I got somewhere with keys %{{func()}}

func() returns a list\

{func()} constructs an anonymous hash from that list

%{} around that tries to dereference what is inside it as a hash reference (ending up with the hash keys wants)

keys # take keys of following HASH
%{   # dereference HASHREF
    {      # construct HASHREF from list
        func() # returns list
    }
}
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yours,
Michael