[racket] FW: weakly held symbols?

This isn't a typo.  The docs are talking about the properties of the symbol
tables for interned and unreadable symbols.  There is no symbol table for
uninterned symbols, so it wouldn't mean anything to talk about it.

Here's what this means for an interned symbol: you can create one, and
while a reference to it exists, it stays in the symbol table.  Any time you
intern the same string, you'll get back that symbol.  However, if all
references to that symbol vanish, the symbol table is free to release that
symbol.  If anyone interns the same string again later, a new symbol will
be created.  For nearly all purposes, this is completely transparent,
because you couldn't possibly have a copy of the old symbol to compare.
There's almost no way to tell that the symbol you got before and the one
you got after were different.  The only way you'd ever know would be either
by tracking memory use statistics, or by comparing the results of something
like eq-hash-code, neither of which should be surprising to find out
behaves impurely.

Carl Eastlund


On Mon, Jan 27, 2014 at 5:53 PM, Jos Koot <jos.koot at gmail.com> wrote:

>  It appears that my previous email was not sent completely. Sorry for
> that. Here is the complete question.
>
>  Hi to all,
>
> Section "3.6 symbols" of the Racket reference manual states:
>
> Interned and unreadable symbols are only weakly held ... but a symbol maay
> disappear when ... used as the key in a weak hash table ...".
>
> I would understand:
>
> UNINTERNED and unreadable symbols are only weakly held ... but a symbol
> may disappear when ... used as the key in a weak hash table ...".
>
> May be just a typo, but as I am not sure I understand the docs well, I
> post my question here instead of posting a bug report.
>
> Greetings, Jos
>
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20140127/5666345b/attachment-0001.html>