Rails ActiveSupport::Concern and method evaluation - ruby-on-rails

Question

I have this application which uses Devise with current_user helper. When I create a module, current_user becomes nil after I mention an attribution to it even though it never happens.
class PagesController < ApplicationController
include ModuleTest
def index
a_test_method
end
end
And the ModuleTest:
module ModuleTest
extend ActiveSupport::Concern
def a_test_method
puts "(BEFORE)===========> #{current_user.inspect}"
current_user = nil if false
puts "(AFTER) ===========> #{current_user.inspect}"
end
end
Output:
(BEFORE)===========> #<User id: 1>
(AFTER) ===========> nil
However, if I delete/comment out this line # current_user = nil if false, current_user remains valid:
(BEFORE)===========> #<User id: 1>
(AFTER) ===========> #<User id: 1>
Would this be related to lazy evaluation somewhat?
EDIT
The whole problem relies on how Ruby defines variables when a statement is not evaluated:
2.3.4 (main):0 > defined? this_never_seen_variable_before
=> nil
2.3.4 (main):0 > this_never_seen_variable_before = "value" if false
=> nil
2.3.4 (main):0 > defined? this_never_seen_variable_before
=> "local-variable"
2.3.4 (main):0 >
2.3.4 (main):0 > this_never_seen_variable_before_2
NameError: undefined local variable or method `this_never_seen_variable_before_2' for main:Object
from (pry):119:in `<main>'
2.3.4 (main):0 > this_never_seen_variable_before_2 = "value" if false
=> nil
2.3.4 (main):0 > this_never_seen_variable_before_2
=> nil
2.3.4 (main):0 >
How does this work underneath?

Answer 1

current_user is a helper method provided by Devise, not a local variable.
There is no such helper method named current_user=. You can prove this by changing current_user = nil to self.current_user = nil and see it crash. But this is irrelevant to your issue.
So the result is, you defined a local variable current_user between the 2 puts, which shadows the helper method with the same name.
The weird thing is, although current_user = nil is not executed because of the if false, the local variable still gets defined, and its value is implicitly set to nil. This is why your second puts shows nil. Even if you change your current_user = nil to current_user = :someone, your second puts should still show nil.