require Tie::SubstrHash; tie %myhash, "Tie::SubstrHash", $key_len, $value_len, $table_size;
Upon tying a new hash to this package, the developer must specify the
size of the keys that will be used, the size of the value fields that the
keys will index, and the size of the overall table (in terms of the number
of key/value pairs, not hard memory). These values will not change for the
duration of the tied hash. The newly allocated hash table may now have
data stored and retrieved. Efforts to store more than
elements will result in a fatal error, as will efforts to store a value
$value_len characters in length, or to reference through a
key not exactly
$key_len characters in length. While these constraints
may seem excessive, the result is a hash table using much less internal
memory than an equivalent freely allocated hash table.
Because the current implementation uses the table and key sizes for the hashing algorithm, there is no means by which to dynamically change the value of any of the initialization parameters.