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Re^4: How to identify the package of a subroutine given only a reference to it

by drclaw (Acolyte)
on Feb 02, 2022 at 00:51 UTC ( #11141039=note: print w/replies, xml ) Need Help??


in reply to Re^3: How to identify the package of a subroutine given only a reference to it
in thread How to identify the package of a subroutine given only a reference to it

I'm partial to array backed objects where applicable. But I've never actually tried a blessed code ref... until 5 minutes ago after reading your reply! It might be a good solution to my application.

Out of interest, do you have insight on how perl knows to call the underlying code ref and not a method that may or may not be in the package? An extra lookup/check must be done when called?

#eg $code_ref_obj->();#calls code ref directly $code_ref_obj->a_method(); #Call a method on the object
Thanks again for you comments
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Re^5: How to identify the package of a subroutine given only a reference to it
by LanX (Sage) on Feb 02, 2022 at 01:00 UTC
    > do you have insight on how perl knows to call the underlying code ref

    I'm not sure I understand, your demo nailed it.

    • $code_ref->(ARGS) without method name is de-referencing the code-ref.
    • $obj->method_name(ARGS) with method name is looking up the "blessed" package inside the structure of the scalar and will try to resolve the method there.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery

      My question wasn't very directional... I was wanting to know the relative performance of a blessed code ref vs a unblessed code ref

      So I put together a little benchmark comparing:

      1. calling a code ref directly
      2. blessing a code ref and calling it directly
      3. blessing a code ref and calling another method in the object

      Blessing the code ref does have a performance impact when using it as a code ref compared to an unblessed code ref. However it is cheap compared to calling a method on the object

      use strict; use warnings; use feature ":all"; use Benchmark qw<cmpthese>; my $count=$ARGV[0]//1; package SUB_TEST { sub new { bless sub {1}, __PACKAGE__} sub method { 1 } } my $obj=SUB_TEST->new(); my $sub=sub {1}; cmpthese($count, { blessed=>sub {$obj->()}, method=>sub{$obj->method()}, sub=>sub{$sub->()} } );
      Output:
      Rate method blessed sub method 18939394/s -- -30% -39% blessed 27173913/s 43% -- -12% sub 30864198/s 63% 14% --

        Benchmarking is always tricky: providing subrefs to benchmark makes it easier to get the code right, but if the target code is very fast the sub call overhead can swamp the results. Providing strings instead gets rid of that overhead, but is far harder to get right because the code will be evalled in a different context.

        Using a string version of the benchmark, I confirm your results on my system perl (5.28) but the difference almost entirely disappears with 5.34 (which is also quite a bit faster overall):

        % perl benchmark Rate methodic blessy direct methodic 16017006/s -- -31% -40% blessy 23189661/s 45% -- -13% direct 26673243/s 67% 15% -- % /opt/v5.34.0/bin/perl benchmark Rate methodic blessy direct methodic 21275455/s -- -39% -39% blessy 34927866/s 64% -- -0% direct 35023414/s 65% 0% -- % cat benchmark use strict; use warnings; use Benchmark; our($mcount, $bcount, $dcount) = (0) x 3; package Methodic { sub new { return bless {} } sub method { ++$::mcount } }; package Blessy { sub new { return bless sub { ++$::bcount } } }; sub direct { ++$::dcount } our $methodic = Methodic->new; our $blessy = Blessy->new; our $direct = \&direct; Benchmark::cmpthese(-1, { methodic => q{$::methodic->method()}, blessy => q{$::blessy->()}, direct => q{$::direct->()}, }); %

        Note also that if you look at the counts after the benchmark has run, you'll see larger number than those that were reported. IIRC this is because Benchmark tries to calculate the overhead of calling and adjust results for it, and should not be taken as a sign that it can't count. :)

        > Blessing the code ref does have a performance impact when using it as a code ref compared to an unblessed code ref.

        I doubt this, I can't think of reason why this should happen

        I think your benchmark could be flawed.

        Cheers Rolf
        (addicted to the Perl Programming Language :)
        Wikisyntax for the Monastery

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