module ActiveSupport::Cache

# => returns MyOwnCacheStore.new
ActiveSupport::Cache.lookup_store(MyOwnCacheStore.new)

If the first argument is not a Symbol, then it will simply be returned:

# => same as: ActiveSupport::Cache::FileStore.new('/tmp/cache')
ActiveSupport::Cache.lookup_store(:file_store, '/tmp/cache')

class's constructor:
Any additional arguments will be passed to the corresponding cache store

# => returns a new ActiveSupport::Cache::MemCacheStore object
ActiveSupport::Cache.lookup_store(:mem_cache_store)

# => returns a new ActiveSupport::Cache::MemoryStore object
ActiveSupport::Cache.lookup_store(:memory_store)

For example:
store class under the ActiveSupport::Cache namespace will be created.
If you pass a Symbol as the first argument, then a corresponding cache

ActiveSupport::Cache::MemoryStore object will be returned.
If no arguments are passed to this method, then a new

Creates a new Store object according to the given options.

def lookup_store(store = nil, *parameters)
  case store
  when Symbol
    options = parameters.extract_options!
    # clean this up once Ruby 2.7 support is dropped
    # see https://github.com/rails/rails/pull/41522#discussion_r581186602
    if options.empty?
      retrieve_store_class(store).new(*parameters)
    else
      retrieve_store_class(store).new(*parameters, **options)
    end
  when Array
    lookup_store(*store)
  when nil
    ActiveSupport::Cache::MemoryStore.new
  else
    store
  end
end