430 lines
17 KiB
OCaml
430 lines
17 KiB
OCaml
(***********************************************************************)
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(* *)
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(* OCaml *)
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(* *)
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(* Xavier Leroy, projet Cristal, INRIA Rocquencourt *)
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(* *)
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(* Copyright 1996 Institut National de Recherche en Informatique et *)
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(* en Automatique. All rights reserved. This file is distributed *)
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(* under the terms of the GNU Library General Public License, with *)
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(* the special exception on linking described in file ../LICENSE. *)
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(* *)
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(***********************************************************************)
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(** Byte sequence operations.
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A byte sequence is a mutable data structure that contains a
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fixed-length sequence of bytes. Each byte can be indexed in
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constant time for reading or writing.
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Given a byte sequence [s] of length [l], we can access each of the
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[l] bytes of [s] via its index in the sequence. Indexes start at
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[0], and we will call an index valid in [s] if it falls within the
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range [[0...l-1]] (inclusive). A position is the point between two
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bytes or at the beginning or end of the sequence. We call a
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position valid in [s] if it falls within the range [[0...l]]
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(inclusive). Note that the byte at index [n] is between positions
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[n] and [n+1].
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Two parameters [start] and [len] are said to designate a valid
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range of [s] if [len >= 0] and [start] and [start+len] are valid
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positions in [s].
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Byte sequences can be modified in place, for instance via the [set]
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and [blit] functions described below. See also strings (module
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{!String}), which are almost the same data structure, but cannot be
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modified in place.
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Bytes are represented by the OCaml type [char].
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@since 4.02.0
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*)
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external length : bytes -> int = "%string_length"
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(** Return the length (number of bytes) of the argument. *)
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external get : bytes -> int -> char = "%string_safe_get"
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(** [get s n] returns the byte at index [n] in argument [s].
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Raise [Invalid_argument] if [n] not a valid index in [s]. *)
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external set : bytes -> int -> char -> unit = "%string_safe_set"
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(** [set s n c] modifies [s] in place, replacing the byte at index [n]
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with [c].
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Raise [Invalid_argument] if [n] is not a valid index in [s]. *)
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external create : int -> bytes = "caml_create_string"
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(** [create n] returns a new byte sequence of length [n]. The
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sequence is uninitialized and contains arbitrary bytes.
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Raise [Invalid_argument] if [n < 0] or [n > ]{!Sys.max_string_length}. *)
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val make : int -> char -> bytes
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(** [make n c] returns a new byte sequence of length [n], filled with
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the byte [c].
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Raise [Invalid_argument] if [n < 0] or [n > ]{!Sys.max_string_length}. *)
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val init : int -> (int -> char) -> bytes
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(** [Bytes.init n f] returns a fresh byte sequence of length [n], with
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character [i] initialized to the result of [f i] (in increasing
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index order).
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Raise [Invalid_argument] if [n < 0] or [n > ]{!Sys.max_string_length}. *)
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val empty : bytes
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(** A byte sequence of size 0. *)
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val copy : bytes -> bytes
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(** Return a new byte sequence that contains the same bytes as the
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argument. *)
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val of_string : string -> bytes
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(** Return a new byte sequence that contains the same bytes as the
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given string. *)
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val to_string : bytes -> string
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(** Return a new string that contains the same bytes as the given byte
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sequence. *)
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val sub : bytes -> int -> int -> bytes
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(** [sub s start len] returns a new byte sequence of length [len],
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containing the subsequence of [s] that starts at position [start]
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and has length [len].
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Raise [Invalid_argument] if [start] and [len] do not designate a
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valid range of [s]. *)
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val sub_string : bytes -> int -> int -> string
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(** Same as [sub] but return a string instead of a byte sequence. *)
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val extend : bytes -> int -> int -> bytes
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(** [extend s left right] returns a new byte sequence that contains
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the bytes of [s], with [left] uninitialized bytes prepended and
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[right] uninitialized bytes appended to it. If [left] or [right]
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is negative, then bytes are removed (instead of appended) from
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the corresponding side of [s].
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Raise [Invalid_argument] if the result length is negative or
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longer than {!Sys.max_string_length} bytes. *)
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val fill : bytes -> int -> int -> char -> unit
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(** [fill s start len c] modifies [s] in place, replacing [len]
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characters with [c], starting at [start].
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Raise [Invalid_argument] if [start] and [len] do not designate a
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valid range of [s]. *)
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val blit : bytes -> int -> bytes -> int -> int -> unit
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(** [blit src srcoff dst dstoff len] copies [len] bytes from sequence
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[src], starting at index [srcoff], to sequence [dst], starting at
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index [dstoff]. It works correctly even if [src] and [dst] are the
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same byte sequence, and the source and destination intervals
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overlap.
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Raise [Invalid_argument] if [srcoff] and [len] do not
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designate a valid range of [src], or if [dstoff] and [len]
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do not designate a valid range of [dst]. *)
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val blit_string : string -> int -> bytes -> int -> int -> unit
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(** [blit src srcoff dst dstoff len] copies [len] bytes from string
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[src], starting at index [srcoff], to byte sequence [dst],
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starting at index [dstoff].
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Raise [Invalid_argument] if [srcoff] and [len] do not
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designate a valid range of [src], or if [dstoff] and [len]
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do not designate a valid range of [dst]. *)
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val concat : bytes -> bytes list -> bytes
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(** [concat sep sl] concatenates the list of byte sequences [sl],
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inserting the separator byte sequence [sep] between each, and
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returns the result as a new byte sequence.
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Raise [Invalid_argument] if the result is longer than
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{!Sys.max_string_length} bytes. *)
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val cat : bytes -> bytes -> bytes
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(** [cat s1 s2] concatenates [s1] and [s2] and returns the result
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as new byte sequence.
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Raise [Invalid_argument] if the result is longer than
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{!Sys.max_string_length} bytes. *)
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val iter : (char -> unit) -> bytes -> unit
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(** [iter f s] applies function [f] in turn to all the bytes of [s].
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It is equivalent to [f (get s 0); f (get s 1); ...; f (get s
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(length s - 1)); ()]. *)
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val iteri : (int -> char -> unit) -> bytes -> unit
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(** Same as {!Bytes.iter}, but the function is applied to the index of
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the byte as first argument and the byte itself as second
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argument. *)
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val map : (char -> char) -> bytes -> bytes
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(** [map f s] applies function [f] in turn to all the bytes of [s]
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(in increasing index order) and stores the resulting bytes in
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a new sequence that is returned as the result. *)
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val mapi : (int -> char -> char) -> bytes -> bytes
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(** [mapi f s] calls [f] with each character of [s] and its
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index (in increasing index order) and stores the resulting bytes
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in a new sequence that is returned as the result. *)
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val trim : bytes -> bytes
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(** Return a copy of the argument, without leading and trailing
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whitespace. The bytes regarded as whitespace are the ASCII
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characters [' '], ['\012'], ['\n'], ['\r'], and ['\t']. *)
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val escaped : bytes -> bytes
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(** Return a copy of the argument, with special characters represented
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by escape sequences, following the lexical conventions of OCaml.
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Raise [Invalid_argument] if the result is longer than
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{!Sys.max_string_length} bytes. *)
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val index : bytes -> char -> int
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(** [index s c] returns the index of the first occurrence of byte [c]
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in [s].
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Raise [Not_found] if [c] does not occur in [s]. *)
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val rindex : bytes -> char -> int
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(** [rindex s c] returns the index of the last occurrence of byte [c]
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in [s].
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Raise [Not_found] if [c] does not occur in [s]. *)
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val index_from : bytes -> int -> char -> int
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(** [index_from s i c] returns the index of the first occurrence of
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byte [c] in [s] after position [i]. [Bytes.index s c] is
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equivalent to [Bytes.index_from s 0 c].
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Raise [Invalid_argument] if [i] is not a valid position in [s].
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Raise [Not_found] if [c] does not occur in [s] after position [i]. *)
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val rindex_from : bytes -> int -> char -> int
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(** [rindex_from s i c] returns the index of the last occurrence of
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byte [c] in [s] before position [i+1]. [rindex s c] is equivalent
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to [rindex_from s (Bytes.length s - 1) c].
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Raise [Invalid_argument] if [i+1] is not a valid position in [s].
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Raise [Not_found] if [c] does not occur in [s] before position [i+1]. *)
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val contains : bytes -> char -> bool
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(** [contains s c] tests if byte [c] appears in [s]. *)
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val contains_from : bytes -> int -> char -> bool
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(** [contains_from s start c] tests if byte [c] appears in [s] after
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position [start]. [contains s c] is equivalent to [contains_from
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s 0 c].
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Raise [Invalid_argument] if [start] is not a valid position in [s]. *)
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val rcontains_from : bytes -> int -> char -> bool
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(** [rcontains_from s stop c] tests if byte [c] appears in [s] before
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position [stop+1].
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Raise [Invalid_argument] if [stop < 0] or [stop+1] is not a valid
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position in [s]. *)
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val uppercase : bytes -> bytes
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[@@ocaml.deprecated "Use Bytes.uppercase_ascii instead."]
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(** Return a copy of the argument, with all lowercase letters
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translated to uppercase, including accented letters of the ISO
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Latin-1 (8859-1) character set.
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@deprecated Functions operating on Latin-1 character set are deprecated. *)
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val lowercase : bytes -> bytes
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[@@ocaml.deprecated "Use Bytes.lowercase_ascii instead."]
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(** Return a copy of the argument, with all uppercase letters
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translated to lowercase, including accented letters of the ISO
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Latin-1 (8859-1) character set.
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@deprecated Functions operating on Latin-1 character set are deprecated. *)
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val capitalize : bytes -> bytes
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[@@ocaml.deprecated "Use Bytes.capitalize_ascii instead."]
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(** Return a copy of the argument, with the first character set to uppercase,
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using the ISO Latin-1 (8859-1) character set..
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@deprecated Functions operating on Latin-1 character set are deprecated. *)
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val uncapitalize : bytes -> bytes
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[@@ocaml.deprecated "Use Bytes.uncapitalize_ascii instead."]
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(** Return a copy of the argument, with the first character set to lowercase,
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using the ISO Latin-1 (8859-1) character set..
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@deprecated Functions operating on Latin-1 character set are deprecated. *)
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val uppercase_ascii : bytes -> bytes
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(** Return a copy of the argument, with all lowercase letters
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translated to uppercase, using the US-ASCII character set.
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@since 4.03.0 *)
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val lowercase_ascii : bytes -> bytes
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(** Return a copy of the argument, with all uppercase letters
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translated to lowercase, using the US-ASCII character set.
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@since 4.03.0 *)
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val capitalize_ascii : bytes -> bytes
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(** Return a copy of the argument, with the first character set to uppercase,
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using the US-ASCII character set.
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@since 4.03.0 *)
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val uncapitalize_ascii : bytes -> bytes
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(** Return a copy of the argument, with the first character set to lowercase,
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using the US-ASCII character set.
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@since 4.03.0 *)
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type t = bytes
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(** An alias for the type of byte sequences. *)
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val compare: t -> t -> int
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(** The comparison function for byte sequences, with the same
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specification as {!Pervasives.compare}. Along with the type [t],
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this function [compare] allows the module [Bytes] to be passed as
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argument to the functors {!Set.Make} and {!Map.Make}. *)
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val equal: t -> t -> bool
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(** The equality function for byte sequences.
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@since 4.03.0 *)
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(** {4 Unsafe conversions (for advanced users)}
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This section describes unsafe, low-level conversion functions
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between [bytes] and [string]. They do not copy the internal data;
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used improperly, they can break the immutability invariant on
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strings provided by the [-safe-string] option. They are available for
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expert library authors, but for most purposes you should use the
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always-correct {!Bytes.to_string} and {!Bytes.of_string} instead.
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*)
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val unsafe_to_string : bytes -> string
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(** Unsafely convert a byte sequence into a string.
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To reason about the use of [unsafe_to_string], it is convenient to
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consider an "ownership" discipline. A piece of code that
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manipulates some data "owns" it; there are several disjoint ownership
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modes, including:
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- Unique ownership: the data may be accessed and mutated
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- Shared ownership: the data has several owners, that may only
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access it, not mutate it.
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Unique ownership is linear: passing the data to another piece of
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code means giving up ownership (we cannot write the
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data again). A unique owner may decide to make the data shared
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(giving up mutation rights on it), but shared data may not become
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uniquely-owned again.
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[unsafe_to_string s] can only be used when the caller owns the byte
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sequence [s] -- either uniquely or as shared immutable data. The
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caller gives up ownership of [s], and gains ownership of the
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returned string.
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There are two valid use-cases that respect this ownership
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discipline:
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1. Creating a string by initializing and mutating a byte sequence
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that is never changed after initialization is performed.
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{[
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let string_init len f : string =
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let s = Bytes.create len in
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for i = 0 to len - 1 do Bytes.set s i (f i) done;
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Bytes.unsafe_to_string s
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]}
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This function is safe because the byte sequence [s] will never be
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accessed or mutated after [unsafe_to_string] is called. The
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[string_init] code gives up ownership of [s], and returns the
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ownership of the resulting string to its caller.
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Note that it would be unsafe if [s] was passed as an additional
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parameter to the function [f] as it could escape this way and be
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mutated in the future -- [string_init] would give up ownership of
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[s] to pass it to [f], and could not call [unsafe_to_string]
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safely.
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We have provided the {!String.init}, {!String.map} and
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{!String.mapi} functions to cover most cases of building
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new strings. You should prefer those over [to_string] or
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[unsafe_to_string] whenever applicable.
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2. Temporarily giving ownership of a byte sequence to a function
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that expects a uniquely owned string and returns ownership back, so
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that we can mutate the sequence again after the call ended.
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{[
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let bytes_length (s : bytes) =
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String.length (Bytes.unsafe_to_string s)
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]}
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In this use-case, we do not promise that [s] will never be mutated
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after the call to [bytes_length s]. The {!String.length} function
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temporarily borrows unique ownership of the byte sequence
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(and sees it as a [string]), but returns this ownership back to
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the caller, which may assume that [s] is still a valid byte
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sequence after the call. Note that this is only correct because we
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know that {!String.length} does not capture its argument -- it could
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escape by a side-channel such as a memoization combinator.
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The caller may not mutate [s] while the string is borrowed (it has
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temporarily given up ownership). This affects concurrent programs,
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but also higher-order functions: if [String.length] returned
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a closure to be called later, [s] should not be mutated until this
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closure is fully applied and returns ownership.
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*)
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val unsafe_of_string : string -> bytes
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(** Unsafely convert a shared string to a byte sequence that should
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not be mutated.
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The same ownership discipline that makes [unsafe_to_string]
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correct applies to [unsafe_of_string]: you may use it if you were
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the owner of the [string] value, and you will own the return
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[bytes] in the same mode.
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In practice, unique ownership of string values is extremely
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difficult to reason about correctly. You should always assume
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strings are shared, never uniquely owned.
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For example, string literals are implicitly shared by the
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compiler, so you never uniquely own them.
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{[
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let incorrect = Bytes.unsafe_of_string "hello"
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let s = Bytes.of_string "hello"
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]}
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The first declaration is incorrect, because the string literal
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["hello"] could be shared by the compiler with other parts of the
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program, and mutating [incorrect] is a bug. You must always use
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the second version, which performs a copy and is thus correct.
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Assuming unique ownership of strings that are not string
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literals, but are (partly) built from string literals, is also
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incorrect. For example, mutating [unsafe_of_string ("foo" ^ s)]
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could mutate the shared string ["foo"] -- assuming a rope-like
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representation of strings. More generally, functions operating on
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strings will assume shared ownership, they do not preserve unique
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ownership. It is thus incorrect to assume unique ownership of the
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result of [unsafe_of_string].
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The only case we have reasonable confidence is safe is if the
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produced [bytes] is shared -- used as an immutable byte
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sequence. This is possibly useful for incremental migration of
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low-level programs that manipulate immutable sequences of bytes
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(for example {!Marshal.from_bytes}) and previously used the
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[string] type for this purpose.
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*)
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(**/**)
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(* The following is for system use only. Do not call directly. *)
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external unsafe_get : bytes -> int -> char = "%string_unsafe_get"
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external unsafe_set : bytes -> int -> char -> unit = "%string_unsafe_set"
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external unsafe_blit :
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bytes -> int -> bytes -> int -> int -> unit
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= "caml_blit_string" "noalloc"
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external unsafe_fill :
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bytes -> int -> int -> char -> unit = "caml_fill_string" "noalloc"
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