Rails: Render collection partial: Getting size of collection inside partial

Ah. Wanted to answer the question. But found correct answer. Anyway here is a tip on future. You can investigate the Rails mechanism with Ruby metaprogramming. For example by calling method 'Kernel#local_variables' in a view which in my case outputs:

[0] = :local_assigns
[1] = :output_buffer
[2] = :row
[3] = :row_counter
[4] = :row_iteration
[5] = :highlighted_description
[6] = :source_description

in case of

  <%= render partial: 'card', collection: @offers, as: :row %>

The following is possible since Rails Version 4.2:

Inside the partial you have access to a function/variable called collection_iteration. Calling collection_iteration.size will give you the total.

From the changelog:

The iteration object is available as the local variable #{template_name}_iteration when rendering partials with collections.

It gives access to the size of the collection being iterated over, the current index and two convenience methods first? and last?.