I wanted to add a few convenience methods to statement handles (as if it didn't have enough already). Specifically, I wanted to be able to do

$sth->selectrow_arrayref(...)
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when the existing convention is

$dbh->selectrow_arrayref($sth, ...)
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Here's the approach I took:

use strict;
use warnings;

use DBI qw( );

# ----------------------------------------

BEGIN {
   package MyDBI;

   our @ISA = 'DBI';
}

# ----------------------------------------

BEGIN {
   package MyDBI::db;

   our @ISA = 'DBI::db';
}

# ----------------------------------------

BEGIN {
   package MyDBI::st;

   our @ISA = 'DBI::st';

   sub bind_params {
      my $sth = $_[0];
      for my $i (1..$#_) {
         $sth->bind_param($i, $_[$i])
            or return;
      }
      return 1;
   }

   sub _do_selectrow {
      my ($method, $sth, $attr) = splice(@_, 0, 3);
      $sth->execute(@_)
         or return;
      my $row = $sth->$method()
         or return;
      $sth->finish();
      return $row;
   }

   sub _do_firstrow {
      my ($method, $sth, $attr) = splice(@_, 0, 3);
      $sth->execute(@_)
         or return;
      my $row = $sth->$method()
         or return $sth->set_err($DBI::stderr, "No rows returned");
      $sth->finish();
      return $row;
   }

   sub selectrow_hashref  { return _do_selectrow('fetchrow_hashref', @
+_); }
   sub firstrow_hashref   { return _do_firstrow ('fetchrow_hashref', @
+_); }

   sub selectrow_arrayref { return _do_selectrow('fetchrow_arrayref', 
+@_); }
   sub firstrow_arrayref  { return _do_firstrow ('fetchrow_arrayref', 
+@_); }

   sub selectrow_array    { my $row = _do_selectrow('fetchrow_arrayref
+', @_) or return;  return wantarray ? @$row : $row->[0]; }
   sub firstrow_array     { my $row = _do_firstrow ('fetchrow_arrayref
+', @_) or return;  return wantarray ? @$row : $row->[0]; }
}

# ----------------------------------------

1;
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You could surely override do using this method. Create the three classes, setup their inheritance relationship, and override do in ::db.