Re: The trap of reference numification

[itub]

in reply to The trap of reference numification

I don't know if it's that rare; I've seen it used quite a bit to generate an object ID of some sort (stringification is also used for that). If you add that as a warning, many currently warning-free programs would start spewing lots of warnings, which might be annoying... But I agree that in principle such a warning would be useful, and I imagine the same drawbacks apply whenever a new warning is added.

[friedo]

In my experience object IDs almost always use the stringified reference as a hash key (the usual way for inside-out objects.) Or Scalar::Util::refaddr is used (as in Class::Std and PBP.)

refaddr returns the numified reference, but Scalar::Util already turns warnings off when munging that. (And SU does it in a rather bizarre way with a regex and hex instead of using direct numification for reasons that remain mysterious to me.)

I don't think there are many common uses of numified references outside those two contexts.

Update: Actually it looks like the issue with refaddr is fixed in recent versions. It uses int now.

[dragonchild]

Comparisons between objects. Depending on my mood, I'll use eq or == interchangably. Before we go ahead and do this, there needs to be considerable discussion. This will end up being a bigger change than expected.

[friedo]

I don't think anyone was proposing that it be done without major discussion. I assume that the usual erudite discourse and flamewars to light up the night sky will take place on p5p. Personally, I think the change would be worth the effort.

[Roy Johnson]

Comparisons are one thing, but I seriously doubt you do math ops on them (like in this case, using the modulus operator). If the warning recognized that situation, I suspect it would be pretty close to The Right Thing.

[demerphq]

And SU does it in a rather bizarre way with a regex and hex instead of using direct numification for reasons that remain mysterious to me.

The answer to that is simple: overloading. Up until later perls (and even in them im not sure) there was no way to bypass overloaded nummification. Thus 0+$ref is inherently dangerous on a blessed ref. However there is and has always been a way to bypass overloaded stringification which conveniently contains the reference address in hex. Thus the only generally safe pureperl way to get the address of a ref is via this technique.

Having said that SU doesn't use the pure perl code except on older perl builds on OS'es/Machines that dont have XS installed. The XS code it uses for refaddr() is much more efficient and bypasses all of these problems.