It does persist—you've autovivified $r as a reference to an array, but that array is still empty: 

% perl -Mstrict -wle 'my $r = undef; map ++$_, @$r; print $r;'
ARRAY(0x10116180)

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In reply to Re^3: Dereferencing undef as an array: Bug or WAD? by ChemBoy
in thread Dereferencing undef as an array: Bug or WAD? by BrowserUk

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