Re: [Caml-list] Re: immutable strings (Re: Array 4 MB size limit)

[Alain Frisch <Alain.Frisch@inria.fr>]

Brian Hurt wrote:
> Note that this also eliminates an inefficiency of ocaml.  When you use a
> constant string, it has to allocate a new string for you.  Consider
> Ocaml's response to the expression:
> 
> "foo" == "foo";;
> 
> The reason ocaml returns false in the above expression is that when you
> give a constant string in an expression, Ocaml first has to make a copy
> of that string (in case you modify it), and then it returns the copy. 

This is not true. The two strings above are physically different because
the two constants appear at different location of the source.

The expression

let f () = "foo" in f () == f ()

evaluates to true. The block for "foo" is allocated only once; the
string is not copied not each time the body of f is evaluated.
As a consequence,

let f () = "foo" in (f ()).[0] <- 'F'; f ()

returns "Foo".

-- Alain