What is this in Ruby? ||=

Question

While programming routes in Sinatra, I came across code listed as this:

before do
  session[:lists] ||= []
end

What is this operation doing ||= []?

Huh, googling "ruby ||=" actually doesn't give anything useful, from what I could see. Try googling "ruby or equals" instead. — alexanderbird, Nov 17 '16 at 23:20
The Rails tag should be removed as this is a pure-Ruby question. — Cary Swoveland, Nov 17 '16 at 23:42
Symbolhound is better for this sort of thing: http://symbolhound.com/?q=ruby+%7C%7C%3D — mu is too short, Nov 17 '16 at 23:45
Questions like this aren't bad to ask but they do suggest you don't have an adequate Ruby reference to work from. — tadman, Nov 18 '16 at 05:34

score 2 · Answer 1 · edited May 23 '17 at 11:53

2

x ||= value is a way to say "if x contains a falsey value, including nil, assign value to x"

That's setting session[:lists] equal to [] if session[:lists] is falsey.

edited May 23 '17 at 11:53

Community

answered Nov 17 '16 at 23:21

Tristan Rice

score 1 · Answer 2 · answered Nov 17 '16 at 23:21

1

It sets [] to session[:lists] when it's nil or falsy

2 Answers2