$fs4->{_structure}{'/Users/dotfiles/perl5/my_modules'}{BLAH}{Crap}

##</code><code>##

(
   (
      (
         (
            $fs4 //= { }
         )->{_structure} //= { }
      )->{ '/Users/dotfiles/perl5/my_modules' } //= { }
   )->{ BLAH } //= { }
)->{ Crap }

##</code><code>##

no autovivification;