Question

I have a local variable in an erb template:

<% thumbnail_width = 50 %>

I’m using this for sizing some thumbnail images.

But now I realize that a number of templates will need to access this variable.

Where should I move it to and what type of variable should it be?

Answer 1

There are several solutions, depending on how this variable interacts with the Rails environment.

Configurations

You can use a global configuration file (see for example SimpleConfig plugin). This is the preferred choice when the variable might change depending on the environment.

Constants

You can define a constant if the variable should be accessible in many different places and contexts. For example, you might want to create the file

config/initializers/defaults.rb

and write there all your default configurations and constants. A constant defined here will be automatically available all over your Rails application.

Helpers

If your variable is tied to a specific section of the application, for instance a view, you might want to take advantage of Rails helpers.
In your specific case, you can create an image helper in your application_helper.rb

module ApplicationHelper

  THUMBNAIL_WIDTH = 50  

  def thumbnail_tag(source, options = {})
    image_tag(source, options.reverse_merge(:width => THUMBNAIL_WIDTH))
  end

end

Then use the helper when you need to create a thumbnail instead of copying the same logic over and over in every file.