`include module type of struct include BatHashtbl end`

Operations over hashtables.

This module replaces Stdlib's Hashtbl module. All functions and types are provided here.

- author Xavier Leroy (base module)

- author Damien Doligez (base module)

- author Nicolas Cannasse

- author David Teller

`type ('a, 'b) t = ('a, 'b) Stdlib.Hashtbl.t`

A Hashtable with keys of type 'a and values 'b

`type statistics = Stdlib.Hashtbl.statistics`

## Base operations

`val create : int -> ('a, 'b) t`

`Hashtbl.create n` creates a new, empty hash table, with initial size `n`. For best results, `n` should be on the order of the expected number of elements that will be in the table. The table grows as needed, so `n` is just an initial guess.

`val length : ('a, 'b) t -> int`

`Hashtbl.length tbl` returns the number of bindings in `tbl`. Multiple bindings are counted multiply, so `Hashtbl.length` gives the number of times `Hashtbl.iter` calls its first argument.

`val is_empty : ('a, 'b) t -> bool`

`Hashtbl.is_empty tbl` returns `true` if there are no bindings in `tbl`, false otherwise.

`val add : ('a, 'b) t -> 'a -> 'b -> unit`

`Hashtbl.add tbl x y` adds a binding of `x` to `y` in table `tbl`. Previous bindings for `x` are not removed, but simply hidden. That is, after performing `Hashtbl.remove` `tbl x`, the previous binding for `x`, if any, is restored. (Same behavior as with association lists.)

`val remove : ('a, 'b) t -> 'a -> unit`

`Hashtbl.remove tbl x` removes the current binding of `x` in `tbl`, restoring the previous binding if it exists. It does nothing if `x` is not bound in `tbl`.

`val remove_all : ('a, 'b) t -> 'a -> unit`

Remove all bindings for the given key

`val replace : ('a, 'b) t -> 'a -> 'b -> unit`

`Hashtbl.replace tbl x y` replaces the current binding of `x` in `tbl` by a binding of `x` to `y`. If `x` is unbound in `tbl`, a binding of `x` to `y` is added to `tbl`. This is functionally equivalent to `Hashtbl.remove` `tbl x` followed by `Hashtbl.add` `tbl x y`.

`val modify_def : 'b -> 'a -> ('b -> 'b) -> ('a, 'b) t -> unit`

`Hashtbl.modify_def v k f tbl` does the same as `Hashtbl.modify k f tbl` but `f v` is inserted in `tbl` if `k` was unbound.

- since 2.1

`val modify_opt : 'a -> ('b option -> 'b option) -> ('a, 'b) t -> unit`

`Hashtbl.modify_opt k f tbl` allows to remove, modify or add a binding for `k` in `tbl`. `f` will be called with `None` if `k` was unbound. first previous binding of `k` in `tbl` will be deleted if `f` returns `None`. Otherwise, the previous binding is replaced by the value produced by `f`.

- since 2.1

`val copy : ('a, 'b) t -> ('a, 'b) t`

Return a copy of the given hashtable.

`val clear : ('a, 'b) t -> unit`

Empty a hash table.

`val reset : ('a, 'b) t -> unit`

Empty a hash table and shrink the size of the bucket table to its initial size.

- since 3.9.0 and OCaml 4.00

`val stats : ('a, 'b) t -> statistics`

`Hashtbl.stats tbl` returns statistics about the table `tbl`: number of buckets, size of the biggest bucket, distribution of buckets by size.

- since 4.00.0 and batteries 3.5.1

## Sequences

`val to_seq : ('a, 'b) t -> ('a * 'b) Stdlib.Seq.t`

Iterate on the whole table. The order in which the bindings appear in the sequence is unspecified. However, if the table contains several bindings for the same key, they appear in reversed order of introduction, that is, the most recent binding appears first.

The behavior is not specified if the hash table is modified during the iteration.

- since 3.9.0 and OCaml 4.07

`val to_seq_keys : ('a, _) t -> 'a Stdlib.Seq.t`

Same as `Seq.map fst (to_seq m)`

- since 3.9.0 and OCaml 4.07

`val to_seq_values : (_, 'b) t -> 'b Stdlib.Seq.t`

Same as `Seq.map snd (to_seq m)`

- since 3.9.0 and OCaml 4.07

`val add_seq : ('a, 'b) t -> ('a * 'b) Stdlib.Seq.t -> unit`

Add the given bindings to the table, using `add`

- since 3.9.0 and OCaml 4.07

`val replace_seq : ('a, 'b) t -> ('a * 'b) Stdlib.Seq.t -> unit`

Add the given bindings to the table, using `replace`

- since 3.9.0 and OCaml 4.07

`val of_seq : ('a * 'b) Stdlib.Seq.t -> ('a, 'b) t`

Build a table from the given bindings. The bindings are added in the same order they appear in the sequence, using `replace_seq`, which means that if two pairs have the same key, only the latest one will appear in the table.

- since 3.9.0 and OCaml 4.07

## Enumerations

`val keys : ('a, 'b) t -> 'a BatEnum.t`

Return an enumeration of all the keys of a hashtable. If the key is in the Hashtable multiple times, all occurrences will be returned.

`val values : ('a, 'b) t -> 'b BatEnum.t`

Return an enumeration of all the values of a hashtable.

`val enum : ('a, 'b) t -> ('a * 'b) BatEnum.t`

Return an enumeration of (key,value) pairs of a hashtable.

`val of_enum : ('a * 'b) BatEnum.t -> ('a, 'b) t`

Create a hashtable from a (key,value) enumeration.

## Lists

`val of_list : ('a * 'b) list -> ('a, 'b) t`

Create a hashtable from a list of (key,value) pairs.

- since 2.6.0

`val to_list : ('a, 'b) t -> ('a * 'b) list`

Return the list of (key,value) pairs.

- since 2.6.0

`val bindings : ('a, 'b) t -> ('a * 'b) list`

Alias for `to_list`.

- since 2.6.0

## Searching

`val find_all : ('a, 'b) t -> 'a -> 'b list`

`Hashtbl.find_all tbl x` returns the list of all data associated with `x` in `tbl`. The current binding is returned first, then the previous bindings, in reverse order of introduction in the table.

`val find_default : ('a, 'b) t -> 'a -> 'b -> 'b`

`Hashtbl.find_default tbl key default` finds a binding for `key`, or return `default` if `key` is unbound in `tbl`.

`val find_option : ('a, 'b) t -> 'a -> 'b option`

Find a binding for the key, or return `None` if no value is found

`val find_opt : ('a, 'b) t -> 'a -> 'b option`

`Stdlib`-compatible alias for `find_option`.

- since 3.9.0

`val exists : ('a -> 'b -> bool) -> ('a, 'b) t -> bool`

Check if at least one key-value pair satisfies `p k v`

`val mem : ('a, 'b) t -> 'a -> bool`

`Hashtbl.mem tbl x` checks if `x` is bound in `tbl`.

## Traversing

A number of higher-order functions are provided to allow purely functional traversal or transformation of hashtables. These functions are similar to their counterparts in module `BatEnum`.

Whenever you wish to traverse or transfor a hashtable, you have the choice between using the more general functions of `BatEnum`, with `keys`, `values`, `enum` and `of_enum`, or the more optimized functions of this section.

If you are new to OCaml or unsure about data structure, using the functions of `BatEnum` is a safe bet. Should you wish to improve performance at the cost of generality, you will always be able to rewrite your code to make use of the functions of this section.

`val iter : ('a -> 'b -> unit) -> ('a, 'b) t -> unit`

`Hashtbl.iter f tbl` applies `f` to all bindings in table `tbl`. `f` receives the key as first argument, and the associated value as second argument. Each binding is presented exactly once to `f`. The order in which the bindings are passed to `f` is unspecified. However, if the table contains several bindings for the same key, they are passed to `f` in reverse order of introduction, that is, the most recent binding is passed first.

`val for_all : ('a -> 'b -> bool) -> ('a, 'b) t -> bool`

`Hashtbl.for_all p tbl` check if the predicate `p k v` holds for all bindings currently in `tbl`.

`val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) t -> 'c -> 'c`

`Hashtbl.fold f tbl init` computes `(f kN dN ... (f k1 d1 (f k0 d0 init))...)`, where `k0,k1..kN` are the keys of all bindings in `tbl`, and `d0,d1..dN` are the associated values. Each binding is presented exactly once to `f`. The order in which the bindings are passed to `f` is unspecified. However, if the table contains several bindings for the same key, they are passed to `f` in reverse order of introduction, that is, the most recent binding is passed first.

`val map : ('a -> 'b -> 'c) -> ('a, 'b) t -> ('a, 'c) t`

`map f x` creates a new hashtable with the same keys as `x`, but with the function `f` applied to all the values

`val map_inplace : ('a -> 'b -> 'b) -> ('a, 'b) t -> unit`

`map_inplace f x` replace all values currently bound in `x` by `f` applied to each value.

- since 2.1

`val filter : ('a -> bool) -> ('key, 'a) t -> ('key, 'a) t`

`filter f m` returns a new hashtable where only the values `a` of `m` such that `f a = true` remain.

`val filter_inplace : ('a -> bool) -> ('key, 'a) t -> unit`

`filter_inplace f m` removes from `m` all bindings that does not satisfy the predicate f.

- since 2.1

`val filteri : ('key -> 'a -> bool) -> ('key, 'a) t -> ('key, 'a) t`

`filteri f m` returns a hashtbl where only the key, values pairs `key`, `a` of `m` such that `f key a = true` remain.

`val filteri_inplace : ('key -> 'a -> bool) -> ('key, 'a) t -> unit`

`filteri_inplace f m` performs as filter_inplace but `f` receive the value in additiuon to the key.

- since 2.1

`val filter_map : ('key -> 'a -> 'b option) -> ('key, 'a) t -> ('key, 'b) t`

`filter_map f m` combines the features of `filteri` and `map`. It calls `f key0 a0`, `f key1 a1`, `f keyn an` where `a0,a1..an` are the elements of `m` and `key0..keyn` the corresponding keys. It returns a hashtbl with associations `keyi`,`bi` where `f keyi ai = Some bi`. When `f` returns `None`, the corresponding element of `m` is discarded.

`val filter_map_inplace : ('key -> 'a -> 'a option) -> ('key, 'a) t -> unit`

`filter_map_inplace f m` performs like filter_map but modify `m` inplace instead of creating a new Hashtbl.

`val merge : ('a -> 'b option -> 'c option -> 'd option) -> ('a, 'b) t -> ('a, 'c) t -> ('a, 'd) t`

`merge f a b` returns a new Hashtbl which is build from the bindings of `a` and `b` according to the function `f`, that is given all defined keys one by one, along with the value from `a` (if defined) and the value from `b` (if defined), and has to return the (optional) resulting value.

It is assumed that each key is bound at most once in `a` and `b`. See `merge_all` for a more general alternative if this is not the case.

- since 2.10.0

`val merge_all : ('a -> 'b list -> 'c list -> 'd list) -> ('a, 'b) t -> ('a, 'c) t -> ('a, 'd) t`

`merge_all f a b` is similar to `merge`, but passes to `f` all bindings for a key (most recent first, as returned by `find_all`). `f` must then return all the new bindings of the merged hashtable (or an empty list if that key should not be bound in the resulting hashtable). Those new bindings will be inserted in reverse, so that the head of the list will become the most recent binding in the merged hashtable.

- since 2.10.0

## The polymorphic hash primitive

`val hash : 'a -> int`

`Hashtbl.hash x` associates a positive integer to any value of any type. It is guaranteed that if `x = y` or `Pervasives.compare x y = 0`, then `hash x = hash y`. Moreover, `hash` always terminates, even on cyclic structures.

## Boilerplate code

### Printing

`val print : ?first:string -> ?last:string -> ?sep:string -> ?kvsep:string -> ('a BatInnerIO.output -> 'b -> unit) -> ('a BatInnerIO.output -> 'c -> unit) -> 'a BatInnerIO.output -> ('b, 'c) t -> unit`

## Override modules

The following modules replace functions defined in `Hashtbl` with functions behaving slightly differently but having the same name. This is by design: the functions meant to override the corresponding functions of `Hashtbl`.

`module Exceptionless = BatHashtbl.Exceptionless`

Operations on `Hashtbl` without exceptions.

`module Infix = BatHashtbl.Infix`

Infix operators over a `BatHashtbl`

`module Labels = BatHashtbl.Labels`

Operations on `Hashtbl` with labels.

## Functorial interface

`module type HashedType = BatHashtbl.HashedType`
`module type S = BatHashtbl.S`

The output signature of the functor `Hashtbl.Make`.

`module Make = BatHashtbl.Make`

Functor building an implementation of the hashtable structure. The functor `Hashtbl.Make` returns a structure containing a type `key` of keys and a type `'a t` of hash tables associating data of type `'a` to keys of type `key`. The operations perform similarly to those of the generic interface, but use the hashing and equality functions specified in the functor argument `H` instead of generic equality and hashing.

`module Cap = BatHashtbl.Cap`

Capabilities for hashtables.

`include module type of struct include BatHashtbl.Exceptionless end`
`val find : ('a, 'b) BatHashtbl.t -> 'a -> 'b option`
`val modify : 'a -> ('b -> 'b) -> ('a, 'b) BatHashtbl.t -> (unit, exn) BatPervasives.result`