diff options
| -rw-r--r-- | stdlib/string.mli | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/stdlib/string.mli b/stdlib/string.mli index 94d600e62..efdecea48 100644 --- a/stdlib/string.mli +++ b/stdlib/string.mli @@ -14,6 +14,7 @@ (* $Id$ *) (** String operations. + Given a string [s] of length [l], we call character number in [s] the index of a character in [s]. Indexes start at [0], and we will call a character number valid in [s] if it falls within the range @@ -26,22 +27,29 @@ substring of [s] if [len >= 0] and [start] and [start+len] are valid positions in [s]. - One should be aware that string constants are shared: + Caml strings can be modified in place, for instance via the + {!String.set} and {!String.blit} functions described below. This + possibility should be used rarely and with much care, however, since + both the Caml compiler and most Caml libraries share strings as if + they were immutable, rather than copying them. In particular, + string literals are shared: a single copy of the string is created + at program loading time and returned by all evaluations of the + string literal. Consider for example: {[ - # let f () = "foo";; val f : unit -> string = <fun> # (f ()).[0] <- 'b';; _ : unit = () # f ();; _ : string = "boo" - ]} - Many functions from the standard library may return string constants. - Users should use [String.copy] to make sure they are not modifying a - shared string constant. + Likewise, many functions from the standard library can return string + literals or one of their string arguments. Therefore, the returned strings + must not be modified directly. If mutation is absolutely necessary, + it should be performed on a fresh copy of the string, as produced by + {!String.copy}. *) |