[SOLVED] Why doesn't Rails throw an exception when we access an undefined instance variable in the view?

Why doesn't Rails throw an exception when we access an undefined instance variable in the view?

Suppose we have the following implementation:

app/controllers/cars_controller.rb

class CarsControllers < ApplicationController
  def index
    @test = '7'
  end
end

app/views/cars/index.html.erb

My test variable is <%= @test %>.
Here is an undefined variable <%= @test2 %>.

How come accessing @test2 doesn't throw an exception (Given we are trying to access an instance variable)?

Solution

It doesn't pose a problem in your example because @test2 simply returns nil when undefined.

You can verify this in an irb console session:

2.6.2 :001 > @test2
 => nil

However ... if you were to call a method assumed to be provided by @test2 then you'd have a problem:

2.6.2 :002 > @test2.name
Traceback (most recent call last):
        1: from (irb):2
NoMethodError (undefined method `name' for nil:NilClass)

In that case, you definitely would receive an error when Rails tried to render the view.