Rails: creating a hash inside an initializers file and using it

Question

I am using one file in the initializers directory to declare constants for use in different parts of the application.

FIRST_STR = "First Name"
LAST_STR = "Last Name"
new_user_hash = Hash.new
new_user_hash[ "first" ] = FIRST_STR
new_user_hash[ "last" ] =  LAST_STR

I have no problem using FIRST_STR and LAST_STR in different parts of the application, but when I try to use new_user_hash, I get the following error message:

undefined local variable or method `new_user_hash' for #<#:0x007f8da5752da0>

Is it not possible to define/declare a hash in one file and use it in another?

Where are you trying to use new_user_hash? It can't be accessed outside of that file since it's a local variable. — Andrew Marshall
– Andrew Marshall, Commented May 12, 2012 at 16:25

Kyle Burton · Accepted Answer · 2012-05-12 16:59:07Z

7

I think you may be running into scoping—new_user_hash is a local and may not be available to the rest of the application. If you make it a global (by calling it $new_user_hash) it will be available. In the case of FIRST_STR and LAST_STR, they are constants which are effectively globals.

Update your code to be either:

$new_user_hash = { "first" => FIRST_STR, "last" => LAST_STR }

or

NEW_USER_HASH  = { "first" => FIRST_STR, "last" => LAST_STR }

And you will be able to access $new_user_hash or NEW_USER_HASH from the other parts of your application.

Another strategy is to define a module:

module MyAppConfig
  NEW_USER_HASH = { "first" => FIRST_STR, "last" => LAST_STR } 
end

Then elsewhere you can access it by prefixing it with the module name:

MyAppConfig::NEW_USER_HASH["first"]

This is a more accepted approach since it doesn't create more global variables.

edited May 12, 2012 at 16:59

answered May 12, 2012 at 16:51

Kyle Burton

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5 Comments

Andrew Marshall Over a year ago

MyAppConfig probably makes more sense as a module, since it's not meant to be new-ed and is merely a container for encapsulating constants.

Kyle Burton Over a year ago

That is a great point Andrew. Thanks, I'll update my answer.

Joseph Mouhanna Over a year ago

Thanks for all the suggestions. I will try some stuff and post what works. Yes, it's a scoping issue. When I moved the Hash declaration to the file I was using it in, it worked fine.

Joseph Mouhanna Over a year ago

Is the module approach to help avoid a name conflict only, or are there other advantages to using the module approach?

Kyle Burton Over a year ago

Andrew's suggestion is a good one: since there is no implementation (i.e. no state) there is no need to make it a class -- you'd never instantiate it (call new) and it really has no behavior of its own, it's just there to namespace the data. Does this make sense?

Cristian Bica · Accepted Answer · 2012-05-12 21:38:22Z

0

You should use a config management gem: https://www.ruby-toolbox.com/categories/Configuration_Management

answered May 12, 2012 at 21:38

Cristian Bica

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