Contravariant arguments for CaffeineProxyManager

[namhptran]

Hi, using CaffeineProxyManager has a problem of having to cast using raw types which may not be type safe. This should improve the experience and provide some type safety for custom settings applied to the cache.

[vladimir-bukhtoyarov]

Hello @namhptran

Could you provide example of code when you faced with unchecked cast?

[namhptran]

@vladimir-bukhtoyarov the test that is already there is very similar to what I had to do to use Caffeine

protected ProxyManager<String> getProxyManager() {
  Caffeine<String, RemoteBucketState> builder = (Caffeine) Caffeine.newBuilder().maximumSize(100);
  return new CaffeineProxyManager<>(builder, Duration.ofMinutes(1));
}

This however provides warnings Unchecked assignment: 'com.github.benmanes.caffeine.cache.Caffeine' to 'com.github.benmanes.caffeine.cache.Caffeine<java.lang.String,io.github.bucket4j.distributed.remote.RemoteBucketState>' due to casting to raw type then unchecked casting back to a generic.

Alternatively, this was my original desired approach, but it doesn't work when it really should

protected ProxyManager<String> getProxyManager() {
  return new CaffeineProxyManager<>(Caffeine.newBuilder().maximumSize(100), Duration.ofMinutes(1));
}

This doesn't compile due to trying to assign Caffeine<Object, Object> to a Caffeine<K, RemoteBucketState>

Ideally CaffeineProxyManager should allow for contravariance on the Caffeine builder type, and we should avoid having to cast to raw types where possible

[vladimir-bukhtoyarov]

Looks reasonable. Thank you.

[vladimir-bukhtoyarov]

Released with version 8.3.0