(if you don’t read my blog for the geeky thrill of it, you may want to give this post a miss ;))

Follow my little IRB session, if you will:

>> nil or "val"
=> "val"

>> puts (nil or "val").inspect
=> "val"

>> x = nil || "val"
=> "val"

>> x
=> "val"

>> y = nil or "val"
=> "val"

(wait for it…)

>> y
=> nil


Seriously, ruby. What the crap?

Okay, so I just figured out what’s going on here. “or” works both as a logic operator and a conditional statement. Just like you can do:

x = something_dangerous() rescue "x failed!"

and

puts "x is greater than 10" if x > 10

It would seem you can also do

x = some_value or puts "i guess the assignment didn't evaluate to true"

Meaning that in my example above:

y = nil or "val"

Ruby evaluates it as:

(y = nil) or ("val")

(i.e. in the second set of brackets, y is not actually assigned to anything)

Of course, || is solely a logic operator. Which is why it looks like you get different behaviour when you use || instead of or.

When I found out about ruby supporting both sets of logic operators (&&, ||, !) and (and, or, not), I thought it was dumb, but just a matter of preference which type you prefer.

When I found out that the symbol-based ones bind tighter than the keywords, I winced a little and noted to myself never to rely on that, because it’s neither readable or obvious.

Now that I’ve stumbled upon this latest gem of knowledge, It just makes me cringe…