# Method ADT.CritBit.IPv4Tree()->encode_key()

Method encode_key

  ``string` encode_key(`mixed` `o`)`
  ``mixed` decode_key(`string` `o`)`

Description

  These callbacks can be implemented when inheriting IPv4Tree in order to allow for arbitrary key types. encode_key is similar to the `lfun::_hash()` callback. This only works as expected when it is possible to implement a unique representation for keys. These callbacks are called everytime a key is stored or indexed in the tree.