XS: how to destroy HV* that was used internally?

OlegG has asked for the wisdom of the Perl Monks concerning the following question:

Suppose I have following class implemented with XS

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "ppport.h"

typedef struct {
    HV* set;
    char foo;
} My_Class;

MODULE = My::Class    PACKAGE = My::Class

SV*
new(char* class)
    PREINIT:
        My_Class *self;
    CODE:
        Newx(self, 1, My_Class);
        self->set = newHV();
        self->foo = 0;

        RETVAL = newSV(0);
        sv_setref_pv(RETVAL, class, (void *)self);
    OUTPUT:
        RETVAL

void
DESTROY(My_Class *self)
    CODE:
        /* HOW TO DESTROY self->set HERE*/
        Safefree(self);
[download]

Where I'll use self->set internally, which type is HV*. In the constructor (new) newHV() creates HV with reference count 1. So, as I understand, to be destroyed reference count should be decreased to 0. But as I found we have only SvREFCNT_dec() which argument may be SV* and not HV*.

So, what is a solution here?
May be I just need to call Safefree(self->set)?
Or get reference to self->set into SV* variable and call SvREFCNT_dec on it?

Comment on XS: how to destroy HV* that was used internally? Download Code

Replies are listed 'Best First'.
Re: XS: how to destroy HV* that was used internally? by salva (Canon) on Sep 18, 2014 at 07:49 UTC
`SvREFCNT_dec((SV*)hv);` All internal Perl data structures are derived from SV, so that you can do thinks like that.	[reply] [d/l]
Re^2: XS: how to destroy HV* that was used internally? by OlegG (Monk) on Sep 18, 2014 at 08:43 UTC
Thank you! Also found that for me it works without type casting. But, ok, I'll use it And after all I found similar question on stackoverflow with similar answer.	[reply]
Re^3: XS: how to destroy HV* that was used internally? by ikegami (Patriarch) on Sep 18, 2014 at 14:07 UTC
That's because `SvREFCNT_dec` already casts for you. In fact, it casts in a way that will detect if the input was `const`, so doing `SvREFCNT_dec((SV)hv)` instead of `SvREFCNT_dec(hv)` is actually harmful. If you ever use `(SV)x`, consider using `MUTABLE_SV(x)` instead.	[reply] [d/l] [select]