Provided by: ocaml-nox_4.05.0-10ubuntu1_amd64 
NAME
Bytes - Byte sequence operations.
Module
Module Bytes
Documentation
Module Bytes
: sig end
Byte sequence operations.
A byte sequence is a mutable data structure that contains a fixed-length sequence of bytes. Each byte can
be indexed in constant time for reading or writing.
Given a byte sequence s of length l , we can access each of the l bytes of s via its index in the
sequence. Indexes start at 0 , and we will call an index valid in s if it falls within the range
[0...l-1] (inclusive). A position is the point between two bytes or at the beginning or end of the
sequence. We call a position valid in s if it falls within the range [0...l] (inclusive). Note that the
byte at index n is between positions n and n+1 .
Two parameters start and len are said to designate a valid range of s if len >= 0 and start and start+len
are valid positions in s .
Byte sequences can be modified in place, for instance via the set and blit functions described below.
See also strings (module String ), which are almost the same data structure, but cannot be modified in
place.
Bytes are represented by the OCaml type char .
Since 4.02.0
val length : bytes -> int
Return the length (number of bytes) of the argument.
val get : bytes -> int -> char
get s n returns the byte at index n in argument s .
Raise Invalid_argument if n is not a valid index in s .
val set : bytes -> int -> char -> unit
set s n c modifies s in place, replacing the byte at index n with c .
Raise Invalid_argument if n is not a valid index in s .
val create : int -> bytes
create n returns a new byte sequence of length n . The sequence is uninitialized and contains arbitrary
bytes.
Raise Invalid_argument if n < 0 or n > Sys.max_string_length .
val make : int -> char -> bytes
make n c returns a new byte sequence of length n , filled with the byte c .
Raise Invalid_argument if n < 0 or n > Sys.max_string_length .
val init : int -> (int -> char) -> bytes
Bytes.init n f returns a fresh byte sequence of length n , with character i initialized to the result of
f i (in increasing index order).
Raise Invalid_argument if n < 0 or n > Sys.max_string_length .
val empty : bytes
A byte sequence of size 0.
val copy : bytes -> bytes
Return a new byte sequence that contains the same bytes as the argument.
val of_string : string -> bytes
Return a new byte sequence that contains the same bytes as the given string.
val to_string : bytes -> string
Return a new string that contains the same bytes as the given byte sequence.
val sub : bytes -> int -> int -> bytes
sub s start len returns a new byte sequence of length len , containing the subsequence of s that starts
at position start and has length len .
Raise Invalid_argument if start and len do not designate a valid range of s .
val sub_string : bytes -> int -> int -> string
Same as sub but return a string instead of a byte sequence.
val extend : bytes -> int -> int -> bytes
extend s left right returns a new byte sequence that contains the bytes of s , with left uninitialized
bytes prepended and right uninitialized bytes appended to it. If left or right is negative, then bytes
are removed (instead of appended) from the corresponding side of s .
Raise Invalid_argument if the result length is negative or longer than Sys.max_string_length bytes.
val fill : bytes -> int -> int -> char -> unit
fill s start len c modifies s in place, replacing len characters with c , starting at start .
Raise Invalid_argument if start and len do not designate a valid range of s .
val blit : bytes -> int -> bytes -> int -> int -> unit
blit src srcoff dst dstoff len copies len bytes from sequence src , starting at index srcoff , to
sequence dst , starting at index dstoff . It works correctly even if src and dst are the same byte
sequence, and the source and destination intervals overlap.
Raise Invalid_argument if srcoff and len do not designate a valid range of src , or if dstoff and len do
not designate a valid range of dst .
val blit_string : string -> int -> bytes -> int -> int -> unit
blit src srcoff dst dstoff len copies len bytes from string src , starting at index srcoff , to byte
sequence dst , starting at index dstoff .
Raise Invalid_argument if srcoff and len do not designate a valid range of src , or if dstoff and len do
not designate a valid range of dst .
val concat : bytes -> bytes list -> bytes
concat sep sl concatenates the list of byte sequences sl , inserting the separator byte sequence sep
between each, and returns the result as a new byte sequence.
Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.
val cat : bytes -> bytes -> bytes
cat s1 s2 concatenates s1 and s2 and returns the result as new byte sequence.
Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.
val iter : (char -> unit) -> bytes -> unit
iter f s applies function f in turn to all the bytes of s . It is equivalent to f (get s 0); f (get s
1); ...; f (get s (length s - 1)); () .
val iteri : (int -> char -> unit) -> bytes -> unit
Same as Bytes.iter , but the function is applied to the index of the byte as first argument and the byte
itself as second argument.
val map : (char -> char) -> bytes -> bytes
map f s applies function f in turn to all the bytes of s (in increasing index order) and stores the
resulting bytes in a new sequence that is returned as the result.
val mapi : (int -> char -> char) -> bytes -> bytes
mapi f s calls f with each character of s and its index (in increasing index order) and stores the
resulting bytes in a new sequence that is returned as the result.
val trim : bytes -> bytes
Return a copy of the argument, without leading and trailing whitespace. The bytes regarded as whitespace
are the ASCII characters ' ' , '\012' , '\n' , '\r' , and '\t' .
val escaped : bytes -> bytes
Return a copy of the argument, with special characters represented by escape sequences, following the
lexical conventions of OCaml. All characters outside the ASCII printable range (32..126) are escaped, as
well as backslash and double-quote.
Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.
val index : bytes -> char -> int
index s c returns the index of the first occurrence of byte c in s .
Raise Not_found if c does not occur in s .
val index_opt : bytes -> char -> int option
index_opt s c returns the index of the first occurrence of byte c in s or None if c does not occur in s .
Since 4.05
val rindex : bytes -> char -> int
rindex s c returns the index of the last occurrence of byte c in s .
Raise Not_found if c does not occur in s .
val rindex_opt : bytes -> char -> int option
rindex_opt s c returns the index of the last occurrence of byte c in s or None if c does not occur in s .
Since 4.05
val index_from : bytes -> int -> char -> int
index_from s i c returns the index of the first occurrence of byte c in s after position i . Bytes.index
s c is equivalent to Bytes.index_from s 0 c .
Raise Invalid_argument if i is not a valid position in s . Raise Not_found if c does not occur in s
after position i .
val index_from_opt : bytes -> int -> char -> int option
index_from _opts i c returns the index of the first occurrence of byte c in s after position i or None if
c does not occur in s after position i . Bytes.index_opt s c is equivalent to Bytes.index_from_opt s 0 c
.
Raise Invalid_argument if i is not a valid position in s .
Since 4.05
val rindex_from : bytes -> int -> char -> int
rindex_from s i c returns the index of the last occurrence of byte c in s before position i+1 . rindex s
c is equivalent to rindex_from s (Bytes.length s - 1) c .
Raise Invalid_argument if i+1 is not a valid position in s . Raise Not_found if c does not occur in s
before position i+1 .
val rindex_from_opt : bytes -> int -> char -> int option
rindex_from_opt s i c returns the index of the last occurrence of byte c in s before position i+1 or None
if c does not occur in s before position i+1 . rindex_opt s c is equivalent to rindex_from s
(Bytes.length s - 1) c .
Raise Invalid_argument if i+1 is not a valid position in s .
Since 4.05
val contains : bytes -> char -> bool
contains s c tests if byte c appears in s .
val contains_from : bytes -> int -> char -> bool
contains_from s start c tests if byte c appears in s after position start . contains s c is equivalent
to contains_from s 0 c .
Raise Invalid_argument if start is not a valid position in s .
val rcontains_from : bytes -> int -> char -> bool
rcontains_from s stop c tests if byte c appears in s before position stop+1 .
Raise Invalid_argument if stop < 0 or stop+1 is not a valid position in s .
val uppercase : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are deprecated.
Return a copy of the argument, with all lowercase letters translated to uppercase, including accented
letters of the ISO Latin-1 (8859-1) character set.
val lowercase : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are deprecated.
Return a copy of the argument, with all uppercase letters translated to lowercase, including accented
letters of the ISO Latin-1 (8859-1) character set.
val capitalize : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are deprecated.
Return a copy of the argument, with the first character set to uppercase, using the ISO Latin-1 (8859-1)
character set..
val uncapitalize : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are deprecated.
Return a copy of the argument, with the first character set to lowercase, using the ISO Latin-1 (8859-1)
character set..
val uppercase_ascii : bytes -> bytes
Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII
character set.
Since 4.03.0
val lowercase_ascii : bytes -> bytes
Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII
character set.
Since 4.03.0
val capitalize_ascii : bytes -> bytes
Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character
set.
Since 4.03.0
val uncapitalize_ascii : bytes -> bytes
Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character
set.
Since 4.03.0
type t = bytes
An alias for the type of byte sequences.
val compare : t -> t -> int
The comparison function for byte sequences, with the same specification as Pervasives.compare . Along
with the type t , this function compare allows the module Bytes to be passed as argument to the functors
Set.Make and Map.Make .
val equal : t -> t -> bool
The equality function for byte sequences.
Since 4.03.0
=== Unsafe conversions (for advanced users) This section describes unsafe, low-level conversion functions
between bytes and string. They do not copy the internal data; used improperly, they can break the
immutability invariant on strings provided by the -safe-string option. They are available for expert
library authors, but for most purposes you should use the always-correct Bytes.to_string and
Bytes.of_string instead. ===
val unsafe_to_string : bytes -> string
Unsafely convert a byte sequence into a string.
To reason about the use of unsafe_to_string , it is convenient to consider an "ownership" discipline. A
piece of code that manipulates some data "owns" it; there are several disjoint ownership modes,
including:
-Unique ownership: the data may be accessed and mutated
-Shared ownership: the data has several owners, that may only access it, not mutate it.
Unique ownership is linear: passing the data to another piece of code means giving up ownership (we
cannot write the data again). A unique owner may decide to make the data shared (giving up mutation
rights on it), but shared data may not become uniquely-owned again.
unsafe_to_string s can only be used when the caller owns the byte sequence s -- either uniquely or as
shared immutable data. The caller gives up ownership of s , and gains ownership of the returned string.
There are two valid use-cases that respect this ownership discipline:
1. Creating a string by initializing and mutating a byte sequence that is never changed after
initialization is performed.
let string_init len f : string = let s = Bytes.create len in for i = 0 to len - 1 do Bytes.set s i (f i)
done; Bytes.unsafe_to_string s
This function is safe because the byte sequence s will never be accessed or mutated after
unsafe_to_string is called. The string_init code gives up ownership of s , and returns the ownership of
the resulting string to its caller.
Note that it would be unsafe if s was passed as an additional parameter to the function f as it could
escape this way and be mutated in the future -- string_init would give up ownership of s to pass it to f
, and could not call unsafe_to_string safely.
We have provided the String.init , String.map and String.mapi functions to cover most cases of building
new strings. You should prefer those over to_string or unsafe_to_string whenever applicable.
2. Temporarily giving ownership of a byte sequence to a function that expects a uniquely owned string and
returns ownership back, so that we can mutate the sequence again after the call ended.
let bytes_length (s : bytes) = String.length (Bytes.unsafe_to_string s)
In this use-case, we do not promise that s will never be mutated after the call to bytes_length s . The
String.length function temporarily borrows unique ownership of the byte sequence (and sees it as a string
), but returns this ownership back to the caller, which may assume that s is still a valid byte sequence
after the call. Note that this is only correct because we know that String.length does not capture its
argument -- it could escape by a side-channel such as a memoization combinator.
The caller may not mutate s while the string is borrowed (it has temporarily given up ownership). This
affects concurrent programs, but also higher-order functions: if String.length returned a closure to be
called later, s should not be mutated until this closure is fully applied and returns ownership.
val unsafe_of_string : string -> bytes
Unsafely convert a shared string to a byte sequence that should not be mutated.
The same ownership discipline that makes unsafe_to_string correct applies to unsafe_of_string : you may
use it if you were the owner of the string value, and you will own the return bytes in the same mode.
In practice, unique ownership of string values is extremely difficult to reason about correctly. You
should always assume strings are shared, never uniquely owned.
For example, string literals are implicitly shared by the compiler, so you never uniquely own them.
let incorrect = Bytes.unsafe_of_string hello let s = Bytes.of_string hello
The first declaration is incorrect, because the string literal hello could be shared by the compiler with
other parts of the program, and mutating incorrect is a bug. You must always use the second version,
which performs a copy and is thus correct.
Assuming unique ownership of strings that are not string literals, but are (partly) built from string
literals, is also incorrect. For example, mutating unsafe_of_string ("foo" ^ s) could mutate the shared
string foo -- assuming a rope-like representation of strings. More generally, functions operating on
strings will assume shared ownership, they do not preserve unique ownership. It is thus incorrect to
assume unique ownership of the result of unsafe_of_string .
The only case we have reasonable confidence is safe is if the produced bytes is shared -- used as an
immutable byte sequence. This is possibly useful for incremental migration of low-level programs that
manipulate immutable sequences of bytes (for example Marshal.from_bytes ) and previously used the string
type for this purpose.