abc} and $hashtest{abc} because I want the false condition to be based on more than $hashtest{abc} being undef. I also want it to evaluate to false if it's an empty string or 0, in addition to undef. In that case because the second condition is not protected by defined I need to make sure that the key exists. TBH I don't remember the last time I even used exists.

To summarize:

# generally pointless, I would not use the mere existence of the key t
+o mean anything; check it's value
if ( exists $hashtest{abc} and defined $hashtest{abc} ) {
  print qq{This is worthless IMO.\n};
}

Rather just do this if undef is taken as does not exist.

if (defined $hashtest{abc}) {
  print qq{Better than 'exists'; check for the value being undef or no
+t undef.\n};
}

And if I want to check the value, something like:

if (defined $hashtest{abc} and $hashtest{abc}) {
  print qq{Also, better than 'exists' and when I want to make sure the
+ value is not "falsey"\n};
}

[haukex]

I do defined $hashtest{abc} and $hashtest{abc} because I want the false condition to be based on more than $hashtest{abc} being undef.

In that case, simply using $hashtest{abc} in boolean context is enough to cover undef as well. (Personally I'd add the defined test if I'm going to be using an operator that will give me a warning when used with an undef value.)

I would not use the mere existence of the key to mean anything

The difference between defined and exists becomes quite significant if one iterates over the hash (keys, values, each).