See this p5p thread from 18 months ago for a description of some limitations of restricted-hash-based fields and some strong anti-compile-time-checking sentiment on the part of some (including rejection of a patch to put the checking back in bleadperl). types.pm, is unfortunately IMO uncommented to the point of unmaintainability.

In reply to Re: use fields; # damnit by ysth
in thread use fields; # damnit by nothingmuch

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