Understanding the “||” OR operator in If conditionals in Ruby

Question

Just briefly, why are the following three lines not identical in their impact?

if @controller.controller_name == \"projects\" || @controller.controller_name          


        

Answer 1

the exact semantics of || are:

• if first expression is not nil or false, return it
• if first expression is nil or false, return the second expression

so what your first expression works out to is, if @controller.controller_name == "projects", then the expression short-circuits and returns true. if not, it checks the second expression. the second and third variants are essentially if @controller.controller_name == "projects", since "projects" || "parts" equals "projects". you can try this in irb:

>> "projects" || "parts"
=> "projects"

what you want to do is

if ["projects", "parts"].include? @controller.controller_name