http://www.perlmonks.org?node_id=1075456


in reply to Hash creation problem

There is a Perl feature that is specifically designed to deal with this sort of thing:   it goes by the somewhat fancy-pants moniker, auto-vivification, which is “to spring to life automatically.”   Consider these two statements: 

 my $foo = undef;
$foo->{'bar'}{'bletch'}{'sneeze'} ++;

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A lot of automatic voodoo “just happens” here.   $foo immediately becomes a hashref; it acquires the key 'bar' which also becomes a hashref, which itself now has the key 'bletch'; ditto 'sneeze'; and this element automatically becomes an integer, automatically zero, which is incremented to 1.

Therefore, in Perl it requires very little code at all in order to construct arbitrarily-complex reference based data structures in memory.   Or, thanks to a powerful reference-count based memory manager, to maintain those structures without leaks.   There are many aspects of Perl that are “what all the fuss is about,” and this is certainly one of them.

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Re^2: Hash creation problem
by agentorange (Sexton) on Feb 19, 2014 at 15:51 UTC

    Unfortunately it's this voodoo that I just have failed to get my head around.

    BrowserUK I really appreciate that and having read up on unpack can understand it too. hippo - thank you that helps.

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