instance method available?

# File activesupport/lib/active_support/messages/serializer_with_fallback.rb, line 134
            def available?
              return @available if defined?(@available)
              # Check the dependency before loading the wrapper that warns if it is missing.
              gem "msgpack", ">= 1.7.0"
              require "msgpack"
              require "active_support/message_pack"
              @available = true
            rescue LoadError
              @available = false
            end