Belt_internalBucketsType
type opt('a) = Js.undefined('a);
type container('hash, 'eq, 'c) = {
mutable size: int,
mutable buckets: array(opt('c)),
hash: 'hash,
eq: 'eq,
};
let toOpt: opt('a) => option('a);
let return: 'a => opt('a);
let emptyOpt: Js.undefined('a);
let make: hash:'hash => eq:'eq => hintSize:int => container('hash, 'eq, _);
let clear: container(_, _, _) => unit;
let isEmpty: container(_, _, _) => bool;