class ActiveSupport::Cache::MemCacheStore

raw: true, will fail and return +nil+.
Decrementing a non-numeric value, or a value written without

cache.decrement("baz") # => 4
cache.write("baz", 5, raw: true)

To set a specific value, call #write passing raw: true:

cache.decrement("foo") # => 0

does not support negative counters.
If the key is unset or has expired, it will be set to 0. Memcached

Returns the updated value.
Decrement a cached integer value using the memcached decr atomic operator.

def decrement(name, amount = 1, options = nil)
  options = merged_options(options)
  instrument(:decrement, name, amount: amount) do
    rescue_error_with nil do
      @data.with { |c| c.decr(normalize_key(name, options), amount, options[:expires_in], 0) }
    end
  end
end