class ActiveSupport::HashWithIndifferentAccess

counters.assoc(:zoo) # => nil
counters.assoc(:foo) # => ["foo", 1]
counters.assoc('foo') # => ["foo", 1]

counters[:foo] = 1
counters = ActiveSupport::HashWithIndifferentAccess.new

either a string or a symbol:
Same as Hash#assoc where the key passed as argument can be

def assoc(key)
  super(convert_key(key))
end