signature REF structure Ref : REF
Common operations on references.
The type ref and its constructor, as well as the functions !, := and :=: are available in the top-level environment.
See also: General
signature REF = sig datatype ref = datatype ref type 'a t = 'a ref val ! : 'a ref -> 'a val := : 'a ref * 'a -> unit val :=: : 'a ref * 'a ref -> unit val exchange : 'a ref * 'a -> 'a val app : ('a -> unit) -> 'a ref -> unit val map : ('a -> 'b) -> 'a ref -> 'b ref val modify : ('a -> 'a) -> 'a ref -> unit val equal : 'a ref * 'a ref -> bool end
The type of mutable references.
Returns the value referred to by re.
Makes the reference re refer to value a.
Swaps the values referred to by the references re1 and re2.
Makes the reference re refer to value a and returns the previously referred to value in a single atomic operation. This function can be used to program mutexes and similar locking mechanisms.
Applies the function f to the value referred to by the reference re. Equivalent to f (!re).
Creates a new reference that refers to the value f a, where a is the value referred to to by re. Equivalent to ref (f (!re)).
Makes the reference re refer to the value f a, where a is the value previously referred to. Note that this is not an atomic operation, since f might perform arbitrary computations. As long as no unconditional assignments are performed in between, it is guaranteed that no thread can access the value referred to before the operation completes, however. The reference refers to a future of f a until that point. Ignoring concurrency issues, the above expression is equivalent to re := f (!re).
An explicit equality function on references. Equivalent to op=.