Ruby unknown + on trying to join 2 strings - ruby

Question

So, I'm learning Ruby and immediately, have stumbled upon something rater peculiar when trying to concatenate 2 strings to one. Here's the code, with irrevelant parts stripped, lets just say Sinatra runs it:
class CMS
# Set the site path root.
#sitePath = "./site"
get '/' do
renderCache = File.readlines(#sitePath + "index.liquid")
end
end
And on loading the page, I am greeted with
NoMethodError at /
undefined method `+' for nil:NilClass
on the renderCache = File.readlines(#sitePath + "index.liquid") line. Why is it refusing to concatenate the strings?

Answer 1

You can't set instance variables at the class level. You need to set them in an instance method.
Look's like you're using sinatra so you can do this:
See here for how to make a "before filter" like one does in Rails apps. This solution is for the modular style of Sinatra app.
To show an example:
class CMS < Sinatra::Base
before do
#sitePath = "./site"
end
get '/' do
renderCache = File.readlines(#sitePath + "index.liquid")
end
end
CMS.run!
You could also keep your existing code if you use a constant instead of an instance variable:
class CMS
# Set the site path root.
SitePath = "./site"
get '/' do
renderCache = File.readlines(CMS::SitePath + "index.liquid")
end
end
To explain how I read your error and looked for the error:
undefined method '+' for nil:NilClass means you're calling + on something which is nil. Referencing the code shows that the nil variable is #sitePath. Undefined instance variables will evaluate to nil. This is different than standard variables, which will raise an undefined variable error.