Self optimizing iterable

[MRAB]

Zac Burns wrote:
> Greetings,
> 
> I would like a set like object that when iterated maintains a count of
> where iteration stopped and then re-orders itself based on that count
> so that the iteration stopped on the most bubble to the top.
> 
> An example use case for this would be for something like a large table
> of regular expressions that would be iterated over trying to match in
> some string. If some regular expressions are more statistically more
> successful then the iteration will generally be short.
> 
> Does anyone know of a pre-existing recipe for this or feel like taking
> on the challenge?
> 
> Bonus points for:
>    Best possible BigO notation on switching order and iteration
>    Threadsafety
>    Extend to also include a mapping version
> 
That's not a set, but a Most Recently Used list.