You could give the filename "<&DATA" to your module, if you wouldn't insist on the 3-arg form of open. That is a design defect in your class. Another way would be

sub load_widgets
{
   my($self,$infh)=@_;
         #   ^ IMPORTANT!!!
   $infh=new IO::File("<",$infh)unless ref$infh; 
                                #sorry open($fh...) needs undef
   ...
}
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if you think of preventing magic open by the user.