To make it more explicit for anyone reading the code, you can use the dereference operator between the []s thus:

$AoA[$i]->[$j]= $whatever;
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This means access an element of @AoA, dereference it and then access an element of the list you find there.

It's optional as far as the interpreter is concerned, but sometimes it's worth being more explicit.

Maybe one of those times is when you need a more visible reminder that you'll need to deep copy your data structures, to follow on from GrandFather's comment.