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Re^4: If Not Replace

by tchrist (Pilgrim)
on Sep 12, 2011 at 15:13 UTC ( #925491=note: print w/ replies, xml ) Need Help??

in reply to Re^3: If Not Replace
in thread If Not Replace

Ah ... sorry I was wrongly thinking perl's auto extending of arrays is the same thing as autoviv.
Youíre right in that both behaviors derive from a common principle that Perl takes care of memory allocation for you. This is very different from C, Java, or even Python, all of which blow up if you try to overindex an array, and certainly never auto‐allocate new ones to multiple levels as occurs with autoviv.

Itís just that the way the jargon has developed in Perl culture, the word autoviv always involves implicit allocation of references (into previously undefined lvalues that are getting dereferenced), not merely extending an existing string, array, or hash with non-reference data.

Non‐autoviv examples:

my $s = "a"; $s .= "abcdefghijklmop"; my @a = (0 .. 4); $a[55] = "frog"; my %h = (red => 1, blue => 2, yellow => 3); $h{green} = 6.02e23;
Autoviv examples:
my $hr = undef; $hr->{radish} = "crunch"; # yes autoviv $hr->{banana} = "squish"; # no autoviv my @a = ("a" .. "z"); $a[0][1] = "new level"; # yes autoviv $a[0][9] = "new element"; # no autoviv my %h = ( ); $h{little}{dog} = "puppy" ; # yes autoviv $h{little}{cat} = "kitten"; # no autoviv $h{male}{cattle} = "bull"; # yes autoviv $h{male}{cat} = "tom"; # no autoviv

See the difference?

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