Question

I am working with a custom renderer, and I used some copy paste from another site. I can’t seem to figure out what this piece is doing right here.

"#{options[:callback]}(#{data})"

Here is the piece of code in full context.

  ActionController.add_renderer :as3 do |data, options|
    data = ActiveSupport::JSON.encode(data) unless data.respond_to?(:to_str)
    data = "#{options[:callback]}(#{data})" unless options[:callback].blank?
    self.content_type ||= Mime::JSON
    self.response_body = data
  end

Answer 1

It’s simple string interpolation. It will produce a string like this, where callback is the value of options[:callback], and value is whatever is in the variable data.

"callback(value)"

In Ruby, double-quoted strings support interpolation via #{} syntax. That is, if you have a variable x containing the value 3, the string "The value of x is #{x}" will be evaluated to "The value of x is 3". Inside a #{} you can have any arbitrarily complex Ruby expression, including array/hash indexing. So, the first part of the string, "#{options[:callback]}" is simply substituting the value of options[:callback] into the string.

The next part, the () is simply raw string data, not executable code. Inside the (), you have a second #{} substitution of data. It might be clearer if you replace the two variable substituions with x and y:

 x = 3
 y = 4
 "#{ x }(#{ y })"

The above will evaluate to the string "3(4)"