oracular (3) ArrayLabels.3o.gz

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NAME

       ArrayLabels - Array operations.

Module

       Module   ArrayLabels

Documentation

       Module ArrayLabels
        : sig end

       Array operations.

       The labeled version of this module can be used as described in the StdLabels module.

       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 .

       Raises 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 .

       Raises 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.

       Raises 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.

       Since 4.03

       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 in order  to
       the integers 0 to n-1 .

       Raises 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) .

       Raises 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 init_matrix : dimx:int -> dimy:int -> f:(int -> int -> 'a) -> 'a array array

       init_matrix ~dimx ~dimy ~f returns a two-dimensional array (an array of arrays) with first
       dimension dimx and second dimension dimy  ,  where  the  element  at  index  (  x,y  )  is
       initialized  with f x y .  The element ( x,y ) of a matrix m is accessed with the notation
       m.(x).(y) .

       Since 5.2

       Raises Invalid_argument if dimx or dimy is negative or greater than Sys.max_array_length .
       If  the return type of f is float , 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 .

       Raises 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 .

       Raises  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 .

       Raises 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.

       Raises 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 .

       Raises Invalid_argument if the length of l is greater than Sys.max_array_length .

   Iterators
       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 map_inplace : f:('a -> 'a) -> 'a array -> unit

       map_inplace ~f a applies function f to all elements of a , and  updates  their  values  in
       place.

       Since 5.1

       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 mapi_inplace : f:(int -> 'a -> 'a) -> 'a array -> unit

       Same as ArrayLabels.map_inplace , but the function is applied to the index of the  element
       as first argument, and the element itself as second argument.

       Since 5.1

       val fold_left : f:('acc -> 'a -> 'acc) -> init:'acc -> 'a array -> 'acc

       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:('acc -> 'a -> 'acc * 'b) -> init:'acc -> 'a  array  ->  'acc  *  'b
       array

       fold_left_map  is  a combination of ArrayLabels.fold_left and ArrayLabels.map that threads
       an accumulator through calls to f .

       Since 4.13

       val fold_right : f:('a -> 'acc -> 'acc) -> 'a array -> init:'acc -> 'acc

       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 .

   Iterators on two arrays
       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 .

       Since 4.05

       Raises 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)|] .

       Since 4.05

       Raises Invalid_argument if the arrays are not the same size.

   Array scanning
       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) .

       Since 4.03

       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) .

       Since 4.03

       val for_all2 : f:('a -> 'b -> bool) -> 'a array -> 'b array -> bool

       Same as ArrayLabels.for_all , but for a two-argument predicate.

       Since 4.11

       Raises 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.

       Since 4.11

       Raises 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 set (i.e. there
       is an x in set such that compare a x = 0 ).

       Since 4.03

       val memq : 'a -> set:'a array -> bool

       Same  as  ArrayLabels.mem  ,  but uses physical equality instead of structural equality to
       compare array elements.

       Since 4.03

       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 .

       Since 4.13

       val find_index : f:('a -> bool) -> 'a array -> int option

       find_index  ~f a returns Some i , where i is the index of the first element of the array a
       that satisfies f x , if there is such an element.

       It returns None if there is no such element.

       Since 5.1

       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.

       Since 4.13

       val find_mapi : f:(int -> 'a -> 'b option) -> 'a array -> 'b option

       Same  as  find_map  ,  but  the  predicate is applied to the index of the element as first
       argument (counting from 0), and the element itself as second argument.

       Since 5.1

   Arrays of pairs
       val split : ('a * 'b) array -> 'a array * 'b array

       split [|(a1,b1); ...; (an,bn)|] is ([|a1; ...; an|], [|b1; ...; bn|]) .

       Since 4.13

       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.

       Since 4.13

   Sorting and shuffling
       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 < 0

       -  if cmp x y >= 0 and cmp y z >= 0 then cmp x z >= 0

       When  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 >= j

       val 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 shuffle : rand:(int -> int) -> 'a array -> unit

       shuffle ~rand a randomly permutes a 's element using rand for randomness. The distribution
       of permutations is uniform.

       rand must be such that a call to rand n returns a uniformly distributed random  number  in
       the range [ 0 ; n-1 ].  Random.int can be used for this (do not forget to Random.self_init
       the generator).

       Since 5.2

   Arrays and Sequences
       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.

       Since 4.07

       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.

       Since 4.07

       val of_seq : 'a Seq.t -> 'a array

       Create an array from the generator

       Since 4.07

   Arrays and concurrency safety
       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.

   Atomicity
       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 ).

   Data races
       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
       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.