def exist?(key, options = {})
      invoke(:exist?, key) do |store|
        store.exists(namespaced_key(key, merged_options(options)))
      end
    end
def exist?(key, options = {})
      invoke(:exist?, key) do |store|
        store.exists(namespaced_key(key, merged_options(options)))
      end
    end
Returns `true` if the cache contains an entry for the given key.

 @param [String] key Key for lookup
 @param [Hash] options Optional overrides

 @example

   cache.exist?('some-key') # => false
   cache.exist?('some-key', namespace: 'cache') # => true