Just a note from perlref because people make this mistake:

...
$$arrayref[0] = "January";
$$hashref{"KEY"} = "VALUE";
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It's important to understand that we are specifically not dereferencing $arrayref[0] or $hashref{"KEY"} there. The dereference of the scalar variable happens before it does any key lookups. ...

Because of being able to omit the curlies for the simple case of $$x, people often make the mistake of viewing the dereferencing symbols as proper operators, and wonder about their precedence. If they were, though, you could use parentheses instead of braces. That's not the case.