[containers-users] hashing

[Simon Cruanes]

Hello,

I released 0.18 a few days ago, a small release. There are a few
deprecated functions around containers right now, but I'm considering a
possibly more breaking change.

The module CCHash (in core) is one of the modules I dislike the most, as
I had to write a custom hash function, and the type of hasher:

type 'a hash_fun = state -> 'a -> state

is pretty annoying to work with in practice. Hashtbl.Make, for instance,
requires `val hash : 'a -> int`. I am considering replacing this module
with a new one, that would be based on `'a hash_fun = 'a -> int` (only
positive ints), and combine hashes using variants of `Hashtbl.seeded_hash`.
Something like

```
type 'a hash_fun = 'a -> int

val hash : 'a hash_fun  (* hashtbl.hash *)
val int : int hash_fun
val string : string hash_fun
(* ... *)

val combine : int -> int -> int (* hashtbl.seeded_hash *)

val hash_list : 'a hash_fun -> 'a list hash_fun
(* relies on combine *)

val pair : 'a hash_fun -> 'b hash_fun -> ('a * 'b) hash_fun
(* relies on combine *)
```

Opinions on this? Would this break anyone's code except mine?

-- 
Simon Cruanes

http://weusepgp.info/
key 49AA62B6, fingerprint 949F EB87 8F06 59C6 D7D3  7D8D 4AC0 1D08 49AA 62B6
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