BrowserUK,
Thanks, but it does not work I tried to remove the line from the BEGIN block and I also completely removed the block. Either option did not make a difference to the error message.
The actual benchmark script coming with this package is running fine in my environment and I cannot spot my error. The current code - which still produces the above quoted error is:

package Variant;

use strict;
use warnings;

use Exporter;
use Class::Accessor;

our ( @EXPORT, @EXPORT_OK, %EXPORT_TAGS );

@EXPORT    = qw();
%EXPORT_TAGS= ();
@EXPORT_OK    = qw();

use base ( qw(Exporter Class::Accessor) );
our ( $VERSION, $LAST_ERROR );

__PACKAGE__->mk_accessor( qw(name nodes) );
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I have noticed, that the benchmark example as well as the examples in the documentation use either a base class with all fields defined or Class::Fields as base class. I intend - and only then does using Class:Accessor make sense to me to include it in a base class that does not yet know which fields are in my derived classes. Are there any issues with this setup? Do I need to define the fields of my class before calling mk_accessor( @fieldnames )