I'm surprised nobody has mentioned called_as_method from Devel::Caller.

use Devel::Caller qw( called_as_method );

sub new {
    croak "must call new as method" unless called_as_method(0);
    ...
};

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In reply to Re^4: Is "ref($class) || $class" a bad thing? by adrianh
in thread Is "ref($class) || $class" a bad thing? by stvn

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