Question

I am new to Ruby and I did the following:

c = {}
# Some code in the middle
c['a'] = c['a'] or 0

Now I would expect this to work like this: if c['a'] is nil, then c['a'] or 0 would return 0. So the value of c['a'] should be 0.

However the value of c['a'] is nil. Why does this happen?

Answer 1

or is not the same as || in Ruby. What you have becomes grouped like so:

(c['a'] = c['a']) or 0

which will basically do nothing. You should use || instead:

c['a'] = c['a'] || 0

or simply:

c['a'] ||= 0

Note that and/&& has the same behavior as or/||.