Additionally it's worth noting that $#name is an lvalue allowing to resize the array @name

  DB<2> @a=1..10

  DB<3> $#a = 3

  DB<4> x @a
0  1
1  2
2  3
3  4
[download]

In other words autovivification is necessary to allow this feature.

Lvalues can be passed around, Perl can't be sure if it's only used for a read access.