HashMap.StringSpecalized when key type is string, more efficient than the generic type
let make: hintSize:int => t('b);let clear: t('b) => unit;let isEmpty: t(_) => bool;setDone tbl k v if k does not exist, add the binding k,v, otherwise, update the old value with the new v
let size: t(_) => int;let valuesToArray: t('a) => array('a);let getBucketHistogram: t(_) => array(int);let logStats: t(_) => unit;