Weak(3) OCaml library Weak(3)NAMEWeak - Arrays of weak pointers and hash tables of weak pointers.
Module
Module WeakDocumentation
Module Weak
: sig end
Arrays of weak pointers and hash tables of weak pointers.
=== Low-level functions ===
type 'a t
The type of arrays of weak pointers (weak arrays). A weak pointer is a
value that the garbage collector may erase whenever the value is not
used any more (through normal pointers) by the program. Note that
finalisation functions are run after the weak pointers are erased.
A weak pointer is said to be full if it points to a value, empty if the
value was erased by the GC.
Notes:
-Integers are not allocated and cannot be stored in weak arrays.
-Weak arrays cannot be marshaled using Pervasives.output_value nor the
functions of the Marshal module.
val create : int -> 'a t
Weak.create n returns a new weak array of length n . All the pointers
are initially empty. Raise Invalid_argument if n is negative or
greater than Sys.max_array_length -1 .
val length : 'a t -> int
Weak.length ar returns the length (number of elements) of ar .
val set : 'a t -> int -> 'a option -> unit
Weak.set ar n (Some el) sets the n th cell of ar to be a (full) pointer
to el ; Weak.set ar n None sets the n th cell of ar to empty. Raise
Invalid_argument Weak.set if n is not in the range 0 to Weak.length a -
1 .
val get : 'a t -> int -> 'a option
Weak.get ar n returns None if the n th cell of ar is empty, Some x
(where x is the value) if it is full. Raise Invalid_argument Weak.get
if n is not in the range 0 to Weak.length a - 1 .
val get_copy : 'a t -> int -> 'a option
Weak.get_copy ar n returns None if the n th cell of ar is empty, Some x
(where x is a (shallow) copy of the value) if it is full. In addition
to pitfalls with mutable values, the interesting difference with get is
that get_copy does not prevent the incremental GC from erasing the
value in its current cycle ( get may delay the erasure to the next GC
cycle). Raise Invalid_argument Weak.get if n is not in the range 0 to
Weak.length a - 1 .
val check : 'a t -> int -> bool
Weak.check ar n returns true if the n th cell of ar is full, false if
it is empty. Note that even if Weak.check ar n returns true , a subse‐
quent Weak.get ar n can return None .
val fill : 'a t -> int -> int -> 'a option -> unit
Weak.fill ar ofs len el sets to el all pointers of ar from ofs to ofs +
len - 1 . Raise Invalid_argument Weak.fill if ofs and len do not des‐
ignate a valid subarray of a .
val blit : 'a t -> int -> 'a t -> int -> int -> unit
Weak.blit ar1 off1 ar2 off2 len copies len weak pointers from ar1
(starting at off1 ) to ar2 (starting at off2 ). It works correctly
even if ar1 and ar2 are the same. Raise Invalid_argument Weak.blit if
off1 and len do not designate a valid subarray of ar1 , or if off2 and
len do not designate a valid subarray of ar2 .
=== Weak hash tables ===
=== A weak hash table is a hashed set of values. Each value may magi‐
cally disappear from the set when it is not used by the rest of the
program any more. This is normally used to share data structures with‐
out inducing memory leaks. Weak hash tables are defined on values from
a Hashtbl.HashedType module; the equal relation and hash function are
taken from that module. We will say that v is an instance of x if equal
x v is true. The equal relation must be able to work on a shallow copy
of the values and give the same result as with the values themselves.
===
module type S = sig end
The output signature of the functor Weak.Make .
module Make : functor (H : Hashtbl.HashedType) -> sig end
Functor building an implementation of the weak hash table structure.
OCamldoc 2013-10-24 Weak(3)
