`unsync::Cache::get_or_insert_with` about quick-cache HOT 7 CLOSED

Yeah, allowing the cache to be overweight might have large implications.

If we ignore that part, I could probably add support for get_or_insert to return a Option<&mut V> kind of thing w/o extra lookups.

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Even just insert returning a Result<&mut V, V> would work for pretty much everything in my case. Basically either V is in the cache and I can refer to it that way, or it was not inserted for any reason, in which case I can still grab a reference of the value and do something with it without duplicating the effort to regenerate it.

But that would require not calling on_evict if the item hasn't actually been inserted into the cache.

Thanks for the quick response.

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I tried to add APIs that would satisfy your use case, but it's elusive to them to co-exists with non-guaranteed admission and the lifecycle hooks. It might take another round of refactors to get it exactly right.

Can you check if

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I think I could implement what I need with get_mut_or_guard. get_mut_or_insert_with, as far as I understand would require me to duplicate the logic acting on the value if I wanted to do something with it regardless of whether the value was able to make it into the cache or not. Something like this perhaps:

let already_used = false;
value = cache.get_mut_or_insert_with(key, || {
    let mut value = generate();
    already_used = true;
    use(&mut value);
    value
});
if !already_used {
    use(&mut value);
}

Not too terrible, though in this particular application it would perhaps be better if get_mut_or_insert_with either invoked the callback XOR returned a reference, not potentially both. That would allow dropping the already_used type of flag.

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Thanks for responding so quickly and spending your time on implementing this! Much appreciated!

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I merged #23 on master now, I'll keep the issue open until I make a crates.io release with it.

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0.5 has now been published

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