Understanding the "||" OR operator in If conditionals in Ruby
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
The difference is the order of what's happening. Also the || isn't doing what you think it does in the 2 and 3.
You can also do
if ['projects','parts'].include?(@controller.controller_name)to reduce code in the future if you need to add more matches.
There's a few different things going on there:
if @controller.controller_name == "projects" || @controller.controller_name == "parts"this gives the behaviour you want I'm assuming. The logic is pretty basic: return true if the controler name is either "projects" or "parts"
Another way of doing this is:
if ["projects", "parts", "something else..."].include? @controller.controller_nameThat will check if the controller name is somewhere in the list.
Now for the other examples:
if @controller.controller_name == ("projects" || "parts")This won't do what you want. It will evaluate ("projects" || "parts") first (which will result in "projects"), and will then only check if the controller name is equal to that.
if @controller.controller_name == "projects" || "parts"This one gets even wackier. This will always result in true. It will first check if the controller name is equal to "projects". If so, the statement evaluates to true. If not, it evaluates "parts" on it's own: which also evaluates to "true" in ruby (any non nil object is considered "true" for the purposes of boolean logic")