return { my %row = %{$self->[1]} };
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Note that this copies the hash to %row and then copies that into an anonymous hash. This second copy is of no use. Either avoid the copy into %row or just return a reference to it:

    return +{ %{$self->[1]} };
#or
    return do { my %row = %{$self->[1]}; \%row };
#or
    my %row = %{$self->[1]};
    return \%row;
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And there are other ways to do it, of course. Several ways that don't work:

    return { %{$self->[1]} };
    # {} interpretted as a block

    return \my %row = %{$self->[1]};
    # \ binds tighter than =, so same as:
    # (\my %row) = %{$self->[1]};

    return \( my %row = %{$self->[1]} );
    # flattens hash and returns ref to each item
[download]

and several others that don't work either. (:

                - tye