module Hashtbl: Core_hashtbl
For a list of hashtable functions see Hashtbl_intf.S.
To create a hashtable with string keys use String.Table.
let table = String.Table.create () ~size:4 in
List.iter ~f:(fun (key, data) -> Hashtbl.set table ~key ~data)
[ ("A", 1); ("B", 2); ("C", 3); ];
Hashtbl.find table "C"
Here 4 need only be a guess at the hashtable's future size.
There are other similar pre-made hashtables, eg
Int63.Table or Symbol.Reuters.Table.
To create a hashtable with a custom key type use Hashable.
module Key = struct
module T = struct
type t = String.t * Int63.t with sexp
let compare = compare
let hash = Hashtbl.hash
end
include T
include Hashable.Make (T)
end
let table = Key.Table.create () ~size:4 in
List.iter ~f:(fun (key, data) -> Hashtbl.set table ~key ~data)
[ (("pi", Int63.zero), 3.14159);
(("e", Int63.minus_one), 2.71828);
(("Euler", Int63.one), 0.577215);
];
Hashtbl.find table ("pi", Int63.zero)
Performance may improve if you define equal and hash explicitly, eg:
let equal (x, y) (x', y') = String.(=) x x' && Int63.(=) y y'
let hash (x, y) = String.hash x + Int63.hash y * 65599
include Core_hashtbl_intf.Hashtbl