What does ||= (or-equals) mean in Ruby?

Question

What does the following code mean in Ruby?

||=

Does it have any meaning or reason for the syntax?

Answer 1

If X does NOT have a value, it will be assigned the value of Y. Else, it will preserve it's original value, 5 in this example:

irb(main):020:0> x = 5
=> 5
irb(main):021:0> y = 10
=> 10
irb(main):022:0> x ||= y
=> 5

# Now set x to nil. 

irb(main):025:0> x = nil
=> nil
irb(main):026:0> x ||= y
=> 10