Both Moo and Moose generated inlined versions of their constructors and accessors that mean that there's only a single method call being involved. As such, run

Both Moo and Moose generated inlined versions of their constructors and accessors that mean that there's only a single method call being involved. As such, runtime is just as fast as any other perl code that uses accessor methods rather than poking into its own internals. Plus, of course, once you've got a Devel::NYTProf profile showing that a particular accessor is a hot spot, you can still poke into your own internals for that particular purpose to resolve the bottleneck. So, no, not really; generally you only pay a cost for the pieces of cleverness that you actually use, especially given the existence of Moo for fast-startup code where you don't need the MOP.