What does || exactly Mean?

Question

Recently I saw code like

i < 0 ||

I wonder what is "||" exactly mean? How to say that in english?

Answer 1

Logical "or"

A || B is true when either A is true or B is true, or when both A and B are true.

http://www.tutorialspoint.com/ruby/ruby_operators.htm

Answer 2

The || operator is similar to the keyword or but is different from the keyword or in extremely important ways. Below are two great write-ups on the topic, comparing the two and showing you how to use either one:

• http://devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby/
• New version, with video: http://devblog.avdi.org/2014/08/26/how-to-use-rubys-english-andor-operators-without-going-nuts/

---

The most important thing to note in what Avdi says, is that || cannot be used for flow control, whereas or can be.

For example...

a = :value
c = b || a
#de Since `b` is undefined/null, `c` will be set to `:value`

c = b || puts("Failure!") #de This will raise an exception!

c = b or puts("Failure!") #de Will set `c` to `NilClass` and output "Failure!"