# Functor Weak.Make

    module Make: functor (H : Hashtbl.HashedType) -> S  with type data = H.t

Functor building an implementation of the weak hash set structure. `H.equal` can't be the physical equality, since only shallow copies of the elements in the set are given to it.

Parameters:

`H` | : | `Hashtbl.HashedType`

    type data

The type of the elements stored in the table.

    type t

The type of tables that contain elements of type `data`. Note that weak hash sets cannot be marshaled using `output_value` or the functions of the `Marshal` module.

    val create : int -> t

`create n` creates a new empty weak hash set, of initial size `n`. The table will grow as needed.

    val clear : t -> unit

Remove all elements from the table.

    val merge : t -> data -> data

`merge t x` returns an instance of `x` found in `t` if any, or else adds `x` to `t` and return `x`.

    val add : t -> data -> unit

`add t x` adds `x` to `t`. If there is already an instance of `x` in `t`, it is unspecified which one will be returned by subsequent calls to `find` and `merge`.

    val remove : t -> data -> unit

`remove t x` removes from `t` one instance of `x`. Does nothing if there is no instance of `x` in `t`.

    val find : t -> data -> data

`find t x` returns an instance of `x` found in `t`. Raise `Not_found` if there is no such element.

    val find_opt : t -> data -> data option

`find_opt t x` returns an instance of `x` found in `t` or `None` if there is no such element.

- Since 4.05

    val find_all : t -> data -> data list

`find_all t x` returns a list of all the instances of `x` found in `t`.

    val mem : t -> data -> bool

`mem t x` returns `true` if there is at least one instance of `x` in `t`, false otherwise.

    val iter : (data -> unit) -> t -> unit

`iter f t` calls `f` on each element of `t`, in some unspecified order. It is not specified what happens if `f` tries to change `t` itself.

    val fold : (data -> 'a -> 'a) -> t -> 'a -> 'a

`fold f t init` computes `(f d1 (... (f dN init)))` where `d1 ... dN` are the elements of `t` in some unspecified order. It is not specified what happens if `f` tries to change `t` itself.

    val count : t -> int

Count the number of elements in the table. `count t` gives the same result as `fold (fun _ n -> n+1) t 0` but does not delay the deallocation of the dead elements.

    val stats : t -> int * int * int * int * int * int

Return statistics on the table. The numbers are, in order: table length, number of entries, sum of bucket lengths, smallest bucket length, median bucket length, biggest bucket length.