If this to live in core there needs to be a compat function found in core in cache-compat.php. This function would need to work for ALL object cache implementation, including and not limited to memcached.

I personally think this is going be nearly impossible, as it is hard to know the implementation details of every object cache. But without that compatible layer, this can not live in core 😞

This function would need to work for ALL object cache implementation, including and not limited to memcached.

It's a FAQ and the suggested approch is using prefixes, which I believe wp-memcached is already using heavily.

Please use remove test for wp_cache_get_linked_meta and revert changes to comments and spacing that are not required for this change.

If this is going to make it into core, then we are going to need some constant, like WP_ALLOW_CACHE_GROUPS. Drop-in providers, will have to define this. That way, developers / core can work out if we can even use this function.

Thoughts?

If this is going to make it into core, then we are going to need some constant, like WP_ALLOW_CACHE_GROUPS. Drop-in providers, will have to define this. That way, developers / core can work out if we can even use this function.

Reminds me of get_theme_support() and add_theme_support().

If we default to flushing the entire cache (in the compatibility method), can you give an example how and where WP_ALLOW_CACHE_GROUPS would be used?

I am not sure we do need the global WP_ALLOW_CACHE_GROUPS as I test for a flush_group function
method_exists( $wp_object_cache, 'flush_group' )
and return false if not available so the calling code and handle it