my $class = ref $proto || $proto;
    ...
    bless $self, $class;
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Don't do that. It generates a function/method that implies both constructor and clone semantics. new should be a class function that generates a new initialised object. An explicit copy or clone method (not class function) should be used to generate a cloned instance of an existing object. new() function: incorrect? and its replies discuss the topic at some length.