Don't write Perl code in XS. Write in XS only the parts that wrap the C library. And write the XS wrapper using a C-friendly interface (you might even want to use Inline::C to write the wrapper to encourage not trying to write Perl code in XS). Then make a nice Perl-like interface over that by writing that interface in Perl.

This will reduce how buggy your code is (XS code is so easy to write bugs in), will surely give you a more robust and Perl-friendly interface, will make it easier to maintain, enhance, and debug your code.

And even with this approach, I would avoid writing subs that try to act as both a method and as a non-method. If you want to support exporting non-method subroutines, then just have exportable tiny wrappers that call the methods (or, if there is absolutely no object data, then you can make the methods be tiny wrappers around the non-methods).

double cos( double x )
/* No need to write the trivial XS wrapper, just the declaration */
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package Math::MyWrapper;
use Math::MyWrapper::XS();
use Exporter 'import';
our @EXPORT_OK = qw< cos ... >;
sub new {
    require Math::MyWrapper::Class;
    return "Math::MyWrapper::Class";
}
sub cos {
    my( $x ) = @_;
    return Math::MyWrapper::XS::cos( $x );
}
...
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package Math::MyWrapper::Class;
use Math::MyWrapper();
for my $sub ( @Math::MyWrapper::EXPORT_OK ) {
    eval "sub $sub { Math::MyWrapper::$sub( \@_[1..\$#_] ) }; 1"
        or  die "Error building $sub method: $@\n";
}
1
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So if you want your function (be it perl or XS code) to tell the difference, you need to make the function be called in a slightly different way to make a distinction

Dave.

Well the difference is: the method call gives the instance of the object as the only argument, the function call a number (For cos: $instance->cos; or MyModule::Math::cos(42);) and thats what I try to do with sv_isobject(). But this dows not work and I don't see my error.

But this dows not work

Can you be much more specific please. In which way does it not work? Under what circumstances does it not work? Have you single-stepped that XS function under a debuggger? At what point does the behaviour deviate from what you expect? Etc.

Dave.

use strict;
use warnings;

use Inline C => Config =>
  CLEAN_AFTER_BUILD => 0,
  BUILD_NOISY => 1;

use Inline C => <<'EOC';

double wrap_cos(SV * in) {

  if(sv_isobject(in)) {
    HV *self_hv = MUTABLE_HV(SvRV(in));
    SV **callback_ptr = hv_fetchs(self_hv, "Number", 0);
    return cos(SvNV(*callback_ptr));
  }
  return cos(SvNV(in));
}

EOC

my $angle = 0.5;

my $x = {'Number' => $angle};
bless $x;

print wrap_cos($x), "\n";     # Output: 0.877582561890373
print wrap_cos($angle), "\n"; # Output: 0.877582561890373
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#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "INLINE.h"

double wrap_cos(SV * in) {

  if(sv_isobject(in)) {
    HV *self_hv = MUTABLE_HV(SvRV(in));
    SV **callback_ptr = hv_fetchs(self_hv, "Number", 0);
    return cos(SvNV(*callback_ptr));
  }
  return cos(SvNV(in));
}


MODULE = try_pl_96f2  PACKAGE = main  

PROTOTYPES: DISABLE


double
wrap_cos (in)
    SV *    in
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I implemented your snippet in my XS and it worked properly. Then I started again to test why my code didn't work. It was simply a problem of declaration: if I declare the SV * zahl inside the if-else statement the compiler somehow doesn't get that the variable will be declared anyways and starts to throw a massive amount of errors at me. Your code did work because you avoided the declaration of this additional SV *. Somehow I feel quite dumb now. Thanks for the help, all!