Re: [Caml-list] Concatenation of static strings?

From: "Ashish Agarwal" <agarwal1975@gmail.com>
To: caml-list@yquem.inria.fr
Cc: david.baelde@ens-lyon.org
Subject: Re: [Caml-list] Concatenation of static strings?
Date: Thu, 24 Jan 2008 18:02:48 -0500	[thread overview]
Message-ID: <d8be5ae20801241502q5190bcceje287e1f224d5648a@mail.gmail.com> (raw)
In-Reply-To: <53c655920801190255p71346ac9ka45adf0e1cef2d17@mail.gmail.com>

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I was hoping there would be some follow up discussion on the code below, but
haven't seen anything yet. Can someone please clarify why this is not
considered a bug (or is it). Given that s is locally scoped within f, I do
not see why f returns different answers.

> # let f () = let s = "bla" in let c = s.[0] in s.[0] <- 'c' ; c ;;
> val f : unit -> char = <fun>
> # f () ;;
> - : char = 'b'
> # f () ;;
> - : char = 'c'

On Jan 19, 2008 5:55 AM, David Baelde <david.baelde@gmail.com> wrote:
> Nice, I didn't know about the stripping of the first whitespaces.
>
> Speaking of static strings, the static string allocation done by OCaml
> is not compatible with the mutability of strings. I've been told that
> the issue was raised a long time ago, so I'm not filing this as a bug,
> but since I could not find any information on the web I thought
> someone here might be able to recall what motivated the decision in
> former discussions. Maybe the issue is considered a little price to
> pay for the optimization, since we rarely use string mutations..
>
> The issue can be witnessed with the following code, on 3.10, either in
> the interactive loop or with any compiler:
>
> # let f () = let s = "bla" in let c = s.[0] in s.[0] <- 'c' ; c ;;
> val f : unit -> char = <fun>
> # f () ;;
> - : char = 'b'
> # f () ;;
> - : char = 'c'
>
> This is to be contrasted with arrays, which are mutable too but not
> statically allocated as for strings (let f () = let s =
> [|'b';'l';'a'|] in let c = s.(0) in s.(0) <- 'c' ; c).
>
> And for Erik, a test that tells us that concatenations are not done
statically:
>
> # let f () = let s = "b"^"la" in let c = s.[0] in s.[0] <- 'c' ; c ;;
> val f : unit -> char = <fun>
> # f () ;;
> - : char = 'b'
> # f () ;;
> - : char = 'b'
>
> Cheers,
>
> David
>
>
>
>
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