I know there are religious wars fought over part of what I'm about to ask. I'm not here for any of that. I'm just curious why in my rails application helper I cannot have a global level variable honored.

Should I be able to do something like this:

module ApplicationHelper

magic_variable = HashWithIndifferentAccess.new(
{
      blah:       "primary",
      blah_blah:  "secondary",
})

  def random_help
     # do something cool with magic_variable?
  end

end 

I know there are religious wars fought over part of what I'm about to ask. I'm not here for any of that. I'm just curious why in my rails application helper I cannot have a global level variable honored.

Should I be able to do something like this:

module ApplicationHelper

magic_variable = HashWithIndifferentAccess.new(
{
      blah:       "primary",
      blah_blah:  "secondary",
})

  def random_help
     # do something cool with magic_variable?
  end

end 

• ruby-on-rails
• ruby
• global-variables
• helper

• 1 Global variables in Ruby use the sigil $. ruby-doc./docs/ruby-doc-bundle/UsersGuide/rg/globalvars.html – max Commented Mar 20 at 11:56
• I spaced on that. but it feels weird to not access even with ::variable – Michael K Madison Commented Mar 26 at 22:05

2 Answers 2

TLDR: It's not global variable, it's local variable and you try to use it out its scope

It's even not instance variable, not class variable, and not constant

Variables defined like your magic_variable inside a module or a class are local to that scope but are not available inside methods etc.

From the docs

Generally, the scope of a local variable is one of

• proc{ ... }

• loop{ ... }

• def ... end

• class ... end

• module ... end

• the entire program (unless one of the above applies)

You can use:

• a global variable ($magic_variable)
• an instance variable (@magic_variable)
• a class variable (@@magic_variable)
• a constant (MAGIC_VARIABLE)

And probably only last one is good by semantics for your situation

module ApplicationHelper
  CONSTANT = {
    blah: "primary",
    blah_blah: "secondary",
  }.with_indifferent_access.freeze

  def random_help
    # do something cool with CONSTANT
  end
end

Constants are public by default, so you can also use ApplicationHelper::CONSTANT somewhere outside that module

It doesn't have anything to do with the ApplicationHelper or Rails, it is just Ruby's scoping rules.

If you go into a rails console or preferably just a plain 'ol irb console, you can play around with this:

$ irb

some_var = "foo"

def some_method
  puts some_var
end

some_method # call the method

This will raise an exception:

undefined local variable or method `some_var' for main (NameError)

If you want that accessible in all helpers, just wrap it in a method:

def magic_variable
  HashWithIndifferentAccess.new({ blah: "primary", blah_blah: "secondary" })
end

This won't let you mutate/change it, though. You'll need to store it in an instance variable or wrap it in a class that enables you to set it.