Re: Blessing with unknown classnames (updated x 2)

> What happens when a ref is blessed into a non-existent class. Afterall bless's 2nd argument is a string and not a package qualifier.

You don't reveal the answer on purpose?

The package/class is created.

you can check by inspecting the %main:: stash, where all packages live

  DB<30>  bless [1,2,3] => 'nonexistent'

  DB<31> p $main::{'nonexistent::'}
*main::nonexistent::
  DB<32>
[download]

and I think ° it's not only the typeglob but also the stash %nonexistent:: is created, which will result in several hundreds of bytes of overhead

  DB<32> p *{$main::{'nonexistent::'}}{HASH}
HASH(0x2e7b830)
  DB<33>
[download]

So better don't try to automatically bless into millions of pseudo packages ...

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery}

PS: According to some statistics this was my 10000st post here ... frightening.

update

°) I couldn't find a pure Perl way to check if the HASH slot of a package:: like entry is filled, without autovivifying that package. It's a very quantum-brainf*ck thing, the observation is changing the result.

Update

For clarification: using bless to solve the semipredicate problem is totally fine in my eyes.

Just be aware that the package will exist. And this globally.

So you should care about a naming convention in your own namespace.

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Re^2: Blessing with unknown classnames by choroba (Cardinal) on Apr 01, 2021 at 23:44 UTC
Run `perl -we 'bless {}, "A$_" for 1 .. 2000000'` [download] and what your memory meter. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re^3: Blessing with unknown classnames by Discipulus (Canon) on Apr 02, 2021 at 07:45 UTC
Nice, on my windows 10 box each package seems to eat ~1k of memory: `perl -we "sub mem{system qq(tasklist /FI \"PID eq $$\"\|findstr perl)}; + mem();bless {}, qq(A$_) for 1 .. 1000000;mem()" perl.exe 29356 Console 1 6 +.616 K perl.exe 29356 Console 1 1.353 +.656 K` [download] and quite the same on my Linux box: `perl -we 'sub mem{system qq(cat /proc/$$/status \| grep ^VmSize)}; mem( +);bless {}, qq(A$_) for 1 .. 1000000;mem()' VmSize: 23768 kB VmSize: 1234168 kB` [download] Obviously the package is empty.. `perl -MDevel::Symdump -e "bless {},'notexisting';print Devel::Symdump- +>new('noexisting')->as_string" arrays functions hashes ios packages scalars unknowns` [download] ..holding just the `AUTOLOAD` `use strict; use warnings; my %before = %main::; bless {},'nonexistent'; my %after = %main::; foreach my $symbol (sort keys %after) { next if exists $before{$symbol}; local myglob = $after{$symbol}; if ( defined myglob{HASH} ) { my %val = %{ myglob{HASH} }; print "HASH \%$symbol = ( "; while( my ($key, $val) = each %val ) { print "$key=>'$val', "; } print ")\n" ; } } __END__ HASH %nonexistent:: = ( AUTOLOAD=>'nonexistent::AUTOLOAD', )` [download] ..but: For various obscure reasons, typeglobs are always created with a Null SV in the SCALAR slot. L* There are no rules, there are no thumbs.. Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.	[reply] [d/l] [select]
Re^4: Blessing with unknown classnames by LanX (Saint) on Apr 02, 2021 at 08:46 UTC
It doesn't matter if the package is empty, a STASH was created to hold the symbols. And the initial overhead for a hash is profound, even if it's empty. Like I said several hundreds of bytes. Furthermore do I remember someone explaining that packages which become classes receive further optimization. In order to speed up method lookup (IIRC), but I don't really know the details.. I'm not aware of any application which tries to generate a massive amount of pseudo packages, I'm just saying it might not be the best idea to create many global data structures which are never destroyed. And if you only generate a small number, take care about controlling the namespace, because they are global. Fun fact: As a side effect of my experiments I was even able to block a package name in a way that any further `package blocked_name;` would globally fail. Like: "Hey I hate Moose, if you use my module in your project you won't be able to ever use Moose later!" ;-) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^4: Blessing with unknown classnames by LanX (Saint) on Apr 03, 2021 at 01:04 UTC
> ..holding just the AUTOLOAD hmm interesting ... it's only the scalar `$AUTOLOAD` which is created and not any sub `&AUTOLOAD` And the value is `undef` I'd say that's only a random side-effect (probably bug), there is no use of `$AUTOLOAD` without `&AUTOLOAD` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^3: Blessing with unknown classnames by LanX (Saint) on Apr 03, 2021 at 01:46 UTC
FWIW using Devel::Peek to inspect the glob `*PKG::` shows the created hash-ref, too. :) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^3: Blessing with unknown classnames by LanX (Saint) on Apr 02, 2021 at 00:04 UTC
Thx! Like expected! :) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply]