You could do something with rusts feature system and macros. In essence you'd have a macro that would run a different line of code if your feature is enabled ve

You could do something with rusts feature system and macros. In essence you'd have a macro that would run a different line of code if your feature is enabled versus disabled, so you could use the unbounded lookup on the array. That said, this would be a user implementation and wouldn't be likely to be provided by the standard Library