perlxs new() returning undef

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

I've got a perlxs module that maps a pointer to a C struct to a perl object. Here's the typemap:

TYPEMAP
cstruct * T_OBJECT
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My question is, in my new() method, I would like to return undef on failure. What is the correct method for doing this? Does something like this work:

cstruct *
new( field )
    int field;
  CODE:
    if( something_wrong() )
    {
        /*** is this correct below??? ***/
        RETVAL = (cstruct *)&PL_sv__undef;
    }
  OUTPUT:
    RETVAL
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Is the cast above the correct way? Or should I have my constructor return an SV* and then coerce my pointer into an IV? Thanks for the help.

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(tye)Re: perlxs new() returning undef by tye (Sage) on Mar 14, 2001 at 01:09 UTC
First, I find no T_OBJECT in my typemap file. Perhaps you meant T_PTROBJ? If so, then no, `RETVAL= PL_sv__undef` isn't the thing to do. When in doubt, use the source! From typemap: `INPUT T_PTROBJ if (sv_derived_from($arg, \"${ntype}\")) { IV tmp = SvIV((SV)SvRV($arg)); $var = INT2PTR($type,tmp); } else croak(\"$var is not of type ${ntype}\") OUTPUT T_PTROBJ sv_setref_pv($arg, \"${ntype}\", (void)$var);` [download] so your code ends up doing: `sv_setref_pv(ST(0),"cstruct",(void)&PL_sv__undef);` so you'd get a new object that is a blessed reference to undef (well, unless that attempt fails, which it probably does). You have a couple of ways you can go. You could extend the typemap to handle a failure case: `OUTPUT OUTPUT T_PTROBJ if( NULL != $var ) sv_setref_pv($arg, \"${ntype}\", (void)$var); else sv_setsv( $arg, &PL_sv__undef );` [download] Or something close to that. Update: The "other ways" I decided not to describe since they seemed inferior after I saw how easy that was. - tye (but my friends call me "Tye")	[reply] [d/l] [select]

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(tye)Re: perlxs new() returning undef
by tye (Sage) on Mar 14, 2001 at 01:09 UTC

First, I find no T_OBJECT in my typemap file. Perhaps you meant T_PTROBJ?

If so, then no, RETVAL= PL_sv__undef isn't the thing to do. When in doubt, use the source! From typemap:

INPUT
T_PTROBJ
    if (sv_derived_from($arg, \"${ntype}\")) {
        IV tmp = SvIV((SV*)SvRV($arg));
        $var = INT2PTR($type,tmp);
    }
    else
        croak(\"$var is not of type ${ntype}\")

OUTPUT
T_PTROBJ
    sv_setref_pv($arg, \"${ntype}\", (void*)$var);
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sv_setref_pv(ST(0),"cstruct",(void*)&PL_sv__undef);

undef

You have a couple of ways you can go. You could extend the typemap to handle a failure case:

OUTPUT
OUTPUT
T_PTROBJ
    if(  NULL != $var  )
        sv_setref_pv($arg, \"${ntype}\", (void*)$var);
    else
        sv_setsv( $arg, &PL_sv__undef );
[download]

Or something close to that.

Update: The "other ways" I decided not to describe since they seemed inferior after I saw how easy that was.

tye

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