The Perl 5 module Hash::Util::FieldHash::Compat use Hash::Util::FieldHash or ties, depending on availability. Under older perls this module provides a drop in compatible api to Hash::Util::FieldHash using perltie. When Hash::Util::FieldHash is available it will use that instead. This way code requiring field hashes can benefit from fast, robust field hashes on Perl 5.10 and newer, but still run on older perls that don't ship with that module. See Hash::Util::FieldHash for all the details of the API.