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Postings from September 2023
On 2023-09-08 16:27, Dave Mitchell wrote:
> Internally, perl is mainly based around Scalar Value (SV) structures,
> which hold a single value. Entities such as $x or $a[0] are all SVs. These
> SVs include a reference count (RC) field which, when it reaches zero,
> triggers the freeing of the SV. For the basics, consider the following
> code:
>
> sub f {
> my $x = ...;
> my $y = ...;
> return \$y;
> }
> my $ref = f();
>
> On return from the function, the SV associated with $x is freed in a
> timely manner. This is because its RC starts as 1, and is reduced to 0 on
> scope exit. Conversely, the SV bound to $y has its RC increased to 2 by a
> reference being taken to it, then back down to 1 when $y goes out of
> scope. So it lives on, accessible as $$ref. This is all good.
<mode=pedantic>
Unless something like:
my $y= sub { $x };
</>
> [...] Thus items in @_ are in danger of being prematurely freed.
On @_, I remember splice() behaving different from shift(),
which could easily hurt your debugging experience.
I then refactored many splice() calls to shifts.
And never spliced @_ again.
> It is intended that eventually, PERL_RC_STACK will become the default,
> and then the only, build option.
Yes please.
-- Ruud
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