I do care. To quote from the OP.

What else should I be catering for? (Preferably with hints on how to detect and handle it :).

And from another post later in the thread:

Dealing with scalars that might be NVs, IVs, UVs and readonly is only the first part of the exercise. There are also RVs, tied scalars, blessed scalars etc. When I posted, I was hoping for insights into dealing with these also. I never expected to get hung up on dealing with readonly inputs.

I'm also curious if SvPVX() can yield you some pointers to interesting things, ...

I think I may be misunderstanding you? I look up SvPVX() and found

#define SvPVX(sv)  ((XPV*)  SvANY(sv))->xpv_pv
[download]

And SvANY() is

#define SvANY(sv)    (sv)->sv_any
[download]

Which doesn't clarify much?

sv_catsv handles "get magic", so overloaded strings shouldn't be a problem. It doesn't handle "set magic", though, so if the first scalar is tied and it does something funny with STORE -- like store an uppercased version of the input -- that won't happen.

#!/usr/bin/perl
package TiedScalar;
use strict;
use warnings;
use base qw( Tie::Scalar );

sub TIESCALAR {
    my ( $classname, $initial_value ) = @_; 
    return bless \$initial_value, __PACKAGE__;
}

sub FETCH { return ${ +shift } }

sub STORE { 
    my ($self, $value) = @_;
    $$self = uc($value);
}

package main;
use strict;
use warnings;

use Inline C => << '__C__', NAME => 'test', CLEAN_AFTER_BUILD => 0;
#include <stdio.h>

SV* test( SV *a, SV *b ) {
    if( SvREADONLY( a ) )
        a = newSVpv( SvPVX( a ), 0 );
    else
       SvREFCNT_inc( a );

    if( !SvOK( a ) )
        sv_setpvn( a, "", 0 );

    sv_catsv( a, b );
    return a;
}

__C__

my ( $q, $p );

tie $q, 'TiedScalar', "bill"; 
tie $p, 'TiedScalar', "fred"; 

print test( $q, $p ) . "\n"; 

$q .= $p;
print "$q\n";
[download]

As for the exotic values via SvPVX, I can't think of an example that would cause any more problems than say, packed ints.

As for nulls in read-only scalars, I would think sv_catsv would handle that case, no?

As for nulls in read-only scalars, I would think sv_catsv would handle that case, no?

This doesn't

a = newSVpv( SvPVX( a ), 0 );
[download]

It is another place that doesn't handle magic either.

I don't know what you mean by "any more problems than say, packed ints". Does this mean you've thought of a case where SvPVX() doesn't return a pointer to the string value of a scalar? Surely there are some. Isn't that problem enough?

- tye        

OK, acknowledged. That line should really be...

a = newSVsv(a);
[download]

--
Marvin Humphrey
Rectangular Research ― http://www.rectangular.com