RE: [Caml-list] Differences between Array and Strings

[David Allsopp <dra-news@metastack.com>]

Radu Grigore wrote:
> On Friday, April 29, 2011 12:51:59 PM UTC+1, louis....@ens.fr wrote:
> > > let l () = "1" ;;
> > > [...]
> > > l()==l();;
> > # val l : unit -> string = <fun>
> > # [...]
> > # - : bool = true
> 
> Is there a good reason for this behavior?

Whether it's good is debatable, but in most instances you don't want a fresh string being allocated each time for a constant value as it would be a waste of time and memory (most strings are used immutably).

> My first thought was that that code should behave the same as
> 
>   let f () = ref () in f () == f ()
> (A satisfying explanation would *not* involve the compiler.)

Look at the OCaml language specification - "1" is a constant and the result of that expression is the constant itself (6.7.1). [|1|] is an array expression and the result of that expression is a "1-element array, whose element(s) are initialized with the value(s) 1" (roughly quoting section 6.7.3). i.e. an array expression implies the creation of the array as its result but a constant evaluation does not.

C behaves in the same (or at least in a very similar) way... not that that could ever be used as a justification for behaviour in a sane language like OCaml ;o)
 

David