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Strings (type
string) are now immutable by default. In-place modification must use the typebytesof byte sequences, which is distinct fromstring. This corresponds to the-safe-stringcompile-time option, which was introduced in OCaml 4.02 in 2014, and which is now the default. -
Object types can now extend a previously-defined object type, as in
<t; a: int>. -
Destructive substitution over module signatures can now express more substitutions, such as
S with type M.t := type-exprandS with module M.N := path. -
Users can now define operators that look like array indexing, e.g.
let ( .%() ) = List.nth in [0; 1; 2].%(1) -
New escape
\u{XXXX}in string literals, denoting the UTF-8 encoding of the Unicode code pointXXXX. -
Full Unicode support was added to the Windows runtime system. In particular, file names can now contain Unicode characters.
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An alternate register allocator based on linear scan can be selected with
ocamlopt -linscan. It reduces compilation time compared with the default register allocator. -
The Num library for arbitrary-precision integer and rational arithmetic is no longer part of the core distribution and can be found as a separate OPAM package.
See also: detailed list of changes.