1Weak(3) OCaml library Weak(3)
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6 Weak - Arrays of weak pointers and hash tables of weak pointers.
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9 Module Weak
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12 Module Weak
13 : sig end
14 Arrays of weak pointers and hash tables of weak pointers.
17 === Low-level functions ===
26 type 'a t
28 The type of arrays of weak pointers (weak arrays). A weak pointer is a
31 value that the garbage collector may erase at any time. A weak pointer
32 is said to be full if it points to a value, empty if the value was
33 erased by the GC. Note that weak arrays cannot be marshaled using Per‐
34 vasives.output_value or the functions of the Marshal module.
35 val create : int -> 'a t
40 Weak.create n returns a new weak array of length n . All the pointers
43 are initially empty. Raise Invalid_argument if n is negative or
44 greater than Sys.max_array_length -1 .
45 val length : 'a t -> int
50 Weak.length ar returns the length (number of elements) of ar .
53 val set : 'a t -> int -> 'a option -> unit
58 Weak.set ar n (Some el) sets the n th cell of ar to be a (full) pointer
61 to el ; Weak.set ar n None sets the n th cell of ar to empty. Raise
62 Invalid_argument Weak.set if n is not in the range 0 to Weak.length a -
63 1 .
64 val get : 'a t -> int -> 'a option
69 Weak.get ar n returns None if the n th cell of ar is empty, Some x
72 (where x is the value) if it is full. Raise Invalid_argument Weak.get
73 if n is not in the range 0 to Weak.length a - 1 .
74 val get_copy : 'a t -> int -> 'a option
79 Weak.get_copy ar n returns None if the n th cell of ar is empty, Some x
82 (where x is a (shallow) copy of the value) if it is full. In addition
83 to pitfalls with mutable values, the interesting difference with get is
84 that get_copy does not prevent the incremental GC from erasing the
85 value in its current cycle ( get may delay the erasure to the next GC
86 cycle). Raise Invalid_argument Weak.get if n is not in the range 0 to
87 Weak.length a - 1 .
88 val check : 'a t -> int -> bool
93 Weak.check ar n returns true if the n th cell of ar is full, false if
96 it is empty. Note that even if Weak.check ar n returns true , a subse‐
97 quent Weak.get ar n can return None .
98 val fill : 'a t -> int -> int -> 'a option -> unit
103 Weak.fill ar ofs len el sets to el all pointers of ar from ofs to ofs +
106 len - 1 . Raise Invalid_argument Weak.fill if ofs and len do not des‐
107 ignate a valid subarray of a .
108 val blit : 'a t -> int -> 'a t -> int -> int -> unit
113 Weak.blit ar1 off1 ar2 off2 len copies len weak pointers from ar1
116 (starting at off1 ) to ar2 (starting at off2 ). It works correctly
117 even if ar1 and ar2 are the same. Raise Invalid_argument Weak.blit if
118 off1 and len do not designate a valid subarray of ar1 , or if off2 and
119 len do not designate a valid subarray of ar2 .
120 === Weak hash tables ===
126 === A weak hash table is a hashed set of values. Each value may magi‐
130 cally disappear from the set when it is not used by the rest of the
131 program any more. This is normally used to share data structures with‐
132 out inducing memory leaks. Weak hash tables are defined on values from
133 a Hashtbl.HashedType module; the equal relation and hash function are
134 taken from that module. We will say that v is an instance of x if equal
135 x v is true. The equal relation must be able to work on a shallow copy
136 of the values and give the same result as with the values themselves.
137 ===
138 module type S = sig end
140 The output signature of the functor Weak.Make .
143 module Make : functor (H : Hashtbl.HashedType) -> sig end
147 Functor building an implementation of the weak hash table structure.
150OCamldoc 2007-05-24 Weak(3)