Re: 31395511: "Don’t attempt to modify constant strings"

["João Távora" <joaotavora@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1046 bytes --]

On Sat, Jun 6, 2020 at 2:43 AM Paul Eggert <eggert@cs.ucla.edu> wrote:

> On 6/5/20 4:19 PM, João Távora wrote:
> > I totally agree it is
> > undefined behaviour to change structure of literals (quoted or
> > self-evaluating objects), also in Common Lisp, because compilers are
> > probably allowed to reuse parts of the internal structure of such
> > objects.  But that's a far cry from having two different manifestations
> > of `equal` such objects _be_ the same object, but only for compiled
> > code.
>
> I don't understand this remark, as the idea that "compilers are allowed to
> reuse
> parts" necessarily implies that (eq "a" "a") can be t if the compiler
> decides to
> reuse the string.


Depending on the implementation of sequences, it could reuse only the
later parts of the sequences to maintain uniqueness and still have


> Certainly in Common Lisp (eq "Foo" "Foo") might be true or
> false (this specific example is called out in CLtL 6.3).
>

I stand corrected.  I was simply mistaken :-)

João

[-- Attachment #2: Type: text/html, Size: 1624 bytes --]