Re^3: hash and array mismatch


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Re^3: hash and array mismatch

by GrandFather (Saint)

on May 10, 2007 at 19:19 UTC ( #614740=note: print w/replies, xml )

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in reply to Re^2: hash and array mismatch
in thread hash and array mismatch

It is called "autovivification". Have a read through perlreftut and perlref.

You have seen it happen in a light weight way whenever you assign a value to an array element that hadn't been used before. It is a little more interesting in the case of a reference which you are using for the first time, but is one of the underpinnings of creating and managing "interesting" data structures in Perl, as indeed was the case here.

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Comment on Re^3: hash and array mismatch

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Re^4: hash and array mismatch
by TGI (Parson) on May 10, 2007 at 20:19 UTC

I knew that autovivification would let you do things like $foo{a}{b}{c} = 7; I just didn't know that it worked for push and friends as well. Which is funny, because in perlreftut, it discusses the push related aspect.

I know I read perlreftut a few years ago. I guess this tidbit failed to stick.

For reference purposes, you can also do:

my ($foo, $bar, $baz);
$foo->[1] = 92;  # $foo = [92]
print $bar->[0]; # $bar = [];
print @{ $baz }; # DIES - $baz not in lvalue context, no autoviv.
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Thanks for the pointer to autovivification. I obviously didn't understand it properly when I was first learning, and never really came back to the subject. Methinks I need to carefully reread Chapter 8 of Programming Perl.

TGI says moo

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