What's a tight way to reference a variable that may not be defined in a partial?

I have a few local variables in my partials which may or may not be passed by the template that renders them, for instance: on_question_page. If I'm on the page I pass it as true but elsewhere I skip it.

The problem is th开发者_如何学Cat I can't reference that variable directly because in the places it isn't defined it throws an error.

This means that I end up with a lot of code like this at the top of my partials:

on_question_page = defined?(on_question_page) ? on_question_page : false

Messy. Is there a cleaner way to access these optional variables?

You can use on_question_page ||= false to assign false if on_question_page is undefined or false or nil, that is, something which evaluates to false when tested with boolean operators.

you might use ||= operator

on_question_page ||= false

How about defining the default value at a position which is always included and overriding it in your partial?

That way you do not need to check whether it is available and you could even change the default value easily if required.

I think the solution would be to use bindings and a helper:

# whatever_helper.rb
def local_set(ref, view_binding)
  eval(ref.to_s, view_binding)
rescue NameError
  false
end

# my_neet_view.html.erb
<h1>Question</h1>

<%= local_set("on_question_page", binding) %>

Bindings allow us to pass the evaluation context of the view in to a helper and do all the messy work in there. This moves the logic out of the view and in to a helper.