[RFC] Fragment caching

[erino]

Summary

Add a class method to slice class allowing easy fragment caching of the entire view

Motivation

To add this currently means wrapping the entire view in a cache block

For example, consider FooSlice:

# app/slices/foo/foo_slice.rb

class FooSlice < Slice
end

<!-- app/slices/foo/views/show.html.erb -->
<div>
  <p>
    <%= some_expensive_method %>
  </p>
</div>

Adding the cache block would give the resulting code, potentially adding an extra level of indentation to most of the file.

<!-- app/slices/foo/views/show.html.erb -->
<% cache slice do %>
  <div>
    <p>
      <%= some_expensive_method %>
    </p>
  </div>
<% end %>

Rather then having to add a cache block to the view, we would prefer to add a class method/macro to the slice to signify that the entire view should be fragment cached.

# app/slices/foo/foo_slice.rb

class FooSlice < Slice
  fragment_cache_view
end

This method could allow the passing of optional extra cache keys:

fragment_cache_view 'addition-key'

[jgwhite]

Could we give fragment_cache_key a block if we wanted to use dynamic keys?

class FooSlice < Slice
  fragment_cache_view do
    [Time.now.to_i, rand, 'trollface']
  end
end