This is a fine module. It has one caveat that the author understands, but doesnâ€™t call out in the documentation: unlike real constants, the deferred constants produced by this module wonâ€™t be inlined in any code that is compiled before the deferred calculation has been triggered. So depending on why you are using constants instead of other mechanisms like read-only variables, this module may or may not be of use to you. This is a fundamental caveat; it is not possible to resolve without special support in the compiler and op tree.
(As for Burak GÃ¼rsoyâ€™s negative review, please ignore. He criticises that this module injects weird subs â€“ in Perl, all constants are subs of a particular form (cf. the source of constant.pm). He also criticises the use of goto â€“ in Perl, goto has several forms, one of which provides an explicit tail call, which form is quite commonly used, particularly in all sorts of meta-programming. I found nothing surprising or unusual in my reading of the moduleâ€™s source.)