module Array: ArrayLabels
type'a
t ='a array
An alias for the type of arrays.
val length : 'a array -> int
Return the length (number of elements) of the given array.
val get : 'a array -> int -> 'a
get a n
returns the element number n
of array a
.
The first element has number 0.
The last element has number length a - 1
.
You can also write a.(n)
instead of get a n
.
Invalid_argument
if n
is outside the range 0 to (length a - 1)
.val set : 'a array -> int -> 'a -> unit
set a n x
modifies array a
in place, replacing
element number n
with x
.
You can also write a.(n) <- x
instead of set a n x
.
Invalid_argument
if n
is outside the range 0 to length a - 1
.val make : int -> 'a -> 'a array
make n x
returns a fresh array of length n
,
initialized with x
.
All the elements of this new array are initially
physically equal to x
(in the sense of the ==
predicate).
Consequently, if x
is mutable, it is shared among all elements
of the array, and modifying x
through one of the array entries
will modify all other entries at the same time.
Invalid_argument
if n < 0
or n > Sys.max_array_length
.
If the value of x
is a floating-point number, then the maximum
size is only Sys.max_array_length / 2
.val create_float : int -> float array
create_float n
returns a fresh float array of length n
,
with uninitialized data.
val init : int -> f:(int -> 'a) -> 'a array
init n ~f
returns a fresh array of length n
,
with element number i
initialized to the result of f i
.
In other terms, init n ~f
tabulates the results of f
applied to the integers 0
to n-1
.
Invalid_argument
if n < 0
or n > Sys.max_array_length
.
If the return type of f
is float
, then the maximum
size is only Sys.max_array_length / 2
.val make_matrix : dimx:int -> dimy:int -> 'a -> 'a array array
make_matrix ~dimx ~dimy e
returns a two-dimensional array
(an array of arrays) with first dimension dimx
and
second dimension dimy
. All the elements of this new matrix
are initially physically equal to e
.
The element (x,y
) of a matrix m
is accessed
with the notation m.(x).(y)
.
Invalid_argument
if dimx
or dimy
is negative or
greater than Sys.max_array_length
.
If the value of e
is a floating-point number, then the maximum
size is only Sys.max_array_length / 2
.val append : 'a array -> 'a array -> 'a array
append v1 v2
returns a fresh array containing the
concatenation of the arrays v1
and v2
.
Invalid_argument
if
length v1 + length v2 > Sys.max_array_length
.val concat : 'a array list -> 'a array
Same as ArrayLabels.append
, but concatenates a list of arrays.
val sub : 'a array -> pos:int -> len:int -> 'a array
sub a ~pos ~len
returns a fresh array of length len
,
containing the elements number pos
to pos + len - 1
of array a
.
Invalid_argument
if pos
and len
do not
designate a valid subarray of a
; that is, if
pos < 0
, or len < 0
, or pos + len > length a
.val copy : 'a array -> 'a array
copy a
returns a copy of a
, that is, a fresh array
containing the same elements as a
.
val fill : 'a array -> pos:int -> len:int -> 'a -> unit
fill a ~pos ~len x
modifies the array a
in place,
storing x
in elements number pos
to pos + len - 1
.
Invalid_argument
if pos
and len
do not
designate a valid subarray of a
.val blit : src:'a array -> src_pos:int -> dst:'a array -> dst_pos:int -> len:int -> unit
blit ~src ~src_pos ~dst ~dst_pos ~len
copies len
elements
from array src
, starting at element number src_pos
, to array dst
,
starting at element number dst_pos
. It works correctly even if
src
and dst
are the same array, and the source and
destination chunks overlap.
Invalid_argument
if src_pos
and len
do not
designate a valid subarray of src
, or if dst_pos
and len
do not
designate a valid subarray of dst
.val to_list : 'a array -> 'a list
to_list a
returns the list of all the elements of a
.
val of_list : 'a list -> 'a array
of_list l
returns a fresh array containing the elements
of l
.
Invalid_argument
if the length of l
is greater than
Sys.max_array_length
.val iter : f:('a -> unit) -> 'a array -> unit
iter ~f a
applies function f
in turn to all
the elements of a
. It is equivalent to
f a.(0); f a.(1); ...; f a.(length a - 1); ()
.
val iteri : f:(int -> 'a -> unit) -> 'a array -> unit
Same as ArrayLabels.iter
, but the
function is applied to the index of the element as first argument,
and the element itself as second argument.
val map : f:('a -> 'b) -> 'a array -> 'b array
map ~f a
applies function f
to all the elements of a
,
and builds an array with the results returned by f
:
[| f a.(0); f a.(1); ...; f a.(length a - 1) |]
.
val mapi : f:(int -> 'a -> 'b) -> 'a array -> 'b array
Same as ArrayLabels.map
, but the
function is applied to the index of the element as first argument,
and the element itself as second argument.
val fold_left : f:('a -> 'b -> 'a) -> init:'a -> 'b array -> 'a
fold_left ~f ~init a
computes
f (... (f (f init a.(0)) a.(1)) ...) a.(n-1)
,
where n
is the length of the array a
.
val fold_left_map : f:('a -> 'b -> 'a * 'c) -> init:'a -> 'b array -> 'a * 'c array
fold_left_map
is a combination of ArrayLabels.fold_left
and ArrayLabels.map
that threads an
accumulator through calls to f
.
val fold_right : f:('b -> 'a -> 'a) -> 'b array -> init:'a -> 'a
fold_right ~f a ~init
computes
f a.(0) (f a.(1) ( ... (f a.(n-1) init) ...))
,
where n
is the length of the array a
.
val iter2 : f:('a -> 'b -> unit) -> 'a array -> 'b array -> unit
iter2 ~f a b
applies function f
to all the elements of a
and b
.
Invalid_argument
if the arrays are not the same size.val map2 : f:('a -> 'b -> 'c) -> 'a array -> 'b array -> 'c array
map2 ~f a b
applies function f
to all the elements of a
and b
, and builds an array with the results returned by f
:
[| f a.(0) b.(0); ...; f a.(length a - 1) b.(length b - 1)|]
.
Invalid_argument
if the arrays are not the same size.val for_all : f:('a -> bool) -> 'a array -> bool
for_all ~f [|a1; ...; an|]
checks if all elements
of the array satisfy the predicate f
. That is, it returns
(f a1) && (f a2) && ... && (f an)
.
val exists : f:('a -> bool) -> 'a array -> bool
exists ~f [|a1; ...; an|]
checks if at least one element of
the array satisfies the predicate f
. That is, it returns
(f a1) || (f a2) || ... || (f an)
.
val for_all2 : f:('a -> 'b -> bool) -> 'a array -> 'b array -> bool
Same as ArrayLabels.for_all
, but for a two-argument predicate.
Invalid_argument
if the two arrays have different lengths.val exists2 : f:('a -> 'b -> bool) -> 'a array -> 'b array -> bool
Same as ArrayLabels.exists
, but for a two-argument predicate.
Invalid_argument
if the two arrays have different lengths.val mem : 'a -> set:'a array -> bool
mem a ~set
is true if and only if a
is structurally equal
to an element of l
(i.e. there is an x
in l
such that
compare a x = 0
).
val memq : 'a -> set:'a array -> bool
Same as ArrayLabels.mem
, but uses physical equality
instead of structural equality to compare list elements.
val find_opt : f:('a -> bool) -> 'a array -> 'a option
find_opt ~f a
returns the first element of the array a
that satisfies
the predicate f
, or None
if there is no value that satisfies f
in the
array a
.
val find_map : f:('a -> 'b option) -> 'a array -> 'b option
find_map ~f a
applies f
to the elements of a
in order, and returns the
first result of the form Some v
, or None
if none exist.
val split : ('a * 'b) array -> 'a array * 'b array
split [|(a1,b1); ...; (an,bn)|]
is ([|a1; ...; an|], [|b1; ...; bn|])
.
val combine : 'a array -> 'b array -> ('a * 'b) array
combine [|a1; ...; an|] [|b1; ...; bn|]
is [|(a1,b1); ...; (an,bn)|]
.
Raise Invalid_argument
if the two arrays have different lengths.
val sort : cmp:('a -> 'a -> int) -> 'a array -> unit
Sort an array in increasing order according to a comparison
function. The comparison function must return 0 if its arguments
compare as equal, a positive integer if the first is greater,
and a negative integer if the first is smaller (see below for a
complete specification). For example, compare
is
a suitable comparison function. After calling sort
, the
array is sorted in place in increasing order.
sort
is guaranteed to run in constant heap space
and (at most) logarithmic stack space.
The current implementation uses Heap Sort. It runs in constant stack space.
Specification of the comparison function:
Let a
be the array and cmp
the comparison function. The following
must be true for all x
, y
, z
in a
:
cmp x y
> 0 if and only if cmp y x
< 0cmp x y
>= 0 and cmp y z
>= 0 then cmp x z
>= 0When sort
returns, a
contains the same elements as before,
reordered in such a way that for all i and j valid indices of a
:
cmp a.(i) a.(j)
>= 0 if and only if i >= jval stable_sort : cmp:('a -> 'a -> int) -> 'a array -> unit
Same as ArrayLabels.sort
, but the sorting algorithm is stable (i.e.
elements that compare equal are kept in their original order) and
not guaranteed to run in constant heap space.
The current implementation uses Merge Sort. It uses a temporary array of
length n/2
, where n
is the length of the array. It is usually faster
than the current implementation of ArrayLabels.sort
.
val fast_sort : cmp:('a -> 'a -> int) -> 'a array -> unit
Same as ArrayLabels.sort
or ArrayLabels.stable_sort
, whichever is
faster on typical input.
val to_seq : 'a array -> 'a Seq.t
Iterate on the array, in increasing order. Modifications of the array during iteration will be reflected in the sequence.
val to_seqi : 'a array -> (int * 'a) Seq.t
Iterate on the array, in increasing order, yielding indices along elements. Modifications of the array during iteration will be reflected in the sequence.
val of_seq : 'a Seq.t -> 'a array
Create an array from the generator
Care must be taken when concurrently accessing arrays from multiple domains: accessing an array will never crash a program, but unsynchronized accesses might yield surprising (non-sequentially-consistent) results.
Every array operation that accesses more than one array element is not atomic. This includes iteration, scanning, sorting, splitting and combining arrays.
For example, consider the following program:
let size = 100_000_000
let a = ArrayLabels.make size 1
let d1 = Domain.spawn (fun () ->
ArrayLabels.iteri ~f:(fun i x -> a.(i) <- x + 1) a
)
let d2 = Domain.spawn (fun () ->
ArrayLabels.iteri ~f:(fun i x -> a.(i) <- 2 * x + 1) a
)
let () = Domain.join d1; Domain.join d2
After executing this code, each field of the array a
is either 2
, 3
,
4
or 5
. If atomicity is required, then the user must implement their own
synchronization (for example, using Mutex.t
).
If two domains only access disjoint parts of the array, then the observed behaviour is the equivalent to some sequential interleaving of the operations from the two domains.
A data race is said to occur when two domains access the same array element without synchronization and at least one of the accesses is a write. In the absence of data races, the observed behaviour is equivalent to some sequential interleaving of the operations from different domains.
Whenever possible, data races should be avoided by using synchronization to mediate the accesses to the array elements.
Indeed, in the presence of data races, programs will not crash but the observed behaviour may not be equivalent to any sequential interleaving of operations from different domains. Nevertheless, even in the presence of data races, a read operation will return the value of some prior write to that location (with a few exceptions for float arrays).
Float arrays have two supplementary caveats in the presence of data races.
First, the blit operation might copy an array byte-by-byte. Data races between such a blit operation and another operation might produce surprising values due to tearing: partial writes interleaved with other operations can create float values that would not exist with a sequential execution.
For instance, at the end of
let zeros = Array.make size 0.
let max_floats = Array.make size Float.max_float
let res = Array.copy zeros
let d1 = Domain.spawn (fun () -> Array.blit zeros 0 res 0 size)
let d2 = Domain.spawn (fun () -> Array.blit max_floats 0 res 0 size)
let () = Domain.join d1; Domain.join d2
the res
array might contain values that are neither 0.
nor max_float
.
Second, on 32-bit architectures, getting or setting a field involves two separate memory accesses. In the presence of data races, the user may observe tearing on any operation.