Why `remove_expired` is not a public function?

[vi]

let _ = the_cache.iter() is obvious workaround, but less readable and maintainable.

Removing expired elements can be significant if their destructors do something, so that function may be called periodically on timer.

[stusmall]

I guess this question is why would you want to clean it out?

[vi]

To make expired entries actually expire and free up resources (e.g. file descriptors).

If you just don't touch TtlCache, I expect it to still hold even long-expired entries, which may in turn refer to more things.

[stusmall]

I've resisted adding one because if a program relies on cleaning up resources by manually calling remove_expire() they either have too long cache times or intialized the cache with too high of a capacity. Manually going in and calling remove_expired() will help delay the potential resource exhaustion issue but doesn't remove it.

V's that impl Drop make a better case for prematurely purging the cache though. Mind if I think about this one a bit more?

[vi]

either have too long cache times or intialized the cache with too high of a capacity

Or sometimes idles and not uses the cache for prolonged periods of time.

If cached entries are heavy (refers to a lof of memory, contains sockets, etc.), it can be problematic even with low times and low capacity.

[alopatindev]

It'd be essential to make both remove_expired and len public.

In my case I need to measure current number of unexpired items; every new added item has the same TTL, so it's okay to call remove_expired before each insert (although making remove_expired removing no more than a constant number of items at a time might be even a better idea).

Can we make len public as well? Thanks.