What is the difference between these two Ruby symbols?

Question

I discovered this after playing around with object ids.

ObjectSpace._id2ref(2648)
=> :**
ObjectSpace._id2ref(6688)
=> :**
ObjectSpace._id2ref(2648) == ObjectSpace._id2ref(6688)
=> false

The first one is the symbol for the exponentiation operator;

2.send(ObjectSpace._id2ref(2648), 3)
=> 8
2.send(ObjectSpace._id2ref(6688), 3)
NoMethodError: undefined method `**' for 2:Fixnum

But the second one somehow isn't? I assume they just look the same after being passed to #print. But what is the difference? Is one of them somehow a unicode symbol?

UPDATE: The second one is probably the new double splat for keyword arguments, but I can't seem to verify this.

Sambo

In which Ruby version you are ? I got Range error. 2.0.0-p-353 – Kaleb

Weird. From pry -v I get Pry version 0.9.12.6 on Ruby 2.0.0. – Sambo

Object ids aren't necessarily the same across Ruby invocations so there's not much anyone can say unless you can provide explicit steps that reproduce what you're seeing. OTOH, id = ':**'.object_id; puts ObjectSpace._id2ref(id) is suggestive so why not check the class of the _id2ref return values? – Identification

@muistooshort You raised valid point. – Kaleb

It indeed raise an range error as Arup says, but it further says RangeError: 0x00000000001a20 is not symbol id value, so that number seems to fit in the possible range for symbol objects. – Mitosis

@muistooshort Interesting! I can't find a more deterministic way to produce the second object. I found them by running the equivalent of 10000.times{ |n| ObjectSpace._id2ref(n).inspect }. – Sambo

What is the value of ObjectSpace._id2ref(6688).to_s.codepoints? It could be some odd character, possibly U+2217: ASTERISK OPERATOR (which is 8727 in decimal). – Apathy

Both objects return [42, 42]. Very mysterious... – Sambo

@AlexAltair Yes, I’ve managed to reproduce it now, I get them at object_id 2648 and 6728 on my machine. – Apathy

I suspect this might have something to do with keyword arguments, which use ** to indicate an options hash in an arguments list. I can’t reproduce the issue on 1.9.3. It looks like there is an extra ‘hidden’ ** symbol that doesn’t appear in the symbol table but can be found by looking at ObjectSpace. – Apathy

Hm... I think you're probably right. I can't find a way to verify it using #send. Are splat and double splat even proper methods? What are they called on? Mysteries abound. – Sambo

Answer 1

These commands may be illuminating:

ObjectSpace._id2ref(2648).class.ancestors
ObjectSpace._id2ref(6688).class.ancestors

Reduction

Alas, as they are both symbols, this only tells us things about all symbols. – Sambo