RubyOnRails local_assigns

http://api.rubyonrails.org/classes/ActionView/Template.html#method-i-local_assigns

Returns a hash with the defined local variables.

Given this sub template rendering:

<%= render "shared/header", { headline: "Welcome", person: person } %>
You can use local_assigns in the sub templates to access the local variables:

local_assigns[:headline] # => "Welcome"

current_index = local_assigns[:index] || default_index
from = (local_assigns[:from] || default_from) + ["#{current_index}:#{component.name}"]
version = :v4 

json.array! component.get_parts_in_order(@status).each_with_index.to_a do |part, index|
          json.partial! 'api/v2/components/component', component: part, from: from, index: index
        end