Module Stdlib.Obj

Operations on internal representations of values.

Not for the casual user.

type t
external repr : 'a -> t = "%identity"
external obj : t -> 'a = "%identity"
external magic : 'a -> 'b = "%identity"
val is_block : t -> bool
external is_int : t -> bool = "%obj_is_int"
external tag : t -> int = "caml_obj_tag"
external size : t -> int = "%obj_size"
external reachable_words : t -> int = "caml_obj_reachable_words"

Computes the total size (in words, including the headers) of all heap blocks accessible from the argument. Statically allocated blocks are excluded.

external field : t -> int -> t = "%obj_field"
external set_field : t -> int -> t -> unit = "%obj_set_field"

When using flambda:

set_field MUST NOT be called on immutable blocks. (Blocks allocated in C stubs, or with new_block below, are always considered mutable.)

The same goes for set_double_field and set_tag. However, for set_tag, in the case of immutable blocks where the middle-end optimizers never see code that discriminates on their tag (for example records), the operation should be safe. Such uses are nonetheless discouraged.

For experts only: set_field et al can be made safe by first wrapping the block in Sys.opaque_identity, so any information about its contents will not be propagated.

external set_tag : t -> int -> unit = "caml_obj_set_tag"
val double_field : t -> int -> float
val set_double_field : t -> int -> float -> unit
external new_block : int -> int -> t = "caml_obj_block"
external dup : t -> t = "caml_obj_dup"
external truncate : t -> int -> unit = "caml_obj_truncate"
external add_offset : t -> Stdlib.Int32.t -> t = "caml_obj_add_offset"
val first_non_constant_constructor_tag : int
val last_non_constant_constructor_tag : int
val lazy_tag : int
val closure_tag : int
val object_tag : int
val infix_tag : int
val forward_tag : int
val no_scan_tag : int
val abstract_tag : int
val string_tag : int
val double_tag : int
val double_array_tag : int
val custom_tag : int
val final_tag : int
val int_tag : int
val out_of_heap_tag : int
val unaligned_tag : int
val extension_constructor : 'a -> extension_constructor
val extension_name : extension_constructor -> string
val extension_id : extension_constructor -> int

The following two functions are deprecated. Use module Marshal instead.

val marshal : t -> bytes
val unmarshal : bytes -> int -> t * int
module Ephemeron : sig ... end