They are unconditionally implemented at least as far back as 5.6.0 as far as I can tell. The error message is erroneous, resulting from a bad installation of Scalar::Util. You'd get that error if Scalar::Util couldn't find its compiled XS component, for example.

In reply to Re^2: CGI::FormBuilder and unimplemented weak references; Ideas? by ikegami
in thread CGI::FormBuilder and unimplemented weak references; Ideas? by hesco

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